Polyethers (ACS symposium series ; 6)

Polyethers E d w i n J. Vandenberg, Editor

A symposiu Division of Polymer Chemistry at the 167th Meeting of the American Chemical Society, Los Angeles, Calif., A p r i l 2, 1974.

ACS SYMPOSIUM SERIES 6

AMERICAN

CHEMICAL

SOCIETY

WASHINGTON, D. C. 1975

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Library of Congress

Data

Polyethers. ( A C S symposium series; 6 ) Includes bibliographical references and index. 1. Polymers and polymerization—Congresses. 2. Ethers—Congresses. I. Vandenberg, Edwin J., 1 9 1 8 - ed. II. American Chemical Society. Division of Polymer Chemistry. III. Series: American Chemical Society. A C S symposium series; 6. QD380.P63 I S B N 0-8412-0228-1

547'.84 74-30327 A C S M C 8 6 1-207 ( 1 9 7 5 )

Copyright © 1975 American Chemical Society A l l Rights Reserved P R I N T E D IN THE U N I T E D S T A T E S O F A M E R I C A

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series Robert F. Gould, Series Editor

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

FOREWORD The A C S S Y M P O S I U M SERIES was founded i n 1974

to provide

a medium for publishing symposia quickly i n book form. The format of the SERIES parallels that of its predecessor, A D V A N C E S I N C H E M I S T R Y SERIES, except that i n order to save time the papers are not typese mitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published i n the A C S S Y M P O S I U M SERIES are original contributions not published elsewhere i n whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

PREFACE >Tphis book is based largely on the papers presented at a "Polyether" Symposium i n honor of D r . Charles C . Price, Benjamin Franklin Professor of Chemistry at the University of Pennsylvania, on the occasion of his receiving the Creative Invention A w a r d of the American Chemical Society for his pioneering U.S. Patent 2,866,774 on elastomeric polyether urethanes. One of the symposiu and C . C . Price has already been published i n /. Polymer Set., Polym. Phys. E d . (1974) 12, 1395. In addition, two papers are included from P. Dreyfuss and T. Saegusa with S. Kobayashi, outstanding polyether researchers who were not able to participate i n the symposium. The Price Award patent covers elastomeric polyurethanes made from the reaction of diisocyanates with the propylene oxide adducts of polyols. These polyether urethanes have proved to be of great commercial value as foamed rubber products, which have contributed greatly to the comfort and well-being of mankind. Approximately 1 billion lbs of these superior foamed products are used each year i n the United States, particularly i n cushioning for furniture and cars. In addition to the Award patent, D r . Charles C . Price has played a broad, pioneering role i n the polyether field. I n organizing the symposium, the editor sought new contributions on polyethers which generally related to D r . Price's work which is described i n part i n his Award address at the beginning of this book. The editor thanks D r . Charles C . Price and the other contributors for their outstanding papers and for their cooperation i n organizing, presenting, and publishing this symposium. EDWIN J. VANDENBERG

November 11, 1974 Wilmington, Del.

vii In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1 Polyethers CHARLES C. PRICE Department of Chemistry, University of Pennsylvania, Philadelphia,Penn.19174

A.

Introduction

Several inherent c h a r a c t e r i s t i c s of the ether l i n k a g e have stimulated extensive research and development o f l i n e a r polymers with ether l i n k s i n the polymer backbone (1,2). The ether l i n k ­ age has low p o l a r i t y and low vander Waals i n t e r a c t i o n character­ istics (ΔΗ = 87.5 cal/g f o r pentane vs. 83.9 cal/g f o r d i e t h y l e t h e r ) . The carbon-oxygen bond has a lower b a r r i e r to r o t a t i o n than the carbon-carbon bond (2.7 kc/m f o r dimethyl ether vs. 3.3 f o r propane) and thus provides a lower b a r r i e r to coiling and u n c o i l i n g of chains. The ether oxygen has an even lower ex­ cluded volume than a methylene group (vander Waals radii of 1.4 Å v s . 2.1 Å) and thus, o f all backbone u n i t s , has the s m a l l e s t "excluded volume". This a l s o is a f a c t o r which permits greater chain flexibility. The carbon-oxygen bond has as great a bond energy (85 kc/m) as a carbon-carbon bond (82 kc/m) and much g r e a t e r h y d r o l y t i c r e s i s t a n c e than e s t e r , a c e t a l or amide l i n k s . vap

These u s e f u l c h a r a c t e r i s t i c s have, in the past two decades, led to extensive commercial development and use of a v a r i e t y of p o l y e t h e r s . Poly(propylene oxide) has become the b a s i s of the l a r g e s c a l e , world-wide development of "one-shot" polyurethan foam rubber, f o r mattresses, f u r n i t u r e , cushions, padding, e t c . P o l y ( t e t r a h y d r o f u r a n ) has been an important component of Corfam s y n t h e t i c l e a t h e r s u b s t i t u t e and of elastic f i b r e s . Linear poly(2,6-xylenol) i s made on a large s c a l e as an engineering plastic with an important combination of p r o p e r t i e s , such as high g l a s s t r a n s i t i o n temperature, good thermal stability, good electrical p r o p e r t i e s , e x c e l l e n t adhesion and ready s o l u b i l i t y in common organic s o l v e n t s . In each o f these p o l y e t h e r s , the ether l i n k is p a r t of the "backbone" of the polymer chain. In each, the ether linkage makes an important c o n t r i b u t i o n to the p h y s i c a l p r o p e r t i e s and chemical stability on which the utility i s based. Since the chemistry of the generation of polyethers has been d i f f e r e n t from that of the classical v i n y l p o l y m e r i z a t i o n 1

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

2

processes, many academic i n v e s t i g a t o r s have a l s o been i n v o l v e d i n studying the mechanism, stereochemistry and other aspects o f polyether formation. I t i s our purpose here to present some of the r e s u l t s o f these s t u d i e s f o r those polyether systems i n which we have been p a r t i c u l a r l y i n t e r e s t e d , the polyepoxides, the poly(£-phenylene ethers) and the a l t e r n a t i n g poly(£-phenylenemethylene e t h e r s ) . B.

Polyepoxides

Epoxide p o l y m e r i z a t i o n can be described i n terms of three d i f f e r e n t mechanisms; (1) a n i o n i c (base-catalyzed), (2) c a t i o n i c ( a c i d - c a t a l y z e d ) , and (3) coordinate. The t h i r d a c t u a l l y com­ bines features of the f i r s t two extremes, since i t involves c o o r d i n a t i o n o f the monomer oxygen a t a Lewis a c i d c a t a l y s t s i t e ( L ) , followed by a l k o x i d e already boun

ο

θ

+

C ^ ι ,ο

C

^ C ». ^ 0

φ \

(1)

0

G

0 ^ L

~>

L '

-

0

G

>

L

(3)

°

C

G

0

The ring-opening step i n each case i s a n u c l e o p h i l i c sub­ s t i t u t i o n and, i n every case where the stereochemistry has been e s t a b l i s h e d , has been shown to occur with i n v e r s i o n of c o n f i g u ­ r a t i o n at the carbon atom undergoing n u c l e o p h i l i c attack (.3,4). The e t h e r - l i k e oxygen i n the s t r a i n e d three-membered r i n g thus behaves l i k e a good " l e a v i n g group. In the monomer i t s e l f , a strong n u c l e o p h i l e such as alkoxide i o n i s r e q u i r e d f o r S^2 11

a t t a c k . However, when the epoxide i s converted to an oxonium s t a t e , as i n the c a t i o n i c process, i t becomes such a good " l e a v i n g " group that even the weakly n u c l e o p h i l i c oxygen of the monomer i s able to attack e f f e c t i v e l y . The c h a r a c t e r i z a t i o n o f the epoxide oxygen as a good " l e a v i n g " group i s supported by the f a c t that i t not only can undergo S 2 displacement but E e l i m i n a t i o n . For example, t e t r a M

9

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

PRICE

Polyethers

3

methylethylene oxide, on treatment with a c a t a l y t i c amount of a base such as potassium t^-butoxide, undergoes " e l i m i n a t i o n " almost q u a n t i t a t i v e l y (5^.

Θ 0 t-BuO

+

H6H C •

0 ν

C

2

CH

t-BuOH C H

3

(

I

+

3

CH =Ç - Ç — CH CH 2

CH

3

)

OH II

+

CH

0

ZZ C —

I

2

I I

C —CH

CH

0

3

CH

B ( l ) . A n i o n i c . Because of the i n t e r v e n t i o n of the E2 process, only ethylene oxide i s r e a d i l y converted to highpolymer by b a s e - c a t a l y s i s . The p o l y m e r i z a t i o n can be c a r r i e d out so that one polymer molecule forms f o r each c a t a l y s t molec u l e added (5). With propylene oxide, however, the E2 r e a c t i o n intervenes and serves, i n e f f e c t , as a c h a i n - t r a n s f e r process. The a l k y l o x i d e i o n formed by e l i m i n a t i o n i s , of course, capable of i n i t i a t i n g a new chain, now capped at one-end by an a l l y l ether group (6).

CH 0CH CH0© 3

2

******* Q0

OH +CH =CHCH 0© 2

2

The maximum molecular weight of base-catalyzed propylene o x i d e polymer i s l i m i t e d by the r a t i o of the r a t e s of propagation (k ) to t r a n s f e r ( k ) ; s i n c e at operable temperatures k ^ / k ^ i t r

100,

t h i s i s 6000 awu. I t was t h i s molecular-weight l i m i t i n g chain t r a n s f e r which led us to seek s y n t h e t i c approaches to b u i l d i n g a c r o s s l i n k e d rubber s t r u c t u r e from poly(propylene oxide) chains. T h i s was s u c c e s s f u l l y accomplished i n 1949 by b u i l d i n g branched chain

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

4

l i q u i d polymer, followed by conversion i n t o a rubber network s t r u c t u r e by r e a c t i o n with d i i s o c y a n a t e s (7).

CH CH-CH V 0 3

2

+

Base (CH OH) - = 2 »

C

2

4

C[CH 0(CH CHO)„H] CH 2

f

4

3

+ HO(CH^HO)„H CH,

The a l l y l ether end group i s preserved only under m i l d c o n d i t i o n s of p o l y m e r i z a t i o n . Studies on i t s disappearance under more vigorous c o n d i t i o n s l e d to discovery of the basec a t a l y z e d rearrangement of a l l y l to c i s - p r o p e n y l ethers (8,9,10, 11) and p o s t u l a t i o n of a t r a n s i t i o n complex i n v o l v i n g oxygenpotassium c o o r d i n a t i o n to e x p l a i n the c i s - s t e r e o s p e c i f i c i t y .

ROCH CH=CH 2

2

*

»»

CH=CH

This rearrangement was a l s o found to extend to a l l y l although without c i s - s t e r e o s p e c i f i c i t y (12).

R NCH,CH=CH, 2

-

amines,

R NCH=CHCH, 2

t>Butylethylene oxide was s t u d i e d i n the hope that a s t r u c t u r e not p e r m i t t i n g E2 e l i m i n a t i o n to an a l l y l oxide would lead to high molecular weight polymer (5). However, the S 2 d i s placement i s also much slower i n t h i s monomer, presumably due to s t e r i c hindrance. Under the more vigorous c o n d i t i o n s necessary f o r p o l y m e r i z a t i o n , another c h a i n t r a n s f e r process must occur, although i t s exact nature has not yet been e s t a b l i s h e d . In any event, the l i m i t i n g molecular weight f o r poly (t.-butyl ethylene oxide) i s about 2000.

t-Bu 0CH CH0© ?

<*)

(IV)

+

CH -CH-Bu-t \ / 0

/

2

(III)

OH +?

(5)

I t i s of i n t e r e s t to note that t-butoxide i o n adds to I I I more r e a d i l y than does IV, a neopentyl-type a l k o x i d e (5).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Polyethers

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One of the unexpected d i s c o v e r i e s i n studying base-catalyzed p o l y m e r i z a t i o n o f I I I was that, i n bulk, i t gives a stereoregul a r , c r y s t a l l i n e polymer shown to be d i f f e r e n t by melting p o i n t , X-ray d i f f r a c t i o n p a t t e r n and s o l u t i o n nmr from the c r y s t a l l i n e i s o t a c t i c polymer. The f i r s t guess (13) that i t must be s y n d i o t a c t i c was proven t o be i n c o r r e c t and i t was shown to be i n s t e a d r e g u l a r l y a l t e r n a t i n g i s o t a c t i c and s y n d i o t a c t i c se­ quences (abridged to "isosyn") (14). Such a sequence can be explained by a propagation step i n which the c o n f i g u r a t i o n of the incoming monomer must be opposite to that o f the penultimate u n i t . An hypothesis, i l l u s t r a t e d below, was proposed to account f o r such an unexpected s e l e c t i v i t y f a c t o r . The main feature of the proposal i s the importance of c h e l a t i o n of the ion-paired c a t i o n ( K ) with at l e a s t the l a s t and n e x t - t o - l a s t ether oxygens. The geometry of t h i s c h e l a t e i s mainly d i c t a t e d by the r e q u i r e ment that the penultimat formation. A few reasonabl e t r y of the t r a n s i t i o n s t a t e (14) then i n d i c a t e the necessary preference f o r the c o n f i g u r a t i o n o f the incoming epoxide to be opposite to that of the penultimate u n i t . +

R

C-CHj \ / 0

The importance of c h e l a t i o n by Κ to ether groups i n determining the s t e r e o s e l e c t i o n i s supported by observation on the polymerization of s e v e r a l s u b s t i t u t e d phenyl g l y c i d y l ethers (14). In t h i s case the s t e r e o s e l e c t i o n i s f o r a l l i s o t a c t i c

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

6

r a t h e r than a l t e r n a t i n g isosyn sequences. This can be accommo­ dated i n t r a n s i t i o n s t a t e by the assumption that, i n c o n t r a s t to R = Jt-Bu, where R p r e f e r s to be as f a r from K ® a s p o s s i b l e , f o r R = ArOCH^, the oxygen w i l l seek to coordinate t o K © i n the t r a n s i t i o n s t a t e . This w i l l r e q u i r e the incoming monomer to have the d - c o n f i g u r a t i o n i n f o r R = ArOCH^. The importance of t h i s p a r t i c u l a r c h e l a t i o n i s supported by the observations that £-methoxy and £-methyl groups increase the y i e l d of c r y s t a l l i n e i s o t a c t i c polymer, while £-chloro o r 2,6-dimethyl groups decrease the i s o t a c t i c f r a c t i o n (14). The general importance o f the c h e l a t i o n i n e s t a b l i s h i n g stereo­ chemistry i s supported by the observations that a d d i t i o n o f d i c y c l o h e x y l 18-crown-6 ether i n an amount equivalent to c a t a l y s t , or o f solvents c o o r d i n a t i n g s t r o n g l y with Κ , such as dimethyls u l f o x i d e or hexamethylphosphortriamid (HMPT) markedl decreas the c r y s t a l l i n e polyme phenyl g l y c i d y l ether (14) I n c i d e n t a l l y , our part i n the discovery o f the remarkable u t i l i t y o f DMSO as a solvent f o r base-catalyzed r e a c t i o n s (15,11, 5) was stimulated by our d e s i r e t o f i n d a solvent s u i t a b l e f o r study o f base-catalyzed epoxide polymerization under homogeneous c o n d i t i o n s . DMSO has one drawback i n that i t can p a r t i c i p a t e i n c h a i n - t r a n s f e r . This decreases the molecular weight (as com­ pared to comparable c o n d i t i o n s i n HMPT) and incorporates s u l f o x i d e groups i n the polymer from the f o l l o w i n g t r a n s f e r process (5).

0

Θ

t_-BuE0 g + D M S O — — O H + CH SOCH —CH SCH CH CHO 3

Dimsyl anion

2

e

3

2

2

e

t-Bu

This process then can compete with the u n i d e n t i f i e d t r a n s f e r r e a c t i o n to monomer ( r e a c t i o n ( 5 ) ) . The use o f DMSO a l s o l e d us to a study o f the decomposition of dimsyl i o n a t elevated temperatures. The i d e n t i f i c a t i o n o f methyl mercaptide, methylsulfenate and m e t h y l s u l f i n a t e ions and a number o f methylated butadienes was accounted f o r by the scheme on the next page. An i n t e r e s t i n g and unexpected s i d e l i g h t of our studies o f _t-butyl ethylene oxide arose from the demonstration by Tani (17) t h a t , i n the nmr spectrum, the u p f i e l d o f the three backbone hydrogens i n the polymer i s the t e r t i a r y hydrogen, contrary to normal expectation (13). In i s o t a c t i c polymer, these three hydrogens appear as double doublets a t Q = 3.0, 3.4 and 4.0 ppm. Our assumption that the downfield hydrogen (J = 4.0 ppm) was the methine (13) was proven i n c o r r e c t by Tani (17). When he r e p l a c e d t h i s H by D, i t was the u p f i e l d absorbance (| = · ° ) which disappeared, l e a v i n g the other two as doublets. A year 3

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1. PRICE

Poly ethers

CH SCH 3

7 Heat

f

[CH ] + C H S O

e

2

3

Slow

e

3

[CH -§-CH 3

CH SCH 3

2

CH S0 © + C H S 2

3

e

2

+ 3[CH ]

e

2

H

CH^H + HO

)

0

+ CH =CH-CH=CH ) 2

2

I CH SOCH

e 2

3

CH SO + C H , C H C H , etc. 3

e

5

8

6

10f

7

12

e a r l i e r , a s i m i l a r unexpected u p f i e l d nmr s h i f t had been reported f o r the methylene group i n neopentyl methyl ether and neopentyl R η = 3.4, 3.0 4.0 dimethyl amine (18). T h i s l e d us to the proposal that t h i s "neo­ p e n t y l e f f e c t " was due to a p r e f e r r e d conformation of the neo­ p e n t y l methylene hydrogens as f a r as p o s s i b l e from the lone p a i r s on oxygen and n i t r o g e n (19). This idea was a l s o shown to e x p l a i n the downfield chemical s h i f t of methyl ethers, s u l f i d e , s e l e n i d e s , amines, phosphines, a r s i n e s , f l u o r i d e , c h l o r i d e and bro­ mide without any " e l e c t r o n e g a t i v i t y " f a c t o r but only the very simple p o s t u l a t e that there i s no downfield s h i f t o f hydrogen by an adjacent lone p a i r trans to a proton, but by a f i x e d amount f o r a lone p a i r i n the skew (or gauche) conformation to the adjacent hydrogen (20). B(2). C a t i o n i c Polymerization. While a l k y l s u b s t i t u t i o n s on the ethylene oxide r i n g are detrimental to the a n i o n i c polym­ e r i z a t i o n process, they are b e n e f i c i a l to the c a t i o n i c process. Ethylene oxide i t s e l f gives only low-molecular weight o i l s by the u s u a l strong Lewis a c i d c a t a l y s t s such as BF^ or AtC&y O* 1

t

n

e

other hand, tetramethylethylene oxide, which gives no polymer by base, i s r e a d i l y converted by BF« to a s o l i d polymer decomposing

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

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above 300° C and i n s o l u b l e i n a l l common solvents (21). This m a t e r i a l must be o f a t l e a s t moderately high molecular weight to e x h i b i t these p r o p e r t i e s but i t s i n s o l u b i l i t y has s© f a r prevented a molecular weight determination. The a c t i v a t i n g e f f e c t o f e l e c t r o n donor groups, such as methyl groups, i s a l s o shown by the p o l y m e r i z a t i o n o f c i s - and trans-2-butène oxides. Vandenberg used these monomers t o o f f e r the f i r s t proof that the r i n g opening r e a c t i o n i n c a t i o n i c polyme r i z a t i o n proceeded with c l e a n i n v e r s i o n o f c o n f i g u r a t i o n (22). CH,

CH

\

3

Et /M 3

J

H-C—C-H

V

(S)

CH

—0-j—C

H0 -78° 2

H

CH*

BuLi

Λ

!

3

HO- C I H

H-C—V-CH

I

BuLi

3

I

3

(rac)

(R)

Et AI

H C-OH I CH

CH

H

3

C-04-

(R)

(R) VII

CH

Η

/γ.

3

HO-C —

CH

I

3

C-OH

3

H0 -78° 2

(S)

° (S)

(R)

vm

(meso)

(S)

This same stereochemistry f o r r i n g opening has been shown f o r the case o f c i s and trans-1,2-dideuterioethylene oxide f o r c a t i o n i c , a n i o n i c and c o o r d i n a t i o n p o l y m e r i z a t i o n (4,23). Vandenberg s s t u d i e s with V I I and V I I I l e d to the i n t e r ­ e s t i n g discovery that, whereas V I I gave amorphous polymer, V I I I gave a c r y s t a l l i n e polymer, mp ^ 1 0 0 ° , i n 97% y i e l d , even when r a c - V I I I was used as s t a r t i n g m a t e r i a l . Thus one concludes that f o r VII, r i n g opening of the oxonium intermediate can occur e q u a l l y r e a d i l y a t the S-carbon (to g i v e an RR u n i t ) o r the Rcarbon (to g i v e an SS u n i t ) . In the p o l y m e r i z a t i o n o f r a c - V I I I however, the formation o f c r y s t a l l i n e polymer must mean that the r e a c t i v e oxonium intermediate from an S-unit r e a c t s h i g h l y p r e f ­ e r e n t i a l l y with S-VIII. This appears to be an e x c e l l e n t example of " c h a i n end" s t e r e o s e l e c t i o n (22). When an S-VIII approaches an 1

(S) >

C

H

3

/ (S) ,

3

3

Θ + 0 Η (S)

\

CH

\

I CH

(S)

3

Γ vST 3

CH

3

(S)

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Polyethers

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oxonium intermediate d e r i v e d from S-VIII, as i l l u s t r a t e d , with the two three-membered r i n g s i n a f a v o r a b l e r i g h t angled o r i e n t a ­ t i o n , an H i n V I I I confronts a methyl i n the oxonium r i n g and v i c e v e r s a . I f the approaching monomer were R-VIII, then there would be two h i g h l y unfavorable methyl-methyl c o n f r o n t a t i o n s . Thus the stereochemistry of the growing chain end d i c t a t e s the stereochemistry of the incoming monomer. Β(3). Coordination P o l y m e r i z a t i o n . S t e r e o s e l e c t i v e polym­ e r i z a t i o n s of epoxides have played an important r o l e i n d e v e l ­ oping the mechanistic concepts f o r t h i s major development i n polymer chemistry. The f i r s t r e p o r t by Natta o f i s o t a c t i c p o l y ­ propylene (24) appeared a few months before the P r u i t t and Baggett patent i s s u e d on the p r e p a r a t i o n of i s o t a c t i c p o l y ­ propylene oxide (25). Undoubtedly the work of P r u i t t and Baggett antedated that o f Natta f i r s t paper before ou Baggett polymer was indeed i s o t a c t i c (26). The c h i r a l i t y (asymmetry) of the methine carbon i n propylene oxide and i n i t s polymer has provided many e x t r a experimental parameters to use i n s t u d i e s o f the mechanism o f s t e r e o s e l e c t i v e p o l y m e r i z a t i o n by c o o r d i n a t i o n c a t a l y s t s . The f i r s t proposal of the c o o r d i n a t i o n p o l y m e r i z a t i o n scheme t o e x p l a i n s t e r e o s e l e c t i v e o/-olefin and o l e f i n oxide p o l y m e r i z a t i o n arose from the propylene oxide s t u d i e s (26,27). There are many e f f e c t i v e c a t a l y s t systems, such as FeCl^propylene oxide, d i e t h y l z i n c - w a t e r and trialkylaluminum-water acetylacetone r e a c t i o n products. For none i s the exact s t r u c t u r e of the c a t a l y s t s i t e e s t a b l i s h e d . For a l l , the number of polymer molecules formed i s small compared to the metal atoms used to make the c a t a l y s t . T h i s suggests that the f r a c t i o n o f metal atoms at c a t a l y s t s i t e s must be at l e a s t as s m a l l . While the d e t a i l e d s t r u c t u r e of a c a t a l y s t s i t e remains to be e l u c i d a t e d , s e v e r a l important f e a t u r e s of these c a t a l y s t s are now known. Perhaps the most important feature was e s t a b l i s h e d by Tsuruta (28) who proved that the s t e r e o s e l e c t i v i t y was not a f e a t u r e of the c h i r a l i t y o f the growing end but was b u i l t i n t o the c a t a l y s t s i t e i t s e l f ( " c a t a l y s t - s i t e " c o n t r o l ) . The normal c a t a l y s t p r e p a r a t i o n gives an equal number of R- and S - c h i r a l c a t a l y s t s i t e s which s e l e c t i v e l y coordinate with R- and S-monomer, r e s p e c t i v e l y . This was demonstrated by s t a r t i n g with 75% Rand 25% S-monomer. A f t e r extensive p o l y m e r i z a t i o n , the recovered monomer was o f unchanged o p t i c a l p u r i t y . I f the c h i r a l i t y o f the c a t a l y s t s i t e were due to the c h i r a l i t y of the growing chain ("chain end" c o n t r o l ) one would expect that the growing chains would assume a 75 to 25 r a t i o . The p r e f e r e n t i a l r e a c t i v i t y f o r R-monomer would then be 9 to 1 ( r a t h e r than the experimentally observed 3 to 1) and the recovered monomer should tend toward a 50:50 mixture with i n c r e a s i n g conversion. The c h i r a l i t y of the c a t a l y s t s i t e s can be i n f l u e n c e d i n

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10

POLYETHERS

some cases. For example, Tsuruta (29) has shown that the c a t a ­ l y s t made from R-borneol and d i e t h y l z i n c i s s t e r e o e l e c t i v e , i . e . , i t w i l l polymerize RS-propylene oxide g i v i n g i s o t a c t i c polymer with an excess of R-monomer u n i t s and l e a v i n g the unreacted monomer r i c h i n the S-isomer. This behavior can be accounted f o r by assuming that R-borneol produces the two c h i r a l c a t a l y s t s i t e s i n unequal numbers. A number of other c h i r a l a l c o h o l s and R-monomer f a i l e d to give s t e r e o e l e c t i v e c a t a l y s t , i . e . , they gave c a t a l y s t which behaved as though i t had equal numbers of R- and S - s i t e s (29,30). One p o s s i b l e explanation which has been o f f e r e d (31) i s that the more hindered bornyl group prevents i t from m i g r a t i n g from the c a t a l y s t s i t e L i n the propagation step ( r e a c t i o n ( 3 ) ) . Other simpler groups are known to migrate, becoming end groups i n the polymer (29,32). Another e f f e c t i v e s t e r e o e l e c t i v e c a t a l y s t f o r both epoxide and e p i s u l f i d e p o l y m e r i z a t i o S-) J:-butylethylene g l y c o One of the key f e a t u r e s of the s t e r e o s e l e c t i v e c o o r d i n a t i o n c a t a l y s t s f o r propylene oxide p o l y m e r i z a t i o n i s that, while they can give i s o t a c t i c polymer with a very high r a t i o of i s o t a c t i c to s y n d i o t a c t i c sequences (e.g. > 370) (34), i n the same r e a c t i o n mixture a l a r g e p a r t of the polymer i s amorphous. Even when Rpropylene oxide i s used as s t a r t i n g m a t e r i a l , much of the product i s amorphous polymer of low o p t i c a l r o t a t i o n c o n t a i n i n g many Spropylene oxide u n i t s (30). T h i s amorphous polymer has been shown to c o n t a i n head-tohead u n i t s as the imperfections i n s t r u c t u r e . T h i s was shown by degradation and i s o l a t i o n of the dimer g l y c o l s (35,36).

1. -/OCHCH V I ^ CH 3

0

H O

( f

3

=—• 2. LAH

H0CHCH 0CHCH 0H I I CH CH ix 9

3

9

+

C H

2> ° 2

CHL χ J

3

^HOCH CH) O 2

XI

2

GH

3

The diprimary (XI) and disecondary (X) dimer g l y c o l s w i l l a r i s e only from head-to-head u n i t s i n the polymer. F o r t u n a t e l y , the three isomeric g l y c o l s can be separated by g l c . For i s o ­ t a c t i c polymer or amorphous polymer made by base c a t a l y s i s of RS-monomer, l i t t l e i f any X and XI were found. The amorphous polymer separated from i s o t a c t i c polymer prepared f o r a v a r i e t y of c o o r d i n a t i o n c a t a l y s t s gave 25 to 40% of X and XI. F u r t h e r ­ more, the c o r r e l a t i o n of the head-to-head content from such degradative s t u d i e s with the o p t i c a l a c t i v i t y of the amorphous f r a c t i o n u s i n g R-monomer with the same c a t a l y s t shows that f o r every head-to-head u n i t there i s one R-monomer converted to an S-polymer u n i t . T h i s proves that, at the c o o r d i n a t i o n s i t e

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Poly ethers

11

g i v i n g amorphous polymer, the abnormal r i n g opening which occurs at the secondary carbon, to give the head-to-head u n i t , has done so with i n v e r s i o n of c o n f i g u r a t i o n . A more recent s i m i l a r study of amorphous polymer accompanying i s o t a c t i c polymer i n the polymerization of RS-jt-butylethylene oxide by c o o r d i n a t i o n c a t a l y s t s has shown that i t a l s o contains head-to-head u n i t s (14). In t h i s case, the 1°, 2°dimer g l y c o l , which was only 30 t o 40% of the dimer mixture, could be separated i n t o i t s erythro and threo isomers by g l c . The i s o t a c t i c polymer gave, as expected, almost e x c l u s i v e l y the erythro-isomer, while the amorphous f r a c t i o n s gave only 40-45% e r y t h r o and 55-60% threo. These data combined i n d i c a t e that a t y p i c a l c o o r d i n a t i o n c a t a l y s t , such as Et^Zn-H^O, contains i s o t a c t i c c a t a l y s t s i t e s and amorphous c a t a l y s t s i t e s The i s o t a c t i c s i t e s are h i g h l y selective i n coordinatin t i o n (3), step 1) and opening only at the primary carbon of the epoxide r i n g (react i o n (3), step 2). The amorphous c a t a l y s t s i t e can coordinate e q u a l l y w e l l with R- or S-monomer i n step 1, and has very l i t t l e preference f o r attack at the primary o r secondary carbon i n the r i n g opening propagation step. Not much q u a n t i t a t i v e information i s a v a i l a b l e on the r e l a t i v e r e a c t i v i t i e s of epoxides i n copolymerization. With base i n DMSO, phenyl g l y c i d y l ether i s 7 times more r e a c t i v e than p r o p y l ene oxide, presumably due to the i n d u c t i v e electron-withdrawing e f f e c t o f the phenoxy group (37). A £-chloro-substituent enhances the r e a c t i v i t y o f PGE while a £-methoxy group diminishes it. That c o o r d i n a t i o n c a t a l y s t s e x h i b i t p r o p e r t i e s c l o s e r to c a t i o n i c than a n i o n i c c a t a l y s t s i s i n d i c a t e d by the opposite i n f l u e n c e o f £-chloro and £-methoxy groups i n PGE, the l a t t e r now being the more r e a c t i v e (38). Furthermore, propylene oxide i s 50% more r e a c t i v e than phenyl g l y c i d y l ether and e p i c h l o r o h y d r i n 33% l e s s r e a c t i v e u s i n g Et^At-H^O as a c a t a l y s t . C.

Polyphenylene Oxides

The thermal and chemical s t a b i l i t y o f diphenyl ether has long been recognized as suggesting i n t e r e s t i n g and u s e f u l prope r t i e s f o r high polymers IbuiÎÊ with t h i s s t r u c t u r a l u n i t (2). The development o f s u c c e s s f u l methods f o r preparing such s t r u c tures has been a challenge to the s y n t h e t i c chemist. The r e markable chemistry o f the processes discovered has a l s o l e d t o s i g n i f i c a n t new f a c t s and hypotheses about the behavior o f phenoxy r a d i c a l s . The i n v e s t i g a t i o n s i n our l a b o r a t o r y were o r i g i n a l l y i n s p i r e d by the work o f Hunter and h i s students (39). They concluded that the amorphous products formed from t r i h a l o p h e n o l s on treatment with v a r i o u s o x i d i z i n g agents were low-molecular weight polymers formed by l o s s o f a halogen atom i n e i t h e r the 2- or 4-

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

12

POLYETHERS

p o s i t i o n . We decided to i n v e s t i g a t e t h i s r e a c t i o n f u r t h e r , but w i t h 4~halo-2,6-xylenols as monomers. T h i s proved s u c c e s s f u l when c a t a l y s t s were used which Cook (40,41) found u s e f u l i n converting 2 , 4 , 6 - t r i - t - b u t y l p h e n o l to i t s s t a b l e blue f r e e r a d i c a l . Under these c o n d i t i o n s , 4-bromo-2,6x y l e n o l can be converted to a high-molecular weight polymer i n seconds, l i b e r a t i n g the bromine as bromide i o n . In the absence of oxidant c a t a l y s t , no bromide i o n i s l i b e r a t e d even a f t e r months. The p o l y m e r i z a t i o n i s thus obviously not a n u c l e o p h i l i c displacement. Furthermore, i t has the c h a r a c t e r i s t i c s of a chain r e a c t i o n , s i n c e polymer formed even at only 5% conversion i s of high molecular weight (42). While the polymer has a very low b r i t t l e temperature (-150°), i t s high g l a s s - t r a n s i t i o n tempera­ ture (> 200°) makes i t very hard to c r y s t a l l i z e . The polymer i s

L

CH

3

J

normally amorphous and s o l u b l e i n the usual organic s o l v e n t s , such as benzene. By h e a t i n g a s o l u t i o n i n α-pinene overnight, i t separates as c r y s t a l l i n e polymer, mp 275° (43). The commercial synthesis of p o l y x y l e n o l (sometimes r e f e r r e d to as PPO, £ply(uhenylene oxide)) i s c a r r i e d out by the oxida­ t i v e c o u p l i n g of 2,6-xylenol. This remarkable r e a c t i o n was d i s ­ covered by Hay and h i s coworkers (44). One i n t r i g u i n g f e a t u r e of t h i s p o l y m e r i z a t i o n i s that i t i s a stepwise condensation. The product at 50% conversion i s a low-molecular weight o i l . The dimer (XIII) and trimer i n t h i s m a t e r i a l are as e a s i l y polymeri z a b l e as the monomer. The accepted mechanism i n v o l v e s coupling of aryloxy intermediates to give quinone k e t a l s (45,46,47). The Dutch workers i n p a r t i c u l a r s t u d i e d many simple models

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Polyethers

to determine what s t r u c t u r a l f a c t o r s and c o n d i t i o n s favored con­ v e r s i o n of XIV to XV by d i r e c t rearrangement (a) or through d i s ­ s o c i a t i o n and recombination (b). One of the i n t r i g u i n g features of the o x i d a t i v e coupling i s the question of the features d i c t a t i n g C-0 coupling to give dimer X I I I vs_. C-C coupling to give the diphenoquinone XVI. For

o x i d a t i o n by Ag20 (48) or MnO^ (47), excess oxidant gives polyx y l e n o l , while excess x y l e n o l gives XVI. Even under the Hay con­ d i t i o n s , replacement of one methyl by t^-butyl or both by _i-Pr l e d to the diphenoquinone as the main product. The r a t e of phenol o x i d a t i o n under the Hay c o n d i t i o n s i s f i r s t order i n c a t a l y s t , f i r s t order i n 0^ pressure and zero order i n phenol, although the magnitude of the r a t e i s q u i t e s e n s i t i v e to s u b s t i t u t i o n s i n the phenol r i n g , being favored by e l e c t r o n - r e l e a s i n g groups (49). We have suggested the scheme on the next page to account f o r these observations. The dimer X I I I could a r i s e e i t h e r by coupling of two f r e e f r e e r a d i c a l s or by attack of a r a d i c a l , l i b e r a t e d i n the transformation from Β to C i n Scheme I to remove ArO* from D. Decreased base c o o r d i n a t i o n on Cu (by l i g a n d concentration, l i g a n d hindrance or ortho hindrance i n the phenol) favors C-G coupling (50). We have proposed the modified Scheme I I to exl a i n t h i s behavior. The e s s e n t i a l f e a t u r e i s that decreased ase c o o r d i n a t i o n at Cu increases the a f f i n i t y of the Cu f o r the

f

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

14

POLYETHERS

Scheme I

ArO^

y \

(pyrV

\(

,(pyr>2

(Pyr)

2

(pyr)2

gAr

CI

Β + 2ArOH, -2ArO-

ArO.

yPL Cu°


N

-2ArO-

(fast)

Vf

Cf

ipyr)

fast

CI 2

+ 2ArOH, (fast)

OAr

(pyr)

OH

CI

2

D oxygen of the i n c i p i e n t A r O r a d i c a l . Since the i n c i p i e n t r a d i ­ c a l remains bound to Cu at oxygen, i t couples at the exposed 4carbon.

ArO

pyr

fK

x

Cu" pyr

Cu

11

CI

OAr

A' 2ArOH|(-2HP)

/

HO.

pyr

/

Cu"

\

ci D'

/

y

CI

M e

7

M

\

Η

Cu" OH \

Me

pyr

Me

diphenoquinone

The behavior of Ag 0 and freshly-prepared MnO^ can also be f i t i n t o t h i s scheme, using MnO^ as an example, f o r excess oxidant there might be only one phenol coordinated on manganese (E) while f o r excess phenol, two (or more) ( F ) . The manganese i n (E), as compared to (F), would be more " n e u t r a l i z e d " by hydroxyl groups, would thus be a weaker Lewis 2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

PRICE

15

Poly ethers

ArO

OH X

I V Mh

HO

ArO*

+

Mn

i:[I

(OH),

OH (E)

ArO

\

I V Μη

m

OR ArO»

'

X

^

OAr

(F) (R = H or Ar) . Me

ψ

OR

III

Λ3-

Me

V

/ RO

XIV

\ OAr

a c i d and could thus more r e a d i l y l i b e r a t e a f r e e aryloxy r a d i c a l , envisaged as necessary f o r G-0 c o u p l i n g . In ( F ) , the manganese would be a stronger Lewis a c i d and, l i k e A , would form a stronger bond to the a r y l oxygen, would not l i b e r a t e the f r e e aryloxy r a d i c a l and would t h e r e f o r e g i v e C-C coupling. 1

D.

Arylene-Alkylene

Copolymers

Dewar has reported that 2,6-dihalo-l,4-diazooxides can be converted by p h o t o l y s i s to poly(2,6-dihalophenylene oxides) (51,52). Dewar has proposed that the r o l e of X halogen i s to promote s i n g l e t to t r i p l e t i n t e r c o n v e r s i o n f o r the intermediate e

X

/— H

*

N

"\

χ

HN0

2

λ-OH

Ν

X

XVII

— /

hv

a f t e r l o s s of ^ (52). When t h i s r e a c t i o n was attempted with X = C H no polymer was obtained, unless the r e a c t i o n was c a r r i e d out i n THF or dioxane. S t i l l e (53) and we (54) discovered concurrently and independently that t h i s p o l y m e r i z a t i o n i n v o l v e s i n c o r p o r a t i o n of the c y c l i c ether s o l v e n t . Scheme I I I does account f o r the r e g u l a r a l t e r n a t i n g 1:1 3>

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

16

POLYETHERS

Scheme I I I

CH θ

CH

3

0 - ^ ^ - Ν

2

3

ί

hv(slow)

\_y CH

CH 3 XVII

3

I

(fast)

GO-\^-0(CHt CH

)0 - ^ ^ - N 4

CH

3

2

®

3

THF |(fast) e

O-Xyl-0(CH ) -0-Xyl-Oe^] 2

4

(fast) etc. polymer obtained. Most o f the polymers obtained were low molec­ u l a r weight, low melting and s o l u b l e . Only a small amount (ca. 5%) o f high molecular weight c r y s t a l l i n e polymer was obtained and t h a t was deposited as a f i l m on the g l a s s s u r f a c e o f the reac­ tion vessel. In c o n c l u s i o n , while i t i s evident that much has been learned about r e a c t i o n s producing polyethers and important f a c t o r s which a f f e c t them, there remain i n t r i g u i n g unanswered questions. While there has been much s p e c u l a t i o n , i t i s not c l e a r that we know i n any d e t a i l the s t r u c t u r a l f e a t u r e s o f s t e r e o s e l e c t i v e and s t e r e o e l e c t i v e c o o r d i n a t i o n c a t a l y s t s f o r epoxide p o l y m e r i z a t i o n .

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1. PRICE

Polyethers

17

For o x i d a t i v e coupling o f 2,6-xylenol, there has also been much s p e c u l a t i o n about the nature o f the c a t a l y s t , but again there i s much y e t to be learned. In both cases, i t seems c l e a r that the c e n t r a l s t r u c t u r a l questions revolve around the nature of r e a c t i v e groups coordinated around one or more metal atoms. In the case of the p o l y m e r i z a t i o n o f 4-bromo-2,6-xylenol, the f r e e r a d i c a l chain r e a c t i o n hypothesis r e s t s on r e l a t i v e l y slender evidence. We are i n the process of attempting to study the r e a c t i o n under homogeneous c o n d i t i o n s which may provide more s u b s t a n t i a l evidence f o r the mechanism i n v o l v e d . The author wishes to express h i s a p p r e c i a t i o n to the many coworkers who have been involved i n our s t u d i e s o f p o l y e t h e r s . We a l s o acknowledge the f i n a n c i a l support of the General T i r e and Rubber Company and of the U. S. Army Quartermaster Corps. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. C., 15. 16. 17. 18.

N a t i o n a l Research Council-Quartermaster Corps A r c t i c Rubber Conference, Washington, D. C., 30 January-2 February 1949. Quartermaster Corps High Temperature Rubber Conference, Washington, D. C., 3-4 November 1953. Vandenberg, E. J., J. Amer. Chem. Soc. (1961) 83, 3538; J . Polymer S c i . Β (1964) 2, 1085. P r i c e , C. C. and Spector, R., J. Amer. Chem. Soc. (1966) 88, 4171. P r i c e , C. C. and Carmelite, D. D., J. Amer. Chem. Soc. (1966) 88, 4039. P r i c e , C. C. and S t . P i e r r e , L. E., J. Amer. Chem. Soc. (1956) 78, 3432. P r i c e , C. C., U. S. Pat. 2,866,744 (30 Dec. 1958); The Chemist (1961) 38, 1. Dege, G. C., H a r r i s , R. L. and MacKenzie, H. S., J. Amer. Chem. Soc. (1959) 81, 3374. Simons, D. M. and Verbanc, J. J., J. Polymer S c i . (1960) 44, 303. Prosser, T. S., J. Amer. Chem. Soc. (1961) 83, 1701. Snyder, W. H. and P r i c e , C. C., J. Amer. Chem. Soc. (1961) 83, 1773. P r i c e , C. C. and Snyder, W. Η., Tetrahedron L e t t . (1962) 69. P r i c e , C. C. and Fukutani, H., J. Polymer Chem. A-1 (1968) 6, 2653. P r i c e , C. C., Akkapeddi, Μ. Κ., deBona, Β. T. and F u r i e , Β. J. Amer. Chem. Soc. (1972) 94, 3964. Cram, D. J., Richborn, B. and Knox, G. R., J. Amer. Chem. Soc. (1960) 82, 6412. P r i c e , C. C. and Yukuta, Toshio, J. Org. Chem. (1969) 34, 2503. T a n i , H. and Oguni, N., Polym. L e t t . (1969) 2, 803. Goldberg, S. I., Lam F.-L. and Davis, J. E., J. Org. Chem. (1967) 32, 1648.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

18

19. 20. 21.

W.,

P r i c e , C. C., Tetrahedron L e t t . (1971) 4527. P r i c e , C. C., J. Org. Chem. (1973) 38, 615. Cairns, T. L. and Joyce, R. Μ., Jr., U. S. Pat, 2,445,912 (1948); Ishida, S., B u l l . Chem. Soc. Japan (1960) 33, 924. 22. Vandenberg, E. J., J. Polymer S c i . (1960) 47, 489. 23. Yokoyama, J. Μ., Ochi, Η., Tadokoro, H. and P r i c e , C. C., Macromolecules (1972) 5, 690. 24. Natta, G., J. Polymer S c i . (1955) 16, 143. 25. P r u i t t , M. E. and Baggett, J. M., U. S. Pat. 2,706,182 (12 A p r i l 1955). 26. P r i c e , C. C. and Osgan, M., J. Amer. Chem. Soc. (1956) 78, 690, 4787. 27. P r i c e , C. C. and Osgan, M., J. Polymer Sci. (1959), 34, 153. 28. Tsuruta, T., Inoue, S., Yoshida, N. and Yokota, Y., Makromol. Chem. (1965) 81, 191; see a l s o Tsuruta, T., J. Polymer Sci. D (1972) 180. 29. Inoue, S., Tsuruta (1962) 53, 215; Inoue, S., Tsuruta, T. and Yoshida, Ν., Makromol. Chem. (1964) 79, 34. 30. Chu, Ν. S. and P r i c e , C. C., J. Polymer S c i . A-1 (1963) 1, 1105. 31. P r i c e , C. C., "The Polyethers", i n "The Chemistry o f the Ether Linkage", Saul P a t a i , Ed., Interscience, Ν. Y., Ν. Y. (1967). 32. Ebert, P. E. and P r i c e , C. C., J. Polymer S c i . (1959) 34, 157. 33. Sepulchre, M., Spassky, N. and Sigwalt, P., Macromolecules (1972) 5, 92. 34. P r i c e , C. C. and Tumolo, A. L., J. Polymer S c i . A-1 (1967) 5, 175. 35. P r i c e , C. C. and Spector, R., J. Amer. Chem. Soc. (1965) 87, 2069. 36. P r i c e , C. C. and Tumolo, A. L., J. Polymer S c i . , A-1 (1967) 5, 407. 37. P r i c e , C. C., A t a r a s h i , Y. and Yamamoto, R., J. Polymer Sci. A-1, (1969) 7, 569. 38. P r i c e , C. C. and Brecker, L., J. Polymer S c i . A-1, (1969) 7, 575. 39. Hunter, W. H. and Dahlen, M. Α., J. Amer. Chem. Soc. (1932) 54, 2456. 40. Cook, C. D., et al., J. Org. Chem. (1953) 18, 261. 41. Cook, C. D., et al., J. Amer. Chem. Soc. (1956) 78, 2002, 3797, 4159. 42. P r i c e , C. C. and Staffin, G., Army-Navy-Air Force Elastomer Conference, Dayton, Ohio, October 1958; J. Amer. Chem. Soc. (1960) 82, 3632; U. S. Pat. 3,382,212 (7 May 1968). 43. Butte, W. Α., P r i c e , C. C. and Hughes, R. Ε., J. Polymer S c i . (1962) 61, 528. 44. Hay, A. S., Blanchard, H. S., Endres, G. F. and Eustance, J. J. Amer. Chem. Soc. (1959) 81, 6335.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

PRICE

45. 46. 47. 48. 49. 50. 51. 52. 53. 54.

Polyethers

19

Cooper, G. D., Blanchard, H. S., Endres, G. F. and Finkbeiner, H., J. Amer. Chem. Soc. (1965), 87, 3996. M i j s , W. J., van Lohuizen, O. E., Bussink, J. and V o l l b r a c h t L., Tetrahedron (1967) 23, 2253. McNeils, E., J. Org. Chem. (1966) 31, 1255. Lindgren, B. O., Acta Chem. Scand. (1960) 14, 1203. P r i c e , C. C. and Nakaoka, Κ., Macromolecules (1971) 4, 363. Hay, A. S., F o r t s c h r . Hochpolym.-Forsch. (1967) 496. Dewar, M. J. S. and James, Α. Ν., J. Chem. Soc. (1958) 917. Dewar, M. J. S. and Narayanaswami, Κ., J. Amer. Chem. Soc., (1964), 86, 2422. Stille, J. Κ., Cassidy, P. and Plummer, L., J. Amer. Chem. Soc. (1963) 85, 1318. Kunitake, T. and P r i c e , C. C., J. Amer. Chem. Soc. (1963) 85, 761.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2 Poly(Propylene Ether) Polyols Prepared With a Zinc Hexacyanocobaltate Complex Catalyst R. A . L I V I G N I , R. J. H E R O L D , O . C . E L M E R ,

and S. L. A G G A R W A L

The General Tire and Rubber Co., Research and Development Division, Akron, Ohio 44329

Introduction A new class of catalysts for the polymerization of 1 , 2 - e x p o x ides was discovered in our laboratories and subsequently patented (1) in 1969. These catalysts consist of complexes containing hexacyanometalate salts. The composition of a typical catalyst c a nberepresentedas:Zn [Co(CN) ] 2.4(CH OCH CH OCH )0.85ZnCl 4.4H O. These c o m p l e x e s a r e u n i q u e as polymerization catalysts for 1,2-epoxides in two respects. First, they are not especially sensitive to the a t m o s p h e r e a n d will retain their activity when stored at room t e m p e r a t u r e in a conventionally c a p p e d vial. S e c o n d , these catalysts are not only useful for preparing high molecular w e i g h t poly ( p r o p y l e n e o x i d e ) r u b b e r (2), but they are equally effective when u s e d with certain low molecular weight hydroxyl containing compounds (initiators) to form poly(propylene e t h e r ) polyols h a v i n g good hydroxyl functionality. The latter feature of these catalysts is the topic of this paper. An unsymmetrically substituted epoxide, such as propylene oxide, c a n u n d e r g o ring o p e n i n g to give two different p r o d u c t s : 3

6

2

3

2

2

2

2

2

0

CHj-CH-CH + HA 2

OH A • CHj CH-CH A + CH3CH-CH7OH ?

NORMAL

ABNORMAL

These p r o d u c t s have been designated (3) normal and abnormal, with respect to addition of the nucleophile on the unsubstituted or substituted c a r b o n a t o m of the e p o x i d e . The n o r m a l i s o m e r is f o r m e d under basic or neutral conditions, via an S 2 reaction b e t w e e n t h e nucleophile and the unsubstituted methylenic c a r b o n of the ring. Attack at the unsubstituted carbon atom is favored primarily by steric factors. W i t h more acidic reaction conditions, increasing amounts of the abnormal product a r e f o r m e d , since the substituted c a r b o n atom provides a more stable c a r b e n ium ion intermediate. N

20

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

LiviGNi E T A L .

Ρ'oly(Propylene

21

Ether) Poly ois

Poly(propylene ether) p o l y o l s are important intermediates i n t h e p r e p a r a t i o n o f p o l y u r e t h a n e foams and e l a s t o m e r s . They a r e g e n e r a l l y p r e p a r e d b y b a s e c a t a l y s i s , s u c h as b y t h e u s e o f po­ t a s s i u m h y d r o x i d e , and c o n s i s t o f a l m o s t e x c l u s i v e l y t h e n o r m a l product having the secondary h y d r o x y l group at the t e r m i n a l u n i t . S t . P i e r r e a n d P r i c e (k) f o u n d t h a t t h e s e p o l y m e r s c o n t a i n b o t h a l l y l a n d p r o p e n y l u n s a t u r a t i o n . Dege and c o w o r k e r s (5)reported t h a t t h e amount o f t e r m i n a l u n s a t u r a t i o n l i m i t s t h e m o l e c u l a r w e i g h t o f t h e s e p o l y m e r s and d e c r e a s e s t h e i r u t i l i t y i n c h a i n e x ­ tension reactions with diisocyanates. The u n s a t u r a t i o n i s i n t r o ­ d u c e d b y a c h a i n t r a n s f e r r e a c t i o n t o monomer, a s s u g g e s t e d b y Gee and c o w o r k e r s (6) and p r o b a b l y o c c u r s a t t h e p r i m a r y h y d r o ­ gen o f t h e m e t h y l g r o u p ( 7 ) . A new c h a i n i s t h e n f o r m e d w h i c h c o n t a i n s a n a l l y l e t h e r g r o u p a t one end.

A R-O-CHj-ÇH-ΟΓ + H-CH7CH-CH2 CH 3

H R-0-CHjÇ-OH + CHfCH-CHyO" CH

3

Some o f t h e s e t e r m i n a l a l l y l g r o u p s c a n u n d e r g o r e a r r a n g e m e n t (8) t o p r o p e n y l g r o u p s i n t h e b a s i c medium. We have s t u d i e d , i n d e t a i l , t h e f o r m a t i o n o f p o l y ( p r o p y l e n e ether) d i o l s b y the r e a c t i o n o f propylene oxide w i t h 1,5-pentan e d i o l c a t a l y z e d by t h e hexacyanometalate complex: Z n [Co(CN) ] 2Λ(ϋΗ OCHQCHQOCEQ)0.85 Z n C l g L t a g O . The h y d r o x y l t y p e p r e s e n t i n t h e d i o l s , p r e p a r e d w i t h t h i s c a t a l y s t , has b e e n f o u n d b y S i g g i a s a c e t y l a t i o n method (£) t o b e a l m o s t e x c l u s i v e l y s e c o n d ­ a r y , w i t h o n l y k-10% o f t h e h y d r o x y l s b e i n g o f t h e p r i m a r y t y p e . 3

6

a

3

!

Experimental K i n e t i c S t u d i e s . A l l c h e m i c a l s u s e d were r i g o r o u s l y p u r i ­ fied. P r o p y l e n e o x i d e and 1 , 5 - p e n t a n e d i o l w e r e vacuum d i s t i l l e d f r o m a n h y d r o u s c a l c i u m s u l f a t e . n - P e n t a n e , n-hexane, and t e t r a h y d r o f u r a n w e r e vacuum d i s t i l l e d f r o m c a l c i u m h y d r i d e . The same b a t c h o f z i n c h e x a c y a n o c o b a l t a t e ( i l l ) c o m p l e x c a t a l y s t was u s e d i n a l l o f t h e k i n e t i c s t u d i e s . I t was p r e ­ pared by s l o w l y adding a s o l u t i o n o f calcium hexacyanocobaltate ( I I I ) (6.6Ο grams) i n a m i x t u r e o f w a t e r (^4-8.0 grams) and 1 , 2 d i m e t h o x y e t h a n e (2^.0 grams) t o a s o l u t i o n o f z i n c c h l o r i d e (5.28 grams) i n w a t e r (6.0 g r a m s ) . To t h e r e s u l t i n g c o m b i n a t i o n , , a s o l u t i o n c o n t a i n i n g 1 , 2 - d i m e t h o x y e t h a n e (27-5 grams) i n w a t e r (82.5 grams) was added. The r e s u l t i n g s l u r r y was t r e a t e d w i t h a n aqueous s o l u t i o n c o n t a i n i n g 25$>, 1 , 2 - d i m e t h o x y e t h a n e , b y w e i g h t ,

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

22

i n a W e b e e l l C o n t i n u o u s D i a l y z e r - M o d e l B, e q u i p p e d w i t h c e l l o phane membranes. D i a l y s i s was d i s c o n t i n u e d a f t e r l 6 h o u r s . The c o m p l e x was r e c o v e r e d b y c e n t r i f u g a t i o n s u s p e n d e d i n d r y n-hexane, t h e n c o l l e c t e d b y vacuum f i l t r a t i o n a n d d r i e d a t room tempe r a t u r e u n d e r vacuum. S i n c e t h e h e x a c y a n o m e t a l a t e complexes c a n be o f v a r i a b l e c o m p o s i t i o n , i t i s i m p o r t a n t t o have some means o f d e t e r m i n i n g w h e t h e r a c o m p l e x w i l l have s u f f i c i e n t a c t i v i t y i n a n e p o x i d e polymerization. This i s p o s s i b l e by examining the i n f r a r e d a b s o r p t i o n s p e c t r a (2) o f N u j o l m u l l s o f t h e s e c o m p l e x e s . F o r l i q u i d 1,2-dimethoxyethane (glyme), t h e strong absorption a t 851 cm"" h a s b e e n a s s i g n e d ( 1 0 ) t o t h e m e t h y l e n i c r o c k i n g mode. In a h i g h l y a c t i v e c a t a l y s t c o n s i s t i n g o f z i n c hexacyanocobaltate, glyme, z i n c c h l o r i d e and water, t h i s a b s o r p t i o n i s s h i f t e d t o 838 cm"" , w h e r e a s i n a c a t a l y s t o f l o w a c t i v i t y , t h e a b s o r p t i o n o c c u r s a t 857 cm"" . K i n e t i l e n e e t h e r ) d i o l was p r e p a r e c o b a l t a t e ( i l l ) c o m p l e x c a t a l y s t were c a r r i e d o u t i n c a p p e d b o t t l e s u n d e r a n i t r o g e n a t m o s p h e r e . The e x t e n t o f r e a c t i o n was c a l c u l a t e d f r o m a measurement o f t o t a l s o l i d s a f t e r t h e p r o p y l e n e o x i d e was removed b y e v a p o r a t i o n . Rate s t u d i e s on "seeded" p o l y m e r i z a t i o n s were c a r r i e d o u t b y c h a r g i n g r e a c t a n t s i n a n a l l g l a s s r e a c t o r a t 10~ T o r r , a n d f o l l o w i n g t h e c o u r s e o f t h e r e action dilatometrically. S p e c i a l g l a s s e q u i p m e n t was c o n s t r u c t e d f o r t h e s e m a n i p u l a t i o n s , a s shown i n F i g u r e 1. I n c r e m e n t a l monomer a d d i t i o n s t u d i e s , b e a r i n g o n t h e mechani s m o f i n i t i a t i o n a n d t e r m i n a t i o n , w e r e done u n d e r a n i t r o g e n atmosphere i n b o t t l e s . The b o t t l e s were f i t t e d w i t h a p e r f o r a t e d cap h a v i n g a b u t y l g a s k e t w h i c h was e x t r a c t e d u s i n g a m i x t u r e o f e t h a n o l w i t h 32$> b y w e i g h t o f t o l u e n e . These p o l y m e r i z a t i o n s w e r e c a r r i e d o u t a t a n i n i t i a l c a t a l y s t c o n c e n t r a t i o n o f 0.OhQ w e i g h t p e r c e n t a n d a t 50°C. 5

1

1

1

6

M o l e c u l a r W e i g h t C h a r a c t e r i z a t i o n . G e l p e r m e a t i o n chromat o g r a p h y was c a r r i e d o u t u s i n g a W a t e r s A s s o c i a t e s i n s t r u m e n t . P o l y m e r s f r o m i n c r e m e n t a l monomer a d d i t i o n s w e r e a n a l y z e d i n t e t r a h y d r o f u r a n a t room t e m p e r a t u r e u s i n g a 1 0 , 1 0 , a n d 10 A d e s i g n a t e d column s e t packed w i t h S t y r a g e l . A l l o t h e r p o l y m e r s w e r e a n a l y z e d i n b e n z e n e s o l u t i o n . One p e r c e n t s o l u t i o n s o f p o l y m e r were i n j e c t e d f o r one m i n u t e w i t h t h e i n s t r u m e n t o p e r a t i n g at a f l o w r a t e o f 1 ml/min. Number-average m o l e c u l a r w e i g h t s w e r e d e t e r m i n e d i n b e n z e n e , u s i n g a M e c h r o l a b V a p o r P r e s s u r e Osmometer(VPO). 6

4

3

F u n c t i o n a l i t y Determination. H y d r o x y l c o n t e n t s were d e t e r m i n e d u s i n g t h e p h t h a l i c a n h y d r i d e method a n d u n s a t u r a t i o n was m e a s u r e d b y a m e t h o x y m e r c u r a t i o n m e t h o d , b o t h a c c o r d i n g t o ASTM D28U9 (11). C a r b o n y l c o n t e n t s were o b t a i n e d u s i n g h y d r o x y l a m i n e h y d r o c h l o r i d e , a c c o r d i n g t o S. S i g g i a (12).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

LiviGNi E T A L .

F*oly{Propylene Ether) Polyols

23

F u n c t i o n a l i t y determinations, using the Williams Plastometer ( 1 3 ) , w e r e c a r r i e d o u t o n a one gram sample a t a f o r c e o f 5000 + 5 grams. The p o l y u r e t h a n e s were p r e p a r e d "by r e a c t i n g t h e p o l y (propylene ether) d i o l s w i t h 2,^-tolylene diisoeyanate, i n the p r e s e n c e o f 0.0h% s t a n n o u s o c t a n o a t e a s a c a t a l y s t , f o r k-0 h o u r s a t 120°C. A p l u g t a k e n f r o m t h e c e n t e r o f t h e r u b b e r h a v i n g a d i a m e t e r o f 13 mm a n d w e i g h t o f one gram was u s e d i n t h e m e a s u r e ment. The W i l l i a m s p l a s t i c i t y was e x p r e s s e d i n m i l s a n d t a k e n as t h e h e i g h t o f t h e s p e c i m e n a f t e r a t h r e e m i n u t e p e r i o d u n d e r the l o a d s p e c i f i e d . R e s u l t s and D i s c u s s i o n Kinetic studies. The r a t e o f f o r m a t i o n o f p o l y ( p r o p y l e n e e t h e r ) d i o l u s i n g 1 , 5 - p e n t a n e d i o l as an i n i t i a t o r and t h e z i n c h e x a c y a n o c o b a l t a t e comple The r e a c t i o n r a t e c u r v e monomer p o l y m e r i z a t i o n s t u d y , a s w e l l a s a p o l y m e r i z a t i o n c a r r i e d out i n n-pentane (10.7 m o l / l ) . Each o f t h e e x p e r i m e n t a l p o i n t s r e p r e s e n t s a s e p a r a t e r u n i n w h i c h t h e p o l y m e r i z a t i o n was t e r m i n a t e d a t t h e s p e c i f i e d t i m e a n d r e s i d u a l monomer a n d s o l v e n t r e moved. The g e n e r a l f e a t u r e s o f t h e s e p o l y m e r i z a t i o n s a r e t h e i n i t i a l l y s l o w c o n s u m p t i o n o f monomer e x t e n d i n g o v e r t h r e e t o f o u r h o u r s f o l l o w e d b y t h e r a p i d d i s a p p e a r a n c e o f monomer t o i t s t o t a l consumption. The c a t a l y s t , i n i t i a l l y i n s o l u b l e i n e i t h e r o f t h e r e a c t i o n m e d i a , i s o b s e r v e d t o become a l m o s t t o t a l l y d i s p e r s e d when t h e r e a c t i o n r a t e b e g i n s t o show r a p i d a c c e l e r a t i o n . The s o l u t i o n s , a t t h i s t i m e , show o n l y a s l i g h t t u r b i d i t y . F o l l o w i n g t h e i n i t i a l slow disappearance o f propylene o x i d e , t h e monomer i s consumed a c c o r d i n g t o f i r s t - o r d e r k i n e t i c s , a s shown by t h e s t r a i g h t l i n e p l o t s o f l o g [ M ] / [ M ] versus time, g i v e n i n F i g u r e 3. G e l p e r m e a t i o n chromatograms w e r e o b t a i n e d o n t h e e n t i r e r e a c t i o n mixture r e s u l t i n g from t h e p o l y m e r i z a t i o n as a f u n c t i o n o f t h e e x t e n t o f c o n v e r s i o n (lh) a n d t h e s e a r e shown i n F i g u r e k. The p e a k p o s i t i o n a t t h e l a r g e s t e l u t i o n volume c o r r e s p o n d s t o the l o w e s t m o l e c u l a r weight s p e c i e p r e s e n t i n t h e r e a c t i o n mixt u r e , which i s the 1,5-pentanediol. T h i s component i s consumed d u r i n g t h e i n i t i a l stage o f t h e r e a c t i o n p r o d u c i n g a h i g h molecul a r weight substance o f n e a r l y constant molecular weight. A t 23.2$ c o n v e r s i o n , t h e g e l p e r m e a t i o n c h r o m a t o g r a m g a v e n o i n d i c a t i o n o f the presence o f 1,5-pentanediol. A s d i s c u s s e d above, there i s a rapid increase i n the rate o fpolymerization o f the p r o p y l e n e o x i d e a t 10^ t o 15^ c o n v e r s i o n . We a t t r i b u t e t h e i n i t i a l l y slow r a t e o f p o l y m e r i z a t i o n t o b o t h t h e consumption o f the 1,5-pentanediol t o form a propylene oxide a d d i t i o n product, as w e l l a s t h e d i s p e r s i o n o f t h e i n i t i a l l y i n s o l u b l e z i n c hexac y a n o c o b a l t a t e complex c a t a l y s t . The m o l e c u l a r w e i g h t o f t h e polymer i s observed t o i n c r e a s e , as noted b y t h e s h i f t o f t h e peak p o s i t i o n towards s m a l l e r e l u t i o n volumes, as t h e r e a c t i o n 0

t

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

PROPYLENE OXIDE-

n-PENTANE

*

2

PROPYLENE Q Π OXIDE

Q

REACTOR FOR POLYETHER "SEED"

-SEED REACTOR EQUIPPED WITH

ù

POLYETHER SEED SPLIT-DOWN Figure 1.

Special glass equipment for "seeded? polymerizations

l.O0.9-

= 13.6 MOL./L. CATALYST = 0.4 G./L. [DIOL] = 0.4 MOL./L.

-O-[M]

0

0

0.8

-•-[M] = 10.7 MOL./L. CATALYST = 0.3 G./L. [DIOL] = 0.3 MOL./L. 0

0.7-

0

0.6-

(n-PENTANE)

0.5'

Q

0.40.30.20.13

4

5

TIME (HRS.)

Figure 2. Formation rate of poly(propylene ether) diol in bulk and n-pentane at 50°C

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

LiviGNi ET AL.

Poly(Propylene Ether) Poly ois

100

0

90 •

Ι

βοτο-

- O - [ M ] = 13.6 M0L./L. CATALYST = 0.4 G./L. [DIOLJo = 0.4 M0L./L.

-D-[M] = 10.7 MOL./L. CATALYST = 0.3 G./L. [DI0L] = 0.3 MOL./L

60-



0

0

(n-PENTANE)

oc

LU g

50-

o υ ^

403020103

4

5

TIME (HRS.) Figure 3.

Figure 4.

First-order rate plots for poly(propylene ether) diol formation at 50°C

Gel permeation chromatograms of reaction mixture at different extents of polymerization

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

26

proceeds. The p o l y m e r f o r m e d h a s a n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n w i t h some t a i l i n g t o w a r d s t h e h i g h m o l e c u l a r w e i g h t values. The n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n o f t h e s e p o l y (propylene ether) d i o l s i s s i m i l a r t o that obtained i n t h e soc a l l e d " l i v i n g p o l y m e r i z a t i o n s " , t h a t i s , those proceeding i n t h e absence o f a c h a i n t e r m i n a t i o n r e a c t i o n . The f a c t o r s w h i c h a r e necessary t o produce polymers having a narrow m o l e c u l a r weight d i s t r i b u t i o n h a v e b e e n d e l i n e a t e d b y F l o r y (15). These a r e : (l) c h a i n p r o p a g a t i o n o f e a c h p o l y m e r m o l e c u l e must p r o c e e d e x c l u s i v e l y b y a d d i t i o n o f monomers t o a n a c t i v e c e n t e r , (2) a l l c h a i n s must have a n e q u a l p r o b a b i l i t y o f u n d e r g o i n g g r o w t h t h r o u g h o u t t h e c o u r s e o f t h e r e a c t i o n , a n d (3) a l l c h a i n s must b e i n i t i a t e d a t thebeginning o f the reaction. Since the p o l y (propylene ether) d i o l s prepared w i t h the zinc hexacyanocobaltate complex c a t a l y s t have a s t u d y was c a r r i e d o u t v i d u a l s t e p s i n t h i s p o l y m e r i z a t i o n c o r r e s p o n d t o t h e above c r i teria. P r o p y l e n e o x i d e was p o l y m e r i z e d u s i n g 1 , 5 - p e n t a n e d i o l a s an i n i t i a t o r a n d z i n c h e x a c y a n o c o b a l t a t e complex as t h e c a t a l y s t . A f t e r p o l y m e r i z a t i o n was c o m p l e t e , a sample was w i t h d r a w n a n d i t s number-average m o l e c u l a r weight determined u s i n g vapor p r e s s u r e osmometry. A n a d d i t i o n a l q u a n t i t y o f p r o p y l e n e o x i d e was a d d e d t o t h e s y s t e m a n d p o l y m e r i z a t i o n o f t h i s i n c r e m e n t was a l l o w e d t o go t o c o m p l e t i o n . A sample was o n c e a g a i n removed, i t s number-average m o l e c u l a r weight d e t e r m i n e d a n d a d d i t i o n a l monomer added. T h i s f i n a l i n c r e m e n t o f p r o p y l e n e o x i d e was p o l y m e r i z e d and t h e number-average m o l e c u l a r w e i g h t o f t h e f i n a l product determined. The r e s u l t s o f t h i s s t u d y a r e g i v e n i n Table I . TABLE I Comparison o f C a l c u l a t e d and Measured M o l e c u l a r Weight o f Poly(Propylene Ether) D i o l s Prepared by Sequential A d d i t i o n o f Propylene

Oxide

ÏL η

Polymer From i n i t i a l p o l y m e r i z a t i o n F r o m f i r s t monomer i n c r e m e n t F r o m s e c o n d monomer i n c r e m e n t ^ Weight o f Polymer Moles o f 1,5-Pentanediol

( M e a s u r e d b v VPO) 169Ο 2350 3130

M

n

η

(C^lc) I783* 2209 30^+9

=

n

Charged

The m o l e c u l a r w e i g h t o f t h e f i r s t sample was c a l c u l a t e d f r o m t h e weight o f polymer o b t a i n e d d i v i d e d b y t h e moles o f 1,5-pentanediol

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

LrviGNi E T A L .

27

Ρ oly (Propylene Ether) Poly ois

charged. The g o o d agreement i n t h e c a l c u l a t e d v e r s u s m e a s u r e d m o l e c u l a r w e i g h t d e m o n s t r a t e s t h a t an i n s i g n i f i c a n t number o f chains r e s u l t d i r e c t l y from t h i s c a t a l y s t , under these c o n d i t i o n s . I n d e e d , i f one c a l c u l a t e s t h e maximum a v a i l a b l e number o f p o t e n ­ t i a l c a t a l y s t g r o w t h s i t e s , assuming f o u r s i t e s p e r z i n c atom p r e s e n t , one f i n d s t h a t t h e r e a r e a t l e a s t 10 t i m e s more c h a i n ends p e r a v a i l a b l e c o o r d i n a t i n g s i t e . T h i s demands t h a t a s p e c i ­ f i c c a t a l y s t s i t e must a c t i v a t e many d i f f e r e n t c h a i n ends d u r i n g polymerization. Comparing the c a l c u l a t e d v e r s u s d e t e r m i n e d molecular weights of the poly(propylene ether) d i o l prepared from t h e i n c r e m e n t a l monomer a d d i t i o n s , i t i s c o n c l u d e d t h a t t h e r e a r e no new p o l y m e r c h a i n s t h a t a r e i n t r o d u c e d d u r i n g t h e s e p o l y m e r i ­ z a t i o n s , e i t h e r f r o m an i n i t i a t i o n r e a c t i o n o r b y a c h a i n t r a n s ­ f e r p r o c e s s w i t h monomer. G e l p e r m e a t i o n chromatograms w e r e o b t a i n e d on a l l t h r e e o f t h e p o l y ( p r o p y l e n e e t h e r ) d i o l s p r e p a r e d i n t h i s s t u d y and a r e show w e i g h t d i s t r i b u t i o n was t a i l i n g towards the h i g h m o l e c u l a r w e i g h t r e g i o n . As i s a l s o a p p a r e n t , the i n c r e a s e i n the number-average m o l e c u l a r w e i g h t w i t h t h e p o l y m e r i z a t i o n o f s u c c e s s i v e monomer i n c r e m e n t s i s d e m o n s t r a t e d b y a s h i f t i n t h e p e a k p o s i t i o n o f t h e chromatograms towards lower e l u t i o n volumes. From these d a t a , i t i s concluded t h a t a l l c h a i n s h a v e e s s e n t i a l l y t h e same p r o b a b i l i t y o f u n d e r ­ g o i n g c h a i n p r o p a g a t i o n a n d t h i s p o l y m e r i z a t i o n must t a k e p l a c e i n the v i r t u a l absence o f a c h a i n t e r m i n a t i o n r e a c t i o n . The hydroxyl f u n c t i o n a l i t y of these poly(propylene ether) d i o l s i s c l o s e t o t h e t h e o r e t i c a l v a l u e o f two, a s i s shown b y t h e v a l u e s c a l c u l a t e d f r o m t h e m e a s u r e d h y d r o x y l number and n u m b e r - a v e r a g e m o l e c u l a r w e i g h t f o r t h e l a s t two p o l y m e r s ; n a m e l y , I . 9 8 + 0.2 and 2.10 + 0.2, r e s p e c t i v e l y . Having e s t a b l i s h e d t h a t the p o l y m e r i z a t i o n o f propylene o x i d e by the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t proceeds i n t h e a b s e n c e o f a c h a i n t e r m i n a t i o n r e a c t i o n , i t was o f i n t e r e s t to study s e p a r a t e l y the chain propagation r e a c t i o n . A non-termi­ n a t e d p o l y m e r " s e e d " was p r e p a r e d and i t s r a t e o f r e a c t i o n w i t h p r o p y l e n e o x i d e was s t u d i e d . The r e s u l t s o f a s e r i e s o f t h e s e s e e d e d p o l y m e r i z a t i o n s c a r r i e d o u t a t 30°, ^0° and 50° a r e g i v e n i n F i g u r e 6, where l o g [ M ] / [ M ] i s p l o t t e d a g a i n s t t i m e . S t r a i g h t l i n e s a r e o b t a i n e d i n t h i s p l o t e x c e p t i n g f o r an o b s e r v ­ able increase i n the r e a c t i o n r a t e i n the i n i t i a l p a r t o f the p o l y m e r i z a t i o n s c a r r i e d o u t a t t h e two l o w e r t e m p e r a t u r e s . It i s concluded from these r e s u l t s t h a t the chain propagation r e a c t i o n i s f i r s t - o r d e r i n monomer c o n c e n t r a t i o n . A n a p p a r e n t a c t i v a t i o n e n e r g y o f 13.7 + 0.8 k c a l / m o l e was c a l c u l a t e d f o r the chain propagation r e a c t i o n i n v o l v i n g the formation of p o l y (propylene ether) d i o l . T h i s v a l u e compares v e r y w e l l w i t h t h a t o f 1^4·. 7 k c a l / m o l e r e p o r t e d b y S h i g e m a t s u and c o w o r k e r s (16) for the sodium h y d r o x i d e c a t a l y z e d a d d i t i o n o f propylene o x i d e t o isopropyl alcohol. The r a t e s o f c h a i n p r o p a g a t i o n o f p r o p y l e n e o x i d e w e r e a l s o 2

0

t

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

-J

1

50 6 Volume of Eluate After Injection, ml Figure 5. Gel permeation chromât ο grams of poly­ propylene ether) diols prepared by incremental monomer addition

0.5 h

TIME (HRS.) Figure 6. Effect of temperature on propagation rate during poly(propylene ether) diol formation

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

LiviGNi E T A L .

Ρoly(Propylene

Ether) Polyols

29

measured f o r the seed, prepared u s i n g the z i n c hexacyanocobaltate c o m p l e x c a t a l y s t , a t two d i f f e r e n t t e m p e r a t u r e s i n n-hexane and tetrahydrofuran. The r e s u l t s f o r t h e s e p o l y m e r i z a t i o n s a r e g i v e n i n F i g u r e 7, where l o g [M] /[M] i s p l o t t e d v e r s u s t i m e . The r e s u l t s a r e u n e x p e c t e d i n t h a t t h e r a t e i s f a s t e r , a t b o t h temp­ e r a t u r e s , i n n-hexane t h a n i n t e t r a h y d r o f u r a n . F o r a t y p i c a l i o n i c p o l y m e r i z a t i o n , one m i g h t e x p e c t t h e o p p o s i t e r e s u l t . However, i f t h e s o l v e n t c o u l d compete w i t h t h e monomer f o r c o ­ o r d i n a t i o n s i t e s , t h i s c o u l d c a u s e a d e c r e a s e i n t h e number o f a c t i v e c e n t e r s g r o w i n g a t any t i m e and r e s u l t i n a d e c r e a s e i n t h e r a t e o f p o l y m e r i z a t i o n . Thus, t h e s l o w e r r a t e o f p o l y m e r i ­ z a t i o n i n t e t r a h y d r o f u r a n , compared t o n-hexane, m i g h t be due t o the e f f e c t caused by c o o r d i n a t i o n o f the e t h e r c o m p e t i t i v e l y w i t h t h e monomer, p r o p y l e n e o x i d e , b e i n g more s i g n i f i c a n t t h a n i t s a c c e l e r a t i n g the r a t e o f r e a c t i o n by s o l v a t i o n o f the i o n p a i r s . 0

t

F u n c t i o n a l i t y Measurements c h a r a c t e r i z e the hydroxyl f u n c t i o n a l i t y of poly(propylene ether) d i o l s p r e p a r e d w i t h the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t was t o compare t h e e q u i v a l e n t s o f -OH g r o u p s p r e s e n t r e l a t i v e t o a l l o t h e r f u n c t i o n a l groups which might comprise polymer c h a i n e n d s . The g r o u p s w h i c h w e r e c o n s i d e r e d , i n a d d i t i o n t o -OH, w e r e ~C=C— a r i s i n g f r o m a c h a i n t r a n s f e r r e a c t i o n w i t h p r o p y l e n e o x i d e , and ^~C=0 i n t r o d u c e d e i t h e r by i s o m e r i z a t i o n o f propy­ l e n e o x i d e f o l l o w e d b y an a l d o l c o n d e n s a t i o n , b y c h a i n o x i d a t i o n , o r b y t h e p r e s e n c e o f i m p u r i t i e s i n t h e monomer (8). A further a s s u m p t i o n i n t h i s a n a l y s i s was t h a t t h e r e a r e o n l y two c h a i n ends p e r c h a i n . U s i n g t h e s e a s s u m p t i o n s , t h e number a v e r a g e m o l e c u l a r w e i g h t o f t h e p o l y m e r was c a l c u l a t e d a n d compared w i t h t h e f r a c t i o n a l amount o f t h i s t e r m i n a l f u n c t i o n a l i t y w h i c h c o n ­ s i s t s o f h y d r o x y l groups. The number a,verage m o l e c u l a r w e i g h t c a l c u l a t e d i n t h i s manner i s i n g o o d a g r e e m e n t w i t h v a l u e s ob­ t a i n e d b y v a p o r p r e s s u r e osmometry, g i v i n g v a l i d i t y t o t h i s a p p r o a c h . The change i n t h e h y d r o x y l f u n c t i o n a l i t y as t h e molecular weight of the polymer i s i n c r e a s e d , c a l c u l a t e d i n the manner d e s c r i b e d , i s g i v e n i n F i g u r e 8 f o r d i o l s p r e p a r e d e x p e r i ­ m e n t a l l y and t h o s e a v a i l a b l e c o m m e r c i a l l y . The a b s c i s s a i n t h i s p l o t r e p r e s e n t s t h e c a l c u l a t e d m o l e c u l a r w e i g h t and t h e o r d i n a t e i s the h y d r o x y l f u n c t i o n a l i t y c a l c u l a t e d from the e q u i v a l e n t s o f f u n c t i o n a l groups present. I t i s o b s e r v e d t h a t t h e r e i s a much more g r a d u a l d e c r e a s e i n t h e h y d r o x y l f u n c t i o n a l i t y w i t h i n c r e a s ­ i n g molecular weight f o r the polymer prepared w i t h the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t than f o r t h e c o m m e r c i a l l y a v a i l a b l e poly(propylene ether) d i o l s , presumably prepared using an a l k a l i m e t a l h y d r o x i d e c a t a l y s t . F o r example, a t a m o l e c u l a r w e i g h t o f 3000, 97$ o f t h e c h a i n ends a r e h y d r o x y l f o r t h e d i o l s p r e p a r e d w i t h the z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s t , w h e r e a s o n l y a b o u t 90$ o f t h e c h a i n ends a r e h y d r o x y l i n t h e commercially a v a i l a b l e d i o l s . Poly(propylene

ether) d i o l s are u s u a l l y chain extended

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

30

POLYETHERS

0.7 0.6

50 C n-HEXANE

0.5 5 0 X TETRAHYDROFURAN

0.4 ο

3

0.3 0.2 0.1

//S

Y f/jS^fi^WZ 2

ο 40°C n-HEXANE

TETRAHYDROFURAN 3 4 5 6 TIME (HRS.)

Figure 7. Effect of solvent on propagation rate during poïy(propylene ether) diol formation

2.0, -•-GENERAL TIRE DIOLS

ο 11 ο

-•-COMMERCIAL DIOLS

11.91

1°

>-

1.8

1.71

1

2 3 4 5 6 7 8 9 MOLECULAR WEIGHT (OH + C=C + C=0) x 10

10 3

Figure 8. Change in hydroxyl functionality with molec­ ular weight for poly(propylene ether) diols

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2. LiviGNi E T A L .

Poly(Propylene Ether) Polyols

31

by r e a c t i o n w i t h diisocyanates. The p o l y u r e t h a n e s r e s u l t i n g f r o m t h i s r e a c t i o n w e r e a l s o u s e d t o compare t h e f u n c t i o n a l i t y o f t h e d i o l s p r e p a r e d w i t h t h e z i n c hexacyano c o b a l t ate complex w i t h those a v a i l a b l e commercially. Of course, t h e extent o f r e a c t i o n reached, and l i m i t a t i o n s o f measuring r e a c t a n t s , as w e l l as t h e f u n c t i o n a l i t y w i l l determine t h ep r o p e r t i e s o f t h e f i n a l product. E x p e r i m e n t a l d i o l s were c h a i n extended w i t h 2 , 4 - t o l y l e n e d i i s o c y a nate and t h e W i l l i a m s p l a s t i c i t y determined f o r t h e r e s u l t i n g r u b b e r s . F i g u r e 9 shows t h e p l a s t i c i t y v a l u e s a s a v a r i a t i o n of the2,4-tolylene diisocyanate equivalents f o r d i o l s o f approxim a t e l y 3500 m o l e c u l a r w e i g h t . The h e i g h t o f t h e maxima i n t h i s figure i s a relative indication of thefunctionality of diols of comparable m o l e c u l a r weight. The W i l l i a m s p l a s t i c i t y depends on t h e m o l e c u l a r w e i g h t o f t h e p o l y ( p r o p y l e n e e t h e r ) d i o l ( i t g o v e r n s t h e amount o f p o l a r g r o u p s p r e s e n t ) , a s w e l l a s t h e o t h e r f a c t o r s a l r e a d y mentioned d i o l s prepared using th a higher p l a s t i c i t y , a t equivalent molecular weights, than t h e commercial d i o l s , again demonstrating t h e r e l a t i v e l y h i g h e r f u n c t i o n a l i t y o f the experimental d i o l s . We have s o f a r b e e n c o m p a r i n g t h e p o l y ( p r o p y l e n e e t h e r ) d i o l s w h i c h r e s u l t f r o m "KOH c a t a l y s i s " a n d t h e z i n c h e x a c y a n o c o b a l t a t e complex c a t a l y s i s w i t h r e s p e c t t o f u n c t i o n a l i t y . I t i s o f value t o compare t h e m o l e c u l a r w e i g h t d i s t r i b u t i o n o f d i o l s p r e p a r e d b y t h e s e two p r o c e s s e s , u s i n g t h e g e l p e r m e a t i o n chromatograms g i v e n i n F i g u r e 10. G e n e r a l l y , t h e l o w m o l e c u l a r weight polymers from b o t h p r o c e s s e s have a narrow m o l e c u l a r w e i g h t d i s t r i b u t i o n . However, the molecular weight d i s t r i b u t i o n o f t h e d i o l s prepared w i t h KOH t a i l t o w a r d s t h e l o w m o l e c u l a r w e i g h t r e g i o n , w h e r e a s t h o s e p r e p a r e d u s i n g t h e z i n c h e x a c y a n o c o b a l t a t e complex t a i l towards the h i g h m o l e c u l a r weight r e g i o n . As a consequence o f t h i s , t h e d i o l s p r e p a r e d w i t h t h e z i n c h e x a c y a n o c o b a l t a t e complex have a h i g h e r b u l k v i s c o s i t y t h a n t h e d i o l s p r e p a r e d w i t h KOH, a t t h e same n u m b e r - a v e r a g e m o l e c u l a r w e i g h t . The g e l p e r m e a t i o n chromat o g r a m o f a d i o l o f m o l e c u l a r w e i g h t o f 12,000, p r e p a r e d w i t h t h e z i n c h e x a c y a n o c o b a l t a t e c o m p l e x i s g i v e n i n F i g u r e 10 a n d demonstrates t h e i n c r e a s e d breadth i n the molecular weight d i s t r i b u t i o n r e s u l t i n g a t higher molecular weights. M e c h a n i s m . The f o l l o w i n g scheme i s o f f e r e d t o a c c o u n t f o r t h e d a t a p r e s e n t e d above. P o l y m e r i z a t i o n p r o b a b l y o c c u r s w i t h t h e g r o w i n g c h a i n c o o r d i n a t e d t o a z i n c atom. The c o o r d i n a t i o n s i t e s a r e i n i t i a l l y made a v a i l a b l e b y d i s p l a c e m e n t o f t h e 1,2dimethoxyethane from the c a t a l y s t , e i t h e r b y propylene o x i d e o r the i n i t i a t o r , 1,5-pentanediol. The 1 , 5 - p e n t a n e d i o l d i s a p p e a r s e a r l y i n t h e r e a c t i o n b e c a u s e o f i t s more a c i d i c n a t u r e a n d g r e a t e r ease o f c o o r d i n a t i o n t h a n t h e secondary h y d r o x y l o f t h e poly(propylene ether). C o o r d i n a t i o n o f a growing c h a i n would decrease t h e f r e e - i o n character o f t h epropagating center, compared t o c a t a l y s i s w i t h a l k a l i m e t a l h y d r o x i d e s . A s a r e s u l t ,

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

I

ι

»

I

3300 3400 350 GRAMS DIOL PER MOL 2 4-TDI f

Figure 9. propylene

Williams plasticity of polyurethanes prepared from poly­ ether) diols at different ratios of 2,4-tolylene diisocyanate

I 125

"

• ^ 150 175 VOLUME OF ELUATE AFTER INJECTION (ML)

Figure 10. Gel permeation chromatogram of com­ mercial polypropylene ether) diol and diols pre­ pared using zinc hexacyanocobaltate complex catalyst

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

LiviGNi E T A L .

Ρoly(Propylene

33

Ether) Polyoh

c h a i n t r a n s f e r t o p r o p y l e n e o x i d e s h o u l d n o t o c c u r as r e a d i l y i n polymerizations catalyzed with the zinc hexacyanocobaltate complex. T h i s l e a d s t o p o l y ( p r o p y l e n e e t h e r ) p o l y o l s w h i c h con­ t a i n a g r e a t e r number o f t e r m i n a l h y d r o x y l g r o u p s . Of a d d i t i o n a l importance i s t h a t the z i n c hexacyanocobaltate catalyst gives more r a p i d p o l y m e r i z a t i o n r a t e s , t h e r e f o r e , l o w e r p o l y m e r i z a t i o n t e m p e r a t u r e s c a n b e u s e d . T h i s s h o u l d a l s o r e d u c e t h e amount o f c h a i n t r a n s f e r t o monomer. S i n c e t h e r e a r e a n i n s u f f i c i e n t number o f c a t a l y s t s i t e s t o be a s s o c i a t e d w i t h e v e r y c h a i n e n d o f t h e d i o l a n d y e t t h e p o l y m e r s have a n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n , a p a r t i c u ­ l a r c a t a l y s t s i t e must a c t i v a t e d i f f e r e n t c h a i n ends d u r i n g t h e c o u r s e o f t h e r e a c t i o n . T h u s , a l l c h a i n ends must h a v e a p p r o x i ­ m a t e l y t h e same p r o b a b i l i t y o f g r o w t h , a l t h o u g h o n l y a f r a c t i o n o f c h a i n ends u n d e r g o c h a i n p r o p a g a t i o n a t a n y t i m e d u r i n g t h e reaction. T h i s may be

CHAIN

PROPAGATION:

/

NACH ÇH-0—-Zn 5

α

H

+ CHfÇH—•

2 +

CH3 CHAIN

H

^CHj-CH-O-CHj-CH-U—Zn

CH3

2 +

CH3

CH3

+

^P CHyCH-0'---Zn

ACTIVATION:

^P CH ÇH-0---Zn n

/

?

CH

2 +

+

^CHyÇH-OH

CH3

3

^P

n

CHjÇH-OH CH

3

2+

m

CH

3

This d e s c r i p t i o n i s quite s i m i l a r t o that given f o r the polymeriz a t i o n o f e t h y l e n e o x i d e i n i t i a t e d b y sodium methoxide i n dioxane and m e t h a n o l , p r o v i d e d b y Gee, H i g g i n s o n a n d M e r r a l l (17). I f the r a t e o f c h a i n end a c t i v a t i o n proceeded a t a v e r y r a p i d r a t e r e l a t i v e t o chain growth, a narrow, symmetrical d i s t r i b u t i o n would be o b t a i n e d . I f t h i s a c t i v a t i o n p r o c e s s was v e r y much s l o w e r t h a n t h e r a t e o f monomer a d d i t i o n , a b r o a d d i s t r i b u t i o n would r e s u l t . I n t h e case o f t h e p o l y ( p r o p y l e n e ether) d i o l s

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

34

prepared w i t h the z i n c hexacyanocobaltate complex, the r a t e o f c h a i n end a c t i v a t i o n must be s u f f i c i e n t l y d i f f e r e n t t o t h a t o f c h a i n g r o w t h t o g i v e some b r o a d e n i n g i n t h e m o l e c u l a r w e i g h t distribution. Alternatively, catalyst sites of different a c t i v i t y may be p r e s e n t . I f s u c h a m e c h a n i s m as d e s c r i b e d above was o p e r ­ a t i n g , i t w o u l d be e x p e c t e d t h a t a more n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n c o u l d be o b t a i n e d b y: ( l ) a d d i n g monomer s l o w l y t o the p o l y m e r i z a t i o n , thus i n c r e a s i n g the degree o f a c t i v a t i o n of d i f f e r e n t c h a i n ends p r i o r t o c h a i n p r o p a g a t i o n ; and (2) i n c r e a s ­ ing the c a t a l y s t c o n c e n t r a t i o n , thus i n c r e a s i n g the f r a c t i o n o f c h a i n s t h a t can u n d e r g o g r o w t h s i m u l t a n e o u s l y . P a r t i a l confirm­ a t i o n o f t h e s e e f f e c t s has b e e n o b t a i n e d f o r t h e p r e p a r a t i o n o f p o l y (propylene ether) t r i o l s . The g e l p e r m e a t i o n chromatograms f o r s u c h p o l y m e r s , p r e p a r e d d u r i n g c o n d i t i o n s where a l l o f t h e p r o p y l e n e o x i d e was a d d e d i n i t i a l l y , and w h e r e t h e p r o p y l e n e o x i d e i s added s l o w l y F i g u r e 11. The i n i t i a t o p r o p a n e . I t i s a p p a r e n t t h a t a c o n s i d e r a b l y more n a r r o w m o l e c u l a r weight d i s t r i b u t i o n i s obtained f o r the polymer prepared u s i n g s l o w I n c r e m e n t a l monomer a d d i t i o n s u b s t a n t i a t i n g t h e m e c h a n i s m proposed. Acknowledgment The a u t h o r s a c k n o w l e d g e t h e v a l u a b l e e x p e r i m e n t a l a s s i s t a n c e o f Mr. J . A. W i l s o n i n t h e k i n e t i c s and m e c h a n i s m s t u d i e s , Mr. J . L. C o w e l l i n s p e c i a l s a m p l e p r e p a r a t i o n s f o r c h a r a c t e r i ­ z a t i o n and Mr. J . S. Duncan i n f u n c t i o n a l i t y d e t e r m i n a t i o n s b y c h a i n e x t e n s i o n . We a l s o w i s h t o t h a n k D r s . R. A. B r i g g s and Ε. E. G r u b e r f o r h e l p f u l d i s c u s s i o n s d u r i n g t h e c o u r s e o f t h i s study. A s p e c i a l note of g r a t i t u d e i s extended to Professor C. C. P r i c e who, a s a c o n s u l t a n t t o o u r l a b o r a t o r y , made many h e l p f u l suggestions. Summary C e r t a i n complexes o f z i n c hexacyanocobaltate are e f f e c t i v e c a t a l y s t s i n the p r e p a r a t i o n o f p o l y (propylene ether) p o l y o l s f r o m l o w m o l e c u l a r w e i g h t h y d r o x y l compounds and p r o p y l e n e o x i d e . The Z n [ C o ( G N ) ] 2 . i | - ( l , 2 - d i m e t h o x y e t h a n e ) 0.85 Z n C l k.k BQO catalyzed polymerization of propylene oxide w i t h 1,5-pentanediol was s t u d i e d . A n i n i t i a l l y s l o w r a t e o f p o l y m e r i z a t i o n i s f o l l o w e d b y a r a p i d r a t e . The n u m b e r - a v e r a g e m o l e c u l a r w e i g h t o f the p o l y (propylene ether) d i o l i s governed e n t i r e l y by the w e i g h t o f the p o l y m e r formed and moles o f 1 , 5 - p e n t a n e d i o l c h a r g e d . U s i n g g e l p e r m e a t i o n c h r o m a t o g r a p h y , i t was e s t a b l i s h e d t h a t t h e p o l y m e r has a n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n . The amount o f c a t a l y s t u s e d i n t h e p o l y m e r i z a t i o n i s i n s u f f i c i e n t t o h a v e a l l c h a i n ends g r o w i n g s i m u l t a n e o u s l y . A mechanism i s proposed which involves a c a t a l y s t s i t e a c t i v a t i n g d i f f e r e n t 3

6

2

s

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2. LiviGNi E T A L .

Ρoly(Propylene

Ether) Polyols

ALL P.O P.O. ADDED SLOWLY

—

VOLUME OF ELUATE AFTER INJECTION (ML.) Figure 11. Effect of monomer addition method on gel permeation chromatogram for polypropylene ether) triols prepared using zinc hexacyanocobaltate complex catalyst

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

36

POLYETHERS

c h a i n s throughout t h e r e a c t i o n , g i v i n g each a n e q u a l chance f o r growth. The p o l y o l s p r e p a r e d w i t h t h e z i n c h e x a c y a n o c o b a l t a t e c a t a l y s t were found t o have b e t t e r f u n c t i o n a l i t y t h a n p o l y ( p r o p y l e n e e t h e r ) p o l y o l s p r e p a r e d b y c o n v e n t i o n a l methods. Literature Cited 1. B e l n e r , R. J., Herold, R. J., M i l g r o m , J., U.S. Patents 3,427,256; 3,427,334; a n d 3,427,335 to General Tire & R u b b e r Company (1969). 2.

H e r o l d , R. J., Livigni, R. A., A d v a n c e s in Chemistry Series, Polymerization Kinetics and T e c h n o l o g y , Number 128, (1973)

208.

3.

P a r k e r , R. Ε., Isaacs,

4. St. Pierre, L. Ε., Price, C. C., J. Am. Chem. S o c . (1956)

78, 5.

3432.

Dege, G. J., Harris, R. L., M a c K e n z i e , J. S., J. Am. Chem.

Soc., (1959) 81, 3374. H.

6. G e e , G., Higginson, W. C. Ε., Taylor, K. J. a n d T r e n h o l m e , W., J. Chem. Soc. (1961) 4298. 7.

S n y d e r , W. H., Taylor, K. J., Chu, Ν. S. a n d Price, C. C., T r a n s . Ν. Y. Acad. of Science Ser. II (1962) 24, (#4) 341.

8.

S i m o n s , D. Μ., Verbanc, J. J., J. P o l y m . Sci. (1960) 44,

303. 9. Siggia, S., Hanna, J. G., A n a l y . Chem. 10. 11.

Iwamoto, R., S p e c t r o c h i m

Acta

(1961) 3 3 , 896.

(1971) 27A, 2385.

"1973 A n n u a l Book of ASTM S t a n d a r d s " , P a r t 26, p . 888, American Society for Testing and Materials, Philadelphia, Pennsylvania 19103.

12.

Siggia, S., "Quantitative Organic G r o u p s " , 3rd Edition, 73-75, J o h n

13.

"1973 A n n u a l Book of ASTM S t a n d a r d s " , American Society for Testing and Pennsylvania 19103.

Analysis Via Functional Wiley & Sons (1963) Part 28, p . 438 Materials, Philadelphia,

14. Pavelich, W. Α., Livigni, R. Α., J. P o l y m . Sci. (1968)

C-21,

215.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

LIVIGNI E T A L .

Ρ*oly'(Propylene Ether) Poly oh

15. Flory, P. J., J. Am. Chem. S o c . (1940) 6 2 ,

37 1561.

16.

S h i g e m a t s u , H., Miura, Y. a n d Ishii, Υ., Kogyo K a g a k u Zasshi (1962) 6 5 , 360. S e e , for e x a m p l e : Frisch, K. C. ed., " R i n g Opening Polymerization", p. 25, Marcel D e k k e r , N.Y. and L o n d o n (1969)

17.

Gee, G., Higginson, W. C. E. and Merrail, J. Chem. S o c .

(1959) 1345.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3 Propylene Oxide Polymers of Varying Stereosequence Distribution S. L. A G G A R W A L and L. F. M A R K E R Research and Development Division, The General Tire and Rubber Co., Akron, Ohio 44329

Introduction In 1956, C. C. P r i c e (1) demonstrated that when l-isomer of propylene oxide i s polymerized w i t h potassium hydroxide c a t a l y s t , a s t e r e o s p e c i f i c and c r y s t a l l i n e polymer i s produced. Yet, the racemic monomer polymerized w i t h the same c a t a l y s t gave an amorphous product. A ferric c h l o r i d e c a t a l y s t on the other hand produced, from e i t h e r racemic or o p t i c a l l y a c t i v e monomer, a crystalline high molecular weight f r a c t i o n having i d e n t i c a l c r y s t a l s t r u c t u r e . These studies demonstrated that long s t e r e o r e g u l a r sequences having e i t h e r d or l c o n f i g u r a t i o n , necessary f o r crystallization, can be produced by one c a t a l y s t , w h i l e another c a t a l y s t may lead to amorphous polymers, which may have only short s t e r e o r e g u l a r sequences of a p a r t i c u l a r c o n f i g u r a t i o n . Poly(propylene oxide) was unique among s t e r e o s p e c i f i c p o l y mers developed up to that time. The monomer has an o p t i c a l cent e r which, under a p p r o p r i a t e synthesis c o n d i t i o n s , can be preserved i n the polymer so that d or l forms could be i d e n t i f i e d at each asymmetric carbon atom. Examination of the c r y s t a l s t r u c ture of i s o t a c t i c poly(propylene oxide) (2) shows that it crystallizes in a helical form and that the c r y s t a l s can accommodate only the h e l i c e s of one o p t i c a l form and are t h e r e f o r e o p t i c a l l y active. A number of c a t a l y s t systems have been developed (3,4,5) which r e s u l t i n propylene oxide polymers of d i f f e r e n t s t e r e o s e quence d i s t r i b u t i o n . In the f o l l o w i n g , we review some of our work on the c h a r a c t e r i z a t i o n of stereosequence length i n propylene oxide polymers prepared w i t h d i f f e r e n t c a t a l y s t s , and more import a n t l y , studies on the e f f e c t of the d i f f e r e n c e s i n stereosesequence length on the crystallization behavior and mechanical p r o p e r t i e s of the polymers. D e s c r i p t i o n of Stereosequence

Distribution

As i n other polymeric systems, both head-to-head

and

38

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3. AGGARWAL A N D M A R K E R

Propylene Oxide Polymers

39

h e a d - t o - t a i l arrangements of consecutive monomer u n i t s have been i d e n t i f i e d i n poly(propylene oxide (6). These arrangements can be detected by chemical means and have important e f f e c t s i n modi­ f y i n g the c r y s t a l l i z a t i o n behavior of the polymer (6 7)· Another s t r u c t u r a l feature that may a f f e c t c r y s t a l l i z a t i o n behavior i s that, f o r a given c o n f i g u r a t i o n (d or 1_) of the repeating u n i t i n the i s o t a c t i c s t e r e o r e g u l a r polymer chain, two d i s t i n c t chains s t r u c t u r e s are p o s s i b l e depending upon the r e l a t i v e p o s i t i o n s of the oxygen and the asymmetric carbon. These may be designated as up and down chain s t r u c t u r e f o r each of the ci and _1 c o n f i g u r a t i o n of the i s o t a c t i c polymer c h a i n . They are superimposable by turning the polymer chain end-over-end ( 8 ) . We recognize such complications as above i n the c r y s t a l l i z a t i o n of s t e r e o r e g u l a r poly(propylene o x i d e ) . The main i n t e r e s t of our s t u d i e s , how­ ever, has been i n the stereosequence d i s t r i b u t i o n i n propylene oxide polymers prepare e f f e c t of stereosequenc polymers. The simplest s t a t i s t i c a l model which has s u f f i c i e n t gener­ a l i t y to represent the sequence d i s t r i b u t i o n i n poly(propylene oxide) i s one i n which the c o n f i g u r a t i o n of the l a s t three mono­ mer u n i t s i n the growing chain determine the c o n f i g u r a t i o n of the next u n i t coming onto the chain. The c o n f i g u r a t i o n of the t r i a d of successive u n i t s may take on e i g h t p o s s i b l e arrange­ ments as l i s t e d i n Table I below. Recent studies have jhown that s e v e r a l types of such t r i a d s may be d i s t i n g u i s h e d from H and carbon-13 NMR spectra (9,10,11). We have adopted a shorthand n o t a t i o n of representing by + the case when two successive u n i t s have the same c o n f i g u r a t i o n , and by - when they have opposite configurations. Triads are r e f e r r e d to as i s o t a c t i c , t r i a d s as s y n d i o t a c t i c , and E„ and E^ as h e t e r o t a c t i c . The A and Β t r i a d s i n a polymer made from a racemic monomer cannot be d i s ­ t i n g u i s h e d from each other by any p h y s i c a l method, and equal pop­ u l a t i o n s , i n any case, of the corresponding A and Β t r i a d s may be assumed. Thus, the number of p o s s i b l e t r i a d s t a t e s of i n t e r ­ est i n a model f o r analyzing stereosequence d i s t r i b u t i o n reduces to f o u r . f<

TABLE I

B)

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

40

We, along with others (12,13,14), have considered a model by which the stereosequence d i s t r i b u t i o n , i . e . , d i s t r i b u t i o n of t r i a d sequences along the polymer chain, i s described as a Markov chain process (15). A d d i t i o n of a new repeating u n i t to a p a r t i ­ c u l a r t r i a d leads to a new t r i a d c o n s i s t i n g o f the l a s t two u n i t s plus the u n i t added. The t r a n s i t i o n p r o b a b i l i t i e s a s s o c i a t e d w i t h the v a r i o u s p o s s i b i l i t i e s that can thus a r i s e from the four t r i a d s can be defined and are given i n Table I I . TABLE I I Transition Probabilities

FOUR PARAMETER MODEL STATf AFTER ADDING MONOMER STATE OF CHAIN END

TRANSITION PROBABILITIES

+4- (ddd, III)

(1-a,)

(l-a )

+— (ddl, lid)

-+ (dll, Idd)

E

4

:

(did, Idl)

2

A

3

(l-a J 3

A

4

(1-o ) 4

The above model p r e d i c t s that the p o p u l a t i o n o f s t a t e Έ,^ i s equal t o that of the s t a t e E^. A l s o , the populations of the t r i a d s t a t e s depend upon only two parameters: (1-°^)/°^ and (l-o^)/^. Thus, i t would not be p o s s i b l e to determine the f o u r parameters: Û ^ , . . Œ needed to f u l l y describe the stereosequence d i s t r i b u t i o n , from the p o p u l a t i o n of the t r i a d s t a t e s as determined, f o r instance, by NMR. In order to f u l l y c h a r a c t e r i z e a l l the f o u r parameters, one would need populations o f t e t r a d s . No s u i t a b l e method has evolved t o be able to do t h i s . However, i f one i s concerned only, as we were, w i t h the a b i l i t y o f polypropylene oxide t o c r y s t a l l i z e (16) then s i n c e #

#

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3.

AGGARWAL A N D M A R K E R

Propylene Oxide Polymers

41

polypropylene oxide c r y s t a l l i z e s only i n the i s o t a c t i c form, we can r e s t r i c t our a t t e n t i o n to i s o t a c t i c ^equences ( i . e . , se­ quences of + u n i t s ) . The p r o b a b i l i t y , Ρ (ξ), that a given se­ quence of +'s i s e x a c t l y of length ξ, i s given by the equation: +

Ρ (ξ)

= Ρ α ^ "

2

^ ! - ^ )

2

In t h i s equation, P^ i s the p r o b a b i l i t y that any t r i a d taken a t random be i n the c o n f i g u r a t i o n Ή - and Q>^ i s the p r o b a b i l i t y _£hat t h i s t r i a d i s followed by a + u n i t . Thus, the p r o b a b i l i t y Ρ (4) i s based only on two parameters, P and a... Q u a l i t a t i v e l y , we can a s s o c i a t e the e q u i l i b r i u m c r y s t a l l i n i t y w i t h the concentra­ t i o n P p and the maximum m e l t i n g p o i n t of the polymer w i t h the p r o b a b i l i t y of forming long sequences which depends onQf^. 1

C h a r a c t e r i z a t i o n of Sequenc A number of recent papers d e s c r i b e the use o f h i g h r e s o l u ­ t i o n NMR spectroscopy i n i d e n t i f y i n g stereosequence d i s t r i b u t i o n i n polypropylene oxide (9-11,17-20). Using Œ - d e u t e r a t e d p o l y propylene oxide and 220 HMz NMR, Oguni e t a l (19) have shown that the s h i f t i n methylene a b s o r b t i o n can be used to i d e n t i f y the s t r u c t u r e s assigned to t a i l - t o - t a i l linkages and to i s o t a c t i c and s y n d i o t a c t i c t r i a d s . They showed that the c r y s t a l l i n e f r a c t i o n of polymer prepared with a d i e t h y l - z i n c - w a t e r c a t a l y s t system d i d not c o n t a i n a measurable amount of t a i l - t o - t a i l l i n k a g e s . Carbon-13 NMR can p o t e n t i a l l y give more i n f o r m a t i o n about triad distribution. Several workers (10,11,18,20) have made use of t h i s technique. The three methine peaks observed i n the NMR s p e c t r a have been assigned to s y n d i o t a c t i c , i s o t a c t i c and heterot a c t i c t r i a d s . Although t h e o r e t i c a l l y d d l and d l l t r i a d s should be non-equivalent, only a s i n g l e type o f h e t e r o t a c t i c t r a i d peak has been found. Since the i n f o r m a t i o n obtained from diad and t r a i d d i s t r i b u t i o n s are mutually c o n s i s t e n t , we consider only the e x i s t e n c e of only a s i n g l e h e t e r o t a c t i c s p e c i e s . In our s t u d i e s (16), we have made use of m e l t i n g p o i n t and c r y s t a l l i n i t y as a f u n c t i o n o f temperature o f polypropylene f r a c t i o n s to o b t a i n the parameters f o r the s t a t i s t i c a l model and f o r c a l c u l a t i o n of the average length of i s o t a c t i c sequences. Polypropylene oxide prepared by three c a t a l y s t systems were s t u d i e d . The c r y s t a l l i n e f r a c t i o n s were those that were i n s o l uble i n e i t h e r acetone a t -20°C or i n i s o p r o p y l a l c o h o l a t 25°C. The m e l t i n g p o i n t and the change i n percent c r y s t a l l i n i t y as a f u n c t i o n of temperature were s t u d i e d by c a r e f u l l y annealing the polymer and then measuring d i l a t o m e t r i c a l l y the change i n d e n s i t y w i t h temperature. Our c a l c u l a t i o n s , of average i s o t a c t i c sequence length and average length o f u n c r y s t a l l i z a b l e sequences from these data were based on F l o r y s theory f o r the c r y s t a l l i z a t i o n and f u s i o n of copolymers (21). The d e t a i l s and equations f

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

42

used f o r these c a l c u l a t i o n s have been described p r e v i o u s l y (16)» I t i s doubtful whether the c o n d i t i o n s of F l o r y ' s theory are adequately f u l f i l l e d but the theory i s q u a l i t a t i v e l y s u c c e s s f u l i n that (a) i t s p r e d i c t i o n of the shape of c r y s t a l l i z a t i o n curves i s i n good agreement w i t h experiment and (b) the r e s u l t s f o r s i m i l a r polymers are i n good agreement w i t h the NMR r e s u l t s of Schaefer In Table I I I are given the m e l t i n g p o i n t , the percent c r y s t a l l i n i t y at room temperature and the average length of c r y s t a l l i z a b l e i s o t a c t i c sequences and of u n c r y s t a l l i z a b l e sequences, f o r the f r a c t i o n s of poly(propylene oxide) prepared w i t h the four c a t a l y s t systems. I t should be noted that, even though the average i s o t a c t i c sequence length of Sample C and D i s about the same, there i s an a p p r e c i a b l e d i f f e r e n c e i n percent c r y s t a l l i n i t y (or average length of u n c r y s t a l l i z a b l e sequences) A l s o Sample A has a much lower degree o i t s m e l t i n g point as compare crystallinity. Such f e a t u r e s as these i n the c r y s t a l l i n e f r a c t i o n s of polypropylene oxide were the reasons f o r us to adopt a p r o b a b i l i t y model r e q u i r i n g that the c o n f i g u r a t i o n of the oncoming u n i t i s governed by the c o n f i g u r a t i o n of the previous three u n i t s (4 parameter model) r a t h e r than by the c o n f i g u r a t i o n of the l a s t one or two u n i t s as has been found to be s a t i s f a c t o r y f o r other systems, e.g., polymethylmethacrylate (14). The E f f e c t of Stereosequence Length on Morphology and zation Kinetics

Crystalli-

The e f f e c t of stereosequence d i s t r i b u t i o n on c r y s t a l l i z a t i o n k i n e t i c s i s dramatic. We have p r e v i o u s l y reported our s t u d i e s on the important e f f e c t s of stereosequence length on c r y s t a l l i z a t i o n k i n e t i c s and morphology of propylene oxide polymers (22)» Here we summarize the main c o n c l u s i o n s of t h i s study, so that r e s u l t s on the time-temperature dependence of mechanical response may be f u l l y a p p r e c i a t e d i n the l i g h t of these c o n c l u s i o n s . When slowly cooled from the melt, the c r y s t a l l i n e f r a c t i o n s of propylene oxide polymers c r y s t a l l i z e i n a s p h e r u l i t i c growth h a b i t . At low degrees of supercooling, r a t h e r l a r g e s p h e r u l i t e s can be grown. The texture of s p h e r u l i t e s grown at the same degree of supercooling i s q u i t e s e n s i t i v e to the stereosequence d i s t r i b u t i o n of the polymer. In F i g u r e 1, we show photomicrographs of s p h e r u l i t e s of two d i f f e r e n t poly(propylene oxide) samples, one of which (Sample A) has long stereosequence length and the other one (Sample C) has short stereosequence l e n g t h . Both s p h e r u l i t e s were grown under isothermal c o n d i t i o n s and at the same degree of s u p e r c o o l i n g . The s p h e r u l i t e s grown from Sample A have a more dense s t r u c t u r e and a g r e a t e r frequency of f i b r i l l a r branching than do s p h e r u l i t e s grown from Sample C. T h i s behavior i s i n accord w i t h the mechanism of s p h e r u l i t e growth proposed by K e i t h and Padden (23) according to which

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Homopolymer Sample

15

Zn(C H ) -H 0

2

5

5

2

2

2

34

2

2

Zn(C H ) -H 0propylamme

2

34

5

Zn(C H )2-H 0cyclohexylamine

2

49

Ferric chloride

66

68

68

75

0.92

0.93

0.992

0.196

0.447

0.710

12.5

14

122

70

28

120

M e l t i n g Temperature, Percent C r y s t a l l i n i t y and Stereosequence Length of C r y s t a l l i n e F r a c t i o n s of Propylene Oxide Polymers From D i f f e r e n t C a t a l y s t s Average Lenth Pi Melt. T r a n s i t i o n % Probability Uncrystal­ CrystalTemp. P r o b a b i l i t y of -f-fIsotactic lizable Catalyst unity °C States Sequence Sequence

TABLE I I I

Ο

POLYETHERS

44

growth occurs by d i f f u s i o n of i m p u r i t i e s or of m a t e r i a l of low t a c t i c i t y away from the s i t e o f c r y s t a l growth. The rate at which these s p h e r u l i t e s grow i s a l s o a f f e c t e d by t a c t i c i t y . Measurements were made of the Isothermal rate of s p h e r u l i t i c growth on a hot stage of a microscope. For t h i s pur­ pose, a sequence camera was used to photograph a u t o m a t i c a l l y the growing s p h e r u l i t e s during c r y s t a l l i z a t i o n . Dilatometric measurements were a l s o made on these polymers i n order to deter­ mine the rate of isothermal c r y s t a l l i z a t i o n from the melt. The f r a c t i o n of the polymer which had c r y s t a l l i z e d at any time was c a l c u l a t e d from the measured density and the known values of the density of c r y s t a l l i n e and amorphous poly(propylene oxide) (8.,^, The isothermal d i l a t o m e t r i c growth rate data were f i t t e d to the equation p r e d i c t e d by the Avrami theory (25,26,27) : 1-(X/X« where X i s the percent c r y s t a l l i n i t y at time t , X i s the percent c r y s t a l l i n i t y at i n f i n i t e time, and T i s a parameter with the dimensions of time, which i s a measure of the r a t e of c r y s t a l l i ­ z a t i o n . For no value of η could the experimental values be made to f i t t h i s equation. The c r y s t a l l i z a t i o n isotherms could be f i t t e d , however, by making the f o l l o w i n g assumptions: OT

%

1.

That the Avrami theory lnd-X/Xj =-(t/ where T

n

3

T c

) [F(t/

T n

)]/[(l/3!)(t/

i s the time constant

F(t/r ) = e" n

can be w r i t t e n i n the form:

t / T

3

T n

) ]

(2)

f o r the n a c l e a t i o n process and

n-l+t/r -(l/2)(t/T ) +(l/3!)(t/r ) 2

n

n

n

3

(3)

These equations imply that the s p e r u l i t e s are i n i t i a t e d from predetermined n u c l e i at a rate comparable to the rate of c r y s t a l l i z a t i o n . This assumption i s confirmed by our micro­ s c o p i c a l measurements. 2.

That the Avrami equation i n the form of Equation (2) gives the volume f r a c t i o n occupied by s p h e r u l i t e s rather than the percent c r y s t a l l i n i t y .

We assume that c r y s t a l l i z a t i o n takes place behind the growing s p h e r u l i t i c boundary at a r a t e such that the degree of c r y s t a l l i n i t y i n any r e g i o n i s a f u n c t i o n , # ( t ' ) of the time elapsed a f t e r the s p h e r u l i t e f r o n t has passed through that region. Under these c o n d i t i o n s , we may w r i t e the equation f o r the the percent c r y s t a l l i n i t y w i t h time as: f

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3. AGGARWAL AND M A R K E R

(X/XJ

Propylene Oxide Polymers

= Ç

<&(t, ) T

£dV(r)/drj

45

d

(4)

T

Here V ( T ) , the value of which i s given by the Avrami equat i o n , i s the volume f r a c t i o n of the i n i t i a l melt included i n s p h e r u l i t e s at time _t; and $ ( t , T ) i s the percent c r y s t a l l i n i t y at time Τ . There £s ample evidence that c r y s t a l l i z a t i o n i n a s p h e r u l i t e continues long a f t e r i t s boundary i s formed. Kovacs (28) has shown that there i s a slow secondary c r y s t a l l i z a t i o n i n polyethylene which continues to very long times. Tung and Buckser (29) have been able to f i t the t a i l end of the d i l a t o m e t r i c curve f o r the c r y s t a l l i z a t i o that t h i s secondary c r y s t a l l i z a t i o t i a l decay. S t e i n and h i s coworkers (30) have observed that even a f t e r s p h e r u l i t e s have occupied the t o t a l volume of the sample, there i s a c o n t i n u i n g change i n the i n t e n s i t y of x-ray s c a t ­ tering. The c r y s t a l l i z a t i o n isotherms can then be f i t t e d by assuming t h a t ® ( t , T ) can be w r i t t e n i n the simple form. #(t,T) = 1-a exp [-(ΐ-τ)/τ] s where a represents the f r a c t i o n of c r y s t a l l i z a t i o n which occurs slowly and Τ , i s the time constant f o r t h i s secondary c r y s t a l ­ l i z a t i o n process. In Table IV, we have summarized the r e s u l t s of the c r y s t a l l i z a t i o n k i n e t i c measurements on poly(propylene oxide) of d i f f e r e n t s t e r e o r e g u l a r i t y . These r e s u l t s lead to the f o l ­ lowing c o n c l u s i o n s . TABLE IV E f f e c t of S t e r e o r e g u l a r i t y on C r y s t a l l i z a t i o n of Propylene Oxide Polymers

Catalyst J

FeCl. ô

Zn(CH H-) H O Isopropylamine 2

2

Spherulitic Primary Growth Crystallization Rate min r min G (cm/min) n e

Kinetics

Secondary Crystallization Α Τ / Τ s c

Cryst Temp, °C

Δτ °C

45 50 5.5

30 25 20

3.5 15 130

12.6 40.2 170

8.2 4.5 0.82

0.26 0.26 0.26

1.7 1.7 1.7

38 43 48

30 25 20

10 22 70

19 40 92

6.0 2.5 0.90

0.26 0.26 0.26

7.6 7.6 7.6

T

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

46

The primary c r y s t a l l i z a t i o n process i s c h a r a c t e r i z e d by three parameters. These are the r a t e of r a d i a l growth of the s p h e r u l i t e , G, the time constant f o r n u c l e a t i o n , Τ , and the time constant f o r the primary c r y s t a l l i z a t i o n process, τ , which i s determined from the avrami equation. A l l three parameters seem to be dependent on the s t e r e o r e g u l a r i t y of the polymer, although the n u c l e a t i o n r a t e seems to be most s t r o n g l y dependent. A more important e f f e c t of s t e r e o r e g u l a r i t y i s found from c o n s i d e r a t i o n of the secondary c r y s t a l l i z a t i o n process. T h i s process i s c h a r a c t e r i z e d by two parameters. These a r e : a., the f r a c t i o n of the c r y s t a l l i z a b l e m a t e r i a l i n v o l v e d i n the secondary c r y s t a l l i z a t i o n process, and τ , the time constant f o r t h i s pro­ cess. The noteworthy r e s u l t i s that the r a t i o ( / ^ ) ^ almost independent of temperature, but very s e n s i t i v e to the s t e r e o ­ r e g u l a r i t y of the polymer. The secondary c r y s t a l l i z a t i o n process i s slower f o r polymer f o r those having longe primary c r y s t a l l i z a t i o n process i s only s l i g h t l y a f f e c t e d by stereoregularity. τ

s

3

0

Mechanical P r o p e r t i e s of V u l c a n i z a t e s of Copolymers of Propylene Oxide The a b i l i t y to c r y s t a l l i z e has an important e f f e c t on the mechanical behavior of rubber v u l c a n i z a t e s . I f the rubber has some c r y s t a l l i n i t y present i n i t i a l l y , the c r y s t a l s act as ad­ d i t i o n a l c r o s s l i n k s i n the system r e s u l t i n g i n increased s t i f f ­ ness. On the other hand, c r y s t a l l i z a t i o n induced by s t r a i n leads to s t r e s s r e l a x a t i o n and i n c r e a s e d s t r e n g t h of the v u l c a n i z a t e s . In order to be able to form c r o s s l i n k e d networks of propy­ lene oxide polymers, a s e r i e s of copolymers was prepared u s i n g a l l y l g l y c i d a l ether as a comonomer. These copolymers were f r a c t i o n a t e d i n t o s t e r e o r e g u l a r and amorphous f r a c t i o n s by c o o l i n g of acetone or i s o p r o p y l a l c o h o l s o l u t i o n s . The d e n s i t y of the s o l u b l e f r a c t i o n s was found to vary l i n e a r l y w i t h the comonomer content. I t was assumed that the s o l u b l e f r a c t i o n s were completely amorphous and that the d e v i a t i o n of the d e n s i t y of the i n s o l u b l e f r a c t i o n s from l i n e a r i t y was a measure of t h e i r percent c r y s t a l l i n i t y . The percent c r y s t a l l i n i t y , Χ , was c a l ­ c u l a t e d by assuming that the c r y s t a l l i n e p o r t i o n s contained only propylene oxide u n i t s , and have the d e n s i t y of c r y s t a l l i n e p o l y ­ p r o p y l e n e o x i d e ) . In Table V are given the mole percent of comonomer, the d e n s i t y , the c a l c u l a t e d value o f X and the g l a s s t r a n s i t i o n temperature f o r the s t e r e o r e g u l a r ( i n s o l u b l e ) f r a c ­ t i o n of copolymers of propylene oxide made w i t h d i f f e r e n t c a t a ­ l y s t s . The designations A, B, C and D represent the c a t a l y s t systems which correspond to the ones used f o r the homopolymers i n Table I I I and are i n the order of decreasing s t e r e o - d i r e c t i n g i n f l u e n c e . The values of X i n c r e a s e w i t h the s t e r e o - d i r e c t i n g i n f l u e n c e of the c a t a l y s t . T h e s u b s c r i p t s 1, 2 i n sample codes β

9

C

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3.

AGGARWAL A N D M A R K E R

Propylene Oxide Polymers

47

i n Table ? r e f e r to the d i f f e r e n t comonomer content i n the co­ polymers made using the same c a t a l y s t system. The g l a s s t r a n s i ­ t i o n temperature of the copolymers, as w e l l as that of the cor­ responding homopolymers, was measured u s i n g a coated e l e c t r o magnetically d r i v e n v i b r a t i n g reed apparatus (31). Almost a l l the s o l u b l e (amorphous) f r a c t i o n s had a Tg of about -57°C., the same as that of the homopolymers with a small average s t e r e o ­ sequence length. The Tg of the i n s o l u b l e f r a c t i o n s given i n Table V v a r i e d i n the same order as the value of X · The gen­ e r a l e f f e c t of the comonomer, however, was to lower the Tg values. The copolymers l i s t e d i n Table V were cured i n the form of 0. 01. t h i c k f i l m s . The cured polymer was cut i n t o s t r i p s one i n c h wide, and these s t r i p s were used f o r subsequent t e s t i n g . No d i r e c t measurement was made of the c r o s s l i n k d e n s i t y of these polymers, but a r e l a t i v R i v l i n p l o t s of the s t r e s s - s t r a i The f o l l o w i n g i s the summary of the r e s u l t s of the s t u d i e s (31) on the e f f e c t of s t e r e o r e g u l a r i t y on stress-induced c r y s t a l ­ l i z a t i o n and mechanical p r o p e r t i e s of the v u l c a n i z a t e s of pro­ pylene oxide copolymers. In the s t u d i e s on s t r e s s - i n d u c e d c r y ­ s t a l l i z a t i o n , s t r e s s (σ) and b i r e f r i n g e n c e (Δ) were measured as a f u n c t i o n of temperature using an Instron t e s t e r f i t t e d w i t h a thermostatted i n s u l a t e d chamber and an o p t i c a l system. In an amorphous rubber, the quantity (Τ·Δ/οτ) (where Τ i s absolute tem­ perature) i s almost constant. Stress-induced c r y s t a l l i z a t i o n leads to the formation of c r y s t a l s o r i e n t e d i n the s t r e t c h i n g d i r e c t i o n which s u b s t a n t i a l l y increase the b i r e f r i n g e n c e . 1.

Samples, such as D«, which have short i s o t a c t i c sequences and high comonomer content, d i s p l a y i d e a l elastomer behavior, i n that the r a t i o of b i r e f r i n g e n c e to s t r e s s i s almost indepen­ dent of temperature and the s t r e s s at constant e l o n g a t i o n i s p r o p o r t i o n a l to absolute temperature. A l l other samples have some c r i t i c a l temperature (e.g., 50°C f o r Sample A^) above which the v u l c a n i z a t e s behave as an i d e a l elastomer. T h i s suggests that Sample does not c r y s t a l l i z e i n e i t h e r the s t r e s s e d or unstressed s t a t e .

2.

In a v u l c a n i z a t e w i t h long i s o t a c t i c sequences (e.g., A^) i n which there i s a measurable degree of c r y s t a l l i n i t y at room temperature, the e f f e c t i v e c r o s s l i n k density as determined by modulus i s l a r g e l y due to the presence of the c r y s t a l l i n e r e ­ gions. Such a sample, when s t r e t c h e d 2007« and. then heated slowly, shows a continuous decrease i n s t r e s s as shown i n F i g u r e 2, f a l l i n g almost to one-tenth of i t s value on heating to 100°C. The b i r e f r i n g e n c e change on heating, a l s o shown i n F i g u r e 2, i s somewhat complicated. The b i r e f r i n g e n c e i n ­ creases w i t h temperature up to 5 5 ° C , then f a l l s o f f r a p i d l y , approaching a constant value at about 75°C. A q u a l i t a t i v e

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Sample Designation

-59.8 -58.0

-58.3 -58.0

-57.0

-57.0

(1.0440) 1.0192

1.0126 1.0213

1.0060

1.0112

49 70

29 60

20

73

Acetone, -20°C Isopropanol, -20°C Acetone, -20°C Isopropanol, -20°C Isopropanol, -20°C Isopropanol, -20°C

8.6

3.0

10.0

4.0

7.5

-50.7 -52.2

2.0

32 24

1.0370 1.0290

59 74

Acetone, 0°C Isopropanol, 0°C

-51.3

P r o p e r t i e s of I n s o l u b l e F r a c t i o n s Percent Density, Crystallinity Tg, °C (gm/cc)

3.2

Wt. Percent Insoluble

Acetone, 0°C

Method of Separation

1.6

Mole Percent Comonomer

Stereoregular ( I n s o l u b l e ) F r a c t i o n s of Copolymers of Propylene Oxide and A l l y l G l y c i d a l Ether

TABLE V

AGGARWAL AND M A R K E R

Propylene Oxide Polymers

Figure 1. Effect of stereoregularity on texture of propylene oxide polymers at same degree of supercooling AT = 30°C? Sample A (left) with long stereosequence length. Sample C (right) with short stereosequence length.

I

ι

30

40

Figure 2.

.

ι

.

50 60 TEMPERATURE, °C

1

70 •

»

—J

80

Force and birefringence changes on heating Sample Α temperature, after elongating 200Ψο

90

Λ

from room

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

50

explanation of t h i s behavior i s that as the temperature i s r a i s e d , unoriented c r y s t a l l i n e m a t e r i a l present at room tem­ perature s t a r t s to melt and i s replaced by o r i e n t e d c r y s t a l ­ l i n e m a t e r i a l which has a higher m e l t i n g p o i n t and higher b i r e f r i n g e n c e than the unoriented polymer. 3.

In some samples, f u r t h e r c r y s t a l l i z a t i o n occurs on s t r e t c h ing. In Figure 3 are shown the s t r e s s o p t i c a l c o e f f i c i e n t [ r a t i o ( Δ / α ) of the b i r e f r i n g e n c e Δ and s t r e s s ^ ] as a func­ t i o n of temperature, f o r three of the samples. These sam­ p l e s were s t r e t c h e d 2007 , heated to 1 0 0 ° C and then cooled slowly from t h i s temperature to below - 2 0 ° C . Measurements of s t r e s s and b i r e f r i n g e n c e were made simultaneously i n t h i s temperature i n t e r v a l . The s t r e s s o p t i c a l c o e f f i c i e n t would be i n v a r i a n t w i t h temperature i f no c r y s t a l l i z a t i o n oc­ curred such was foun -30°C. However, Sampl 5 0 ° C and the c r y s t a l l i z a t i o n i s complete by 0 ° C . Sample s t a r t s c r y s t a l l i z i n g a t about 3 0 ° G and the process i s not complete u n t i l about - 3 0 ° C . Sample C- does not c r y s t a l l i z e above 0 ° G and shows only a s l i g h t tendency to c r y s t a l l i z e even below t h i s temperature. o

4.

At room temperature, when s t r e t c h e d 2007» and allowed to r e ­ lax, there i s greater change i n s t r e s s o p t i c a l c o e f f i c i e n t f o r Sample B- than f o r Sample A^, even though Sample B^ has a c o n s i d e r a b l y lower degree of c r y s t a l l i n i t y . The Sample Aw i t h the h i g h degree of c r y s t a l l i n i t y i n the unstressed s t a t e at room temperature, allows f o r l i t t l e a d d i t i o n a l s t r e s s induced c r y s t a l l i z a t i o n . The Sample B^ w i t h intermediate length of i s o t a c t i c sequences shows small c r y s t a l l i n i t y i n the unstressed s t a t e at room temperature but shows pronounced stress-induced c r y s t a l l i z a t i o n . The r a t e of s t r e s s - i n d u c e d c r y s t a l l i z a t i o n i s very much enhanced at h i g h elongations and at lower temperature.

5.

Dynamic modulus measurements were made over the temperature range of - 5 0 ° C to 3 0 ° C , and the frequency range of 0 . 0 2 to 15 c y c l e s / s e c . There was very l i t t l e dependence of t h i s pro­ perty on frequency except at temperatures c l o s e to the t r a n ­ s i t i o n temperature of the corresponding homopolymers. T h i s i s shown i n Figures 4 and 5 which are p l o t s of the frequency dependence of r e a l and imaginary moduli r e s p e c t i v e l y f o r Sample A„ at temperatures between -30 and 6 5 ° C . This co­ polymer has a long i s o t a c t i c stereosequence length and only 37o of comonomer and shows the g r e a t e s t temperature dependence of dynamic p r o p e r t i e s of a l l the copolymers s t u d i e d . A W i l l i a m s - L a n d e l l - F e r r y (WLF) type of time-temperature super­ p o s i t i o n (32) could be made only by using an unreasonably large s h i f t f a c t o r .

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

AGGARWAL

Propylene Oxide Polymers

AND MARKER

0

+20

+60

+40

+80

TEMPERATURE, °C Figure 3.

Change in stress optical coefficient of copolymers on cooling from 100°C

o.i μ

LU

g 0.5

+45°C +65°C 1.0

0.01

10.0

FREQUENCY (CPS) Figure 4.

Real component of dynamic modulus vs. frequency for propylene oxide copolymer A 2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

52

Since the temperature dependence of the modulus i s much greater than the frequency dependence, i t i s somewhat more i n s t r u c t i v e to p l o t the dynamic modulus at constant frequency as a f u n c t i o n of temperature. In Figure 6, we compare the moduli at 0.1 Hz f o r two copolymers w i t h long stereosequences, but which d i f f e r i n t h e i r comonomer content; copolymer contains 1.6 mole percent, and copolymer A^, 3.2 mole percent of comonomer. The moduli are c o r r e c t e d to 80°C by m u l t i p l y i n g by the f a c t o r T°(K)/353, which assumes that the k i n e t i c theory of rubber e l a s t i c i t y i s obeyed. The d i f f e r e n c e i n modulus at e l e v a t e d temperatures r e f l e c t s the d i f f e r e n c e i n c r o s s l i n k d e n s i t y . Sample A„ has the higher comonomer content and hence the higher degree of cure. At lower temperatures, however, A- has the higher modulus because of the greater degree of c r y s t a l l i n i t y . The break i n the curve at about 60°C corresponds to the m e l t i n g of the c r y s t a l l i n e p o r t i o n s of th In Figure 7, we compar s e r i e s of copolymers c o n t a i n i n g 2-4 mole percent of the comonomer and i n Figure 8 f o r the copolymers c o n t a i n i n g 7-10 mole percent of the comonomer. In these p l o t s , the moduli are c o r r e c t e d to 80°G by m u l t i p l y i n g by the f a c t o r T°(K)/353, which assumes that the k i n e t i c theory of rubber e l a s t i c i t y i s obeyed. The polymers A„, B-,and are i n the order of decreasing stereosequence l e n g t h . The degree of c r y s t a l l i n i t y , as i n d i c a t e d "by the change i n modulus on m e l t i n g , i s i n the same order as that determined from the d e n s i t y of the same polymers. The temperature at which c r y s t a l l i n i t y disappears, as i n d i c a t e d by the break i n the curve, decreases w i t h decreasing s t e r e o r e g u l a r i t y i n the copolymers. This temperature i s about 65°C f o r Sample A , 50°C f o r B^, about 10°C f o r and there i s no evidence of c r y s t a l l i n i t y i n copolymer Sample D^. For Sample and (copolymers that have short i s o t a c t i c sequences and have 2-4 percent comonomer) and f o r a l l the copolymers that have 7-10 mole percent comonomer, the temperature compensated dynamic moduli are almost i n v a r i a n t w i t h temperature. The copolymer with long i s o t a c t i c sequences (Sample A^) on the other hand has sigmoidal curve of dynamic modulus versus temperature. The curve f o r Sample B- i s s i m i l a r to that of the Sample k^j even though on the b a s i s or the comparatively short i s o t a c t i c sequences i n the corresponding homopolymer, we expected i t s dynamic modulus a l s o to be i n s e n s i t i v e to temperature. I t seems that t h i s f r a c t i o n of the polymer had s u f f i c i e n t l y long s t e r e o sequences and a smaller c o n c e n t r a t i o n of the comonomer, which r e s u l t e d i n the observed dynamic modulus versus temperature behavior. In general, the low temperature dynamic modulus (above Tg) at comparable comonomer content i s higher, the greater i s the s t e r e o r e g u l a r i t y , i . e . , the content of i s o t a c t i c t r i a d s , i n the polymer. 2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

AGGARWAL

AND

MARKER

Propylene Oxide Polymers

Figure 6. Dynamic modulus vs. temperature for propylene oxide copolymers A and A t

2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

Figure 7. Dynamic modulus vs. temperature of propylene oxide copolymers. Comonomer 2-4 mole %. Modulus values corrected to 80°C.

Figure 8. Dynamic modulus vs. temperature of propylene oxide copolymers. Comonomer 7-10 mole %. Modulus values corrected to 80°C.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3.

AGGARWAL

AND MARKER

Propylene Oxide Polymers

55

Summary 1·

Stereosequence length of i s o t a c t i c u n i t s i n poly(propylene oxide) i s determined by the c a t a l y s t system used. The stereo­ sequence length of i s o t a c t i c u n i t s i n s t e r e o r e g u l a r p o l y p r o ­ pylene oxide) polymers may be c h a r a c t e r i z e d from t h e i r melt­ ing p o i n t and degree of c r y s t a l l i n i t y . The stereosequence length of i s o t a c t i c u n i t s i n poly(propylene oxide) from f e r ­ r i c c h l o r i d e c a t a l y s t i s considerably longer than those from other c a t a l y s t systems such as d i e t h y l zinc-water and d i e t h y l zinc-water-isopropylamine.

2.

An important e f f e c t of stereosequence length of i s o t a c t i c u n i t s i s on c r y s t a l l i z a t i o n k i n e t i c s and morphology of poly(propylene o x i d e ) . The s p h e r u l i t e s grown from a polymer with long stereosequence greater frequency o l i t e s grown from the polymer that has short stereosequence length. The c r y s t a l l i z a t i o n k i n e t i c data show that c r y s t a l ­ l i z a t i o n continues by a secondary c r y s t a l l i z a t i o n process long a f t e r s p h e r u l i t e s completely occupy the a v a i l a b l e v o l ­ ume i n the polymer. The r a t i o of the r a t e of the secondary c r y s t a l l i z a t i o n process to that of the primary c r y s t a l l i z a ­ t i o n process i s almost independent of temperature but i n ­ creases w i t h i n c r e a s i n g s t e r e o r e g u l a r i t y of the polymer.

3.

The mechanical p r o p e r t i e s of propylene oxide rubbers (co­ polymers of propylene oxide and a l l y l g l y c i d a l ether) depend both on the c a t a l y s t used i n preparing the polymer and on the comonomer content. The mechanical p r o p e r t i e s are very much i n f l u e n c e d by the a b i l i t y of propylene oxide stereosequences i n the copolymer to c r y s t a l l i z e . The c r y s t a l l i n e m a t e r i a l can g i v e a s u b s t a n t i a l increase i n modulus and i n the s t r e n g t h of the polymer on s t r e t c h i n g .

4.

One of the most i n t e r e s t i n g p r o p e r t i e s shown by copolymers of propylene oxide of low s t e r e o r e g u l a r i t y i s the i n v a r i a n c e of modulus and mechanical loss over a broad range of temperature and frequency.

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Wunderlich, B., "Macromolecular Physics V o l . 1, C r y s t a l S t r u c t u r e , Morphology Defects", Academic Press, New York, 1973.

3.

P r u i t t , Μ., and Bagget, J. M., U.S. Patent 2,706,189 ( A p r i l

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In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4 Heterogeneous Nucleation of Isotactic Poly(Propylene Oxide) Crystallization J.

H.

COLE

and

L.

E.

ST-PIERRE

Department of Chemistry, M c G i l l University, Montreal,

Canada

Introduction It is known that when crystallising polymers are cooled from the melt, crystallisation usually begins on impurities i n the melt, such as dust particles or residual catalyst fragments. Homogeneous nucleation, where crystalline nuclei are believed to be formed by random fluctuations of order and segmental energies in the supercooled melt, usually occurs at higher supercoolings. Controlled addition of heterogeneous nuclei can improve many physical properties of a polymer (1) e.g. clarity, density, impact and tensile strength as well as increasing the crystallisation rates leading to shorter processing cycles. Numerous attempts have been made to predict the effectiveness of potential nucleating agents with particular attention having been paid to the crystallisation of isotactic polypropylene (1-5), isotactic polystyrene (6), polyethylene (7-9) and poly(ethylene terephthalate) (10,11). However, l i t t l e can be concluded about the fundamental mechanism of heterogeneous nucleation, or the properties of effective nucleating agents. Most theories of heterogeneous nucleation require that the foreign nucleus reduces the total interfacial free energy and itself provides part of the interface. There results a lowering of the free energy for nucleation and a decreasing of the degree of supercooling required for nucleation. This reduction in interfacial free energy depends on the geometry of the foreign phase and on i t s chemical nature. Hobbs has shown (12) that the abilities of two morphologically different, but chemically identical, graphite fibres to nucleate isotactic polypropylene differed considerably. The same author also showed (13) that a carbon replica of a crystalline isotactic polypropylene surface could increase the nucleation of the polymer during recrystallisation. Thus, the physical, not chemical, nature of the nucleating agent has determined i t s effectiveness. In the present work we have changed the surface chemistry of a particulate f i l l e r , without 58

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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ST-PIERRE

Isotactic Foly(Propylene Oxide) Crystallization

59

altering particle size or geometry. The f i l l e r used was a Cab-o-Sil silica with a surface concentration of 6-8 hydroxy! groups/100 A . By reacting these hydroxyl groups with various reagents the surface can be modified energetically (14). The interfacial energies between the silicas of differing chemical surfaces and a crystallising polymer can be characterised using lew molecular weight model compounds homologous with the polymer. The isosteric heats of adsorption at approximately zero coverage of the model compounds on the silica surfaces were taken as a measure of the interaction energy. Experimentally these were determined by means of the pulse elution technique of vapour phase chromatography. This has been described previously (15). The i n i t i a l investigations using this approach were concerned with the nucleatio methylsiloxane) (16). Silica methoxy, butoxy and trimethylsilyl groups were used as f i l l e r s . It was shown that an increase in f i l l e r concentration decreased the supercooling required to reach a certain critical nucleation rate; also, at the same f i l l e r content, the f i l l e r s having the lower surface energies underwent smaller decreases in supercooling. Further work showed (17) that addition of the f i l l e r s increased the isothermal crystallisation rate of the poly (dimethyl siloxane), and a semi-quantitative relationship between the nucleation rate and polymer-filler interaction energy was established. Based on the Fisher-Turnbull nucleation equation (18) i t was also suggested that there was a linear dependence of the free energy of heterogeneous nucleation on the interaction energy between the polymer and f i l l e r . In the present paper the silica-isotactic poly (propylene oxide) (iPPO) system is examined, with untreated silica and trimethylsilyl coated (1.69 trimethylsilyl groups/100 A ) silica being the nucleating agents. This system was chosen because: (1) iPPO, as shown in the early work of Price and Osgan (19), can crystallise conveniently at or just above room temperature; (2) the model compound used for iPPO, 1,4 p-dioxane, gives net isosteric heats of adsorption of 8.7 and 1.0 Kcal./mole for the untreated and treated silicas respectively. The crystallisation behaviour of the pure iPPO and composites was studied using differential scanning calorimetry and dilatometry. Results from these studies will be qualitatively interpreted in terms of the filler-polymer interaction energy. 2

2

Experimental 1. Samples. The polymer used was provided by Dr. A.E. Gurgiolo (Dow Chemical Co. ). It was prepared

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

60

POLYETHERS

losing a FeCl^propylene oxide catalyst; the fraction insoluble in acetone at -20°C was used in subsequent experiments. According to Aggarwal et a l (20) this sample i s 49% crystalline, and the melting temperature was found dilatometrically to be 75 °C. The molecular weight was estimated from the intrinsic viscosity, [η], in benzene solution at 25 °C using the relation (21) : 4

[η] = 1.12 χ 10~ (Μ )°·

77

ν

4

and was found to be 8.7 χ 10 gm/mole. b. Silicas. Cab-o-Sil M5, an amorphous thermal silica, particle size 12 my, with manufacturers quoted surface area of 200 m /gf was used as received, or after reaction in a high pressure reactor with trimethylchloTOsilane (15). Total carbon analysis of the treate trimethylsilyl groups/10 1

2

c. Composites. Known quantities of silica, previously dried at 130°C and 10""3 torr pressure were added to a 10% solution of iPPO in O C I 4 . Ihe mixture was thoroughly agitated with a stainless steel spatula until the solvent evaporated. Khen the samples were practically dry, and had become granular in form, they were dried at room temperature under vacuum for 6-8 hours. 2. Differential Scanning tolorinetry (D.S.C. ). The crystallisation of iPPO and composites were studied using the Perkin-Elmer Differential Scanning Calorimeter (DCS-1). Liquid nitrogen was used as coolant, with dry nitrogen the sweeping gas. The temperature read out was calibrated using the trans­ ition temperatures of indium (156°C), stearic acid (72°C), distilled water (0°C) and n-decane (-30°C). The procedure followed was to f i r s t melt the samples at 120°C for 30 minutes to ensure complete melting (22) ; they were then cooled at a scan speed of 10°C/min. During this time the sample temperature and (dQ/dT) were monitored continuously. 3. Dilatametry. The isothermal crystallisation rate curves were determined from the dilatometrically measured changes in density. Samples weighing between 1 and 2 gms were sealed under vacuum in glass dilatometers with mercury as the confining liquid. The samples were then melted at 120°C for 30 minutes and then transferred immediately into a water bath controlled to within 0.005°C of the required temperature, using a Hg/ toluene thermoregulator. The changes in height of the mercury column were monitored with time until no further change was observable over a period of 24 hours. Results and Discussion

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Isotactic Poly(Propylene Oxide) Crystallization

61

1. D.S.C. Pure iPPO, on cooling at 10°C/itiin exhibited an exotherm centred at 11.5°C, indicating crystallisation. This exotherm point, reproducible to ±1.0°C, was taken to be the optimum crystallisation temperature (Ibp) · l ^ i s interpretation has been discussed by Teilel'baum et a l (23) in their work on the crystallisation of natural rubber, and by Beck et a l (1) on the crystallisation of isotactic polypropylene. The silica-filled iPPO samples also exhibited exotherms, but the temperatures at which these isotherms appeared depended on the amount of f i l l e r present, and on the surface energy of the f i l l e r . From Fig. 1 i t can be seen that: (1) the optimum crystallisation temperature shifts to higher temperatures as the f i l l e r content i s increased, reaches a maximum, and then decreases; (2) samples with the same silica content, having different interfacial energies d behaviour. The sample silica (1.69 trimethylsilyl groups/100 A ) underwent lesser shifts in T p until a loading of approximately 35 parts of silica/100 parts of iPPO. Also the decrease of T after the maximum of the low energy surface silica composites i s not as great as the high energy surface samples. These phenomena can be explained by the application of heterogeneous nucleation theory (24,25). Silica powder, as an "extraneous solid" can catalyse the nucleation process. For the pure polymer, the steady-state nucleation rate per unit volume (18), ft i s expressed by: 2

Q

op

E_

AG

*

N = N θΐφ{-[2 ^ ] }

(1)

+

kT ° where N Q = ^- (n^ i s the concentration of polymer segments per unit volume and k,T and h are Boltzmann's constant, temperature and Planck's constant respectively). E i s the free energy of activation for transport across the liquid-nucleus interface, and A G * i s the free energy for homogeneously forming a nucleus. Then, in a silica-filled sample: ni

D

Q

N = N .exp{-[ e + - ^ ] } h

g

0

(2)

where A G ^ * i s the free energy for heterogeneous nucleation, and AGh* i s related to A G Q * by the expression (25): AGh* = f(φ)Δ0 *

(3)

ο

with

£(φ

)

= (2-Κχ> φ)α-οο3φ)

2

5

( R 2 f

. 24)

( 4 )

Here φ i s the contact angle between the f i l l e r particle and the polymer, with f (φ) increasing as the wetting angle increases. In particular, when

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

62

POLYETHERS

Φ +

0°,

φ

90°,

f (φ) f (φ)

0

+

i

As the interfacial energy between the polymeric liquid and the f i l l e r decreases, the wetting decreases, and so φ increases, or, as f(φ) increases the interfacial energy decreases. Thus from equations ( 3 ) and ( 4 ) i t i s apparent that the free energy for nucleus formation in the heterogeneous case will always be smaller than that for homogeneous nucleation. It i s reasonable to assume that, in order for a crystal­ lisation exotherm to be detectable by D.S.C., there must exist a critical nucleation rate S . Accordingly, comparison of the •temperatures at which these isotherms appear i s in effect a measurement of the relative rates of nuclei formation in the varioxas samples. Thu with smaller free energie nuclei necessary for observation are present at higher temper­ atures relative to the pure sample. In the pure sample the nucleation i s probably heterogeneous, but the number of nucleat­ ing species present is relatively small. Furthermore, with increasing f i l l e r content, the number of filler-polymer contacts increases with a resultant increase in the number of nuclei, and an upward shift in the exotherm temperature. In addition to changing the quantity of silica present, i t i s also possible to change the nature of the inter­ face present between the f i l l e r and the iPPO. The trimethylsilyl coated f i l l e r has a lower epoxide-silica interfacial energy than that between epoxides and pure silica. Thus the wetting of this sample will be less, and the differences between AGh* and ÙGq* will be diminished (equations ( 3 ) and ( 4 ) ) . At lower loadings this results in smaller shifts from the pure iPPO behaviour? ΔΤ = 9°C for 1 0 parts pure silica, while ΔΤ = 5 . 5 ° C for 1 0 parts trimethylsilyl coated silica. However, as the f i l l e r content i s increased, the number of silica particles present becomes so large that there is effective cros si inking of polymer segments by adsorption on the silica; this increases the transport term, E Q , in equation ( 2 ) , and thus the effective number of nuclei is lessened, resulting in a lowering of T p. Also the decrease in the number of effective nuclei at higher loadings i s greater for the composites contain­ ing pure silica than for the treated silica. This is expected because, as shown by Howard and McConnell, for poly (ethylene oxide) ( 2 6 ) , an epoxide polymer adsorbs more strongly on the hydroxyl group-covered surface than on the trimethylsilylated surface. R

Q

2 . Dilatometry. The kinetics of the isothermal crystal­ lisation of pure and f i l l e d iPPO samples from the melt were studied between 4 5 . 0 0 and 5 5 . 0 0 ° C . The composites contained 1 0

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Isotactic Έ*oly'(Propylene Oxide)

Crystallization

63

parts of filler/100 parts of iPPO. The increase in density was taken as a measure of the increase in overall crystallinity. In Fig. 2, (1 - X-t/Xoo) i s plotted against log (time) for the pure polymer; X t i s the weight fraction of polymer crystallised at time t and Xoo i s the weight fraction of polymer crystallised at infinite time. The sigmoidal isotherms usually found in polymer crystal­ lisation are observed; these represent primary crystallisation i.e. the nucleation and growth of crystalline regions until mutual impingement stops further growth. The second part of curves 2 and 3 as shown in Fig. 3, where the crystallinity increases logarithmically with time, corresponds to secondary crystallisation: this i s usually considered to be the crystal­ lisation of any remaining melt, and rearrangement of parts of the crystal regions grown in the primary phase (27). In Fig. 3 the crystallisatio silica composite i s 90 crystallised. A similar but lesser effect is shown in the low energy surface silica composite. Another parameter characterising the nucleation of the crystallisation i s the apparent induction time; this i s the time during which there i s no apparent change in the height of the mercury column in the dilatometer, when the change in polymer density i s too small to be observed. As shown in Fig. 4 there is an appreciable lengthening of the induction period with i n ­ creasing temperature. At the same crystallisation temperature the induction times vary in the order: Pure iPPO > iPPO + low energy surface silica > iPPO + high energy surface silica. Indeed, at 45.00°C the high energy surface silica composite began to crystallise before the sample reached thermal equilibrium (this was usually reached after 3 minutes). At the same temper­ ature the pure iPPO did not begin to crystallise until 11 minutes had elapsed. The half-time of primary crystallisation, t i , shows a similar dependence on temperature and polymer- f i l l e r interaction energy (see Fig. 5). To find t i , i t was assumed that the contribution of the slow secondary crystallisation process to the primary portion of the overall crystallisation curve was negligible. Thus t i was half the value of the time at the intersection point (see curve 3, Fig. 3), using the extra­ polation method of Vidotto et a l (28) for the crystallisation of isotactic poly butene-1, and used by Groeninckx et a l (11) for the crystallisation of poly (ethylene terephthalate). These results show that, since the primary crystallisation is composed of two processes, primary nucleation and subsequent crystal growth, and as the crystal growth is independent of the origin of the primary nucleus, the silicas act as heterogeneous nucleating agents for iPPO. Also the high energy surface silica is markedly more effective than the low energy surface silica. A semi-quantitative analysis of the time dependence of the

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

64

POLYETHËRS

Time (mins) Figure 2.

Crystallization isotherms for pure iPPO at crystallization temperatures of 2,45.00°C; 2,47.50°C; 3,50.00°C; 4,52.50°C; and 5,55.00°C

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4.

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Isotactic Ρoly(Propylene

Oxide)

Crystallization

T i m e (min) Figure 3. Crystallization isotherms of 1, pure iPPO; 2, iPPO + MeSiCl treated silica; and 3, iPPO + untreated silica. Crystallization temperature = 50.00°C.

0

50 Induction Time (mins)

100

Figure 4. Plots of induction time against crystallization tem­ perature. • = pure iPPO. φ = iPPO + Me SiCl treated silica. Ο = iPPO + untreated silica. 3

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65

POLYETHERS

66

primary crystallisation process was made using the Avrami relationship (29-31): 11

θ = expi-kjt )

(5)

where θ = (dp-d )/(dp-d ), with dp being the polymer density at the end of the primary crystallisation i.e. at the intersection point as drawn on curve 3 in Fig. 3, and do i s the density of the amorphous polymer; d-j- i s the density of the polymer at time t. ki i s the Avrami constant, and η i s the Avrami exponent; η depends on both the type of primary nucleation and the mode of growth of the crystallising polymer. Plots of log(-log6) against log (time) were drawn for a l l samples examined, and typical examples are shown in Fig. 6. From the slopes of these lines, the Avrami exponent η i s obtained. The average η value fo the treated and untreate temperatures except for the untreated silica sample at 45.00°C, which gave an anomalous η value of 2.50. The η values of 3.0, according to the simple Avrami theory suggest either instantaneous nucleation and three-dimensional crystal growth, or a first order nucleation rate and twodimensional crystal growth. However, as Mandelkern has shown (25), a more general Avrami equation can give non-integral values for n, as was found in the crystallisation of pure iPPO; thus i t i s difficult to attach a quantitative interpretation to a value of n. Qualitatively i t may be noted that the constant values of η for both types of silica f i l l e r s at a l l experimental temperature (with the one exception) indicates a similar crystallisation mechanism by both the high and low energy surface silica composites. For thé pure polymer, there operates a different mechanism, showing either a change in heterogeneous nucleation time dependence or in growth morphology. t

0

Summary The effectiveness of chemically different, but physically similar, silica f i l l e r s as nucleating agents in the crystallisation of isotactic poly (propylene oxide) was studied using differential scanning calorimetry and dilatometry. It was found that varying the epoxide-silica interfacial energy by treating a silica surface with trimethylchlorosilane caused a change in i t s nucleating ability; the greater the interfacial energy, the more efficiently the silica nucleates. This effect i s interpreted in terms of the Fisher-Turnbull equation for nucleation, with change in interfacial energy causing a change in the free energy of heterogeneous nucleation. Increase in f i l l e r content of the composites up to a certain loading increased nucleation; additional f i l l e r caused effective

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Isotactic Poly(Propylene

C O L E A N D ST-PIERRE

4500

47-50

Oxide) Crystallization

50 0 0

Crystallisation

52-50

Temperature

5500 (°C)

Figure 5. Plots of half-time of primary crystallization (ti/2) against crystallization temperature. • = pure iPPO. m = iPPO + Me SiCl treated silica. Ο = iFPO -f- untreated silica. ( 3

+ 20 b b

Log(-log0) -2-0

-40

-60 2-0

3-0 Log

40

50

t(min)

Figure 6. Avrami plots of log(—logO) against log t. • = pure iPPO. φ = iPPO + MeSiCl treated silica. Ο = iPPO + untreated silica at different temperatures, a, a\ a" = 52.50° C. b, b\ b" = 47.50°C.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

«S

POLYETHERS

cross-linking of polymer segments, thus increasing the free energy of activation for transport across the liquid polymerf i l l e r interface and so decreasing the nucleation rate. Acknowledgement Acknowledgement i s given to the National Research Council of Canada for financial support which permitted this work to be undertaken. I also acknowledge a debt of gratitude to Professor C.C. Price, a great chemist, a great man and a friend of decades. He has been an inspiration to me and to a host of other former students (L.E.St-P.). Literature Cited 1. Beck, H.N and Ledbetter 9, 2131. 2. Beck,H.N.,J. Appl. Poly. Sci., (1967), 11, 673. 3. Rybnikar, F., J. Appl. Poly. Sci., (1969), 13, 827. 4. Binsbergen, F.L., Polymer, (1970), 11, 253. 5. Binsbergen F.L. and de Lange, B.G.M., Polymer, (1970), 11, 309. 6. Kargin, V.A., Sogolova, T.I., Rapoport-Molodtsova, N.Ya., Dokl. Akad. Nauk. S.S.S.R., (1964), 156, 1406. 7. Cormia, R.L., Price, F.P. and Turnbull, D., J. Chem. Phys., (1962), 37, 1333. 8. Koutsky, J.A., Walton, A.G. and Baer, Ε., Polymer Letters, (1967), 5, 185. 9. Mauritz, K.A., Baer, E. and Hopfinger, A.J., J. Poly. Sci., A2, (1973), 11, 2185. 10. Van Antwerpen, F. and van Krevelin, D.W., J. Poly. Sci., A2, (1972), 10, 2423. 11. Groeninckx, G., Berghmans, Η., Overbergh, N. and Smets, G., J. Poly. Sci., A2, (1974), 12, 303. 12. Hobbs, S.Y., Nature, Physical Science, (1971), 234, (44), 12. 13. Hobbs, S.Y., Nature, Physical Science, (1972), 239, (89), 28. 14. Chahal, R.S., Ph.D. Ihesis, McGill university, (1968). 15. Chahal, R.S. and St-Pierre, L.E., Macromolecules, (1968), 1, 152. 16. Yim, A. and St-Pierre, L.E., Polymer Letters, (1970), 8, 241. 17. Yim, Α., Ph.D. Thesis, McGill University, (1971). 18. Turnbull, D. and Fisher, J.C., J. Chem. Phys., (1949), 17, 71. 19. Price, C.C. and Osgan, M., J. Am. Chem. Soc., (1956), 78, 4787. 20. Aggarwal, S.L., Marker, L., Kollar, W.L. and Geroch, R., J. Poly. Sci., A2, (1966), 4, 715. 21. Allen, G., Booth, C. and Jones, M.N., Polymer, (1964), 5, 195.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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22. 23. 24. 25. 26. 27. 28. 29. 30. 31.

A N D ST-PIERRE

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Oxide)

Crystallization

69

Slonimskii, G.L. and Godovskii, Yu.K.,Vysokomol.Soyed., (1967), 9, 863. Teilel'baum, B.Ya and Anoshina, N.P., vysokomol. Soyed., (1965), 7, 2117. Turnbull, D., Solid State Physics, (1956), 3, 277. Mandelkern, L., "Crystallisation of Polymers", McGraw-Hill Book Co., Inc., New York, 1964. Howard, G.J. and McConnell, P., J. Phys. Chem., (1967), 71, 2974. Keith, H.D., Koll.-Z.Z. Polym., (1969), 231, 421. Vidotto, G., andKovacs,A.J., Koll.-Z.Z. Polym., (1967), 220, 2. Avrami, M., J. Chem. Phys., (1939), 7, 1103. Avrami, M., J. Chem. Phys., (1940),8,212. Avrami, M., J. Chem Phys. (1941) 9 177

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

5 Applied Crystallization Kinetics. III. Comparison of Polyepichlorohydrins of Different Stereoregularity P. D R E Y F U S S B. F. Goodrich Research and Development Center, Brecksville, Ohio 44141

Introduction In the course of some of our work on polyethers, we encountered a series of crystalline polyepichlorohydrins which differed quite markedly in their processing characteristics but otherwise seemed quite s i m i l a r . Differences revealed by the infrared and nuclear magnetic resonance techniques then available were too insignificant to be helpful in their characterization. A l l polymers were shown to be crystalline and isotactic by X - r a y analysis. Small differences in optical activity were measurable. However, these differences were too small to be useful for correlation with physical properties. We found that an examination of their crystallization behavior and rates of crystallization was an extremely sensitive and revealing way of characterizing them. Experimental Microscopy. Thin films (1-2 mils) were pressed at 1 5 0 ° C using a Pasedena press fitted with West SCR controllers. T y p i cally, a small sample was placed between Teflon coated a l u m i num foil sheets, preheated for 30 sec, and held at 25, 000 lb. gauge load for 5 min. Samples were then rapidly transferred to a cooling press and held at 25, 000 lb. gauge load for 5 min. Some of the lower melting samples were pressed at 1 0 0 ° C . Portions of these films were placed on a glass slide and covered with a cover glass. Samples were melted in an air oven at the desired temperature, usually 1 5 0 ° C for the desired time, usually 15 min and then rapidly transferred to a hot stage at Current address: Institute of Polymer Science, University of Akron, A k r o n , Ohio 44325. 70 In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

5.

DREYFUSS

Polyepichlorohydrins

71

constant temperature. The hot stage temperature was controlled by circulating liquid f r o m a Haake NBS bath through the stage. Temperatures, measured by means of a thermocouple in the stage near the sample, were constant to 0. 1 ° C or less. The growth of the spherulites that formed was observed using a Unitron polarizing microscope with crossed polaroids. Photographs were taken with the aid of an A m e r i c a n Optical Co. Photomicrographic camera with a Polaroid Land camera back. Melting was followed using a heating rate of 0. 5 to 1° per min. The slower rate was used in the vicinity of the melting temperature. Dilatometry. Volume-temperature measurements, and c r y s tallization rate measurement dilatometers made f r o lary tubing with mercury as the confining liquid. The procedure followed was very s i m i l a r to that described by Bekkedahl (JJ. Well-fused pellets of appropriate dimensions were pressed at 5 Ram force/lb. Hydraulic Pressure on the gauge and 25 to 120°C (usually 9 0 ° G ) . The pellets were cooled to 4 5 - 5 0 ° C at full pressure before removing f r o m the moid. The sealed dilatometers containing the pellets were evacuated to about 10"* 5 m m Hg while heating at 1 2 5 - 3 5 ° C for about 3 hrs prior to filling with mercury. F o r the rate studies, the prepared dilatometers were placed in a 1 5 0 ° C bath for about 30 min before transferring rapidly to a second bath at the crystallization temperature. Crystallization temperatures were controlled to + 0. 01 °C with the aid of a Dynapac-15 temperature controller. Higher temperatures of the melting bath and longer melting times were tried occasionally. These did not change the observed rates for any of the samples studied. A l l rates are reported in terms of the time, ti., for half the total change in height to occur. Whenever the value of t i was less than about 10 min, we were not able to determine an exact value because crystallization began before thermal equilibrium was achieved. Melting temperatures after isothermal crystallization were obtained in the same bath using heating rates of 0. 3 ° C per min and observing the change in height with temperature which was measured with a calibrated mercury thermometer. Melting temperatures were taken as the temperature where the last traces of crystallinity disappeared.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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POLYETHERS

Results D e s c r i p t i o n of P o l y m e r s . A wide v a r i e t y of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s w e r e e x a m i n e d i n this study. S o m e t y p i c a l e x a m p l e s a r e g i v e n i n T a b l e 1. A l l the p o l y m e r s w e r e p r e p a r e d f r o m r a c e m i c m o n o m e r , but s o m e of t h e m w e r e p r e p a r e d u s i n g i n i t i a t o r s of the type p r e v i o u s l y r e p o r t e d to give p a r t i a l l y o p t i c a l l y a c t i v e p o l y m e r s (2-6). T h e p o l y m e r s w e r e shown to be i s o t a c t i c by c o m p a r i s o n of the o b s e r v e d d - s p a c i n g s with those r e p o r t e d i n the l i t e r a t u r e f o r c r y s t a l l i n e i s o t a c t i c p o l y e p i c h l o r o h y d r i n (8,9). A l s o i n c l u d e d i n T a b l e 1 f o r c o m p a r i s o n a r e s o m e data on p o l y p r o p y l e n e o x i d e s p r e p a r e d with d i f f e r e n t i n i t i a t o r s . Spherulite Morphology readily f o r m s spherulit i n F i g u r e 1, we have o b s e r v e d two k i n d s of s p h e r u l i t e s .

b Figure 1. Polyepichlorohydrin spherulites. Left: Type I spherulites from 329C after melting at 170°C and crystallizing at 50°C for 185 min. (128%). Right: Type II spherulites from 39A after melting at 150°C and crystallizing at 50°C for 222 min. (128x).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Ferric chloride

Polymer from ^ - p r o p y l ene oxide

b

17+5

b

C

c

b c Crystalline, 8.0 , -9.3 c Semicrystalline, 6. 1^, -8 Amorphous, 4 . 9 , + l 25 + 5^, -16 4- 5

0 0 -2. 36 -2.80 -9.75 -10.1

in M - P y r o l at 2 3 ° C

'

7

7

Ref

c

a

D e t e r m i n e d in benzene at 2 0 ° C .

Determined in chloroform at 2 0 ° C .

A is a typical initiator for the preparation of non-optically active but crystalline polymers fr racemic monomer. Β are typical initiators for the preparation of optically active polymer f i racemic monomer.

Potassium hydroxide

Polymer f r o m J - p r o p y l ene oxide

a

Diethyl zincd-borneol

A A Β Β Β Β

Initiate-r

Polymer f r o m racemic propylene oxide

Sample 329C 100Z 162A 2437 2413 2431

Table 1 T y p i c a l Crystalline Polyepichlorohydrins

POLYETHERS

74

B o t h have f i b r i l l a r s t r u c t u r e s but the s t r u c t u r e of T y p e I is c o a r s e r than that of T y p e II. O c c a s i o n a l l y r i n g s a r e o b s e r v e d in T y p e II s p h e r u l i t e s . S o m e t i m e s as shown i n F i g u r e 2 both types of texture a r e o b s e r v e d i n a s i n g l e s p h e r u l i t e . W h e n the s p h e r u l i t e s w e r e o b s e r v e d between c r o s s e d p o l a r o i d s u s i n g a 1st o r d e r r e d plate i n the u s u a l 45° o r i e n t a t i o n , it was found that both types of s p h e r u l i t e s a r e n e g a t i v e l y biréfringent. T h i s is not s u r p r i s i n g s i n c e negative s p h e r u l i t e s have a l s o been o b s e r v e d i n p o l y p r o p y l e n e o x i d e f i l m s (10). N e v e r t h e l e s s , the s p h e r u l i t e s a r e not i d e n t i c a l when v i e w e d with the 1st o r d e r r e d plate. T y p e I is blue i n the s e c o n d and f o u r t h q u a d r a n t s and o r a n g e i n the f i r s t and t h i r d . T y p e II i s s i m i l a r but the q u a d rants a r e s e p a r a t e d by a r e d c r o s s .

Figure 2. Type I and II spherulites both seen in the same spherulite, from 164A melted at 150'C and crystallized at 50°C for 168 min. (128x)

T h e type of s p h e r u l i t e that f o r m s does not s e e m to be a f f e c t e d by the t e m p e r a t u r e at w h i c h the s a m p l e i s m e l t e d o r by the t e m p e r a t u r e of c r y s t a l l i z a t i o n . We have o b s e r v e d the g r o w t h of s p h e r u l i t e s of both types at 30, 50, and 6 0 ° C a f t e r m e l t i n g at 1 5 0 ° C . S i m i l a r m o r p h o l o g y was obtained f r o m the s a m e s a m p l e at a l l t e m p e r a t u r e s . H o w e v e r , as expected, the g r o w t h rate and

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perfection of the spherulites are dependent on the temperature of crystallization. Rates are slower and perfection is greater at temperatures nearer to the polymer melting temperature. We have been able to grow very large spherulites by crystallizing for several days at 5 0 ° C . The morphology does not seem to be affected by the temperature at which the sample is melted prior to crystallization. We have crystallized at 50°C after melting at 130, 150, and 1 7 0 ° C . The morphology obtained f r o m the same sample was similar in all cases. The main difference was that more small spherulites, unresolvable at our usual magnification of 150x, formed after melting at 1 3 0 ° C . Melting Temperatures. The melting temperatures we observe microscopically ar thoseobserved dilatometrically. Some typical results are given in Table 2 and in Figures 3-5. This is not an unexpected result, since polymer melting temperatures are very sensitive to the rate of heating unless extremely slow heating rates, such as 0. 5 ° C per day, are used. A l s o , the heat transfer in a dilatometer and on a hot stage may be quite different. In addition, Table 2 Microscopic and Dilatometric Melting Temperatures of Crystalline Polyepichlorohydrin Polymer 329C 39A 164A 2413 2431 100Z

Microscopic T

m

115-16 119-20 114 and 117

(°C)

Dilatometric T

m

(°C)

113 115 108.5 and 113 115-17 117.5 111

sample preparation and previous heat history can affect the exact melting temperature observed ( j _ l ) . The important point here is that two different melting temperatures have been observe d_boJhjrujcj^^ the same sample and in different samples. In some of the later experiments, samples were held at temperatures between the higher and lower melting temperatures for several hours to verify that the higher melting polymer was not just slower to melt. Thus, there are two families of crystalline polyepichlorohydrins. A s

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Figure 3.

Melting of 329C and 39A after simultaneously melting at 150°C crystallizing at 50°C on the same slide

and

Figure 4. Melting of spherulites of 164A. At 80°C both Type I and Type II spherulites are visible. By 115°C Type I spherulites are melted. Type II spherulites disappear by 117°C (83%).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Figure 5.

Polyepichlorohydrins

Dilatometric melting curve of 164A. Two inflections suggest two different melting temperatures.

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will be discussed below these two families can be related to the stereoregularity of the polymers. Crystallization Rates. We determined growth rates of the spherulites microscopically, but only examined the rates of nucleation qualitatively for reasons that will emerge below. Overall rates of crystallization were determined dilatometrical-

iy. Nucleation of Spherulites. We have examined the rates of crystallization of the two kinds of spherulites microscopically in order to obtain further evidence to aid in understanding the differences observed. We found that different kinds of nucleation apparently occurred in different samples. Some samples gave spherulites of uniform geneous nucleation. Other samples gave spherulites of variable size such as would be expected f r o m sparodic, homogeneous nucleation. Only these latter samples were used in the comparison made below in determinations of overall rates of c r y s t a l l i zation. The number of nuclei that appear in the field of view also varies considerably f r o m sample to sample and even f r o m area to area in the same sample. Nevertheless, throughout our studies it appears that spherulites form more readily f r o m Type II spherulites, that is, f r o m more optically active polymer. Growth Rates of Spherulites. A s shown in Figure 6, both types of spherulites grow in the typical fashion observed many times for spherulites: namely, linearly with time. In the particular examples illustrated it was not possible to follow the growth of 39A for as long as 329C was studied because impingement occurred sooner. The fact that a single straight line can be drawn for both types is fortuitous in as much as the particular spherulites examined happened to have the same diameter at the same initial time. But it is significant that the growth rates determined f r o m the slope of the line do not appear to be different. Both are of the order of 1.5 microns per minute. If either type grows faster, the data in Figure 6 suggests that Type II spherulites grow faster. Overall Rates of Crystallization. We divided our studies of overall rates of crystallization into two areas: reproducibility studies and determination of the temperature of maximum rate of crystallization.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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1. R e p r o d u c i b i l i t y . A s stated above, o b s e r v a t i o n s of the o v e r a l l rate of c r y s t a l l i z a t i o n of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s t u r n e d out to be a p a r t i c u l a r l y s e n s i t i v e was of c h a r a c t e r i z i n g polyepichlorohydrins. T h u s , we have taken s p e c i a l c a r e to c h e c k the r e p r o d u c i b i l i t y of o u r d i l a t o m e t r i c o b s e r v a t i o n s of o v e r a l l r a t e s . We have c a r r i e d out three d i f f e r e n t kinds of a n a l ­ y s i s to c h e c k r e p r o d u c i b i l i t y . F i r s t , we s h o w e d that the data f r o m a n y given d i i a t o m e t e r w e r e s u p e r i m p o s a b l e o v e r the whole range on r e p e a t e d runs at the s a m e t e m p e r a t u r e . T h i s was t r u e f o r both " s l o w " a n d " f a s t " c r y s t a l l i z i n g p o l y m e r s . Second, we d e m o n s t r a t e d that two d i f f e r e n t s a m p l e s of the s a m e p o l y m e r i n two d i f f e r e n t d i l a t o m e t e r s gave r e p r o d u c i b i l i t y of t i m e a s u r e ­ ments o v e r the whole t e m p e r a t u r e range studied. F i n a l l y , we showed that good s u p e r p o s i t i o obtained a t d i f f e r e n t c r y s t a l l i z a t i o d u c i b i l i t y is t y p i c a l of d i l a t o m e t r i c r e s u l t s on c r y s t a l l i n e p o l y ­ m e r s i n g e n e r a l (11). F r o m these studies we conclude that c r y s t a l l i n e polyepichlorohydrin c r y s t a l l i z e s in a n o r m a l r e p r o ­ d u c i b l e m a n n e r . T h e v a r i a t i o n s r e p o r t e d below a r e due to d i f f e r e n c e s i n the p o l y m e r s * 28,

3

Figure 6. Comparison of spherulite growth rates at 50°C after melting at 150°C. Ο = Type I spherulites from 329C. • = Type II spher­ ulites from 39A.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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2. D e t e r m i n a t i o n of the m a x i m u m rate of c r y s t a l l i z a t i o n . T h e rate of c r y s t a l l i z a t i o n of any g i v e n p o l y m e r i s v e r y s e n s i t i v e to the t e m p e r a t u r e a t w h i c h the m e a s u r e m e n t i s c a r r i e d out (11). It goes t h r o u g h a m a x i m u m at a f a i r l y w e l l - d e f i n e d t e m p e r a t u r e . A b o v e that t e m p e r a t u r e , as the m e l t i n g t e m p e r a t u r e i s a p p r o a c h ed, the rate of n u c l e a t i o n i s l o w e r a n d l o w e r a n d the o v e r a l l rate d e c r e a s e s . B e l o w that t e m p e r a t u r e as the g l a s s t r a n s i t i o n tempe r a t u r e i s a p p r o a c h e d , the m e l t b e c o m e s i n c r e a s i n g l y v i s c o u s , the rate of d i f f u s i o n of the p o l y m e r chains d e c r e a s e s , and a slowe r o v e r a l l c r y s t a l l i z a t i o n rate is obtained. Therefore, in order to m a k e m e a n i n g f u l c o m p a r i s o n s of p o l y m e r s p r e p a r e d u n d e r d i f f e r e n t conditions i t was n e c e s s a r y to d e t e r m i n e the e f f e c t of t e m p e r a t u r e on the c r y s t a l l i z a t i o n rate of e p i c h l o r o h y d r i n . We have e x a m i n e d the rat ent p o l y e p i c h l o r o h y d r i n S o m e of o u r m o r e t h o r o u g h studies a r e i l l u s t r a t e d i n F i g u r e 7. A s the f i g u r e i l l u s t r a t e s , the m a x i m u m rate of c r y s t a l l i z a t i o n

Figure 7. Effect of temperature on the crystallization rate of polyepichlorohydrin

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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(lowest t i ) o c c u r s at about 5 0 ° C . T h e r e a r e s e v e r a l i n t e r e s t i n g a n d u n u s u a l f e a t u r e s about c r y s t a l l i z a t i o n r a t e s of p o l y e p i c h l o r o h y d r i n i l l u s t r a t e d i n F i g u r e 7. E v i d e n t l y , t h e r e a r e not one o r even two p o l y e p i c h l o r o h y d r i n s . Instead t h e r e i s a whole f a m i l y of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s . T h e r e a r e the s l o w l y c r y s t a l l i z i n g " m e m b e r s of the f a m i l y l i k e 8 E . T h e s e p o l y m e r s have a r e l a t i v e ly s h a r p m a x i m u m and a n i n t e r m e d i a t e m e l t i n g t e m p e r a t u r e . T h e y c r y s t a l l i z e too s l o w l y and have too n a r r o w a p r o c e s s i n g range to be u s e f u l f o r , say, m o l d e d a r t i c l e s . T h e r e a r e the m e m b e r s with a n " i n t e r m e d i a t e " r a t e of c r y s t a l l i z a t i o n l i k e 100Z. T h e s e p o l y m e r s s u r p r i s i n g l y have a s o m e w h a t l o w e r melting temperature. T h e y too have a r a t h e r s h a r p m a x i m u m in the rate v e r s u s t e m p e r a t u r to p r o c e s s w e l l o v e r a " f a s t c r y s t a l l i z i n g " m e m b e r s , i l l u s t r a t e d by 2413 and 2431. T h e s e p o l y m e r s have the h i g h e s t m e l t i n g t e m p e r a t u r e s we have o b s e r v e d so f a r and a b r o a d m a x i m u m i n rate v e r s u s t e m p e r a t u r e c u r v e that suggests a b r o a d p r o c e s s i n g range. T h e " f a s t c r y s t a l l i z i n g " p o l y m e r s a l s o have the h i g h e s t o p t i c a l r o t a t i o n s that we o b s e r v e d . T h e y c r y s t a l l i z e i n the f o r m of T y p e II s p h e r u l i t e s . We have studied m a n y e x a m p l e s of e a c h type of polymer. F r o m the c u r v e s and the i n t r i n s i c v i s c o s i t i e s g i v e n f o r the p o l y m e r s , i t a p p e a r s that i n the range studied, i n t r i n s i c v i s c o s ity does not have a n i m p o r t a n t effect on c r y s t a l l i z a t i o n rate. A n a p p a r e n t a n o m a l y i l l u s t r a t e d by the data i n F i g u r e 7 i s the r e l a t i o n s h i p o r r a t h e r l a c k of r e l a t i o n s h i p between the o b s e r v e d rate and the m e l t i n g t e m p e r a t u r e . U s u a l l y a l o w e r m e l t i n g t e m p e r a t u r e c o r r e s p o n d s to g r e a t e r s t r u c t u r a l i r r e g u l a r i t y a n d s l o w e r c r y s t a l l i z a t i o n rate (11). In this c a s e 329C has a l o w e r m e l t i n g t e m p e r a t u r e than 8 E and yet c r y s t a l l i z e s m u c h m o r e r a p i d l y . T h e s e o b s e r v a t i o n s a r e d i s c u s s e d below and an e x p l a n ation is g i v e n . ff

3. O v e r a l l c r y s t a l l i z a t i o n rate of blends of " f a s t " a n d " s l o w " c r y s t a l l i z i n g p o l y m e r s . We obtained f u r t h e r e v i d e n c e that the g r e a t e r ease of n u c l e a t i o n of o p t i c a l l y a c t i v e p o l y m e r into T y p e II s p h e r u l i t e s is r e s p o n s i b l e f o r the o b s e r v e d i n c r e a s e i n c r y s t a l l i z a t i o n rate by s t u d y i n g s o l u t i o n blends of 2413 and a nonopti c a l l y a c t i v e p o l y e p i c h l o r o h y d r i n . We found that a d d i t i o n of only 6% of 2413 r e d u c e d the t i a t 5 0 ° C of the 'slow" p o l y m e r f r o m 32 m i n to l e s s than 10 m i n .

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D i s c u s s i o n and Conclusions P o l y m e r i z a t i o n of m o n o m e r s l i k e e p i c h l o r o h y d r i n , O C H — ( C H C l ) , l e a d s to p o l y m e r s w h i c h t h e o r e t i c a l l y c a n have m a n y d i f f e r e n t i s o m e r s . A s a r e s u l t of the v e r y elegant w o r k of P r i c e and c o w o r k e r s (12) a n d of V a n d e n b e r g (13) i n t h e i r m e c h a n i s t i c s t u d i e s of the r i n g opening p o l y m e r i z a t i o n of epoxides, the task of a n a l y z i n g these p o l y m e r s i s s o m e w h a t s i m p l i f i e d . F o r exa m p l e , head-to-head, t a i i - t o - t a i l , and h e a d - t o - t a i l p o l y m e r s a r e a l l t h e o r e t i c a l l y p o s s i b l e , but only h e a d - t o - t a i l need to be c o n s i d e r e d f o r the f o l l o w i n g r e a s o n s . We know that p o l y m e r i z a t i o n o c c u r s by r i n g opening i n w h i c h the bond between o x y g e n a n d the c a r b o n l a b e l l e d w i t h a n a s t e r i s k (the a s y m m e t r i c c a r b o n atom) is b r o k e n . F u r t h e r m o r e kno f r o studie with o p t i c a l l active propyleneoxide the a s y m m e t r i c c a r b o n and that no r a c e m i z a t i o n o c c u r s on p o l y m e r i z a t i o n . We a l s o know that e v e n when o p t i c a l l y a c t i v e monom e r i s used, s o m e a m o r p h o u s p o l y m e r i s p r o d u c e d . P r i c e a n d c o w o r k e r s (7) have found that these i r r e g u l a r i t i e s a r e l a r g e l y , i f not e n t i r e l y units of head-to-head, t a i l - t o - t a i l s t r u c t u r e f o r m e d as a r e s u l t of s o m e r e a c t i o n i n v o l v i n g c l e a v a g e of the bond c o r r e s p o n d i n g to the C H -O bond i n e p i c h l o r o h y d r i n . In a d d i t i o n we know that a l l c r y s t a l l i n e p o l y e p o x i d e s known to date a r e i s o t a c t i c . S y n d i o t a c t i c p o i y e t h e r s r e m a i n a p r o d u c t of the f u t u r e . 3

2

2

A l t h o u g h s i m i l a r s t u d i e s have not been r e p o r t e d f o r p o l y e p i c h l o r o h y d r i n , there i s no r e a s o n to e x p e c t any d i f f e r e n c e s i n m e c h a n i s m of p o l y m e r i z a t i o n f o r this epoxide. It c a n be a s s u m ed that p o l y m e r i z a t i o n l e a d i n g to c r y s t a l l i n e p o l y m e r o c c u r s p r e d o m i n a n t l y by i n v e r s i o n a t the a s y m m e t r i c c a r b o n a t o m a n d r e s u l t s i n h e a d - t o - t a i l p l a c e m e n t of the m o n o m e r . M a i n l y i s o t a c t i c p o l y m e r w i l l be f o r m e d . O u r s t u d i e s a n d p r e v i o u s w o r k have b o r n this out (8, 9, 14, 15). T h e r e s u l t s of this study f u r t h e r r e v e a l that the c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n we have s t u d i e d c o n s i s t s of i s o t a c t i c s e q u e n c e s that c a n c r y s t a l l i z e i n the f o r m of two d i f f e r e n t kinds of s p h e r u l i t e s . We have shown that the two kinds of s p h e r u l i t e s c a n c o c r y s t a i l i z e . A t p r e s e n t o u r e d u c a t e d guess is that a l l the p o l y m e r s we have e x a m i n e d c o n t a i n e i t h e r T y p e I o r a m i x t u r e of T y p e I a n d T y p e II s p h e r u l i t e s in v a r y i n g p r o p o r t i o n s . The p o l y m e r s that c r y s t a l l i z e m o s t r a p i d l y a n d that have the h i g h e s t m e l t i n g t e m p e r a t u r e s have s o m e o p t i c a l a c t i v i t y a n d t h e i r f i l m s c o n t a i n p r e d o m i n a n t l y T y p e II s p h e r u l i t e s . We c o n c l u d e that the T y p e II s p h e r u l i t e s a r e obtained f r o m o p t i c a l l y a c t i v e p o l y m e r s e q u e n c e s . We do not m e a n to i m p l y that a l l s e q u e n c e s i n these

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p o l y m e r s have the s a m e c o n f o r m a t i o n . We m e r e l y w i s h to s u g g e s t that enough of an e x c e s s of one e n a n t i o m e r has p o l y m e r i z e d to give a m e a s u r a b l e r o t a t i o n and that the o v e r a l l s t r u c t u r e of these p o l y m e r s is m o r e r e g u l a r . We s u g g e s t that T y p e I s p h e r u l i t e s a r e obtained f r o m r a c e m i c p o l y m e r that shows l i t t l e o r no o p t i c a l r o t a t i o n . It is unfortunate f r o m a t h e o r e t i c a l point of v i e w that o u r c o n c l u s i o n s cannot be d e f i n i t e l y r e l a t e d to the d e g r e e of o p t i c a l a c t i v i t y i n the p o l y m e r . T o a c c o m p l i s h this we would need to p r e p a r e p o l y m e r of known and v a r i a b l e a m o u n t s of o p t i c a l r o t a tion, p r e f e r a b l y f r o m o p t i c a l l y a c t i v e m o n o m e r . T h i s we have not done. H o w e v e r , we b e l i e v e that o u r r e s u l t s a r e s u f f i c i e n t l y c o n c l u s i v e e v e n without this c o m p a r i s o n . P o l y m e r s of l o w e r m e l t i n g t e m p e r a t u r e ca having a higher meltin a l l y and m o r p h o l o g i c a l l y d i f f e r e n t . R a c e m i c p o l y m e r c r y s t a l l i z e s i n the f o r m of T y p e I s p h e r u l i t e s . A s long as the p o l y m e r has a s u f f i c i e n t l y low c o n c e n t r a t i o n of a t a c t i c s e q u e n c e s , f a i r l y r a p i d c r y s t a l l i z a t i o n c a n o c c u r . H o w e v e r , the r a t e w i l l be s l o w e r than that of p o l y m e r s that l e a d to T y p e II s p h e r u l i t e s . The f r e e e n e r g y b a r r i e r to n u c l e a t i o n of T y p e II s p h e r u l i t e s s e e m s to be l o w e r . P o l y m e r c o n t a i n i n g s o m e o p t i c a l l y a c t i v e s e q u e n c e s c r y s t a l l i z e m o s t r a p i d l y p r i m a r i l y b e c a u s e the rate of n u c l e a t i o n is g r e a t e r . A n i n c r e a s e d r a t e of n u c l e a t i o n c o m b i n e d w i t h the d e m o n s t r a t e d p o t e n t i a l of c o c r y s t a l l i z a t i o n of T y p e I and T y p e II s p h e r u l i t e s a l s o p r o v i d e s an e x p l a n a t i o n f o r the u s e f u l n e s s of f a s t c r y s t a l l i z i n g p o l y e p i c h l o r o h y d r i n i n i n c r e a s i n g the rate of c r y s t a l l i z a t i o n of s i o w c r y s t a l l i z i n g p o l y e p i c h l o r o h y d r i n . In fact, t h e r e is a d i r e c t p a r a l l e l to s o m e of o u r f i n d i n g s r e p o r t e d i n the c a s e of c r y s t a l l i n e p o l y p r o p y l e n e o x i d e , which is s t r u c t u r a l l y the s a m e as p o l y e p i c h l o r o h y d r i n excep t that the c h l o r i n e a t o m on the pendant m e t h y l e n e substituent is r e p l a c e d by a h y d r o g e n atom. Two kinds of s p h e r u l i t e s have b e e n o b s e r v e d in c r y s t a l l i n e p o l y p r o p y l e n e o x i d e (14 ). The two w e r e not shown to c o c r y s t a l l i z e . f T

M

n

n

A ck now ledge me nt I a m e s p e c i a l l y indebted to M. P. D r e y f u s s, M. L . D a n n i s , and R. W. S m i t h f o r h e l p f u l d i s c u s s i o n s at c r i t i c a l points i n this study. I a m g r a t e f u l to P. S. N e a l f o r a s s i s t a n c e with s o m e of the e x p e r i m e n t a l work. I w i s h to thank H. A. T u c k e r and C. A. M a r s h a l l f o r p r o v i d i n g the p o l y m e r s u s e d i n this study and M. H. L e h r f o r s h a r i n g the r e s u l t s of h i s study of the m e c h a n i c a l p r o p e r t i e s of the p o l y m e r s .

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Summary The purposes of this study were to determine what chemical and physical structures are present in polyepichlorohydrin and to correlate these structures with the crystallization rates ob­ served microscopically and dilatometrically. Crystallization rates were shown to be an extremely sensitive way of character­ izing these polymers. F o r example, the study revealed that the crystalline polyepichlorohydrins examined consisted of isotactic sequences that can crystallize as two different kinds of spheru­ lites, arbitrarily called Type I and Type II. The two types can cocrystallize. The polymers that crystallize most rapidly and that have the highest melting temperature have some optical activity. Their films contain predominantly Type II spherulites. Polymers that contain little or no optical activity. These polymers are racemic mixtures. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Bekkedahl, N., J. Research Nat'l. B u r . Standards, (1949), 43, 145. Tsuruta, Τ., Inoue, S., Yoshida, Ν., and Furukawa, J., Makromol. C h e m . , (1962), 53, 215. Tsuruta, Τ., Inoue, S. Yoshida, Ν., and Furukawa, J., (1962), 55, 230. Inoue, S., Tsuruta, T., and Yoshida, Ν., Makromol. Chem., (1964), 79, 34. Tsuruta, Τ., Inoue, S., Ishimori, Μ., and Yoshida, Ν., J . Polym. Sci., C. (1963), (No. 4), 267. Tsuruta, Τ., Macromolecular Reviews, J . Polym. Sci., D, (1972), 179. P r i c e , C. C., and Osgan, M., J. A m . Chem. Soc., (1956), 78, 4787. Kambara, S. and Takahashi, A., Makromol. C h e m . , (1963), 63, 89. Richards, J. R., P h . D . Thesis, University of Pennsylvania, 1961, P a r t III, University M i c r o f i l m s , 61-3547. Magill, J. Η., Makromol. C h e m . , (1965), 86, 283. Mandelkern, L., "Crystallization of Polymers," McGraw­ - H i l l Book Co., New York, Ν. Υ., 1964. P r i c e , C. C., and Spector, R., J. A m . Chem. Soc., (1965) 87, 2069. Vandenberg, E. J., J. Polym. Sci., A-1, (1969), 7, 525.

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14. Perego, G., and C e s a r i , Μ., Makromol. Chem., (1970), 133, 133. 15. Hughes, L. J., Dangieri, T. J., Watros, R. G., and A i l i n g , J., Polymer Preprints, (1968), 9, 1126.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

6 X-ray Structural Analysis of Crystalline Polymers RICHARD J. CELLA* and ROBERT E. HUGHES Department of Chemistry, Cornell University, Ithaca, Ν. Y. 14853

The d e t e r m i n a t i o talline polymers by wide a n g l e X - r a y diffraction tech­ n i q u e s p r e s e n t s f o r m i d a b l e problems w h i c h cannot c o n v e n i e n t l y be t r e a t e d by the c o n v e n t i o n a l methods of structure analysis. Consequently, existing methods need t o be m o d i f i e d and new approaches t o the p r o b l e m d e v e l o p e d t o e x t r a c t the maximum amount of s t r u c t u r a l i n f o r m a t i o n f r o m the a v a i l a b l e e x p e r i m e n t a l d a t a . The n a t u r e of the problems e n c o u n t e r e d will be d i s c u s s e d i n this p a p e r , t o g e t h e r w i t h a description of methods t h a t have been utilized t o overcome them. A subsequent p a p e r will d e a l w i t h the a p p l i c a t i o n s o f t h e s e methods to the d e t e r m i n a t i o n of the m o l e c u l a r s t r u c t u r e of several crystalline polyethers. Characteristically, c r y s t a l s composed of l o n g c h a i n m o l e c u l e s p r o v i d e much l e s s diffraction d a t a than do s i n g l e c r y s t a l s of low m o l e c u l a r weight s u b s t a n c e s , and o f t e n t h i s d a t a i s of v e r y p o o r quality. This i s a d i r e c t consequence of the limited l o n g range o r d e r e x h i b i t e d by crystalline polymers; small crystallite size, imperfect crystallite orientation, structural d e f e c t s , and the p r e s e n c e of a non-crystalline compo­ nent in the sample all c o n t r i b u t e t o the r a p i d a t t e n u a ­ tion of the a v a i l a b l e d a t a . The first of these deficiencies, the l i m i t e d l o n g range t h r e e d i m e n s i o n a l o r d e r , i s the s i n g l e most i m p o r t a n t f a c t o r i n v o l v e d in c r e a t i n g the difficulties e n c o u n t e r e d i n the structural a n a l y s i s of macromolecular m a t e r i a l s . The g r e a t l e n g t h of the polymer c h a i n s and the concomitant possibilities f o r chain entangle­ ments prohibit the m o l e c u l e s from o r d e r i n g themselves *E. I . du Pont de Nemours and Company, ton, Delaware 19898

Inc.,

Wilming­

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over an extended region w i t h a h i g h degree o f r e g u l a r ­ i t y . Furthermore, the i n d i v i d u a l molecules themselves are not p e r f e c t l y r e g u l a r , and often c o n t a i n i n t r i n s i c s t r u c t u r a l defects such a s s t e r i c inversions o f asym­ metric sites, c h a i n branches, and c r o s s l i n k s . Such d e f e c t s d on o t n e c e s s a r i l y p r e v e n t t h e c h a i n f r o m becoming i n c o r p o r a t e d into a c r y s t a l l i n e domain; often­ times a molecule c o n t a i n i n g a minor s t r u c t u r a l imper­ f e c t i o n w i l l manage t opack reasonably w e l l into the s t r u c t u r e , thereby e n l a r g i n g the c r y s t a l l i n e domain but at the same time d e s t r o y i n g the p e r f e c t r e g u l a r i t y o f the assemblage. Another type o fp a c k i n g defect occurs when a "multi-state s t r u c t u r e i s p o s s i b l e . This happens when each successive c h a i n may enter the c r y s t a l l i t e i n any of several s p a t i a l l a c h a i n may b eaccommodate e i t h e r a n ' u p " o ra " d o w n " p o s i t i o n a t w o - s t a t e s t r u c ­ ture w i l l r e s u l t ; i fa side group may assume any o f t h r e e d i f f e r e n t a n g u l a r p o s i t i o n s i nt h e s o l i d phase, then a three-state s t r u c t u r e i sp o s s i b l e . These defects may occur s p o r a d i c a l l y w i t h low p r o b a b i l i t y o r they may occur randomly each time the o p p o r t u n i t y p r e s ­ ents i t s e l f . I nt h e l a t t e r c a s e i ti sl i k e l y t h a t a s t a t i s t i c a l d i s t r i b u t i o n o f several d i f f e r e n t models w i l l h a v e t o b e i n v o k e d i no r d e r t o o b t a i n s a t i s f a c t o r y agreement t othe experimental data. Each o fthe s t r u c t u r a l defects described w i l l tend to attenuate the i n t e n s i t y o f the d i f f r a c t e d beam a t higher s c a t t e r i n g angles, and a s i t u a t i o n i s soon r e a c h e d i n w h i c h t h e s c a t t e r e d b e a m i s o fl o w e r i n t e n ­ s i t y than the background s c a t t e r i n g . This f a l l - o f f o f the d a t a a t h i g h e r s c a t t e r i n g a n g l e s i ss i m i l a r t o t h a t c a u s e d b yt h e r m a l m o t i o n a n d a t o m i c s c a t t e r i n g , but these phenomena also occur i n non-polymeric systems and can b ec o r r e c t e d f o r rather e a s i l y . The c y l i n d r i c a l l y symmetric d i s t r i b u t i o n o f c r y s ­ t a l l i t e s about the f i b e r axis also leads t oa decrease i n the q u a n t i t y o fdata obtainable, although for a n e n t i r e l y d i f f e r e n t reason. The r o t a t i o n a l character o f the d i f f r a c t i o n p a t t e r n causes a l l l a t t i c e plans whose r e c i p r o c a l l a t t i c e points have the same ξ and ζ c o o r d i ­ n a t e s t o d i f f r a c t i n t o t h e s a m e p o i n t i ns p a c e , i r r e ­ s p e c t i v e o ft h e v a l u e o ft h e i r a n g u l a r r e c i p r o c a l l a t t i c e c o o r d i n a t e (l). T h i s l e a d s t o a no v e r l a p p i n g o f r e f l e c t i o n s which would otherwise b e d i s t i n g u i s h a b l e were i tnot f o r the c y l i n d r i c a l symmetry o f the p o l y ­ meric f i b e r . Thus, i n many instances two or more independent r e f l e c t i o n s produce o n l y one observable d i f f r a c t i o n maximum. 1

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I s o t a c t i c poly(propylene oxide), PPO, provides a n u m e r i c a l example of the above c o n s i d e r a t i o n s . U s i n g copper r a d i a t i o n , this polymer should i n p r i n c i p l e g e n e r a t e a p p r o x i m a t e l y 400 u n i q u e r e f l e c t i o n s (regard­ l e s s of whether or not t h e i r i n t e n s i t i e s are large enough to be measurable above background scattering) o u t t o a r e s o l u t i o n o f Ο.77 A. In p r a c t i c e ^ an a c t u a l f i b e r o f P P O y i e l d e d d a t a o u t t o o n l y Ο.97 A, thereby r e d u c i n g t h e p o t e n t i a l n u m b e r o f d a t a t o I78 r e f l e c ­ tions; for this purpose, each allowable r e f l e c t i o n con­ t r i b u t i n g to an o v e r l a p p i n g group of r e f l e c t i o n s is counted separately, and a r e f l e c t i o n is counted whether or not i t is of s u f f i c i e n t i n t e n s i t y to be detectable. When the r o t a t i o n a l symmetry of the f i b e r specimen is taken into c o n s i d e r a t i o n and o v e r l a p p i n g r e f l e c t i o n s are counted as one o b s e r v a t i o n o n l y observations are to be expected. O i n t e n s i t y to be experimentally measurable above the background s c a t t e r i n g . This example d r a m a t i c a l l y i l l u s t r a t e s t h a t a t b e s t l e s s t h a n 25$ of the t h e o r e t i ­ c a l l y a l l o w a b l e data may be observed, and of these less than two-thirds a c t u a l l y are observed. Furthermore, i t should be emphasized that i s o t a c t i c PPO is a polymer w h i c h y i e l d s a r e l a t i v e l y large amount of data, and many examples could be quoted i n which an even smaller f r a c t i o n of the data is a c t u a l l y obtained. The poor q u a l i t y of the data obtained is a conse­ quence of the imperfect alignment of the c r y s t a l l i n e domains w i t h respect to the f i b e r axis of the sample. The c r y s t a l l i t e s are not p e r f e c t l y u n i a x l a l l y oriented, and this m i s o r i e n t a t i o n causes the r e f l e c t i o n s from polymeric substances to appear as elongated arcs rather than as sharp, w e l l defined spots. Measuring the total, or integrated, i n t e n s i t y of these arcs proves to be extremely d i f f i c u l t , and even the simpler task of determining the peak i n t e n s i t y is subject to large e r r o r (2). F u r t h e r m o r e , a l l c r y s t a l l i n e p o l y m e r s c o n t a i n a c e r t a i n amount of n o n - c r y s t a l l i n e m a t e r i a l which produces only diffuse s c a t t e r i n g and has the e f f e c t of i n c r e a s i n g the background l e v e l , thereby r e n d e r i n g even more d i f f i c u l t the process of measuring i n t e n s i t i e s . These two f a c t o r s t a k e n t o g e t h e r , therefore, are r e ­ sponsible f o r the poor q u a l i t y of the data when com­ pared w i t h the accuracy achieved i n single c r y s t a l analyses. The c h a r a c t e r i s t i c features of polymer structures d e s c r i b e d above were d i s c u s s e d at some l e n g t h because they are almost wholly responsible f o r the d i f f i c u l t i e s encountered i n the s t r u c t u r a l analysis of these m a t e r i ­ a l s . Many of the powerful methods existent f o r single

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t a l studies are inadequate when d e a l i n g w i t h such m i t e d amount o fdata, and the poor q u a l i t y o f the merely serves t o i n t e n s i f y the problem. Thus, niques such a s d i r e c t methods, P a t t e r s o n synthesis, somorphous replacement are not a p p l i c a b l e t o p o l y c r y s t a l s t r u c t u r e analyses, and r e s o r t must b e made r i a l a n d e r r o r m e t h o d s t os e l e c t a r e a s o n a b l e t i n g s t r u c t u r e w h i c h must subsequently b e r e f i n e d . The standard technique for r e f i n i n g a proposed s t r u c t u r e i sa l e a s t s q u a r e s a n a l y s i s i n w h i c h the s t r u c t u r a l parameters are s y s t e m a t i c a l l y v a r i e d s o a s to produce the best agreement between the c a l c u l a t e d d i f f r a c t i o n p a t t e r n and the experimental data. When a p p l i e d t o the determination o fpolymer s t r u c t u r e s , however, t h i s method s u f f e r s f r o m two d e f i c i e n c i e s . T h e f i r s t o ft h e s e i s t h a t a l e a s t s q u a r e s refinement w i l l c o n v e r g e t ot h dimensional parameter space, and unless the proposed s t a r t i n g m o d e l i sq u i t e c l o s e t o t h e c o r r e c t s t r u c t u r e this w i l l not b e the g l o b a l minimum. Thus, the l e a s t squares approach w i l l often converge t oan i n c o r r e c t s t r u c t u r e . T h e s e c o n d s h o r t c o m i n g o ft h e l e a s t s q u a r e s method l i e s i nt h e p o o r d a t a t o p a r a m e t e r r a t i o g e n e r a l l y encountered i n polymer s t r u c t u r e s . T y p i c a l l y , the number o fparameters t ob er e f i n e d i n a polymeric s t r u c t u r e i so f t h e same o r d e r o f m a g n i t u d e a s t h a t f o u n d i ns m a l l m o l e c u l e s t r u c t u r e s , y e t t h e r e i s m u c h l e s s data w i t h w h i c h t owork. Consequently, i f one independently refines the atomic p o s i t i o n a l coordinates i n a d d i t i o n t o scale factors and thermal parameters the results w i l l b es t a t i s t i c a l l y meaningless. Thus, f o r these types o f s t r u c t u r e s i twould b eb e n e f i c i a l t o p o s s e s s c o m p u t a t i o n a l m e t h o d s w h i c h d on o t a l l o w a l l o f the atomic coordinates t ovary independently, but r a t h e r which couples them i n a meaningful way t o reduce the number o fparameters i n v o l v e d . The p r e c e d i n g d i s c u s s i o n has d e s c r i b e d the inadequacy o f standard c r y s t a l l o g r a p h i c methods when a p p l i e d to the determination o fpolymer s t r u c t u r e s . The l a c k of an a n a l y t i c a l method o fphase d e t e r m i n a t i o n makes t h e s o l u t i o n o ft h e s e s t r u c t u r e s a m a t t e r o ft r i a l and e r r o r ; t h e r e i sn oa l t e r n a t i v e b u t t o p o s t u l a t e various models and compare the t h e o r e t i c a l l y c a l c u l a t e d i n t e n s i t i e s t ot h o s e a c t u a l l y o b s e r v e d . I tw o u l d b e u s e f u l , therefore, t odevelop computational techniques whereby p h y s i c a l l y r e a l i s t i c models may b es y s t e m a t i c a l l y generated and evaluated i n a s t r a i g h t f o r w a r d , e f f i c i e n t manner. The problem d i v i d e s i t s e l f n a t u r a l l y into two d i s t i n c t parts: (1) t h e c a l c u l a t i o n o f g e o m e t r i c a l l y

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a n d e n e r g e t i c a l l y a l l o w a b l e s t r u c t u r e s , a n d (2) the refinement of these s t r u c t u r e s to produce the b e s t agreement to the a v a i l a b l e X - r a y d a t a . Geometric

C o n s i d e r a t i o n s

It is not p o s s i b l e to r e l y s o l e l y on geometric arguments to determine a polymer s t r u c t u r e ; u l t i m a t e l y , recourse must be made to v a r i a t i o n a l methods. Geomet­ r i c c o n s t r a i n t s , however, are extremely u s e f u l i n e l i m i n a t i n g from c o n s i d e r a t i o n v a s t numbers of p h y s i ­ c a l l y unreasonable s t r u c t u r e s , thereby r e d u c i n g the number of t r i a l models w h i c h need to be i n v e s t i g a t e d . A survey of the many substances whose m o l e c u l a r s t r u c ­ tures have been e s t a b l i s h e d i n d i c a t e s that c e r t a i n s t r u c t u r a l features, namely bond lengths and bond angles, assume value any series of r e l a t e d compounds. On the other extreme, the i n t e r n a l r o t a t i o n angles about single bonds are free to assume a wide range of values, and i n most cases i t is not p o s s i b l e a p r i o r i to a s s i g n values to these parameters w i t h any degree of c e r t a i n t y (the r e l a t i v e i n v a r i a n c e of some m o l e c u l a r parameters i n r e l a t i o n to others is of course a d i r e c t consequence of the energetics i n v o l v e d i n e f f e c t i n g changes i n t h e i r v a lu es , but the problem is b e s t t r e a t e d from a p u r e l y geometric p o i n t of view). Thus, to a good approxima­ t i o n , i t is p o s s i b l e to assume values f o r the bond lengths and bond angles and to use these values i n the g e o m e t r i c a l d e t e r m i n a t i o n of the i n t e r n a l r o t a t i o n angles. Because of the s m a l l amount of d i f f r a c t i o n data a v a i l a b l e this p r a c t i c e is u n i v e r s a l l y followed i n polymer s t u d i e s , and i t is necessary i n order to reduce the a n a l y s i s to manageable p r o p o r t i o n s . If the data allows, i t w i l l be p o s s i b l e to v a r y these values s l i g h t l y at a l a t e r stage i n the s t r u c t u r a l d e t e r m i n a ­ t i o n . Consider a l i n e a r polymer molecule whose s k e l e t a l a t o m s a r e n u m b e r e d 0 , 1, N, and represented by C , Gi, Cjp s u c c e s s i v e l y f r o m one end of the c h a i n to the other. Let r^ represent the v e c t o r from C i _ to C^ a n d l e t 0j_ r e p r e s e n t t h e s u p p l e m e n t o f t h e angle between r. and "?^ · The angle between the two planes determined by r ^ _ and r^, and r ^ and Γ^ , r e s p e c t i v e l y , is measured from the cis p o s i t i o n i n the d i r e c t i o n of clockwise r o t a t i o n of f a c i n g i n the d i r e c t i o n of r ^ . The c h a i n skeleton of a h e l i x w i t h two backbone atoms i n the r e p e a t i n g u n i t may be completely d e s c r i b e d by s p e c i f y i n g the two types of bond lengths, b = Q

1

+

1

1

+ 1

x

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

6.

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Crystalline Polymers

A N D HUGHES

91

= ] Ï 3 - | = . . . = \r \ = ... and b = | r | = |r | = ... = | r j _ | = . .., the two t y p e s o f b o n d a n g l e s 0 i = 0 3 = . . . = 0 j _ = ... and 0 2 = 0 4 = ... = 0 i + i ···* ^ t h e t w o t y p e s o f d i h e d r a l a n g l e s τ.χ = τ = · . . . = τ ι = ... a n d τ = τ = ... T j _ = .... A l t e r n a t i v e l y , the h e l i c a l conformation i s u n i q u e l y determined b y s p e c i f y ­ ing the bond lengths, the bond angles, the r o t a t i o n a l angle about the h e l i x axis, θ (unit twist), and the t r a n s l a t i o n a l distance along the h e l i x axis per repeat u n i t , d ( u n i t t r a n s l a t i o n ) ; t h e r e i so n l y one set o f d i h e d r a l a n g l e s , τχ and τ , c o m p a t i b l e w i t h t h e s e six q u a n t i t i e s . S i m i l a r l y , the s k e l e t a l conformation o fa three a t o m h e l i x i s u n i q u e l y d e t e r m i n e d b ys p e c i f y i n g the f o l l o w i n g q u a n t i t i e s : b i= | r i | = . . |rj_| = 2

±

2

4

+ 1

=

a n <

3

2

4

+

1

2

b

= | r f = ... = | r

2

I

= . . ., b

2

Ϊ + 2

Γ

· · · ,

I

·'·>

=

0 3

~

0 1

. . .

—

=

= .··>

· ·

=

Φ 2_-|-

2

=

· · · 9

Τ" 1

. . .

=

=

T" j _

=

0 i + i · · · 9

= ^2.

=

... = i + i »··^ 3= ... = i + = · · · . this case, however, a knowledge o f the bond lengths, bond angles, θ a n d d i si n s u f f i c i e n t t o d e t e r m i n e a u n i q u e t r i a d [τι, τ , τ } which i s consistent w i t h the given geometric c o n s t r a i n t s . One o f the three d i h e d r a l a n g l e s ( u s u a l l y chosen t ob e τ ) must b e s p e c i f i e d a s an independent v a r i a b l e , and for a given value o f this a n g l e t h e v a l u e s o ft h e o t h e r t w o d i h e d r a l a n g l e s are unique. Various r e l a t i o n s h i p s have been p u b l i s h e d g i v i n g θ and d a s functions o f the bond lengths, bond angles and d i h e d r a l angles for helices c o n t a i n i n g a smany a s s i x b a c k b o n e a t o m s i nt h e r e p e a t i n g u n i t ( 3 - 8 ) . While useful f o r c a l c u l a t i n g the unit twist and u n i t repeat f o r a p a r t i c u l a r h e l i c a l model, these r e l a t i o n s h i p s are o f l i m i t e d u s e i ns t r u c t u r a l a n a l y s i s f o r θ a n d d a r e u s u a l l y k n o w n q u a n t i t i e s , w h i l e l i t t l e o rn o t h i n g i s known about the d i h e d r a l angles. Cognizant o f t h i s , Nagai and Kobayashi have d e r i v e d complex a n a l y t i c a l expressions e x p l i c i t l y g i v i n g the r o t a t i o n a l angles a s functions o f the other h e l i c a l parameters (9). I n the case o fa three atom h e l i x these formulas specify Τ χ a n d τ a s f u n c t i o n s o ft h e b o n d l e n g t h s , b o n d angles, θ, d and τ . A computer program, DIHED, was w r i t t e n w h i c h would solve the necessary matrix equations and c a l c u l a t e a l l allowable h e l i c a l conformations consistent w i t h the imposed stereochemical c o n s t r a i n t s . G i v e n bond lengths, b o n d a n g l e s , θ a n d d., t h e p r o g r a m s y s t e m a t i c a l l y varies τ over any p r e s e l e c t e d range and c a l c u l a t e s the c o r r e ­ s p o n d i n g v a l u e s o f τχ a n d τ ; the coordinates o f the h e l i c a l b a c k b o n e a r e c o m p u t e d i nc y l i n d r i c a l and T

=

a

2

n

d

T

T

2

ΐ

η

3

2

3

2

2

3

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

92

POLYETHERS

C a r t e s i a n c o o r d i n a t e s . S e v e r a l examples o ft h e program output a r e shown g r a p h i c a l l y i n F i g u r e I . Each curve i s t h e l o c u s o f a l lp o s s i b l e d i h e d r a l a n g l e s , [ τ ι ,τ , τ } , f o r t h e h i g h l y symmetric three atom h e l i x w i t h b i = b = b = 1.54 Â , 0 i = 02 = 0 3 = 109.5° , a n d d = 3.60 Â ; t h e c u r v e s c o r r e s p o n d t o θ = ΐ 8 θ ° , 1 2 0 ° , a n d 90°. T h ev a l u e s o fτχ a n d τ a r e read a st h e i n t e r s e c ­ tions o ft h e curve w i t h a v e r t i c a l l i n e drawn t h r o u g h a g i v e n v a l u e o f τ . T h u s , f o r t h e 4χ h e l i x , [ τ = ΐ4θ° , τ ι ( o r τ ) = 1 β ΐ ° , τ ( o r Τ ι ) = 126°} i s a s o l u ­ t i o n o ft h e geometric problem. T h e r i g h t a n dl e f t hand extremes o ft h e curve ( i . e . , τ = 121° o r 1 6 2 ° ) r e p r e ­ sent those conformations f o rw h i c h τχ = τ . F o r τ g r e a t e r t h a n l62° o r l e s s t h a n 121° n o s o l u t i o n s exist and these regions o ft h e space m a y b e excluded from f u r t h e r c o n s i d e r a t i o n . It i sapparen c o n j u n c t i o n w i t h c h e m i c a l l y reasonable values o f t h e b j / s a n d 0j_ s c a n p r o v e e x t r e m e l y u s e f u l . A l t h o u g h n o unique h e l i c a l conformation r e s u l t s , t h e number o f p o s s i b i l i t i e s t ob e i n v e s t i g a t e d i s d r a s t i c a l l y r e d u c e d . 2

3

2

3

3

2

2

3

3

2

3

2

T

E n e r g e t i c

Considerations

The above geometric arguments a r ebased o n n o n i n t e r a c t i n g p o i n t atoms; b y i n t r o d u c i n g t h e side c h a i n substituents a n dr e p l a c i n g t h ep o i n t atoms b y r e a l a t o m s i tb e c o m e s p o s s i b l e t o u s e e n e r g y considerations to f u r t h e r l i m i t t h e number o fp l a u s i b l e models(10-14). E n e r g y c a l c u l a t i o n s may b e c o n d u c t e d a tv a r i o u s levels of s o p h i s t i c a t i o n ranging from hard sphere atoms w i t h square w e l l p o t e n t i a l s t o" s o f t " atoms using a more r e a l i s t i c p o t e n t i a l f u n c t i o n . Furthermore, o n e m a y i n c l u d e t o r s i o n a l a n dv i b r a t i o n a l e n e r g i e s , p o l a r i n t e r a c t i o n s , h y d r o g e n b o n d i n g a n dv a r i o u s o t h e r terms i n t h e c a l c u l a t i o n . In this study, a n elegant energy m i n i m i z a t i o n com­ p u t e r program, PACK, w a s employed t oc a l c u l a t e t h e t o t a l p a c k i n g energies o ft h e s t r u c t u r e s under i n v e s t i ­ g a t i o n . T h ep r o g r a m , b e l o n g i n g t oP r o f e s s o r H . Scheraga, c a l c u l a t e s t h e t o t a l energy o fa n assemblage of molecules b y t a k i n g i n t o account t h e f o l l o w i n g con­ t r i b u t i o n s t ot h e t o t a l e n e r g y o f t h e s y s t e m : fa) non-bonded i n t e r a c t i o n s ho) p o l a r i n t e r a c t i o n s fc) t o r s i o n a l b a r r i e r s id) hydrogen bonding (e) In

bond

a d d i t i o n ,

angle

bending

t h eprogram

and

bond

s t r e t c h i n g

m a y b e used

t og e n e r a t e

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

a n

CELLA

A N D HUGHES

Crystalline Polymers

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

94

POLYETHERS

e n e r g y c o n t o u r map a sa f u n c t i o n parameters. Although a comprehen this program i sbeyond the scope (a) a n d (b) l i s t e d a b o v e r e q u i r e T h e p r o g r a m u s e s a "6-12" p o the non-bonded atomic i n t e r a c t i o n p o t e n t i a l energy, U(r), i sgiven i n t e r n u c l e a r distance, r , by:

o fa n y t w o s t r u c t u r sive d i s c u s s i o n o f o fthis paper, item f u r t h e r e x p l a n a t i o n t e n t i a l t o c a l c u l a t s . The p a i r w i s e a sa f u n c t i o n o f th

a l s . e e

"<'>-Ό(^Γ-*«ο(ξ)' w ε a e t t

here r i s the e q u i l i b r i u m i n t e r n u c l e a r distance and i s the i n t e r a c t i o n energy a tr . The values o f e nd r t obe u s e d f o r a g i v e n a t o m p a i r a r e determined m p i r i c a l l y by studying e s t a b l i s h e d s t r u c t u r e s and f i t i n g the e n e r g e t i c a l l u a l s t r u c t u r e by v a r y i n P o l a r i n t e r a c t i o n s may be i n c l u d e d e i t h e r by using a monopole approximation, which replaces p o l a r bonds b y p o i n t charges on the bonded atoms and then uses a Coulombic p o t e n t i a l , or b y the more i n v o l v e d treatment o f d e l R e (15-16). T h e l a t t e r m e t h o d u s e s a s e m i e m p i r i c a l quantum mechanical approach t o d i s t r i b u t e p a r t i a l charges throughout the molecule; i tthen uses a Coulombic p o t e n t i a l t oc a l c u l a t e the energies o f various charge p a i r s . When a p p l i e d t othe d e t e r m i n a t i o n o f c r y s t a l s t r u c t u r e s the program f i r s t generates the coordinates of the e n t i r e s t r u c t u r a l a r r a y i n accordance w i t h the given space group. I t then c a l c u l a t e s the p a c k i n g energy by i n c l u d i n g a l l p a i r w i s e i n t e r a c t i o n s (both p o l a r and non-bonded), i n c l u d i n g any d e s i r e d c o n t r i b u tions from s p e c i f i c terms such a st o r s i o n a l b a r r i e r s . The s t r u c t u r e i schanged by v a r y i n g any predetermined m o l e c u l a r o rs t r u c t u r a l p a r a m e t e r s a n d t h e e n e r g y i s r e c a l c u l a t e d . By proceeding i n this manner the program s e l e c t s the s t r u c t u r e w h i c h i s o fl o w e s t energy using the g i v e n degrees o ff r e e d o m . Even though the absolute e n e r g i e s c a l c u l a t e d may n o t b ee x a c t , the r e l a t i v e energies are extremely useful i n determining favorable s t r u c t u r e s . B y a p p l y i n g energy c a l c u l a t i o n s t othose s t r u c tures which are g e o m e t r i c a l l y allowable i ti s possible t o r e d u c e t h e n u m b e r o fp r o b a b l e s t r u c t u r e s t o m a n a g e able p r o p o r t i o n s . In g e n e r a l , two or more s t r u c t u r e s w i l l remain which are both e n e r g e t i c a l l y and geometric a l l y reasonable and the d i s t i n c t i o n among them must b e made on the b a s i s o fthe X - r a y d a t a . I f s u c c e s s f u l , however, the u t i l i z a t i o n o fgeometric and energetic c o n s t r a i n t s w i l l generate t r i a l s t r u c t u r e s which are Q

0

Q

ç

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Q

6.

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quite close t othe a c t u a l structure, thereby the e f f i c i e n c y o fthe s t r u c t u r a l refinement S t r u c t u r a l

i n s u r i n g process.

Refinement

An extremely v e r s a t i l e computer program, POLYMIN, which i s designed s p e c i f i c a l l y f o r the s t r u c t u r a l refinement o fc r y s t a l l i n e polymers has been developed. It incorporates several features not found i n standard refinement programs and thereby eliminates many o f the d i f f i c u l t i e s encountered i n t h e i r use. The main advantages o fthe program are that i t : (a) uses l i n e search rather than l e a s t squares m i n i m i z a t i o n (b) maintains geometric and stereochemical constraint (c) u t i l i z e s overlapping and unobserved data in the refinement process. By using a line search minimizer rather than least squares the program does not require that t h e s t r u c t u r e t ob er e f i n e d b ec l o s e t o the c o r r e c t s t r u c ture i norder t oinsure convergence. U n l i k e a least squares treatment, the line search refinement w i l l not of necessity converge t othe nearest minimum, and thus i t has a higher p r o b a b i l i t y o ff i n d i n g the global minimum. The quantity being minimized, however, i s t h e same a sthat b e i n g minimized i nthe l e a s t squares approach: w

m

[

I

o (

m

)

-

I

c(

f f i

)

] 2 =

â

V * I ( m ) ]

2

w i t h w™

= s t a t i s t i c a l

m "fc I ( m )= c o r obs I (m) = c a l Q

c

=

s

dard recte ervat c u l a t

a n

weight

o fthe

m ^

1

observation

=

d e v i a t i o n o fthe m observation d observed i n t e n s i t y o fthe m^ ion e d i n t e n s i t y o fthe m observation 1

The main advantage o fusing this program, however, i s t h a t i t e n a b l e s a r e f i n e m e n t t ob e c a r r i e d o u t subj e c t t ogeometric c o n s t r a i n t s . B yv a r y i n g atomic coordinates a l e a s t squares procedure simultaneously changes bond lengths, bond angles, and d i h e d r a l angles. As stated p r e v i o u s l y , the minimal amount o f data obtainable from polymeric structures makes i t desirable to f i x the bond lengths and bond angles during the course o fa s t r u c t u r a l d e t e r m i n a t i o n i na d d i t i o n t o the h e l i c a l parameters θ and d . Consequently, while a l e a s t squares refinement TTreats the atomic p o s i t i o n s a s

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

96

POLYETHERS

independent parameters, t h e l i n e search refinement program couples the movement o fthe atoms, thereby p r e s e r v i n g the geometrical nature o fthe problem. POLYMIN has the a b i l i t y t orefine a s t r u c t u r e using any or a l l o fthe f o l l o w i n g parameters: fa) scale factors bo) r i g i d b o d y r o t a t i o n s a n d t r a n s l a t i o n s (c) i s o t r o p i c thermal parameters ( i n d i v i d u a l o r o v e r a l l ) id) bond lengths fe) bond angles If) d i h e d r a l angles (g) atomic m u l t i p l y i n g factors D u r i n g the course o fa refinement the parameters ( a ) , (b), (c), and ( f ) would n o r m a l l y b e v a r i e d ; i f t h e d a t a / p a r a m e t e r r a t i o i s f a v o r a b l e i tw o u l d b e p o s s i b l e to refine using ( d The atomic m u l t i p l y i n g factors, ( g ) ,a r e u s e f u l f o r studying m u l t i - s t a t e systems, where i t i s desirable t o d e t e r m i n e t h er e l a t i v e a b u n d a n c e s o f e a c h o f s e v e r a l d i f f e r e n t models. The program i sextremely w e l l suited for the d e t e r m i n a t i o n o fp o l y m e r s t r u c t u r e s i n i t st r e a t m e n t o f unobserved and o v e r l a p p i n g data. Standard l e a s t squares treatments assume that o n l y one r e f l e c t i o n con­ t r i b u t e s t oa n y g i v e n o b s e r v a t i o n ; due t othe c y l i n d r i ­ c a l symmetry o ff i b e r d i f f r a c t i o n patterns a great many of t h e observations are a c t u a l l y s u p e r p o s i t i o n s o f two or more r e f l e c t i o n s . Under these circumstances t h e observed i n t e n s i t y must b ecompared t othe sum o f t h e c o n t r i b u t i n g c a l c u l a t e d i n t e n s i t i e s . Thus, i f £ i n d e ­ pendent r e f l e c t i o n s contribute t othe nr* observation, then 1

A l ( m ) = I (m) - Σ I * (m) Q

11

where iS'(m) i s the c a l c u l a t e d i n t e n s i t y of the q* v t h r e f l e c t i o n c o n t r i b u t i n g t othe m observation. The treatment o funobserved data i s o f necessity d i f f e r e n t from that g i v e n t oobserved data. For these data there i s only a t h r e s h o l d i n t e n s i t y w i t h which t o compare the c a l c u l a t e d v a l u e , and i tbecomes necessary to define a number, f , such that fI (m) i s the most probable value o fthe observed i n t e n s i t y , where I (m) i s now t h e m i n i m u m i n t e n s i t y w h i c h the m** observation w o u l d h a v e t o d i s p l a y i n o r d e r t ob e d e t e c t a b l e above background s c a t t e r i n g ( i thas been shown that f=0.33 Q

0

1

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

6.

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f o r a centrosymmetric space group). i n t e n s i t y i s lower than the t h r e s h o l d a g r e e m e n t i sc o n s i d e r e d t ob e p e r f e c t t i o n t othe l e a s t squares residue, § zero. I f ,h o w e v e r , the c a l c u l a t e d i n than the t h r e s h o l d value then § i sin a m o u n t w [I (m) - f I ( m ) ] . Thus, i n are l a r g e r Ohan the observable thresh used i n d r i v i n g the refinement t othe It has become customary i n X - r a y to describe the agreement between the c a l c u l a t e d s t r u c t u r e f a c t o r s b yu s i n g index, Rp, defined b y m

2

Q

ç

I fthe c a l c u l a t e d value then the and the c o n t r i b u , i st a k e n t o b e t e n s i t y i s l a r g e r cremented b y the t e n s i t i e s which old values are c o r r e c t structure. c r y s t a l l o g r a p h y observed and the r e s i d u a l

Σ| | F ( n ) l - | F ( n ) | | o

c

where η i sthe t o t a l number o fr e f l e c t i o n s (not the number o fobservations .). For purposes o fcomputing R ^ P O L Y M I N d i v i d e s I (m) u p i n t o £ p a r t s i n t h e r a t i o o f the c o n t r i b u t i n g c a l c u l a t e d i n t e n s i t i e s . By t a k i n g the s q u a r e r o o t o ft h e s e " o b s e r v e d and c a l c u l a t e d i n t e n ­ s i t i e s |Fg(n)| and |Fp(n)| r e s p e c t i v e l y are obtained a n d u s e d m t h e c a l c u l a t i o n o fRp,. The terms c o n t r i b u ­ t i n g t o t h e n u m e r a t o r a n d d e n o m i n a t o r o ft h e r e s i d u a l index are a s follows: (1) For observed r e f l e c t i o n s ||F (n)|-|F (n)| | i s a d d e d t o t h e n u m e r a t o r a n d | F ( n ) | i sa d d e d t o t h e denominator. (2) F o r unobservable r e f l e c t i o n s for which | F ( n ) | ^ | F ( n ) | t h e a g r e e m e n t i s t a k e n t ob e e x a c t and n o t h i n g i sa d d e d t o e i t h e r t h e n u m e r a t o r o rt h e denomi­ nator o fRp. These r e f l e c t i o n s are omitted from the c a l c u l a t i o n because t h e i r i n c l u s i o n could r e s u l t i n a m i s l e a d i n g l y l o w v a l u e f o r R-p. (3) For unobservable r e f l e c t i o n s for which |F (n)| < |F |n)| the numerator i sincremented b y I IF (n)| - !*8|F (n)|| and the denominator i s i n c r e ­ m e n t e d b yf sI F ( n ) | . T h e c a l c u l a t i o n o f R i nt h i s f a s h i o n , while s l i g h t l y a r t i f i c i a l , leads t ovalues f o r the r e s i d u a l i n d e x w h i c h c a n b em e a n i n g f u l l y compared t o those v a l u e s f o u n d i nt h e l i t e r a t u r e . When used i n conjunc­ t i o n w i t h the large body o fc r y s t a l l o g r a p h i c knowledge a v a i l a b l e this number provides a useful c r i t e r i o n w i t h w h i c h t oa s s e s s the c o r r e c t n e s s o f the s t r u c t u r e . B y c o n v e n t i o n , R™ i s n o r m a l l y c a l c u l a t e d u s i n g only o b s e r v a b l e r e f l e c t i o n s a n d i ts h o u l d b e p o i n t e d out that adherence t oitems (2) a n d (3) a b o v e w i l l produce a v a l u e o fR w h i c h w i l l b ea tb e s t e q u a l t o t h a t 1

0

1 1

Q

c

0

0

c

0

c

c

0

p

F

F

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

=

Unobservable Reflections

if

m

0

SljJ(m)>I (m)

0

0

w [l (m)-ffilj(m)]

m

w [l (m)-|lj(m)]«

0

= 0 i f Zlj|(m)£l (m)

=

Observable Reflections

to $

0

c

c

o

0

c

0

c

0

= 0 i f |F (n)|*|F (n)|

Q

f*|F (n)|

= 0 i f |F (n)|i|F (n)|

=

i f |F (n)|>|F (n)|

o

Q

= |F (n)|

Denominator

Index

i f |F (n)|>|F (n)|

c

c

||F (n)|-|P (n)||

= ||F (n)|-f*|F (n)||

=

Numerator

Contribution to

to the Least Squares Residue and Residual

Contribution

Contributions

TABLE I

6.

CELLA

A N D HUGHES

Crystalline Polymers

99

c a l c u l a t e d i nt h e u s u a l w a y a n d w i l l m o s t l i k e l y b e s l i g h t l y l a r g e r . I tw a s f e l t , h o w e v e r , that the unob­ s e r v e d r e f l e c t i o n s a r e o fs u f f i c i e n t i m p o r t a n c e t o d e m a n d t h e i r i n c l u s i o n i n t o R-m w h e n t h e c a l c u l a t e d s t r u c t u r e factors are l a r g e r t h a n the threshold values. In other words, any s t r u c t u r a l model w h i c h p r e d i c t s i n t e n s i t y values above the threshold i n t e n s i t y f o r very m a n y o ft h e u n o b s e r v e d d a t a m u s t o fn e c e s s i t y b e i n c o r ­ rect.. I ns i n g l e c r y s t a l w o r k , where t h o u s a n d s o f r e f l e c t i o n s are measurable, this c r i t e r i o n i s unneces­ sary, since any s t r u c t u r e which p r e d i c t s the observable data w i l l very l i k e l y also p r e d i c t the unobservable data. I na n a l y s i s i n v o l v i n g o n l y a l i m i t e d n u m b e r o f data, however, this may not b e the case and such miss­ ing data can then give p o s i t i v e s t r u c t u r a l i n f o r m a t i o n . C o n c l u s i o n This paper has described i n very general terms the u n i q u e p r o b l e m s e n c o u n t e r e d i nt h e d e t e r m i n a t i o n o f t h e molecular p a c k i n g i n polymeric c r y s t a l s . Standard c r y s t a l l o g r a p h i c procedures lose t h e i r u t i l i t y when d e a l i n g w i t h such problems, and a d d i t i o n a l information, such a s stereochemical c o n s t r a i n t s and p a c k i n g energies, s h o u l d b e b r o u g h t t o b e a r i nt h e p r o b l e m . F i n a l l y , a method o fs t r u c t u r a l r e f i n e m e n t w h i c h i s e s p e c i a l l y s u i t e d t op o l y m e r i c s t r u c t u r e s s h o u l d b eemployed i n p l a c e o fc l a s s i c a l l e a s t s q u a r e s m e t h o d s . A subsequent paper w i l l deal w i t h the a p p l i c a t i o n o fthese p r i n c i ­ p l e s a n d t e c h n i q u e s t ot h e d e t e r m i n a t i o n o ft h e c r y s t a l structures o f s e v e r a l c r y s t a l l i n e p o l y e t h e r s . Acknowledgment The authors g r a t e f u l l y acknowledge the c o n t r i b u ­ t i o n s o fP . W a r d a n d R . F l e t t e r i c k t o t h e development of the computer programs DIKED and POLYMIN. W e are a l s o p l e a s e d t oa c k n o w l e d g e f i n a n c i a l s u p p o r t through NIH Grant GM-148J2-02 and a d d i t i o n a l support through the M a t e r i a l s S c i e n c e C e n t e r a tC o r n e l l U n i v e r s i t y . Literature Cited 1. Buerger, M., "X-Ray Crystallography," John Wiley and Sons, Inc., New York, N.Y. (1962). 2. Cella, R. J., Lee, B., and Hughes, R. Ε., Acta Cryst., (1970), A26, (6). 3. Miyazawa, T., J. Polym. Sci., (1961), 55, 215. 4. Hughes, R. Ε. and Lauer, J. L., J. Chem. Phys., (1959), 30 (5), 1 1 6 5 . 5. McCullough, R., Polymer

Letters,

(1965),

3,

509.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

100

POLYETHERS

6. Shimanouski, T. and Mizushima, S., J. Chem. Phys., (1955), 23 (4), 707. 7. Sugeta, H. and Miyazawa, T., Biopolymers, (1967), 5, 673. 8. Kijima, H., Sato, T., Tsuboi, M., and Wada, Α., Bull. Chem. Soc. Jap., (1967), 40, 2544. 9. Nagai, K. and Kobayashi, M., J. Chem. Phys., (1962), 36 (5), 1268. 10. Nemethy, G. and Scheraga, H., Biopolymers, (1965), 3, 155. 11. Scott, R. A. and Scheraga, H., J. Chem. Phys., (1966), 45, 2091. 12. Ooi, T., Scott, R., Vanderkooi, G., and Scheraga, H., J. Chem. Phys., (1967), 46, 4410. 13· DeSantis, P., Giglio, E., Liquori, Α., and Ripamonti, Α., J. Polym. Sci., (1963), 14. Liquori, Α., J. Polym. 12, 209. 15. Del Re, G., Theor. Chim. Acta, (1963), 1, 188. 16. Del Re, G., Rev. Mod.

Sci., Phys.,

(1966), (1965),

Part 34,

C, 604.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

No.

7 Coordination Polymerization of Trimethylene Oxide E.

J.

VANDENBERG

and

A.

E.

ROBINSON*

Research Center, Hercules Inc., Wilmington, Del. 19899

INTRODUCTION General The p o l y m e r i z a t i o n o f oxetanes with c a t i o n i c c a t a l y s t s has been s t u d i e d by many i n v e s t i g a t o r s . (1) (2) Rose(3) i n p a r t i c u l a r , first reported the homopolymerization o f the parent compound, trimethylene oxide (TMO), with a Lewis a c i d c a t a l y s t , boron trifluoride. The use o f c o o r d i n a t i o n c a t a l y s t s to polymerize oxetanes has been reported i n the patent l i t e r a t u r e by Vandenberg. (4) In t h i s work, Vandenberg polymerized oxetanes with the aluminum trialkyl-water-acetylacetone c o o r d i n a t i o n c a t a l y s t ( r e f e r r e d t o as chelate c a t a l y s t ) that he discovered f o r epoxide polymerization(5). This paper d e s c r i b e s the homo- and co-polymerization o f TMO with these c o o r d i n a t i o n c a t a l y s t s . S p e c i f i c TMO copolymers, p a r t i c u l a r l y with unsaturated epoxides such as allyl g l y c i d y l ether (AGE), are shown t o provide the b a s i s f o r a new f a m i l y o f p o l y e t h e r elastomers. These new elastomers are compared with the r e l a t e d propylene o x i d e - a l l y l g l y c i d y l ether (PO-AGE) copolymer elastomers. The historical development and general characteristics o f p o l y e t h e r elastomers and, in particular, the propylene oxide elastomers, are reviewed below. E a r l y Polyether Elastomer Studies Charles C. P r i c e played a p i o n e e r i n g r o l e i n the p o l y e t h e r elastomer f i e l d ( 6 ) . In 1948, as reported in his 1961 Chemist article, P r i c e recognized t h a t an oxygen chain atom would c o n t r i bute g r e a t l y t o chain flexibility and thus enhance elastomeric behavior, p a r t i c u l a r l y s i n c e such polyethers should have low Hercules Research Center C o n t r i b u t i o n No. 1645 * Current address: Hercules Incorporated, Bacchus Works, Magna, Utah 84044

101

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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cohesive energy between chains. At t h a t time, he suggested t h a t poly(propylene oxide) should be a s u p e r i o r elastomer but unfor­ t u n a t e l y soon found that the known methods o f p o l y m e r i z i n g pro­ pylene oxide gave o n l y low polymers, not the d e s i r e d high polymer. However, he q u i c k l y devised a simple way around t h i s impasse, i . e . , the polyurethane approach, which c o n s i s t e d o f making a pro­ pylene oxide adduct o f a p o l y o l and then r e a c t i n g t h i s polyfunct i o n a l p o l y e t h e r with a d i i s o c y a n a t e t o give a p o l y e t h e r urethane network. T h i s approach t o p o l y e t h e r elastomers was p r o t e c t e d by a U.S. p a t e n t ^ which r e c e n t l y r e c e i v e d the C r e a t i v e Invention Award o f the American Chemical S o c i e t y . Although these p o l y e t h e r urethane elastomers proved t o be o f tremendous value i n foam rubber, the more conventional p o l y e t h e r elastomer based on a c r o s s - l i n k a b l e high polymer remained u n a v a i l a b l e . The l a t t e r r e q u i r e d the development o f new c a t a l y s t systems f o r polymerizing propylene oxide. The f i r s t improve polymer was the i r o n c a t a l y s t o f P r u i t t and B a g g e t t ® , i . e . , the simple r e a c t i o n product o f f e r r i c c h l o r i d e and propylene oxide. P r i c e and O s g a n ® recognized that t h i s i r o n c a t a l y s t i n v o l v e d a new p o l y m e r i z a t i o n mechanism—coordination p o l y m e r i z a t i o n - - i n which the propylene oxide coordinates with the i r o n atom before i n s e r t i o n i n t o the propagating polymer chain. P r i c e and Osgan a l s o discovered a new c o o r d i n a t i o n c a t a l y s t f o r polymerizing propylene oxide t o high polymer, i . e . , the aluminum isopropoxidez i n c c h l o r i d e c a t a l y s t systemOH?. In subsequent work with t h i s c o o r d i n a t i o n c a t a l y s t , P r i c e d e s c r i b e d the copolymerization o f PO with an unsaturated epoxide, such as butadiene monoxide(JLL). In the same time p e r i o d o f P r i c e ' s work, H i l l , B a i l e y and F i t z p a t r i c k o f Union Carbide Corporation developed some improved c a t a l y s t s f o r polymerizing ethylene oxide t o high p o l y m e r U ) . These new c a t a l y s t s i n c l u d e d improvements on the very e a r l y sys­ tems o f Staudinger, i . e . , strontium, calcium, and z i n c oxides and carbonates t i l ) , as w e l l as some new, even b e t t e r , systems based on calcium alkoxides (14) and a m i d e s ( 1 6 ) B a i l e y used the l a t t e r systems i n 1958 t o make water-soluble ethylene oxide-unsaturated epoxide copolymers (iD. V u l c a n i z a t e s o f these copolymers were very water s e n s i t i v e and thus not very u s e f u l i n the conventional elastomer area. In 1957, Vandenberg d i s c o v e r e d some e s p e c i a l l y e f f e c t i v e c o o r d i n a t i o n c a t a l y s t s f o r polymerizing epoxides t o high p o l y ­ mers. Some o f these new c a t a l y s t s were the r e a c t i o n products o f organo-compounds o f aluminum, z i n c , and magnesium with w a t e r · An e s p e c i a l l y v e r s a t i l e system was the combination o f organoaluminums with water and a c e t y l acetone. These new c a t a l y s t s were much b e t t e r than e a r l i e r epoxide c a t a l y s t s , g i v i n g g e n e r a l l y higher r a t e s a t lower temperatures, h i g h e r molecular weight, and broader u t i l i t y . As a r e s u l t o f f i n d i n g these s u p e r i o r new c a t a l y s t s , Vandenberg was able t o make many new high polymers from epox2

β

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

A N D ROBINSON

103

Trimethylene Oxide

ides (§) CjJ), i n c l u d i n g a wide spectrum o f new p o l y e t h e r e l a s t o mers. Some o f these new p o l y e t h e r elastomers have been commerc i a l i z e d , such as the e p i c h l o r o h y d r i n elastomers a v a i l a b l e from Hercules Incorporated under the trademark HERCLOi^and from B. F. Goodrich Chemical Co. a l i c e n s e e o f Hercules Incorporated, under the trademark HYDRIN. Very e a r l y i n t h i s work, Vandenberg a l s o made high molecular weight, l a r g e l y amorphous propylene oxideunsaturated epoxide copolymers and recognized i n unpublished s t u d i e s with A. E. Robinson t h e i r p o t e n t i a l value as improved elastomers. Subsequently, Gruber et a l . (12), f General T i r e , p u b l i s h e d d e t a i l e d p r o p e r t i e s o f s i m i l a r propylene oxide-unsaturated epoxide copolymer elastomers. Vandenberg a l s o f i l e d two patent a p p l i c a t i o n s on these copolymers. As a r e s u l t o f patent i n t e r f e r e n c e s i n v o l v i n g the Hercules a p p l i c a t i o n s , a Carbide patent, and a General T i r e a p p l i c a t i o n the l a s t a P r i c e a p p l i c a t i o n , and extensive subsequen p r i o r i t y . Two patents copolymers as new compositions o f m a t t e r ( _ ) (21) T h i s new type o f p o l y e t h e r elastomer i s commercially a v a i l a b l e from Hercules Incorporated under the trademark PARE I®. PAREL elastomer i s a s u l f u r - c u r a b l e copolymer o f propylene oxide and a l l y l g l y c i d y l ether. Some o f the key p r o p e r t i e s o f PAREL elastomer v u l c a n i z a t e s are summarized i n Table I. They have e x c e l l e n t low temperature p r o p e r t i e s ; e x c e l l e n t dynamic p r o p e r t i e s , which are much l i k e those o f n a t u r a l rubber; good ozone r e s i s t a n c e ; and good heataging r e s i s t a n c e . T h i s i n t e r e s t i n g combination o f p r o p e r t i e s i s leading to s u b s t a n t i a l s p e c i a l t y markets i n such a p p l i c a t i o n s as automotive engine mounts. V u l c a n i z a t i o n and s t a b i l i z a t i o n s t u d i e s on PAREL elastomer, as w e l l as a d d i t i o n a l s p e c i f i c p r o p e r t i e s o f PAREL elastomer, are reported i n t h i s book by Boss. The work described above f o r PO copolymers has been extended to the homo- and co-polymers o f oxetanes, p a r t i c u l a r l y TMO, and are reported i n t h i s paper. 0

m

Table I KEY PROPERTIES OF PAREL ELASTOMER VULCANIZATES - E x c e l l e n t low temperature p r o p e r t i e s - E x c e l l e n t dynamic p r o p e r t i e s ( l i k e n a t u r a l

rubber)

- Good ozone r e s i s t a n c e - Good heat aging r e s i s t a n c e EXPERIMENTAL Polymerization Studies General.

Reagents and general procedures f o r making

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

104

c a t a l y s t s , f o r running polymerizations and f o r c h a r a c t e r i z i n g polymers were the same as d e s c r i b e d p r e v i o u s l y ( 5 ) unless other­ wise noted. The c h e l a t e c a t a l y s t s were prepared by the general procedure p r e v i o u s l y given f o r t h i s c a t a l y s t ® . The unmodified EtgAl-O.S H2O c a t a l y s t was made by t h i s same procedure, i n the solvent noted i n Table I I I , by o m i t t i n g the a c e t y l acetone. Monomers. Commercial, p o l y m e r i z a t i o n grade monomers were used as r e c e i v e d . The sources were: ethylene oxide (E0), propy­ lene oxide (PO), and e p i c h l o r o h y d r i n (ECH) from Union Carbide Corp.; a l l y l g l y c i d y l ether (AGE) from S h e l l Chemical Corp.; butadiene monoxide (BMO) from PPG I n d u s t r i e s , Inc. (no longer commercially a v a i l a b l e ) ; and 3,3-bis(chloromethyl) oxetane (BCMO) from Hercules Incorporated (no longer commercially a v a i l a b l e ) . The other monomers d e s c r i b e d below were f i n a l l y p u r i f i e d by f r a c ­ t i o n a t i o n i n a 25-50 p l a t e column at a 25:1 r e f l u x r a t i o . Trimethylene oxid Labs, was f r e e d o f wate ether and then f r a c t i o n a t e d (b.p. 4 8 ° C , η£ 1.3870). 3,3-Bis(allyloxymethyl) oxetane (BAMO) was prepared by adding BCMO (31.0 g., 0 . 2 mole) over 2 h r s . t o a mixture o f a l l y l a l c o h o l (23.2 g., 0.40 mole) and NaOH ( 1 6 . 0 g., 0.4 mole) i n dimethyl s u l f o x i d e (100 ml.) a t 50°C. A f t e r the mixture was heated f o r an a d d i t i o n a l 2 h r s . at 5 0 ° C , water was added, and the w a t e r - i n s o l ­ uble f r a c t i o n recovered, d r i e d , and f r a c t i o n a t e d (b.p. 118°/10 mm., nj50 1.4538). 3,3-Dimethyloxetane was prepared from n e o p e n t y l g l y c o l by the procedure o f Schmoyer and C a s e ( 2 2 ) The f r a c t i o n a t e d product had: b.p. 8 1 ° C , nj* 1.3921. 9

0

Polymer I s o l a t i o n . The procedures used f o r the runs i n Tables II and I I I are given below. Unless otherwise noted, products were d r i e d a t 80°C. i n vacuo (0.4 mm.). Procedure A. Ether was added and then the product was washed twice with 3% HC1 (15 min. t o 1 h r . s t i r p e r wash), and then with water u n t i l n e u t r a l . The e t h e r - i n s o l u b l e ( i f any) was c o l l e c t e d , washed twice with ether and once with 0.05% Santonox i n ether and d r i e d as the e t h e r - i n s o l u b l e f r a c t i o n . The ethers o l u b l e was s t a b i l i z e d with 0.5% Santonox (based on t o t a l s o l i d s ) , the ether s t r i p p e d o f f , and the polymer d r i e d . In Run 7, Table I I I , the e t h e r - s o l u b l e was s t a b i l i z e d with 1% phenyl 3-naphthyl amine. Procedure B. Excess n-heptane (4-6 v o l s . ) was added and the heptane-insoluble polymer was c o l l e c t e d , washed once with heptane, washed once with 0.5% HC1 i n CH3OH, washed n e u t r a l with CH^OH, washed with 0.1% Santonox i n CH3OH, and then d r i e d . Run 5, which was used i n the v u l c a n i z a t i o n s t u d i e s , was s t a b i l i z e d with 1% phenyl 3-naphthyl amine.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

AND

Trimethylene

ROBINSON

Oxide

105

Procedure C. Product p r e c i p i t a t e d with 4 v o l s , o f τιheptane (ether i n Run 3, Table I I ) . The i n s o l u b l e was c o l l e c t e d , washed with η-heptane (or ether, i f used i n i t i a l l y ) , washed with 1% HC1 i n anhydrous ethanol, washed n e u t r a l with CH3OH, washed with 0.4% Santonox i n CH3OH and d r i e d . In Run 2, Table I I , the heptane-insoluble was not HC1 washed but i n s t e a d washed with 0.1% Santonox i n heptane and d r i e d . This product was then f u r t h e r sep­ arated by tumbling 1-gram i n 40 ml. o f H 0 overnight and then c o l ­ l e c t i n g the w a t e r - i n s o l u b l e , washing with H2O, and d r y i n g . The water-soluble was recovered by s t r i p p i n g o f f the water and d r y i n g . 2

Procedure D. Excess ether was added, the e t h e r - i n s o l ­ uble f r a c t i o n was c o l l e c t e d , washed with ether, washed with 0.5% HC1 i n 80-20 ether-methanol, washed n e u t r a l with 80-20 ethermethanol, washed with 0.4% Santonox i n ether and then d r i e d i n vacuo a t 50°C. Polymer C h a r a c t e r i z a t i o n . Inherent v i s c o s i t y was determined under the f o l l o w i n g c o n d i t i o n s : TMO-ECH copolymer, 0.1%, achloronaphthalene, 1 0 0 ° C ; other TMO and DM0 homo and copolymers 0.1%, CHC1 , 2 5 ° C ; TMO-P0-AGE terpolymer and PO-BCMO copolymer, 0.1%, benzene, 2 5 ° C ; BCMO homopolymer, 1.0%, cyclohexanone, 50°C. Unsaturated copolymers were analyzed f o r the unsaturated comonomer by Kemp Bromine No. ( i n CHCI3) (21) after correcting f o r the Bromine No. o f the a n t i o x i d a n t (Santonox, 125 and phenyl 3naphthyl amine, 143). C h l o r i n e - c o n t a i n i n g comonomers were deter­ mined by a c h l o r i n e a n a l y s i s . The composition o f the TMO-EO co­ polymers was determined by C and H a n a l y s i s . The PO content o f the TMO-PO-AGE terpolymer was determined by i n f r a r e d a n a l y s i s . The r e l a t i v e r e a c t i v i t y o f monomers i n copolymerization was c a l c u l a t e d from the f o l l o w i n g equation based on i d e a l copolymer­ ization. In [[ MM ii ll lο ri = 3

In [M ] t 2

where r ^ 2, [M^Jo monomers t i o n s at

i s the r e a c t i v i t y r a t i o o f monomer 1 r e l a t i v e t o monomer and [ M ] are i n i t i a l monomer concentrations o f 1 and 2, and [M-Jt and [ Μ ] ^ are the monomer concentra­ time t during the copolymerization. t

2

n

e

0

2

V u l c a n i z a t i o n Studies V u l z a n i z a t e s were prepared by conventional m i l l i n g and com­ pounding a t 100°F. followed by press c u r i n g according t o the f o r ­ mula i n Table IV unless otherwise noted. The HAF carbon b l a c k was P h i l b l a c k 0 (N-330) o f P h i l l i p s Petroleum Co. A cure r a t e study i s given i n Figure 1. G e l / s w e l l data (wt. %) were deter-

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

106

POLYETHERS

mined i n cyclohexanone a f t e r 4 hours a t 80°C. Tests used t o evaluate v u l c a n i z a t e s were as f o l l o w s : ASTO Test Tensile D412 (miniature, 2 Die C dumbbell) Tear D624 (miniature Die C) Hardness D676 Bashore r e s i l i e n c e D2632 Yerzley oscillograph D945 Torsional r i g i d i t y D1043 Heat Build-up D623 Oven aging D573 Solvent Resistance D1460 ff

Table IV

Elastomer HAF Black ZnO Stearic Acid Sulfur Benzothiazyl d i s u l f i d e Tetramethyl thiuram d i s u l f i d e

10 50 5 1 2 1 2

Cured 30 min. a t 310°F.

CURE TIME - MINUTES AT

Figure

1.

310°F.

Effect of cure time on properties of elastomer

TMO-AGE

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

RESULTS AND

AND

ROBINSON

Trimethylene Oxide

107

DISCUSSION

Polymerization S t u d i e s . TMO homopolymerization. The E t 3 A l - 0 . 5 H O - l . 0 acetylacetone c a t a l y s t polymerized TMO at 65°C. i n heptane d i l u e n t to a high conversion o f a very high molecular weight polymer ( n i h = 12), which was tough, rubbery, and c r y s t a l l i n e , with a 40°C. melting p o i n t (Table I I ) . The polymer was i n s o l u b l e i n η-heptane and methanol but s o l u b l e i n benzene and chloroform. T h i s homopolymer i s apparently s i m i l a r to t h a t prepared by R o s e ® with BF3 c a t a l y s t except t h a t the present product i s o f much higher molecu­ l a r weight and a l i t t l e h i g h e r m e l t i n g . Rose obtained an n i h o f 1.3 at 50°C. and 2.9 at -80°C. with a melting p o i n t o f 35°C. The p o l y m e r i z a t i o n o f TMO i s to be compared with that o f PO s i n c e the monomers an 2

n

n

(-CH CH CH -0-) 2

2

2

n

Eq. 1

TMO

Eq. 2 •0' PO On the b a s i s o f our p r i o r work on PO p o l y m e r i z a t i o n , with t h i s same c h e l a t e c a t a l y s t ® , TMO polymerizes about 10 times more slowly than PO does under the same c o n d i t i o n s . A l s o , the TMO homopolymer i s much l e s s s o l u b l e than poly(propylene o x i d e ) , s i n c e the l a t t e r polymer i s s o l u b l e i n heptane and methanol, both nonsolvents f o r p o l y f t r i m e t h y l e n e o x i d e ) . The TMO homopolymer i s , o f course, c r y s t a l l i n e because o f i t s very r e g u l a r s t r u c t u r e . On the other hand, the poly(propylene oxide) prepared with the c h e l a t e c a t a l y s t i s l a r g e l y amorphous because o f t a c t i c i t y and head-tot a i l v a r i a t i o n s i n s t r u c t u r e which are not p o s s i b l e i n p o l y ( t r i methylene o x i d e ) . T h i s TMO p o l y m e r i z a t i o n with the c h e l a t e c a t a l y s t no doubt i n v o l v e s coordinate propagation and i s the f i r s t such case o f coordinate propagation o f an oxetane. Heretofore, oxetanes have been c a t i o n i c a l l y polymerized. There are s e v e r a l reasons f o r concluding t h a t t h i s c h e l a t e c a t a l y s t system i s a c o o r d i n a t i o n p o l y m e r i z a t i o n . F i r s t , the very h i g h molecular weight obtained at e l e v a t e d temperature with a low r a t e i s c h a r a c t e r i s t i c o f c o o r d i n a t i o n p o l y m e r i z a t i o n r a t h e r than o f c a t i o n i c polymeriza­ t i o n . A l s o , Vandenberg's work on the c i s - and trans-2,3-epoxy-

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

PO AGE

BMO

AGE

45(g) 5(g)

9.4

5.6(f)

n-heptane

n-heptane

n-heptane

AGE

3

Toluene

n-heptane Toluene

92

82

82

92

42

92 92

Diluent Name ml.

ECH

EO

0 20

Comonomer Name

1.0

1.0

1.0

1.0

1.0 0.5 8 4

Catalyst A c e t y l Acetone mmoles per A l (Al Basis)

10

14

.7

7.5

19 12

Time hrs.

e

65

65

65

65

65

65 30

Temp. °C.

27

85 13

Total % Conv.

2

Heptane-insol.(h) Heptane-sol.(i)

Heptane ξ CHjOHinsol.(e)

Ether-insol.(d)

Ether-insol.(d) Ether-sol., Heptane-insol.(e)

Ether-insol.(b) Water-insol.(c) Water-sol. (c)

I s o l a t e d Polymer Procedure Fraction

28 20

89

71

23

5.6 10

67 1.4 12

% Conv.

5.3 4.1

13.5

15.4

8.1

3.3 1.0

12 11.0 6.5

Hjnh

PO AGE 58 10.0 60 9.3

6.5

4.4

12.6

12 55

44 8

% Co-m

(a) Based on 10 g. t o t a l monomer. See Experimental f o r i s o l a t i o n procedure. TMO » t r i m e t h y l e n e o x i d e , EO « ethylene o x i d e , ECH • e p i c h l o r o h y d r i n , AGE = a l l y l g l y c i d y l e t h e r , BMO = butadiene monoxide, and PO * propylene o x i d e . (b) Very s t r o n g , tough, o r i e n t a b l e rubber. C r y s t a l l i n e by x-ray (m.p. • 4 0 C ) . I n s o l u b l e i n H 0, n-heptane and CH3OH. S o l u b l e i n benzene and chloroform. (c) I s o l a t e d from i n i t i a l heptane and methanol-insoluble product. (d) Largely amorphous and rubbery. (e) Amorphous and rubbery. ( f ) 20% o f t o t a l comonomer added i n i t i a l l y , remainder added i n 6 equal p o r t i o n s a t 2-hr. i n t e r v a l s . (g) Added i n 5 equal p o r t i o n s a t 2-hr. i n t e r v a l s . (h) Tough, amorphous rubber ( i ) Tack/ rubber.

No.

T

P o l y m e r i z a t i o n o f TMO w i t h E t A l - 0 . 5 H?Q-Acetyl Acetone C a t a l y s t (a)

Table I I

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3

2

2.7

0.29

3.3

27

94

60

Heptane-and CHjOH-insol. Heptane- and CH*0H-insol.

Β

C

1.5

5.3 65

(a) Based on 10-g. t o t a l monomer. See Experimental f o r i s o l a t i o n d e t a i l s . TMO • t r i m e t h y l e n e o x i d e ; DMO «* 3,3-dimethyl oxetane; BAMO (allyl oxymethy1)oxetane. (b) Unless otherwise noted, c a t a l y s t prepared i n n-heptane w i t h 3 moles o f d i e t h y l e t h e r per aluminum. (c) Ether omitted frow c a t a l y s t p r e p a r a t i o n . (d) Most o f p o l y m e r i z a t i o n occurred i n a few minutes. (e) I n i t i a l l y a t a c k y rubber a f t e r d r y i n g a t 80 C. which s l o w l y c r y s t a l l i z e d t o Λ hard s o l i d o f c a . 50 C. m.p.; heptane-soluble. ( f ) Low c r y s t a l l i n i t y [poly(3,3-dimethyl oxetane) p a t t e r n ] ; heptane-soluble, (gj E t A l - u . S H 0-0.5 a c e t y l acetone c a t a l y s t . e

5.2 27 T o t a l polymer A

27

30

5

4 (g)

40

80

PO BGM0

8

1.3 92

T o t a l polymer (*)

A

92

0

0.08

4

32

n-heptane

90 10

DMO BAMO

7

A

100(d)

0

42

4

48

n-heptane

100

DMO

6

99

T o t a l polymer (e)

C

60

30

19

2 (c)

50

100

BCMO

5

50

6

2

42

Toluene

100

BCMO

4

51

30

2

4

83

Toluene

94 6

TMO BAMO

3

Β

29 47 78

30

0.5 2.0 23

5.5

4

66

48

Toluene

100

TMO

2

Heptane and CtUOH-insol.

Β

49 78

65

Hint*

0.25 2.3

I s o l a t e d Polymer % Conv.

4

48

Toluene

100

TMO

1

Fraction

Procedure

e

Total % Conv.

Catalyst(b) mmoles

Temp. C.

mU

Monomer 1 Name

No.

Time hrs.

Diluent Name

P o l y m e r i z a t i o n o f Oxetanes w i t h Et^Al-0.5 H?0 C a t a l y s t (a)

Table I I I

POLYETHERS

110

butanes c l e a r l y e s t a b l i s h e d t h a t the c h e l a t e c a t a l y s t operates by a c o o r d i n a t i o n mechanism and does not give c a t i o n i c polymerization I t i s perhaps s u r p r i s i n g t h a t TMO polymerizes ten times more slowly than PO, s i n c e i t i s a stronger base than PO by about 4 orders o f magnitude (24)

and thus i t should coordinate much more r e a d i l y with a metal. One explanation f o r the more f a c i l e p o l y m e r i z a t i o n o f PO i s that the g r e a t e r r i n g s t r a i n i n PO, compared with t h a t i n TMO, g r e a t l y f a c i l i t a t e s the r i n g opening propagation step with PO and more than compensates f o r i t s lower c o o r d i n a t i o n tendency because o f i t s lower base s t r e n g t h . TMO polymerizes much f a s t e r (about t e n - f o l d ) with the Et-jAlO.5H2O c a t a l y s t (Table I I I ) and s t i l l gives f a i r l y high molecular weight homopolymer. In t h i s case, based on Vandenberg's p r i o r work with the 2,3-epoxybutanes c a t i o n i c or c o o r d i n a t i o n expected t o be f a s t e r . A l s o , the lower s t e r i c hindrance a t propagation s i t e s with the unmodified organoaluminum-i^O should a l s o permit more f a c i l e c o o r d i n a t i o n and thus f a s t e r c o o r d i n a t i o n p o l y m e r i z a t i o n . The i n c r e a s e d Lewis a c i d c h a r a c t e r o f propagation s i t e s with the unmodified c a t a l y s t could a l s o enhance the coordina t i o n step and thus propagation. TMO Copolymerization With Saturated Epoxides. Copolymerizing TMO with ethylene oxide (EO) i n an 80:20 weight r a t i o with the c h e l a t e c a t a l y s t gave a water-soluble product (90% o f the t o t a l ) which contained only 8% TMO (Run 2, Table I I ) . On the b a s i s o f an i d e a l copolymerization, the EO i s estimated t o enter the copolymer i n t h i s f r a c t i o n approximately 70 times more r e a d i l y than does the TMO. T h i s r e s u l t confirms that a l k y l e n e oxides polymerize much more r e a d i l y than oxetanes with the c h e l a t e c a t a l y s t . A small amount (10% o f the T o t a l ) o f a w a t e r - i n s o l u b l e copolymer c o n t a i n i n g 44% TMO was obtained. T h i s r e s u l t i n d i c a t e s that the c h e l a t e c a t a l y s t contains some s i t e s which give more f a v o r a b l e copolymeri z a t i o n . One p o s s i b l e explanation i s t h a t the unfavorable copolym e r i z a t i o n o f TMO a t the major s i t e s i s due t o s t e r i c hindrance which reduces the a b i l i t y o f TMO t o coordinate a t t h i s s i t e . Based on t h i s hypothesis, l e s s hindered s i t e s would be more f a v o r able f o r copolymerization. An a l t e r n a t e but u n l i k e l y p o s s i b i l i t y i s that there are a l i m i t e d number o f c a t i o n i c s i t e s i n the chelate c a t a l y s t and t h a t these give some copolymer by a more f a v o r a b l e c a t i o n i c propagation mechanism. The copolymerization o f TMO and e p i c h l o r o h y d r i n (ECH) with the c h e l a t e c a t a l y s t and a 50:50 weight r a t i o charge i s more favorable (Run 3, Table I I ) ; again, two f r a c t i o n s , both rubbery i n nature, were obtained which d i f f e r e d i n s o l u b i l i t y and composition. Thus, the c h e l a t e c a t a l y s t again appears t o c o n t a i n a t l e a s t two d i f f e r e n t copolymerization s i t e s . I t i s s i g n i f i c a n t that these two monomers, which probably have s i m i l a r s t e r i c r e quirements, do copolymerize b e t t e r , thus adding credence t o the e a r l i e r proposal that s t e r i c r e s t r i c t i o n s at c e r t a i n s i t e s a f f e c t

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

A N D ROBINSON

Trimethylene Oxide

111

copolymerization. Of course, t h i s r e s u l t i s a l s o evidence f o r a coordination polymerization. TMO Copolymerization With Unsaturated Epoxides and Oxetanes. The low conversion copolymerization o f TMO and a l l y l g l y c i d y l ether (AGE) with the c h e l a t e c a t a l y s t and a 97:3 weight r a t i o charge gave a rubbery, l a r g e l y amorphous, high molecular weight copolymer product which contained about 13% AGE (Run 4, Table I I ) . On the b a s i s o f an i d e a l copolymerization, the AGE enters the copolymer about 14 times more r e a d i l y than TMO does. This r e s u l t i s to be c o n t r a s t e d with the i d e a l PO-AGE copolymerization, with t h i s same c a t a l y s t , i n which the copolymer has the same composit i o n as the i n i t i a l monomer charge. To compare the elastomer behavior o f t h i s TMO elastomer with a comparable PO-AGE elastomer, a procedure was developed f o r making l a r g e r samples o f r e l a t i v e l y uniform TMO-AGE copolymer II). Thus, the copolymerizatio the i n i t i a l charge along with 20% o f the t o t a l AGE used. As the p o l y m e r i z a t i o n proceeded, a d d i t i o n a l AGE was added as i n d i c a t e d i n Table I I . In t h i s way, a high conversion to heptane- and methanol-insoluble, amorphous copolymer c o n t a i n i n g 4.4% AGE was obtained. On the b a s i s o f the s u l f u r v u l c a n i z a t e data that i s presented i n the v u l c a n i z a t e property data s e c t i o n , t h i s product appears to be r e l a t i v e l y uniform. However, t h i s procedure and perhaps even the c a t a l y s t may not be optimal and some degree o f nonuniformity may s t i l l p e r s i s t . A copolymer o f TMO with butadiene monoxide (BMO) was a l s o made by u s i n g the same procedure as i n the l a r g e sample method for TMO-AGE (Run 6, Table I I ) . Since BMO gives i d e a l copolymeri z a t i o n with PO, as does AGE, with the c h e l a t e c a t a l y s t , i t was assumed that the system which worked with TMO-AGE would work with TMO-BMO. A terpolymer o f TMO-PO-AGE was a l s o made by the same general procedure used i n the l a r g e s c a l e TMO-AGE work (Run 7, Table I I ) . The terpolymer was i s o l a t e d i n two f r a c t i o n s o f s i m i l a r composit i o n (ca. 60% PO and 10% AGE), but d i f f e r e n t s o l u b i l i t y , and d i f f e r e n t molecular weight. The highest molecular weight f r a c t i o n was heptane-insoluble, confirming that TMO u n i t s c o n t r i b u t e substantial heptane-insolubility. TMO was a l s o copolymerized with an unsaturated oxetane, 3,3b i s ( a l l y l o x y m e t h y l ) o x e t a n e (BAMO) (Run 3, Table I I I ) . This work was done with the Et3Al-0.5H20 c a t a l y s t . This copolymerization appears to be a n e a r l y p e r f e c t one. Polymerization o f Other Oxetanes. The c a t i o n i c polymerizat i o n o f 3 , 3 - d i s u b s t i t u t e d oxetanes, e s p e c i a l l y 3 . 3 - b i s ( c h l o r o methyl)oxetane (BCMO), has been widely studied(±/t£?. A few experiments with t h i s type o f oxetane u s i n g the Et Al-0.5H2O c a t a l y s t are given i n Table I I I . BCMO polymerizes r e a d i l y with t h i s c a t a l y s t to give high molecular weight polymer, n i h 3.0, at 3

n

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

112

3 0 ° C , provided there i s no ether i n the c a t a l y s t system (Run 5, Table I I I ) . However, with ether present (Run 4, Table I I I ) , the molecular weight i s g r e a t l y reduced as i n d i c a t e d by the 0.3 inherent v i s c o s i t y . The l a r g e e f f e c t o f ether i n d i c a t e s that the E t 3 A l 0.5H O c a t a l y s t i s behaving here as a c a t i o n i c c a t a l y s t with ether a c t i n g as a chain t r a n s f e r agent. The molecular weight without ether i s , however, very high f o r an o r d i n a r y c a t i o n i c c a t a l y s t with BCMO a t these temperatures. U s u a l l y lower temperatures are r e q u i r e d t o o b t a i n high molecular weight polymer from BCMO with Lewis a c i d type c a t a l y s t s Some experiments on the p o l y m e r i z a t i o n o f BCMO with the chelate c a t a l y s t are recorded i n the patent literature(£). In t h i s work, high molecular weight polymer ( n i h P 4.3) obtained a t very high temperatures (200-250°C.) i n a continuous, bulk p o l y m e r i z a t i o n method These data i n d i c a t e that the c h e l a t e c a t a l y s t polymerizes BCM ably the very high temperatur t i v e l y low b a s i c i t y o f BCMot^£). The copolymerization o f PO with BCMO u s i n g the c h e l a t e c a t a l y s t (Run 8, Table I I I ) a t 30°C. i n d i c a t e s that the PO enters the copolymers about t h i r t y f o l d more r e a d i l y than does BCMO, based on i d e a l copolymerization. This r e s u l t i s s i m i l a r t o our f i n d i n g s on the copolymerization o f TMO with ethylene oxide. S i m i l a r explanations no doubt apply. 3,3-Dimethyloxetane (DMO) polymerizes very r a p i d l y a t 0°C. with Et3Al-0.5 H 0 c a t a l y s t t o a high molecular weight, ( n ^ h * 1.6), low m e l t i n g (ca. 5 0 ° C ) , c r y s t a l l i n e polymer (Run 6, Table I I I ) . This p o l y m e r i z a t i o n i s apparently c a t i o n i c , on the b a s i s o f the v e r y r a p i d p o l y m e r i z a t i o n . The small amount o f ether i n the c a t a l y s t does not have a large chain t r a n s f e r e f f e c t , as with BCMO, presumably because o f the much higher base strength o f DMO compared with BCMO and ether. DMO was copolymerized with BAMO (Run 7, Table I I I ) . Because of the very r a p i d p o l y m e r i z a t i o n , i t was d i f f i c u l t t o o b t a i n a low conversion and t o assess the copolymerization behavior o f t h i s monomer p a i r . However, v u l c a n i z a t e p r o p e r t i e s on t h i s product (Table III) were good, i n d i c a t i n g a r e l a t i v e l y uniform copolymer and thus a f a v o r a b l e copolymerization. 2

U

t

0

w

a

s

n

2

V u l c a n i z a t e Studies The various unsaturated copolymers were v u l c a n i z e d with the s u l f u r - a c c e l a t o r system given i n Table IV. TMO-AGE Elastomers. The s u l f u r v u l c a n i z a t e o f the 96-4 TMO-AGE copolymer had high t e n s i l e , modulus, and t e a r strength a t 23°C. a t a good e l o n g a t i o n l e v e l (Table V). The hot t e n s i l e p r o p e r t i e s a t 100°C. are somewhat lower but s t i l l good. C r y s t a l l i n i t y and/or c r y s t a l l i z a t i o n on s t r e t c h i n g could enhance t e n s i l e p r o p e r t i e s a t 2 3 ° C ; apparently t h i s i s not the case, s i n c e the hot t e n s i l e r e s u l t s , which could not i n v o l v e c r y s t a l l i n i t y

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

AND

ROBINSON

THmethylene Oxide

113

e f f e c t s , are i n l i n e with the usual e f f e c t o f increased temper ature on t e n s i l e p r o p e r t i e s . The p r o p e r t i e s obtained i n these studies are a f f e c t e d only s l i g h t l y by i n c r e a s i n g the cure time f o u r f o l d over the optimum used ( F i g . 1 ) . Table V VULCANIZATE PROPERTIES OF TMO-AGE ELASTOMER

Tensile strength, p s i . 300% modulus, p s i . Elongation a t break, % Break s e t , % Hardness, A2 Tear Strength, p . / i R e s i l i e n c e , Bashore Y e r z l e y Dynamic Data Modulus, p s i . Resilience, % Frequency, Hz K i n e t i c Energy, i n . - l b . / c u . i n . Heat Build-up, °F. Tg., °c. V o l . % Swell (5 days a t 60°C.) Toluene H 0 2

23°C. 3190 2590 400 20 82

100°C. 1800 1515 225 0 82

6555 67 7.5 31.7 27 -75

315 0

The TMO-AGE copolymer v u l c a n i z a t e a l s o has e x c e l l e n t r e s i l ience, low heat b u i l d - u p , and a low Tg o f -75°C. (Table V ) . Volume % s w e l l i n toluene i s high but water-swell i s low. A l though not measured, we would expect, based on the heptanei n s o l u b i l i t y o f the amorphous 96-4 TMO-AGE copolymer, that o i l r e s i s t a n c e o f TMO-AGE copolymer would be f a i r l y good. The m e t h a n o l - i n s o l u b i l i t y o f the amorphous TMO-AGE copolymer a l s o suggests that i t should have r e s i s t a n c e t o p o l a r s o l v e n t s . The gum v u l c a n i z a t i o n p r o p e r t i e s o f the TMO-AGE copolymer (Table VI) are low. These data are f u r t h e r evidence that the e x c e l l e n t t e n s i l e p r o p e r t i e s observed f o r the b l a c k - f i l l e d TMOAGE v u l c a n i z a t e s i s not due t o c r y s t a l u n i t y o r c r y s t a l 1 1 z a b i l i t y . The 91% g e l r e s u l t does support our conclusion that the TMO-AGE copolymer i s reasonably uniform. A i r aging f o r 48 hours a t 100°C. does not g r e a t l y a f f e c t the room temperature p r o p e r t i e s o f the TMO-AGE v u l c a n i z a t e (Table V I I ) . These c o n d i t i o n s would s e r i o u s l y degrade the p r o p e r t i e s o f n a t u r a l rubber and thus c l e a r l y show that TMO elastomers, l i k e PO elastomers, are s u p e r i o r i n heat aging t o n a t u r a l rubber. Unfort u n a t e l y we d i d not make an extended a i r aging study on the TMO v u l c a n i z a t e t o determine i t s long term o x i d a t i o n r e s i s t a n c e . One

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

114

POLYETHERS

would expect, however, that the lack o f t e r t i a r y hydrogens i n the TMO chain u n i t would be a favorable f a c t o r . Table VI GUM VULCANIZATE PROPERTIES OF TMO-AGE ELASTOMER Tensile strength, p s i . 300% Modulus, p s i . E l o n g a t i o n at break, % Break s e t , % Hardness, A2 Tear s t r e n g t h , p / i G e l / s w e l l , %/%

515 260 515 10 48 80 91/520

EFFECT OF AIR AGING ON TMO-AGE VULCANIZATE(a) h r s . at 100°C. 0 48 Tensile strength, p s i . 200% Modulus, p s i . Elongation at break Break s e t , % Hardness, A2

3190 2590 400 20 82

3380 2630 290 10 70

(a) S t a b i l i z e d with 1% phenyl 3-naphthylamine. T o r s i o n a l r i g i d i t y versus temperature data f o r the TMO-AGE v u l c a n i z a t e and a comparable PO-AGE v u l c a n i z a t e are given i n Figure 2. The increase i n modulus f o r the TMO v u l c a n i z a t e from 0 to -60° o b v i o u s l y i s due to a low temperature c r y s t a l l i z a t i o n o f t h i s copolymer. Other samples d i d not e x h i b i t t h i s c r y s t a l l i z a t i o n problem. The data do i n d i c a t e that the TMO and PO e l a s tomers have about the same Tg at about -75°C. The low temperature c r y s t a l l i z a t i o n problem o f the TMO e l a s tomer can no doubt be e l i m i n a t e d i n a v a r i e t y o f ways, such as preparing a more uniform copolymer, adding a p l a s t i c i z e r such as an aromatic o i l , and/or a l t e r i n g the composition o f the copolymer. An approach t o a l t e r i n g the TMO-AGE copolymer composition would be to make a terpolymer c o n t a i n i n g PO as described prev i o u s l y . V u l c a n i z a t e data are given on the PO-TMO-AGE elastomers i n Table V I I I . The p r o p e r t i e s are f a i r but i n d i c a t e that the v u l c a n i z a t e s are overcured. The AGE l e v e l was e v i d e n t l y too high f o r the cure system used. The r e s u l t s do confirm the p r e p a r a t i o n o f the d e s i r e d terpolymer and i n d i c a t e that t h i s approach i s feasible.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

A N D ROBINSON

Figure 2.

Trimethtflene Oxide

115

Torsional rigidity vs. temperature for TMO and PO elastomers

Other Qxetane Elastomers. The TMO-butadiene monoxide (BMO) copolymer elastomer (Run 6, Table II) c o n t a i n i n g 6.5% BMO gave i n f e r i o r p r o p e r t i e s (Table VIII) t o the TMO-AGE elastomer with 4.4% AGE d e s c r i b e d i n the previous s e c t i o n . A c t u a l l y the propert i e s were even s l i g h t l y i n f e r i o r t o a 98-2 TMO-AGE copolymer v u l canizate (Table V I I I ) . Thus AGE appears about three times more e f f e c t i v e (on a weight b a s i s ) i n c o n f e r r i n g s u l f u r v u l c a n i z a b i l i t y than BMO. On a molar b a s i s , the d i f f e r e n c e i s even g r e a t e r , i . e . , AGE i s f i v e times more e f f e c t i v e . T h i s same d i f f e r e n c e between BMO and AGE was p r e v i o u s l y observed on comparing PO-BMO elastomer with PO-AGE elastomer. Bis(3,3-allyloxymethyl)oxetane (BAMO), on the other hand, appears t o have about the same order o f e f f e c t i v e n e s s f o r conf e r r i n g s u l f u r c u r a b i l i t y t o a TMO elastomer as does AGE (on an equal double-bond content b a s i s ) . The 88:12 DMO:BAMO elastomer gave only f a i r p r o p e r t i e s s i n c e i t was s u b s t a n t i a l l y overcured with the high l e v e l o f BAMO used (Table V I I I ) . The low heat-build-up does i n d i c a t e that t h i s e l a s tomer i s i n h e r e n t l y a good one. CONCLUSIONS The f i r s t p o l y m e r i z a t i o n o f an oxetane, trimethylene oxide, by c o o r d i n a t i o n p o l y m e r i z a t i o n has been d e s c r i b e d . Copolymers o f TMO with epoxides were r e a d i l y made. Such copolymers provide an i n t e r e s t i n g f a m i l y o f new elastomers. One such elastomer, the TMO-AGE copolymer, was i n v e s t i g a t e d i n some d e t a i l and found t o have a d e s i r a b l e combination o f p r o p e r t i e s . Such TMO elastomers,

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

(a)

88-12

93.5-6.5 98-2 (b) 93.3-6.7

58-32-10 60-31-9

Composition

99 390

625 820 270

-

94 93 100

% Swell

% Gel

1985

2090 3010 3280

2040 2030

Tensile psi.

g

char^

d

b

n

/

inh (c) 100% modulus.

P

a

= 1

S

6

6

? !f · '

0

c

e

d

u

r

e

-

1155 1035 3250

695 (c) 930 (c)

300% Modulus psi.

210

535 770 305

225 200

Elongation

a s c r i b e d i n Run 5, Table I I , u s i n g 2.6% t o t a l AGE i n t h e

(a) Products d e s c r i b e d i n Tables I I andI I I u n l e s s otherwise noted.

DMO-BAMO

TMO-BMO TMO-AGE TMO-BAMO

PO-TMO-AGE, h e p t a n e - i n s o l . " " " " -sol.

Elastomer Name

V u l c a n i z a t e P r o p e r t i e s o f V a r i o u s Oxetane Elastomers

Table V I I I

14

Heat Build-up @ 212°F.

7.

VANDENBERG

AND

ROBINSON

THmethylene Oxide

117

l i k e the PO elastomers, are e x c e l l e n t rubbers with low Tg and high r e s i l i e n c e . A l s o , the TMO elastomers give good t e n s i l e and t e a r p r o p e r t i e s and should have at l e a s t f a i r o i l r e s i s t a n c e . Although abrasion r e s i s t a n c e data has not been obtained, we would expect the good t e n s i l e and t e a r p r o p e r t i e s o f the TMO v u l c a n i z a t e s to favor good abrasion r e s i s t a n c e . There appear to be two main d i s ­ advantages o f the TMO elastomers; f i r s t , the low temperature c r y s t a l l i z a t i o n problem which can no doubt be e a s i l y c o r r e c t e d . Second, and more important, there i s no c u r r e n t economic source of TMO. For example, trimethylene g l y c o l , a p o s s i b l e p r e c u r s o r , s e l l s f o r about $4/lb. i n volume. Thus the development o f t h i s i n t e r e s t i n g f a m i l y o f elastomers based on TMO must await the development o f a low cost route to t h i s monomer. Acknow1edgment The a s s i s t a n c e o f t h i s work i s g r a t e f u l l y acknowledged, p a r t i c u l a r l y Dr. T. J . Prosser f o r the s y n t h e s i s o f 3,3-bis(allyloxymethyl)oxetane, Dr. F. E. Williams f o r the s y n t h e s i s o f 3,3-dimethyloxetane, and S. F. Dieckmann f o r the continuous bulk p o l y m e r i z a t i o n o f 3,3-bis(chloromethyl)oxetane c i t e d . Summary The f i r s t c o o r d i n a t i o n p o l y m e r i z a t i o n o f an oxetane, t r i ­ methylene oxide (TMO), occurs r e a d i l y , much l i k e propylene oxide (PO) , with the Et3Al-H20-acetyl acetone c a t a l y s t at 6 5 ° C , to give high molecular weight polymer ( n ^ ^ up to 12) . TMO copolymerizes with epoxides with t h i s c o o r d i n a t i o n c a t a l y s t . For example, TMO copolymerized w e l l with a l l y l g l y c i d y l ether (AGE) which was about seven times more r e a c t i v e than TMO, i n c o n t r a s t to the PO-AGE copolymerization i n which both monomers are o f equal r e a c t i v i t y . A 96-4 TMO-AGE copolymer prepared under c o n d i t i o n s to make i t r e a ­ sonably uniform gave an i n t e r e s t i n g s u l f u r - c u r a b l e elastomer. P r e l i m i n a r y v u l c a n i z a t e data on t h i s elastomer show good t e n s i l e and t e a r p r o p e r t i e s , a low Tg (-75°C.), high r e s i l i e n c e , and good heat r e s i s t a n c e . Further development of t h i s f a m i l y o f i n t e r e s t ­ ing elastomers r e q u i r e s a lower cost route to TMO. Copolymerizations o f TMO with other epoxides and oxetanes as w e l l as the polymerization o f other oxetanes are a l s o d e s c r i b e d . Literature Cited 1. Boardman, Η., E n c y l . o f Chem. Tech., 2nd Supplement, 655.

(1960),

2. Dreyfuss, P. and Dreyfuss, M. P., "Polymerization o f 1,3 Epoxides" i n "Ring Opening P o l y m e r i z a t i o n " (K. C. F r i s c h and S. L. Reegen, eds.), Marcel Dekker, Inc., New York, 1969, Chap. 2-2.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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3. Rose, J. Β., J. Chem. Soc. 1956, 542, 546. 4. Vandenberg, E. J. (to Hercules Incorporated), U.S. Pat. 3,205,183 (1965). 5. Vandenberg, E. J., J. Polym. Sci., A1, (1969), 7, 525. 6. P r i c e , C. C., Chemist

(1961), 38, 131.

7. P r i c e , C. C., (assigned t o U n i v e r s i t y Pat. 2,866,774 (1958).

o f Notre Dame), U.S.

8. P r u i t t , M. E. and Baggett, J. M., (to Dow Chemical Co.), U.S. Pat. 2,706,181 (1955). 9. P r i c e , C. C. and 78, 4787. 10. Osgan, M. and P r i c e , C. C., J. Polym. Sci., (1959), 34, 153. 11. P r i c e , C. C., (to General T i r e and Rubber Co.), Br. Pat. 893,275 (1962). 12. Hill, F. N., Bailey, Jr., F. E., and F i t z p a t r i c k , J. T., Ind. Eng. Chem., (1958), 50, 5. 13. Staudinger, H. and Lohmann, Η., Ann. Chem. (1933), 505, 41. 14. B a i l e y , Jr., F. Ε., Hill, F. N., and F i t z p a t r i c k , J. T., (to Union Carbide Corp.) U.S. Pat. 3,100,750 (1963). 15. B a i l e y , Jr., F. E., Hill, F. N., and F i t z p a t r i c k , J. T., (to Union Carbide Corp.) U.S. Pat. 2,969,402 (1961). 16. B a i l e y , Jr., F. E., Hill, F. N., and F i t z p a t r i c k , J. T., (to Union Carbide Corp.) U.S. Pat. 3,062,755 (1962). 17. B a i l e y , Jr., F. E., (to Union Carbide Corp.) U.S. Pat. 3,031,439 (1962). 18. Vandenberg, E. J., J. Polym. Sci. (1960), 47, 486. 19. Gruber, Ε. E., Meyer, D. Α., Swart, G. H., and Weinstock, Κ. U., Ind. Eng. Chem. Prod. Res. Develop. (1964), 3 ( 3 ) , 194. 20. Vandenberg, E. J. ( t o Hercules Incorporated), U.S. Pat. 3,728,320 (1973). 21. Vandenberg, E. J. (to Hercules Incorporated), U.S. Pat. 3,728,321 (1973).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7.

VANDENBERG

A N D ROBINSON

Trimethylene Oxide

22. Schmoyer, L. F. and Case, L. C., Nature (1960), 187, 592. 23. Kemp, A. R. and M u e l l e r , G. S., Ind. Eng. Chem. Anal. Ed. (1934), 6, 52. 24. Yamashita, Y., Tsuda, T., Okada, M., and Iwatsuki, S., J. Polym. Sci., A1, (1966), 4, 2121.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

119

8 Vulcanization and Stabilization Studies on Propylene Oxide Rubber C. R. BOSS Research Center, Hercules Inc., Wilmington, Del. 19899

®

Parel elastomer i with a small amount o f allyl g l y c i d y l ether. T y p i c a l samples have reduced s p e c i f i c v i s c o s i t i e s (RSV) between 4 and 12, i n d i c a t i n g molecular weights o f the order o f a million. The unsatura t i o n c o n t r i b u t e d by the allyl glycidyl ether monomer u n i t s provides s i t e s f o r s u l f u r c r o s s - l i n k i n g . V u l c a n i z a t i o n can be e f f e c t e d with combinations o f s u l f u r and s u l f u r donors as used f o r other unsaturated rubbers. A t y p i c a l v u l c a n i z a t i o n formulat i o n i s given i n Table 1. Peroxides are i n e f f e c t i v e f o r c u r i n g t h i s elastomer s i n c e they tend t o degrade r a t h e r than c r o s s - l i n k it. When P a r e l elastomer i s cured with the formulation shown, f o r the recommended 30 minutes at 160°C., the p r o p e r t i e s given in Table 2 are obtained. T h i s paper will summarize some o f the s t u d i e s l e a d i n g t o s e l e c t i o n o f a number o f the components o f t h i s v u l c a n i z a t i o n formulation and t o determination o f the advantageous p r o p e r t i e s o f the v u l c a n i z e d products. Vulcanization S u l f u r cure systems are w e l l known t o be complex in t h e i r r e a c t i o n s and i n the types o f c r o s s - l i n k s they produce(1) (2). There is general agreement that i f s u l f u r alone is used to v u l canize a rubber, most o f the c r o s s - l i n k s will have more than two s u l f u r atoms i n them(1). These p o l y s u l f i d e s are l e s s s t a b l e than monosulfides or d i s u l f i d e s . T h i s phenomenon has been examined i n some v u l c a n i z e d elastomers by u s i n g chemical probes, which modify or break only c e r t a i n kinds o f cross-1inks(3) (4) (5). P a r e l e l a s tomer is more difficult to study i n t h i s f a s h i o n than styrenebutadiene rubber (SBR) or n a t u r a l rubber because many o f these chemical reagents a l s o r e a c t with the C-O bonds o f the p o l y e t h e r . © R e g i s t e r e d trademark o f Hercules Incorporated Hercules Research Center C o n t r i b u t i o n No.

1648

120

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

8.

BOSS

121

Propylene Oxide Rubber

However, triphenylphosphine i s a reagent which can be u t i l i z e d advantageously. I t reduces p o l y s u l f i d e s t o disulfides(§), but does not break the polymer chains i n P a r e l elastomer. To determine the types o f c r o s s - l i n k s which are produced i n representat i v e cure systems, two samples o f v u l c a n i z e d P a r e l elastomer were prepared. One was cured with s u l f u r alone, and the other with the formulation shown i n Table 1. The samples were then t r e a t e d with triphenylphosphine i n benzene. The r e s u l t s o f continuous s t r e s s r e l a x a t i o n measurements run on the products at 150°C. are shown i n Figure 1. The s t a b i l i z e r s were e x t r a c t e d by the benzene used i n the triphenylphosphine treatment so subsequent t e s t s i n a i r could not be compared with previous t e s t r e s u l t s . Therefore, a l l o f these s t r e s s r e l a x a t i o n measurements were made i n n i t r o g e n .

1.0-

• 3Î.

J

I

2

4

0

I 6

I 8

I

I 10

12

1 14

TIME (HRS) RUN IN N AT 150°C UNTREATED; — REACTED 24 HOURS WITH TRIPHENYLPHOSPHINE IN BENZENE. 2

Figure 1.

Effect of polysulfides on the stress relaxation of vulcanized Parel elastomer

Both o f the unextracted samples s u f f e r from a r a p i d i n i t i a l l o s s o f modulus, but the sample cured with s u l f u r has a considerably more severe l o s s . A f t e r the c r o s s - l i n k s were converted from

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

TABLE 1 TYPICAL VULCANIZATION FORMULATION

100 50

FOR PAREL ELASTOMER

PAREL ELASTOMER HAF BLACK

1.0

STEARIC ACID

1.5

NICKEL DIBUTYLDITHIOCARBAMATE

5.0

ZNI

1.5

TETRAETHYLTHIURAM

1.5 1.25

MONOSULFIDE

MERCAPTOBENZOTHIAZOLE SULFUR

TABLE 2 TYPICAL PHYSICAL PROPERTIES OF VULCANIZED PAREL ELASTOMER

100$ MODULUS

465 P . S . I .

300% MODULUS

1740 P . S . I .

TENSILE STRENGTH

2075 P . S . I .

ELONGATION

375 %

HARDNESS (SHORE A)

68

BAYSHORE RESILIENCE

48 %

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

8.

BOSS

123

Propylene Oxide Rubber

p o l y s u l f i d e s to d i s u l f i d e s , both samples had a much s m a l l e r l o s s o f modulus i n the f i r s t few hours o f t e s t . These s t r e s s r e l a x a t i o n r e s u l t s show that p o l y s u l f i d e s are weaker than d i s u l f i d e s . L a i has shown t h a t r e d u c t i o n o f p o l y s u l f i d e s to d i s u l f i d e s 4oes not i n t e r f e r e with the t e n s i l e p r o p e r t i e s o f n a t u r a l rubber^Z.). We d i d not determine whether t h i s was true f o r the P a r e l e l a s t o mer. The s u l f u r content o f these samples was determined a f t e r treatment with benzene alone and a f t e r treatment with t r i p h e n y l phosphine i n benzene. The samples l o s t about 1/3 o f t h e i r s u l f u r i n the benzene. About h a l f o f t h i s l o s s (about 1/6 o f the t o t a l amount o f s u l f u r ) could be a t t r i b u t e d to l o s s o f n i c k e l d i b u t y l d i t h i o c a r b o n a t e (NBC), the s t a b i l i z e r . When these samples were t r e a t e d with triphenylphosphine i n benzene, the sample cured with an a c c e l e r a t o r l o s t about 50% o f i t s o r i g i n a l s u l f u r The one cured with s u l f u r alon have f u r t h e r evidence tha c r o s s - l i n k s , but they represent a s m a l l e r percentage o f the t o t a l when an a c c e l e r a t o r i s used. S t a b i l i z a t i o n and Hydroperoxide

Decomposers

When p r o p e r l y compounded, v u l c a n i z e d P a r e l elastomer i s q u i t e s t a b l e i n hot a i r . N i c k e l d i b u t y l d i t h i o c a r b a m a t e (NBC) has been found to be a very e f f e c t i v e s t a b i l i z e r f o r t h i s rubber. Results o f aging a standard formulation i n a 150°C. a i r oven are shown i n Table 3. The hardness r e s u l t s are given as a change ( i n p o i n t s ) from the o r i g i n a l value, while the percentage o f the o r i g i n a l value i s given f o r the other p r o p e r t i e s . During the f i r s t three days o f aging, the 100% modulus and hardness were higher than the o r i g i n a l v a l u e s , while the e l o n g a t i o n was lower. These changes are probably due to a d d i t i o n a l c r o s s - l i n k i n g . Then the rubber g r a d u a l l y softened and l o s t s t r e n g t h . A f t e r a week, the v u l c a n i z e d elastomer l o s t only about 10% o f i t s 100% modulus, l e s s than o n e - t h i r d o f i t s t e n s i l e s t r e n g t h , and softened very l i t t l e ; the rubber was s t i l l q u i t e s e r v i c e a b l e . A f t e r 10 days under these t e s t c o n d i t i o n s , the elastomer d e t e r i o r a t e d considerably. These heat aging t e s t s show t h a t p r o p e r l y compounded P a r e l elastomer v u l c a n i z a t e s are outstanding i n high temperature oxidation resistance. TABLE 3 CHANGE OF PROPERTIES OF PAREL ELASTOMER AGED IN AIR AT 150°C. DAYS

100£

% OF ORIGINAL ELÔNÊ. MOD. T.S.

CHANGE IN HARDNESS

1

130

95

65

+4

3

145

75

60

+3

7

90

70

65

-2

10

60

30

55

-7

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POLYETHERS

Figure 2 compares the e f f e c t i v e n e s s o f two s t a b i l i z e r s i n P a r e l elastomer. Since the elastomer contains an in-process a n t i o x i d a n t , o n l y a hydroperoxide decomposer was added. The s u p e r i o r i t y o f NBC i n maintaining the p h y s i c a l p r o p e r t i e s o f P a r e l elastomer i s obvious.

Figure 2.

Effect of stabilizer on vulcanized Parel elastomer aged at 150°C

A model system has been used t o e x p l a i n the e f f e c t i v e n e s s o f dithiocarbamates as hydroperoxide decomposers. Table 4 summarizes r e s u l t s o f decomposing t - b u t y l hydroperoxide (TBHP) with d i t h i o carbamates o r d i l a u r y l t h i o d i p r o p i o n a t e (LTDP). The d i t h i o c a r b a mates were t e s t e d at room temperature and at 6 0 ° C , while the experiment with LTDP was run at 100°C. LTDP i s an e f f e c t i v e hydroperoxide decomposer and i s o f t e n used f o r t h i s purpose i n polypropylene and other polymers. It decomposes hydroperoxides c a t a l y t i c a l l y and q u i c k l y at 100-150°C, but not at room temperature Each mole o f NBC r e a c t s with about 6 moles o f hydroperoxide i n 15 minutes at 25°C. The z i n c compound r e q u i r e s s e v e r a l hours at 25° or about 20 minutes at 60°C. to e f f e c t i v e l y decompose TBHP. Undoubtedly more important than the r a t e o f decomposition o f hydroperoxides i s the type o f product obtained. Table 5 l i s t s the major products obtained by completely decomposing TBHP with v a r i o u s s u l f u r compounds. With n i c k e l and z i n c dithiocarbamates

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Propylene Oxide Rubber

TABLE 4 DECOMPOSITION OF TBHP BY SULFUR COMPOUNDS

NBC (25°)

TIME (MIN)

TBHP CONCENTRATION NBC ZEC (60°) (25°)

(MOLAR) ZEC (60°)

LTDP (100°)

0

0.205

0.203

0.201

0.201

0.188

15

0.060

-

0.020

0.188

0.162

30

0.030

0.198-

0.016

0.075

0.108

60

0.029

0.195

0.014

0.026

0.014

0.179

-

-

-

0.019

180 ALL

SOLUTIONS

NBC= n i c k e l d i b u t y l d i t h i o c a r b a m a t e ZEC= z i n c d i e t h y l d i t h i o c a r b a m a t e LTDP= d i l a u r y l t h i o d i p r o p i o n a t e TBHP= t - b u t y l h y d r o p e r o x i d e

TABLE 5 PRODUCTS OF TBHP DECOMPOSITION

ΓΤΒΗΡΙ

STABILIZER NBC

L > s

% TBHP TO TBA DTBP

5

70

5

ZBC

4

80

5

LTDP

5

0

40

(C^HgS)2

5

0

40

10

0

90

so TBA=

2

t-butanol

DTBP- di-t-butylperoxide

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126

POLYETHERS

most o f the hydroperoxide went t o the a l c o h o l , and only a small amount t o the peroxide; LTDP formed the peroxide from TBHP, but not the a l c o h o l . About h a l f o f the TBHP was unaccounted f o r , but n e i t h e r methanol n o r acetone was detected. The products formed from TBHP may e x p l a i n why LTDP does not work w e l l i n P a r e l elastomer. The peroxides formed i n p o l y e t h e r s would not be s t a b l e , so t h e i r decomposition would cause continua t i o n o f the o x i d a t i v e chain r e a c t i o n . Heat Aging Comparison with Other Elastomers P a r e l elastomer, n a t u r a l rubber, and neoprene, compounded with standard recommended formulas f o r each, were heat aged i n a 125°C. f o r c e d d r a f t oven. Figure 3 i s a p l o t o f the change i n t e n s i l e strength and hardness o f the v u l c a n i z e d P a r e l and neoprene elastomers. Neoprene maintaine a f t e r a week a t 1 2 5 ° C with n a t u r a l rubber are not i n c l u d e d i n the f i g u r e because i t f a i l e d so q u i c k l y a t 125°C. I t was s e r i o u s l y d e t e r i o r a t e d i n about 3 days a t 100°C.

1050

65

700

60

350

55

10 DAYS

Figure 3.

50

10 DAYS

Physical properties of Parel and neoprene elastomers aged at 125°C

Compression s e t i s the i n a b i l i t y o f rubber t o r e t u r n t o i t s o r i g i n a l s i z e a f t e r being squeezed. Standard t e s t s u s u a l l y compress the v u l c a n i z e d rubber t o 75% o f i t s o r i g i n a l s i z e f o r 1 o r

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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3 days a t 70°, 100°, o r 125°C. Figure 4 i s a p l o t o f the compress i o n set o f v u l c a n i z e d P a r e l elastomer t e s t e d f o r up t o 7 days a t temperatures from 70° t o 150°C. While r a t h e r h i g h compression s e t was a t t a i n e d i n i t i a l l y there was not much change as the time and temperature increased. F o r example, there was n e a r l y 50% s e t a f t e r 1 day a t 100°, but s t i l l l e s s than 70% a f t e r a week a t 150°C. The r e s u l t s obtained a t 125° and 150°C. are w i t h i n e x p e r i mental e r r o r o f each other.

100r-

90 -

80[-

DAYS Figure 4. Effect of time and temperature on the compression set of vulcanized Parel elastomer

Figures 5 and 6 compare the compression s e t o f v u l c a n i z e d P a r e l , n a t u r a l rubber, and neoprene elastomers a t 100° and 1 5 0 ° C , r e s p e c t i v e l y . At 1 0 0 ° C , the compression s e t o f P a r e l elastomer i s w i t h i n experimental e r r o r o f that o f n a t u r a l rubber; neoprene i s c l e a r l y s u p e r i o r . When the compression s e t t e s t was run f o r a long time at 150°C. (Figure 7), P a r e l elastomer was the best o f these three rubbers. Natural rubber had 100% compression s e t

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

128

POLYETHERS

100

90

80

70

S oc

50

40

30

20 10

0 0

1

2

3

4

5

6

_ 7

-

DAYS

Figure 5.

Compression set at

100°C

w i t h i n three days, probably as a r e s u l t o f o x i d a t i v e degradation. Neoprene had a lower compression set than the P a r e l elastomer v u l c a n i z a t e f o r about f i v e days, but then i t became worse. S t r e s s r e l a x a t i o n measurements were made on cured Parel and neoprene elastomers. The samples were h e l d at 25% e l o n g a t i o n i n our t e s t s . T h i s technique measures chain o r c r o s s - l i n k s c i s s i o n , but does not show the e f f e c t o f any recombination or a d d i t i o n a l c u r i n g that occurs. Such new bonds would be load-bearing i f the sample were p u l l e d f u r t h e r as happens i n an i n t e r m i t t e n t run where the sample i s extended f o r a few seconds, then returned t o i t s o r i g i n a l length f o r about 10 minutes. Since the sample spends about 95% o f i t s time i n the r e l a x e d s t a t e , new bonds are loadbearing the next time the sample i s elongated. Many rubbers undergo a r a p i d l o s s o f modulus i n continuous experiments, but not i n i n t e r m i t t e n t runs. At 70°C. n a t u r a l rubber underwent l e s s r a p i d i n i t i a l l o s s than P a r e l elastomer or neoprene. Since oxidat i v e degradation i s not s i g n i f i c a n t i n 10-20 hours at 7 0 ° C , n a t u r a l rubber was s u p e r i o r to P a r e l elastomer or neoprene i n t h i s t e s t . At 1 0 0 ° C , however, the o x i d a t i v e chain s c i s s i o n or n a t u r a l

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Propylene Oxide Rubber

129

10

01 5

I 1

I

I

2

3

I 4

I

1

L

5

6

7

DAYS

Figure 6.

Compression set at

150°C

rubber was much more r a p i d than that o f e i t h e r o f the s y n t h e t i c rubbers. Therefore, i t s modulus dropped r a p i d l y a f t e r a few hours. Figure 7 shows s t r e s s r e l a x a t i o n r e s u l t s with P a r e l e l a s tomer and neoprene at 1 2 5 ° C ; t h e i r r a t e s o f chain s c i s s i o n are similar. In t h i s t e s t , neoprene maintained a l a r g e r f r a c t i o n o f i t s i n i t i a l modulus than the v u l c a n i z e d Parel elastomer. However, Figure 8 shows s t r e s s r e l a x a t i o n r e s u l t s with these two rubbers at 150°C. Under these c o n d i t i o n s , the g r e a t e r o x i d a t i v e s t a b i l i t y o f the P a r e l elastomer i s more s i g n i f i c a n t than i t s somewhat greater l o s s o f modulus i n the f i r s t few hours o f t e s t . Dynamic

Properties

The dynamic p r o p e r t i e s o f t y p i c a l formulations o f P a r e l elastomer, neoprene, n i t r i l e , and n a t u r a l rubber were measured from -55°C. t o +80°C. u s i n g a v i b r a t i n g reed apparatus. These

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

I

•31 0

PAREL ELASTOMER

I 2

ι 4

I 6

I 8

I

I

1 0 1 2

1 14

TIME (HRS)

Figure 7.

Stress relaxation at

125°C

measurements were made a t a frequency o f about 500 h e r t z a t temperatures below the g l a s s t r a n s i t i o n , and a t about 30 h e r t z a t higher temperatures. The dynamic modulus o f the four rubbers i s p l o t t e d against temperature i n Figure 9. Although the samples were s t r a i n e d l e s s than 0.5%, dynamic modulus r e s u l t s are c a l c u ­ l a t e d by e x t r a p o l a t i n g t o 100% s t r a i n . Therefore, dynamic t e s t s gave h i g h e r modulus values than s t a t i c t e s t s . The g l a s s t r a n s i ­ t i o n temperatures are very obvious, as shown by the r a p i d changes i n modulus. They v a r i e d from about -55°C. f o r P a r e l elastomer t o about 0°C. f o r neoprene. In many a p p l i c a t i o n s , the region o f importance i s from about -25° t o +40°C. The dynamic modulus o f these f o u r rubbers changed l i t t l e as the temperature was increased above 30°C. A t w e l l below room temperature, the dynamic modulus o f P a r e l elastomer and n a t u r a l rubber remained d e s i r a b l y constant. The other two rubbers are so c l o s e t o t h e i r glass t r a n s i t i o n temperatures that the p r o p e r t i e s o f a r t i c l e s prepared from them

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

8.

BOSS

Propylene Oxide Rubber

.31

0

1

I

2

4

131

I

»

I

6

8

10

t

12

ι

14

TIME (HRS) Figure 8.

Stress relaxation at

150°C

would vary c o n s i d e r a b l y a t temperatures encountered i n the winter. Decreasing the l e v e l o f carbon b l a c k o r adding p l a s t i c i z e r s h i f t e d these curves t o lower modulus v a l u e s , and adding p l a s t i c i z e r s lowered the Tg. However, p l a s t i c i z e r s can be l o s t by e x t r a c t i o n or v o l a t i l i t y , and so should be s e l e c t e d t o avoid such l o s s . In a rubber, there i s a time l a g between an a p p l i e d s t r e s s and the r e s u l t i n g s t r a i n . In a dynamic t e s t , the s t r e s s i s ap­ p l i e d i n a s i n u s o i d a l f a s h i o n so t h i s delay can be t r e a t e d as a phase angle - d e l t a . Dynamic r e s u l t s are o f t e n given as the tangent o f d e l t a . Tan β i s a measure o f the r a t i o o f energy absorbed t o energy put i n p e r c y c l e . Heat b u i l d u p i n a f l e x i n g rubber i s dependent upon the energy r e q u i r e d t o s t r a i n the sample (the dynamic modulus), and on tan δ, which i s a measure o f the f r a c t i o n o f t h i s energy r e t a i n e d by the sample as heat. Small values are d e s i r a b l e where heat b u i l d u p may be a problem, while l a r g e r values mean the m a t e r i a l w i l l absorb a l a r g e r f r a c t i o n o f v i b r a t i o n a l energy. Tan <5 o f P a r e l elastomer v u l c a n i z a t e s and o f three other rubbers i s p l o t t e d a g a i n s t temperature i n Figure 10; these data

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

-60

-50

-40

-30

-20

-10

0

10

20

30

40

TEHPERATURE

Figure 9.

50 e

60

70

C

Dynamic modulus vs. temperature

Figure 10.

Tan Β vs. temperature

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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a l s o were obtained on a v i b r a t i n g reed apparatus. P a r e l elastomer gave more constant values above approximately -20°C. than the other rubbers. The large change i n tan δ below room temperature f o r the other rubbers means that they w i l l have v a r i a b l e proper­ t i e s when exposed to outdoor winter c o n d i t i o n s . Summary P a r e l elastomer, a copolymer o f propylene oxide and a l l y l g l y c i d y l ether, has a combination o f p r o p e r t i e s t h a t make i t v e r y u s e f u l i n many rubber a p p l i c a t i o n s . I t can be v u l c a n i z e d with a conventional mixture o f s u l f u r and a c c e l e r a t o r s . The cured elastomer has a low glass t r a n s i t i o n temperature (approximately -55° to - 6 0 ° C ) , and the e x c e l l e n t dynamic p r o p e r t i e s o f n a t u r a l rubber. I t can be made very s t a b l e to high temperature o x i d a t i v e degradation, and i s b e t t e NBC i s added as a s t a b i l i z e r Experimental Rubber samples were Banbury mixed with f i n a l sheeting (and c u r a t i v e s added) on a 6-inch χ 12-inch t w o - r o l l m i l l . A l l samples were press cured. The formulations f o r the various compounds contained the f o l l o w i n g i n g r e d i e n t s (based on p a r t s per hundred o f rubber) and were added i n the order given: Parel elastomer - 1.0 S t e a r i c a c i d , 50. HAF black (N-330), 1.5 N i c k e l d i b u t y l d i t h i o c a r b a m a t e (NBC), 5.0 ZnO, 1.5 Tetramethylthiuram monosulfide (TMTM), 1.5 mercaptobenzathiazole (MBT), 1.25 S u l f u r . Cured 30 minutes at 160°C. Neoprene W

- 0.5 S t e a r i c a c i d , 60. HAF-LS b l a c k (N-326), 5.0 ZnO, 4.0 M a g l i t e D Bar, 2.0 A g e r i t e G e l , 0.5 T h i a t e E. Cured 35 minutes at 154°C.

Natural Rubber

- 2.0 S t e a r i c a c i d , 35. SRF b l a c k (N-770), 1.0 A g e r i t e S t a l i t e S, 0.8, N-oxydiethylene benzothiazole-2-sulfenamide, 2.0 Reogen, 2.5 S u l f u r Cured 30 minutes at 143°C.

Nitrile

(Hycar 1042) - 1.0 S t e a r i c a c i d , 40. HAF black (N-330), 1.0 A g e r i t e Resin D, 5.0 ZnO, 1.5 TMTM, 1.5 MBT, 1.5 S u l f u r . Cured 30 minutes at 160°C.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

134

The v i b r a t i n g reed equipment used i n t h i s work u t i l i z e d the general p r i n c i p l e s presented by R o b i n s o n ^ . The reed was a p i e c e o f rubber about 2 mm. χ 6.3 mm. χ 50 mm. hanging v e r t i c a l l y and clamped a t the upper end. The lower end was d r i v e n magneti­ c a l l y by two f i x e d c o i l s and a small (about 40 mg.) i r o n wire c l i p p e d about the lower end o f the reed. A small c o r r e c t i o n f o r the presence o f t h i s wire was made according t o a method suggested by F o r s m a n Q £ ) . D r i v i n g c u r r e n t was s u p p l i e d by a s t a b l e audio o s c i l l a t o r ; however, frequency was measured by a Beckmann i n t e r n a l timer. Amplitude o f the reed motion was sensed by a l i g h t beam and p h o t o c e l l . Values o f the dynamic modulus (E*) and tangent o f the l o s s angle (tan 6) were c a l c u l a t e d according t o the formulas of Wapman and Forsman (ϋ.) · Decomposition o f t-butylhydroperoxide (TBHP) was c a r r i e d out by f i r s t mixing the TBHP with s o l v e n t The s t a b i l i z e r was weighed i n t o a tube and the TBH put i n t o the tube and th and put i n t o an o i l bath. Samples o f the mixture were t i t r a t e d at i n t e r v a l s by the NaI-Na2S203 technique. Some runs were made overnight t o decompose a l l o f the hydroperoxide. The products were determined by gas chromatography (GC) and i n f r a r e d s p e c t r o ­ scopy. The GC column was a 12 f t . χ 6 mm. g l a s s column with s i l i c o n e grease on Chromasorb W. The column temperature was 90°C. One-half s i z e d ASTM dumbbells o f rubber (^85 m i l s t h i c k ) were aged i n a f o r c e d d r a f t a i r oven. T h e i r t e n s i l e p r o p e r t i e s were measured on a Model LACC S c o t t T e s t e r , a t 20 inches/min. Compres­ s i o n s e t t e s t s were made on buttons 0.5 inch t h i c k and 0.75 i n c h i n diameter. They were compressed 25%, according t o ASTM D-395 method B. Stress r e l a x a t i o n measurements were made on s t r i p s o f rubber, approximately 2" χ 1/2" χ 15 m i l s . They were clamped i n t o an apparatus that f i t s i n t o a w e l l i n a s i l i c o n e o i l bath. The bottom clamp was f i x e d and the top clamp had a r o d connected t o a s t r a i n gauge. The sample was warmed f o r 20 minutes i n a stream o f helium, then i t was elongated 25% and t e s t e d i n a i r o r N 2 . The s t r a i n gauge converted the f o r c e t o an e l e c t r i c a l s i g n a l which was fed i n t o a r e c o r d e r . ff

lf

Literature Cited 1.

A l l i g e r , G. and I. J. Sjothun, " V u l c a n i z a t i o n o f Elastomers" Reinhold P u b l i s h i n g Co., New York, 1964.

2.

Bateman, L., "The Chemistry and Physics o f Rubber-Like Substances" John Wiley and Sons, New York, 1963.

3.

S a v i l l e , B. and A. A. Watson, Rubber Chem. and Technol. (1967) 40, 100.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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4.

Skinner, T. D., ibid. (1972) 45, 182.

5.

Baldwin, F. P., ibid. (1972) 45, 1348.

6.

Moore, C. G., B. R. Trego and J. R. Dunn, J. Appl. Poly. Sci. (1964) 8, 723.

7. Lal, J., Rubber Chem. and Technol. (1970) 43, 664. 8.

Chien, J. C. W. and C. R. Boss, J. Poly. Sci. A-1 (1972) 10, 1579.

9.

Robinson, D. W. J., Soc. Inst. (1965) 32, 2.

10.

Forsman, W. C., p r i v a t

11.

Wapman, P. G. and W. C. Forsman, Trans. Soc. Rheology (1971) 15, 603.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

9 Irregular Structures in Polyepichlorohydrin Κ. E. STELLER Hercules Inc., Wilmington, Del. 19899

Introduction Information concerning the m i c r o s t r u c t u r e o f a polymer is e s s e n t i a l f o r e l u c i d a t i o n o f the p o l y m e r i z a t i o n mechanism. The p o l y m e r i z a t i o n o f s u b s t i t u t e d epoxides such as propylene oxide is p a r t i c u l a r l y i n t e r e s t i n g . This monomer is unsymmetrical, and p o l y m e r i z a t i o n can proceed by attack a t e i t h e r the head o r the tail end. I f both types of ring openings occur in the propagation step, h e a d - t o - t a i l , head-to-head, and tail-to-tail linkages appear i n the polymer c h a i n [eq.(1)].

CH. U-0-

•0-C-CH -0-i 2

HEAD

TAIL

CH

2

HEAD-TO-TAIL UNIT ISOTACTIC (dd a n d i i )

CH

POLYMERIZATION KCH ) 3

:-CH,-0H

L

CH (H)

HEAD-TO-HEAD UNIT (di and i d o r dd a n d U t )

3

CH.3

H(CH-) I •TAIL UNIT i d o r dd and ML )

Hercules Research Center C o n t r i b u t i o n Number 1646

136

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

(1)

9.

137

Polyepichlorohydrin

STELLER

In a d d i t i o n t o t h i s s t r u c t u r a l problem, there is a l s o a stereochemical problem. U n l i k e v i n y l monomers o r α-olefins, propylene oxide has an asymmetric carbon atom before polymeriza­ t i o n . Thus, it is p o s s i b l e to o b t a i n o p t i c a l l y a c t i v e polymers if the p o l y m e r i z a t i o n proceeds with e i t h e r complete r e t e n t i o n or complete i n v e r s i o n a t the asymmetric center. Four d i f f e r e n t dimer u n i t s in the main chain are t h e r e f o r e p o s s i b l e [eq.(1)]. It is common knowledge that the m i c r o s t r u c t u r e o f a polymer has a profound i n f l u e n c e on many o f its p r o p e r t i e s . In f a c t , there have been s e v e r a l such e f f e c t s observed with poly­ (propylene oxide). In 1959, Madorsky and Straus reported that i s o t a c t i c poly(propylene oxide) is somewhat more s t a b l e than the a t a c t i c polymer (1). Aggarwal and coworkers showed that the melting p o i n t o f crystalline poly(propylene oxide) could be r e l a t e d t o the sequence length o f isotactic u n i t s in the poly­ mer (2). Furthermore, tence o f tail-to-tail linkages crystallization o f the polymer and thereby depressed its melting point (3). In polyether research, however, Dr. Charles C. P r i c e was perhaps the first t o recognize the i n f l u e n c e o f polymer micros t r u c t u r e on the r e s u l t a n t p h y s i c a l p r o p e r t i e s . In 1956, he reported the formation o f crystalline, low molecular weight, o p t i c a l l y - a c t i v e polymer from Jt-propylene oxide by potassium hydroxide-catalyzed p o l y m e r i z a t i o n [eq.(2)].

CHo CH

/ CH

2

K0H_

^O^ A

C R Y S T A L L I N E , OPTICALLY A C T I V E POLYMER ( l o w M.W.) CHo CH~ CH., CH„ I I I I -CH -CH-0~CH -CH-0-CH -CH-0-CH.,-CH-03

9

3

3

o

2

3

9

2

%

2

2

JZ JL ISOTACTIC

/ο\

i

( 2 )

This product was i n sharp c o n t r a s t t o the l i q u i d polymer o f the same molecular weight produced from racemic monomer under the same c o n d i t i o n s [eq.(3)].

/

CH \

H

3

KOH

LIQUID POLYMER (SAME M.W. AS EQ. 2) CHo CH I I -CH -CH-0-CH2-CH-0-CH -CH-0-CH -CH-03

3

d,Jt

2

2

CH A

d

3

d

2

CH

3

X

ATACTIC

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

138

He concluded that t h i s remarkable d i f f e r e n c e i n p h y s i c a l proper­ t i e s r e s u l t e d from i d e n t i c a l c o n f i g u r a t i o n o f a l l the asymmetric centers i n the c r y s t a l l i n e polymer. The l i q u i d polymer from racemic monomer, on the other hand, was e v i d e n t l y a stereorandom a t a c t i c polymer (4). Both polymers were l a t e r shown t o be formed almost e x c l u s i v e l y by h e a d - t o - t a i l p o l y m e r i z a t i o n . Vandenberg, P r i c e , and others l a t e r showed that a d d i t i o n o f each epoxide u n i t to the polymer chain occurs with i n v e r s i o n o f c o n f i g u r a t i o n a t the carbon atom where r i n g opening occurs. The asymmetry i n t h i s case i s not d i s t u r b e d , however, because the bond between the oxygen and the asymmetric carbon i s never broken. Dr. P r i c e a l s o showed t h a t f e r r i c c h l o r i d e - c a t a l y z e d polym­ e r i z a t i o n o f e i t h e r %- o r d£-propylene oxide gave polymeric m a t e r i a l which could be separated i n t o amorphous, intermediate molecular weight and c r y s t a l l i n e , high molecular weight f r a c t i o n s [eqs. (4) and (5)]. CH, * / CH

CHo

r

FeCl,

(HIGH M.W.)

- PO

^ 0 £

kB.

^CH CH 2

{

rC

3

FeCU

-

AMORPHOUS, LESS OPTICALLY (INTERMEDIATE M.W.)

SAME AS A BUT OPTICALLY


PO

./

"0'

"*D.

ACTIVE POLYMER (4)

INACTIVE

AND SAME AS Β BUT OPTICALLY

INACTIVE

There was no d e t e c t a b l e d i f f e r e n c e between the products from the o p t i c a l l y a c t i v e and racemic monomers except f o r o p t i c a l a c t i v i t y (4). He l a t e r demonstrated that the amorphous f r a c t i o n s o f poly(propylene oxide) from o p t i c a l l y a c t i v e monomer contained head-to-head sequences (5) and (6). The formation o f head-tohead sequences r e q u i r e s normal h e a d - t o - t a i l opening followed by an abnormal head-to-head attack [eq. (6)]. HEAD-TO-TAIL CH, CH, CH, I I I -CH -CH-0-CH -CH-0-CH -CH-O 2

2

2

CH

-CH

iY

x

2

HEAD-TO-HEAD CH,

CH,

CH,

CHo

CH

-CHg-CH-Q-CHg-CH-O-CHg-CH-O-CHg-CH-O^

3

CH

CH

X χ

X

JL

%

9

/

Vi/°

m

CHo CHo CHo CHo ! I I \ -CH -CH-0-CH -CH-0-CH -CH-0-CH -CH-0-CH-CH -0 3

2

3

2

χ

3

2

X

3

2

*

2

JL

™3 d

%

%

"

(

m= METAL ATOMS OF CATALYST S P E C I E S

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

6

Î

9.

STELLER

Polyepichlorohydrin

139

Since the carbon atom undergoing r i n g opening i n the l a t t e r case i s the asymmetric carbon, i n v e r s i o n o f c o n f i g u r a t i o n occurred each time a u n i t i n s e r t e d head-to-head. The r e s u l t a n t o p t i c a l a c t i v i t y was t h e r e f o r e l e s s . Dr. P r i c e explained that the formation o f any c r y s t a l l i n e polymer a t a l l from racemic monomer must be due to asymmetric c a t a l y t i c s i t e s . These s i t e s e x h i b i t h i g h l y p r e f e r e n t i a l r e a c t i v i t y f o r propylene oxide o f one p a r t i c u l a r c o n f i g u r a t i o n . Thus, he was one o f the f i r s t t o recognize that defects i n the c a t a l y s t or the existence o f s e v e r a l d i f f e r e n t c a t a l y t i c s i t e s can profoundly a f f e c t the r e s u l t a n t polymer m i c r o s t r u c t u r e . When Hercules entered the s p e c i a l t y rubber business i n 1968 with i t s two HERCLOFP e p i c h l o r o h y d r i n elastomers (Table I ) , very l i t t l e was known about t h e i r s t r u c t u r e . As i n d i c a t e d prev i o u s l y , i t should be p o s s i b l e t o change the m i c r o s t r u c t u r e by a l t e r i n g the c a t a l y s t syste of properties. TABLE I - HERCULES EPICHLOROHYDRIN ELASTOMERS

STRUCTURE

HERCLOR H ELASTOMER

HERCLOR C ELASTOMER

-fCH -CH-0^-

-fCH -CH-0-CH -CH -0^

2

CH C1 2

EPICHLOROHYDRIN, MOLE %

100

ETHYLENE OXIDE, MOLE %

0

n

2

2

2

n

CH C1 2

50 50

CHLORINE, %

38.4

26.0

SPECIFIC GRAVITY

1.36

1.27

Tg, °F. (by DTA)

-15

-49

We f i r s t s e t out t o determine the m i c r o s t r u c t u r e o f the e p i c h l o r o h y d r i n homopolymer, HERCLOR H elastomer. Since e p i c h l o r o h y d r i n , l i k e propylene oxide, i s unsymmetrical and contains an asymmetric carbon atom, the polymer chain could contain the same four types o f chain u n i t s as shown p r e v i o u s l y f o r poly(propylene oxide). Our approach to determining the amounts o f i r r e g u l a r head-to-head and t a i l - t o - t a i l s t r u c t u r e s c o n s i s t e d o f r e p l a c i n g a l l the c h l o r i n e s i n p o l y e p i c h l o r o h y d r i n with hydrogens. Since the d e c h l o r i n a t i o n r e a c t i o n does not i n v o l v e the asymmetric center, the r e s u l t a n t poly(propylene oxide) should have the same c o n f i g u r a t i o n around each asymmetric carbon as the o r i g i n a l p o l y epichlorohydrin. The r e s u l t a n t poly(propylene oxide) could then be cleaved t o dimer u n i t s according t o a procedure developed by Vandenberg ( 7 ) . Experimental Dechlorination o f Polyepichlorohydrin. Polyepichlorohydrin (5.0 g., 54 mmoles CI) was t r a n s f e r r e d to a d r y 28-oz. beverage b o t t l e i n a n i t r o g e n - f i l l e d glove bag. The polymer was d i s s o l v e d

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

140

i n 150 ml. o f d i s t i l l e d , d r i e d t e t r a h y d r o f u r a n and t r e a t e d with f r e s h l i t h i u m aluminum hydride [LAH] (5.13 g., 135 mmoles) which was weighed and t r a n s f e r r e d i n the glove bag. The mixture was s t i r r e d 50 hours at 50"C. and quenched with about 900 mmoles o f water i n t e t r a h y d r o f u r a n s o l u t i o n . The r e s u l t a n t poly(propylene oxide) was i s o l a t e d by f i l t r a t i o n and evaporation o f the s o l v e n t i n vacuo. Cleavage o f Poly(propylene o x i d e ) . The d e c h l o r i n a t e d polymer (0.157 g., 2.7 mmoles o f propylene oxide u n i t s ) was d i s s o l v e d i n benzene i n a dry 4-inch p o l y m e r i z a t i o n tube, n - B u t y l l i t h i u m (1.5 mmoles) was added and the s o l u t i o n was tumbled f o r 18 hours a t 25°C. and s t i r r e d 4 hours at 90°C. before being shortstopped with d i s t i l l e d e t h y l a l c o h o l and cooled. Vandenberg s procedure (7) was g r e a t l y s i m p l i f i e d by n e u t r a l i z a t i o n o f the cleavage mixtures while they were s t i l l i t i o m e t r i c t i t r a t i o n wit a l c o h o l . N e u t r a l i z a t i o n was followed by i n j e c t i o n o f i n t e r n a l standard and c e n t r i f u g a t i o n to y i e l d c l e a r samples f o r d i r e c t gas chromatographic a n a l y s i s . f

Gas Chromatographic A n a l y s i s o f Cleavage Mixtures. The above samples were analyzed d i r e c t l y by gas chromatography u s i n g 5% (w/w) Carbowax 1000 on 100/110 mesh Anakrom SD as the packing i n a 12 f t . χ 1/4 i n . O.D. b o r o s i l i c a t e g l a s s column at 150°C. Samples were i n j e c t e d d i r e c t l y i n t o the g l a s s column to avoid any contact with metal. An i n t e r n a l standard (methyl p - t o l u a t e ) and flame i o n i z a t i o n d e t e c t i o n were a l s o employed. Carbon-13 NMR A n a l y s i s o f P o l y e p i c h l o r o h y d r i n . N a t u r a l abundance carbon-13 NMR s p e c t r a at 22.6 MHz were measured i n benzene at 70°C. with proton n o i s e decoupling, u s i n g a Bruker HFX-10 spectrometer equipped with a N i c o l e t 1085 F o u r i e r t r a n s ­ form spectroscopy accessory. Results and D i s c u s s i o n HERCLOR H elastomer was r e a d i l y d e c h l o r i n a t e d by treatment with excess l i t h i u m aluminum hydride [LAH] (2.5 moles/mole o f CI) i n tetrahydrofuran at 50°C. Unreacted hydride was quenched with water, and the polymer samples were i s o l a t e d f o r c h l o r i n e analyses. The observed p s e u d o - f i r s t - o r d e r r a t e constant f o r the disappearance o f c h l o r i n e was found to be 1.9 χ 10*^ minT* under these c o n d i t i o n s ( F i g . 1). Polymers were i s o l a t e d i n about 99% y i e l d a f t e r treatment f o r 50 hours at 50°C. Although they contained l e s s than 0.3% o f the o r i g i n a l c h l o r i n e , they were not otherwise s e r i o u s l y changed. The weight average molecular weights were found to be about 0.5 million. I f no cleavage whatsoever occurred, the molecular weight should decrease from 1.7 m i l l i o n to 1.1 m i l l i o n due simply to the

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

9.

STELLER

Polyepichlorohydrin

141

TIME (HRS Figure 1. Linear (A) and semi-log (B) plots showing dechlorination of HERCLOR H elastomer with lithium aluminum hydride (2.5 moles/ mole CI) in tetrahydrofuran at 50°C

replacement o f c h l o r i n e with hydrogen. The a d d i t i o n a l decrease i n molecular weight occurred when the polymer - e i t h e r p o l y e p i c h l o r o ­ h y d r i n or poly(propylene oxide) - was simply d i s s o l v e d and r e i s o l a t e d under the experimental c o n d i t i o n s . No a d d i t i o n a l de­ crease i n molecular weight was observed when the poly(propylene oxide) was t r e a t e d with LAH f o r 50 hours at 50°C. Since HERCLOR H elastomer could be converted q u a n t i t a t i v e l y to poly(propylene o x i d e ) , the m i c r o s t r u c t u r e could be determined by u s i n g the method developed by Vandenberg f o r poly(propylene oxide) (7). T h i s method c o n s i s t s o f cleavage with η-butyllithium and a n a l y s i s o f the r e s u l t a n t dipropylene g l y c o l f r a c t i o n f o r the various d i f f e r e n t s t r u c t u r a l isomers ( F i g . 2). The r e l a t i v e amounts o f the v a r i o u s types o f dipropylene g l y c o l s i n d i c a t e the r e l a t i v e numbers o f head-to-head and t a i l - t o - t a i l linkages i n the o r i g i n a l polymer. I n i t i a l GC analyses o f the cleavage mixtures were not repro­ d u c i b l e , due t o poor r e s o l u t i o n and t a i l i n g o f the dipropylene g l y c o l GC peaks u n t i l Carbowax 1000 on an i n e r t support such as Anakrom SD was used as the packing i n a g l a s s column. Figure 3 shows the e x c e l l e n t r e s o l u t i o n e v e n t u a l l y obtained with a u t h e n t i c samples o f the dipropylene g l y c o l s . The two d i a s t e r e o i s o m e r i c forms o f the diprimary isomer were r e s o l v a b l e on the GC. The amounts due to each o f the two peaks were summed to give the t o t a l diprimary (or head-to-head) content. The r e s u l t s shown i n Table II c l e a r l y i n d i c a t e that t y p i c a l HERCLOR H elastomer has a very r e g u l a r s t r u c t u r e with 97-99% h e a d - t o - t a i l attachment o f monomer u n i t s . The chromatogram o f a t y p i c a l cleavage mixture (Figure 4) f u r t h e r emphasizes the lack of any s i g n i f i c a n t number o f the i r r e g u l a r head-to-head or t a i l to- t a i l dimers.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

142

T Y P E O F DIMER UNIT IN O R I G I N A L P O L Y M E R

DIPROPYLENE GLYCOL STRUCTURE CH, CH, I I H0-C-CH -Q-C-CH -0H I I H H 2

HEAD-TO-TAIL

2

M I X E D P R I M A R Y - S E C O N D A R Y G L Y C O L , 2d A P A I R S (erythro and threo) CH, C H , I I HO-CH.-C-O-C-CH.-OH • I H H

HEAD-TO-HEAD

D I P R I M A R Y G L Y C O L , MESO AND R A C E M I C

Ç3

Ç3

H

H

TAIL-TO-TAIL H DISECONDARY GLYCOL

Figure 2.

H

Dipropylene glycols resulting from n-butyllithium cleavage of poly(propylene oxide)

TABLE I I

SAMPLE OF DECHLORINATED HERCLOR H ELASTOMER

% OF TOTAL DIPROPYLENE GLYCOLS DISECONDARY MIXED DIPRIMARY DIMER DIMER DIMER

% OF ORIGINAL POLYMER PROPYLENE DIPROPYLENt GLYCOLS GLYCOL

A

1.6

96.7

1 .6

6.0

15.8

Β

0.7

99.3

0

6.3

12.5

Β

0.7

99.3

0

6.1

12.4

Β

0.7

99.3

0

6.2

12.7

Of course, the mixture o f dipropylene g l y c o l s obtained a f t e r d e c h l o r i n a t i o n and cleavage o f HERCLOR H elastomer i s representa­ t i v e o f the o r i g i n a l s t r u c t u r e only i f the f o l l o w i n g c o n d i t i o n s h o l d t r u e . F i r s t , the d e c h l o r i n a t i o n o f HERCLOR H elastomer with LAH does not a l t e r the s t r u c t u r e o f the backbone; second, the cleavage i s completely random; and t h i r d , a l l the dipropylene g l y c o l s are e q u a l l y r e s i s t a n t t o f u r t h e r degradation. Our e f f o r t to v e r i f y these c o n d i t i o n s i s summarized i n Table I I I . A sample of poly(propylene oxide) made with a c a t a l y s t d i f f e r e n t from that used f o r HERCLOR H elastomer was t r e a t e d with LAH (2.5 mmoles/mmole o f propylene oxide) f o r 50 hours a t 50°C. The r e s u l t a n t polymer was i s o l a t e d and cleaved by the normal procedures. Other samples o f the same poly(propylene oxide) were cleaved d i r e c t l y f o r v a r y i n g lengths o f time. The f o l l o w i n g observations are apparent from the data:

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

STELLER

Polyepichlorohydrin

ι. II. Ill. IV. V. VI. VII.

SOLVENT PROPYLENE GLYCOL INTERNAL STANDARD (METHYL p - T O L U A T E ) DISECONDARY DIPROPYLENE GLYCOL MIXED DIPROPYLENE GLYCOL DIPRIMARY I I DIPROPYLENE GLYCOL DIPRIMARY I DIPROPYLENE GLYCOL

Figure 3 . Gas chromatogram showing resolution of the dipropylene glycols

I

II

I. II. III. IV.

SOLVENT PROPYLENE GLYCOL INTERNAL STANDARD (METHYL p - T O L U A T E ) DISECONDARY DIPROPYLENE GLYCOL

V. VI. VII.

MIXED DIPROPYLENE GLYCOL DIPRIMARY I I DI PROPYLENE GLYCOL P O S I T I O N DIPRIMARY I D I P R O P Y L E N E GLYCOL P O S I T I O N

iv

Figure 4.

V

V

1

Gas chromatogram of cleavage mixture from dechlorinated HERCLOR H elastomer

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

18

4

10

18

18

18

YES

NO

NO

NO

NO

NO 4

1

0

0

0

4

4

60.5

63.5

63.4

64.0

61.0

61.2

63.4

6

39.5

36.5

36.6

36.0

39.0

38.8

36.6

t OF DIPROPYLENE GLYCOLS HEAD-TÛ-TAIL IRREGULAR DIMER DIMERS

5.6

5.6

6.3

5.6

5.6

7.4

8.1

12.4

11.9

11.6

10.8

11.5

13.5

13.2

t OF ORIGINAL POLYMER PROPYLENE DIPROPYLENE GLYCOL GLYCOLS

3

•STIRRED 5 0 HOURS AT 50°C. WITH 2.S L A H / C H 0 UNIT BEFORE ISOLATION AND CLEAVAGE WITH •-IUTYLLITHIUM.

18

CLEAVAGE TIME HOURS AT HOURS AT 25*C 90°C

YES

LAH TREATMENT*

EFFECT OF LAH TREATMENT AND EXTENT OF CLEAVAGE

TABLE I I I

9.

STELLER

Polyepichlorohtjdrin

145

(1) The r e l a t i v e amounts o f the dipropylene g l y c o l s formed were n e a r l y i d e n t i c a l whether or not the polymer was t r e a t e d with LAH. Thus, LAH treatment under the cond i t i o n s used caused no i s o m e r i z a t i o n o f the p o l y e t h e r backbone. (2) The r e l a t i v e amounts o f the dipropylene g l y c o l s formed remained constant and were independent o f time. I f cleavage were a nonrandom process, the r a t i o s o f dimers formed at low l e v e l s o f cleavage should be d i f f e r e n t from the r a t i o s observed a f t e r complete cleavage. A l though no data were obtained at very low l e v e l s o f cleavage (cleavage was much more r a p i d than expected), the data are c o n s i s t e n t with a n o n d i s c r i m i n a t o r y cleavage process. (3) The s t a b i l i t i e s o f the dipropylene g l y c o l s under the cleavage c o n d i t i o n there was no i n d i c a t i o further. Further c o n f i r m a t i o n o f the uniformly h e a d - t o - t a i l s t r u c t u r e of HERCLOR H elastomer was obtained from i t s carbon-13 NMR spectrum. Since no l i t e r a t u r e s p e c t r a o f p o l y e p i c h l o r o h y d r i n were a v a i l a b l e f o r comparison, the carbon-13 NMR s p e c t r a o f the p o l y p r o p y l e n e oxide) r e s u l t i n g from d e c h l o r i n a t i o n with LAH were a l s o examined. Published s p e c t r a o f poly(propylene oxide) with d e t a i l e d peak assignments are a v a i l a b l e . Oguni and co-workers have examined the carbon-13 NMR s p e c t r a of c r y s t a l l i n e poly(propylene oxide) and o f amorphous p o l y p r o p y l e n e oxide) made with a base c a t a l y s t (8). They made the peak assignments shown i n Figure 5. The spectrum o f the c r y s t a l l i n e polymer contained three peaks at 17.33, 73.98, and 75.98 ppm. downfield from tetramethy1si1ane. These were i d e n t i f i e d as a r i s ing from methyl, methylene, and methine carbons, r e s p e c t i v e l y . The spectrum o f amorphous poly(propylene oxide) contained three peaks i n the methine carbon r e g i o n with an observed peak area r a t i o o f 25:50:25, and two main peaks i n the methylene carbon region with an observed peak area r a t i o o f 50:50. Since i t i s known that poly(propylene oxide) made with base c a t a l y s t s i s atact i c and contains p r a c t i c a l l y no head-to-head or t a i l - t o - t a i l l i n k ages, i t was reasonable to a s s i g n the two methylene peaks to equal amounts o f i s o t a c t i c and s y n d i o t a c t i c dyads and the three methine carbon peaks t o i s o t a c t i c , h e t e r o t a c t i c , and s y n d i o t a c t i c t r i a d s . Thus, the two peaks observed at 73.98 and 75.98 ppm. i n the spectrum o f the c r y s t a l l i n e i s o t a c t i c polymer were assigned to i s o t a c t i c dyad and t r i a d , r e s p e c t i v e l y . These assignments lead n a t u r a l l y to those o f s y n d i o t a c t i c dyad (73.71 ppm.), syndiot a c t i c t r i a d (75.78 ppm.), and h e t e r o t a c t i c t r i a d (75.90 ppm.). These assignments were r e c e n t l y confirmed by other workers (9). Figure 6 shows the much more complicated NMR spectrum o f a sample o f poly(propylene oxide) known t o c o n t a i n abnormal head-tohead and t a i l - t o - t a i l l i n k a g e s . T h i r t e e n p a r t i a l l y r e s o l v e d peaks

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

146

A

75.98 75.78 75.90

73.98 73.71

Macromolecules Figure 5. Carbon-13 NMR spectra of (A) crystalline poly(propylene oxide) and (B) amorphous poly(propylene oxide) made with t-BuOK catalyst

(8)

75.98 75.78 75.90

73.98 73.71

Macromoiecules Figure 6. Carbon-13 NMR spectrum of amorphous polypropylene oxide) made with an Al(C H,),-H 0 (1:1) catalyst This polymer is known to contain head-to-head and tail-to-tail linkages (8). 2

2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

9.

STELLEB

Polyepichlorohydrin

147

were observed i n the spectrum o f t h i s p a r t i c u l a r sample (8). The carbon-13 NMR s p e c t r a o f HERCLOR H elastomer and the poly(propylene oxide) we obtained by d e c h l o r i n a t i o n with LAH are shown i n Figure 7. The spectrum o f the d e c h l o r i n a t e d product i s seen t o resemble very c l o s e l y that o f poly(propylene oxide) made with the base c a t a l y s t and contains no n o t i c e a b l e peaks due to s t r u c t u r a l imperfections. The two major peaks* i n the methylene carbon region at 73.94 and 73.65 ppm. are i n the r a t i o o f 55 to 45. These were assigned to i s o t a c t i c and s y n d i o t a c t i c dyads which were observed at 73.98 and 73.71 by Oguni and co-workers. The s l i g h t change i n chemical s h i f t i s w i t h i n the experimental e r r o r o f the procedure, e s p e c i a l l y c o n s i d e r i n g the broad peaks obtained by Oguni. Thus, i t seems reasonable that the two peaks at 70.17 and 70.00 ppm. (peak area r a t i o approximately 58 to 42) i n the spectrum o f HERCLOR H elastomer can a l s o be assigned to i s o t a c t i c and s y n d i o t a c t i c dyads. I the spectrum o f HERCLO to permit measurement o f the r e l a t i v e concentrations o f the various t r i a d s t r u c t u r e s . Thus, to o b t a i n information about the t r i a d s t r u c t u r e s i n p o l y e p i c h l o r o h y d r i n , i t must f i r s t be dechlori n a t e d to poly(propylene o x i d e ) .

75.98

Figure 7. Carbon-13 NMR spectra of (A) HERCLOR H elastomer and (B) the poly (propylene oxide) obtained by dechlorination with LAH

*The r e s o l u t i o n was so good that the 73.65 ppm. peak was p a r t i a l l y r e s o l v e d i n t o two peaks. Thus, i t might be p o s s i b l e to see v a r i a t i o n s due to t r i a d s t r u c t u r e s i n t h i s r e g i o n a l s o .

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

148

POLYETHERS

The assignment o f the 70.17 ppm. peak to i s o t a c t i c dyads i n p o l y e p i c h l o r o h y d r i n was confirmed by observing the spectrum o f c r y s t a l l i n e m a t e r i a l prepared by a published procedure (10). Figure 8 shows the carbon-13 NMR s p e c t r a o f c r y s t a l l i n e poly­ e p i c h l o r o h y d r i n and the poly(propylene oxide) i t y i e l d e d by de­ c h l o r i n a t i o n with LAH. The poly(propylene oxide) was a l s o h i g h l y c r y s t a l l i n e (m.p. 64°C. by DTA) and i t s carbon-13 NMR spectrum corresponds c l o s e l y t o that reported f o r the i s o t a c t i c polymer. Thus, the s i n g l e methylene peak at about 70.2 ppm. i n the spectrum of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n i s due t o i s o t a c t i c dyads. The poor r e s o l u t i o n i n t h i s spectrum i s due t o low s o l u b i l i t y o f the c r y s t a l l i n e polymer i n the benzene s o l v e n t . No t r a c e o f the peaks due t o p o l y e p i c h l o r o h y d r i n are observable i n the s p e c t r a o f the poly(propylene oxide) obtained by d e c h l o r i n a t i o n . In a d d i t i o n , the number o f observable peaks does not increase as a r e s u l t o f the LAH treatment. Thi ation reaction results otherwise a l t e r i n g the s t r u c t u r e o f the polymer.

79.7

70.2

76.04

74.00

Figure 8. Carbon-13 NMR spectra of (A) crys­ talline polyepichlorohydrin and (B) the poly(propylene oxide) obtained by dechlorination with LAH

Summary A procedure has been described f o r the determination o f i r r e g u l a r head-to-head and t a i l - t o - t a i l linkages i n p o l y e p i c h l o r o ­ h y d r i n . This procedure i n v o l v e s d e c h l o r i n a t i o n o f the polymer with l i t h i u m aluminum hydride, cleavage o f the r e s u l t a n t poly­ p r o p y l e n e oxide) with η-butyllithium, and a n a l y s i s by gas chroma­ tography t o determine the r e l a t i v e amounts o f the r e s p e c t i v e dipropylene g l y c o l s .

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

9.

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Polyepichlorohydrin

149

The d e c h l o r i n a t i o n r e a c t i o n was shown to r e s u l t i n smooth replacement o f c h l o r i n e with hydrogen without otherwise a l t e r i n g the s t r u c t u r e o f the polymer. The cleavage r e a c t i o n was shown to be random and the dipropylene g l y c o l s to be e q u a l l y r e s i s t a n t to f u r t h e r degradation. Thus, the r e l a t i v e amounts o f the d i p r i m a r y and disecondary dipropylene g l y c o l s formed are i d e n t i c a l to the number o f head-to-head and t a i l - t o - t a i l u n i t s i n the o r i g i n a l polymer. HERCLOR H e p i c h l o r o h y d r i n elastomer was found by t h i s procedure to have a very uniform s t r u c t u r e with more than 97% h e a d - t o - t a i l monomer placements. This s t r u c t u r e was confirmed by examination o f the carbon-13 NMR s p e c t r a o f HERCLOR H elastomer and o f the poly(propylene oxide) obtained by d e c h l o r i n a t i o n with LAH. Acknow1edgment The author i s deeply indebted to Mr. D. L. Winmill f o r the gas chromatography s t u d i e s ; to Dr. E. J . Vandenberg f o r samples of the dipropylene g l y c o l s and c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n ; to Dr. W. J . Freeman o f the U n i v e r s i t y o f Delaware and Dr. G. A. Ward f o r the carbon-13 NMR s p e c t r a and i n t e r p r e t a t i o n s ; and to Mr R. G. Szewczyk f o r c a r e f u l experimental work. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Madorsky, S. L. and S. Straus, J. Poly. Sci. (1959), 36, 183. Aggarwal, S. L., L. Marker, W. L. K o l l a r , and R. Geroch, Advan. Chem. Ser. (1966), 52, 88. Oguni, N., S. Watanabe, M. Maki, and H. T a n i , Macromolecules (1973), 6 ( 2 ) , 195. P r i c e , C. C. and M. Osgan, J. Amer. Chem. Soc. (1956), 78, 4787. P r i c e , C. C., R. Spector, and A. L. Tumolo, J. Poly. Sci. A-1 (1967), 5, 407. P r i c e , C. C., M. K. Akkapeddi, Β. T. DeBona, and B. C. F u r i e , J. Amer. Chem. Soc. (1972), 94(11), 3964. Vandenberg, E. J., J. Poly. Sci. A-1 (1969), 7, 525. Oguni, Ν., K. Lee, and H. T a n i , Macromolecules (1972), 5(6), 819. Uryu, T., H. Shimazu, and K. Matsuzaki, J. Poly. Sci. Β (1973), 11, 275. Vandenberg, Ε. J., Macromolecular Syntheses (1972), 4, 49.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10 Cationic Polymerization of Cyclic Ethers Initiated by Superacid Esters T A K E O S A E G U S A and S H I R O

KOBAYASHI

Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606, Japan

Introduction Superacids are more a c i d i c than 100% s u l f u r i c a c i d , the most f r e q u e n t l y used strong a c i d solvent (1,2). With t h i s respect f l u o r o s u l f u r i c , c h l o r o s u f u r i c , and t r i f l u o r o m e t h a n e s u l f o n i c a c i d s are f a m i l i a r among superacids (3). 2,4,6-Trinitrobenzenesulfonic a c i d i s a l s o a superacid s i n c e it forms a s t a b l e trialkyl oxonium salt (4). Superacid e s t e r s have long been known, e.g., e t h y l c h l o r o s u l f a t e was prepared more than a century ago (5). However, little a t t e n t i o n has been paid on the r e a c t i o n of superacid e s t e r s (6) until r e c e n t l y A l d e r et al., have reported that methyl and e t h y l f l u o r o s u l f a t e s are very e f f e c t i v e a l k y l a t i n g agents f o r n i t r o g e n and/or oxygen c o n t a i n i n g compounds ( 7 ) . We have found that methyl and e t h y l e s t e r s of f l u o r o s u l f u r i c and c h l o r o s u l f u r i c a c i d s are good initiators f o r the c a t i o n i c ring-opening p o l y m e r i z a t i o n of t e t r a h y d r o f u r a n (THF), oxetane, 2-oxazoline, and propylene oxide (8). At almost the same time Smith and Hubin have reported s e m i - q u a n t i t a t i v e s t u d i e s of the THF p o l y m e r i z a t i o n initiated by superacid d e r i v a t i v e s i n c l u d i n g methyl trifluoro­ methanesulfonate (9,10). Very r e c e n t l y we have performed k i n e t i c s t u d i e s of the ring-opening p o l y m e r i z a t i o n of cyclic ethers initiated with superacid e s t e r s (3,11-14). The e s t e r s employed were e t h y l f l u o r o s u l f a t e (EtOSO F), chlorosulfate (EtOSO Cl), tri­ fluoromethanesulfonate (EtOSO CF , "triflate" EtOTf), and 2,4,6trinitrobenzenesulfonate ( " t r i n i t a t e " EtOTn) ; cyclic ether monomers being THF and 3,3-bis(chloromethyl) oxetane (BCMO). K i n e t i c analyses were c a r r i e d out by means of our "phenoxyl endcapping" method (15,16) as w e l l as of Η and F nmr spectroscopy. These methods allowed the d i r e c t determination of the concentra­ t i o n of the propagating species [P*]. Thus, we have d i s c l o s e d new f i n d i n g s which are c h a r a c t e r i s t i c to the superacid e s t e r initiated systems of the THF and BCMO polymerizations (11,12). The present article d e s c r i b e s these r e s u l t s (3,11,12)· C a t i o n i c ring-opening polymerizations of c y c l i c ethers initiated with t y p i c a l Lewis a c i d c a t a l y s t s (conventional initiators) have 2

2

2

3

1

19

150

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

SAEGUSA

AND

KOBAYASHi

r e c e n t l y been reviewed by us Polymerization of

151

Cyclic Ethers

(15,16).

THF

K i n e t i c s of the THF Polymerization by Phenoxyl End-Capping Method (3). In determining [P*] during the THF p o l y m e r i z a t i o n i n i t i a t e d by superacid e s t e r s the phenoxyl end-capping procedure i s shown i n Scheme 1. The r e a c t i o n of sodium phenoxide with the

Et-E-0(CH ) ^ -0^> 2

4

n

Scheme 1 propagating species and with the unreacted i n i t i a t o r should q u a n t i t a t i v e l y produce the polymer phenyl ether and phenetole, r e s p e c t i v e l y . The quant i t a t ivenes s of the r e a c t i o n between sodium phenoxide and the propagating c y c l i c oxonium has been e s t a b l i s h e d i n the previous s t u d i e s by using Lewis a c i d c a t a l y s t s (17,18). Therefore, the r e a c t i o n s of sodium phonoxide with superacid e s t e r s of EtOS0 F and E t O S 0 C l were examined (Table I ) . From the r e s u l t s shown i n Table I Reaction 1 has been regarded 2

2

as q u a n t i t a t i v e (3). This i n d i c a t e s that the phenoxyl endcapping method can be used f o r the k i n e t i c a n a l y s i s of the THF p o l y m e r i z a t i o n by superacid e s t e r i n i t i a t o r s as i n the case of Et 0+BF^~ i n i t i a t o r system (19). The i n i t i a t i o n r e a c t i o n can be formulated as 3

EtOS0 X 2

+

(2)

On the b a s i s of an S 2 i s given by N

mechanism the r a t e equation of

initiation

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

152 Table I . Reactions of EtOSOJC (X=F and CI) with Sodium Phenoxide a t Room Temperature a

EtOS0 X ^ 2

NaOC H

X

6

b) 5

Reaction Time

Yield

(min)

(%)

(mmol)

(mmol) 0.99

F

4.0

10

96

0.59

F

2.9

30

95

1.15

Cl

3.5

5

93

b) S o l u t i o n i n 6 ml of THF.

a) S o l u t i o n i n 3 ml of THF. c) Based on EtOS0 X. 2

c )

Determined by UV a n a l y s i s .

d[I] dt

Μ [I] [M]

(3)

I n t e g r a t i o n of Equation 3 gave

[ I ]n[I] L 1 J

η

r = ki I [M]dt T

(4)

Λ

t

where

i s the r a t e constant of i n i t i a t i o n . I t has already been e s t a b l i s h e d that the propagation of the c a t i o n i c p o l y m e r i z a t i o n of THF i s expressed by

^y^Tl

> 0 ( C H ) - ( Q · A"

· A"

2

4

(5)

According to a bimolecular mechanism the r a t e equation of propagation i s given by

d[M] dt

= k [P*] f[M] - [H]ej D

(6)

where [M] and [M]e represent the instantaneous and e q u i l i b r i u m monomer c o n c e n t r a t i o n s , r e s p e c t i v e l y , and kp i s the r a t e constant of propagation. I n t e g r a t i o n of Equation 6 leads to

F i g u r e 1 shows the [P*] - time (curve A) and monomer conversion - time (curve B) r e l a t i o n s h i p s i n the THF polymerizat-

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

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KOBAYASHi

153

Cyclic Ethers

i o n i n i t i a t e d by EtOSO F i n C I ^ C l a t 0°C. A f t e r 20 hr, [P*] reached to 63% of the feed c o n c e n t r a t i o n of the i n i t i a t o r . The presence of the i n d u c t i o n p e r i o d (curve B) i n d i c a t e s a slow i n i t i a t i o n followed by a f a s t propagation. P l o t s of Equations 4 and 7 were made on the b a s i s of the data of curves A and B, respectively. In both cases s t r a i g h t l i n e s passing through the o r i g i n were obtained, the slopes of which gave values of k i = 0.33 Χ ΙΟ"- 1/mol-sec and kp = 0.66x10-3 1/mol-sec, r e s p e c t i v e l y . Table I I l i s t s the k i n e t i c data of three superacid ester i n i t i a t o r s as w e l l as of an oxonium species of EtgO+'BF^*". 5

Table I I .

K i n e t i c Data of the THF P o l y m e r i z a t i o n with Ester I n i t i a t o r s i n CH C1 S o l u t i o n 2

Superacid

2

+

a)

Initiation kiXlO

5

at 0°C

0.33

0.38

0.80

6.1

b

)

(l/mol» sec) Δ Η * (kcal/mol)

13.5

12.8

10.5

16.4

AS* (e.u.)

-34

-37

-44

-16

Propagation kpxlO

3

a t 0°C

0.66

1.4

1.7

3.7

(l/mol- sec) Δ Hp^(kcal/mol)

13.0

11.8

11.6

12

A S * (e.u.)

-26

-28

-29

-26

p

a) Taken from (15, 16, 19, 20). b) Data at 2.5°C (20).

B u l l . Chem. Soc. Japan (3).

The i n i t i a t i o n i s a d i p o l e - d i p o l e r e a c t i o n to produce an oxonium i o n (Equation 2 ) . The k^ values of superacid e s t e r s a r e 1/20 - 1/10 of that of Et30+BF~ and a t l e a s t 2 Χ 1 0 times smaller than the kp values i n the superacid e s t e r systems. The a c t i v a t i o n parameters e x h i b i t e d r e l a t i v e l y low Δ Η * ( f a v o r a b l e ) and Δ s£ (unfavorable) v a l u e s . This tendency has o f t e n been observed i n d i p o l e - d i p o l e S^2 r e a c t i o n s producing i o n i c s p e c i e s , e.g., the Menschutkin r e a c t i o n (21) and the oxonium formation r e a c t i o n from superacid e s t e r s and tetrahydropyran (Reaction 8) ( 2 2 ) . 2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

154

R0S0 X 2

+

"0(3

=

R

'

0

S

° 2

X

"

(

8

)

The kp v a l u e of EtOSC^F i s extremely s m a l l , e.g., about 1/6 of that of Et30BF^T i n i t i a t o r . The kp values of EtOSC^Cl and EtOS0 CF3 are between those of EtOSC^F and Et30 BF4~. Since the a c t i v a t i o n parameters of the propagation are very c l o s e to those of Et30 BF4~", i t i s reasonable to conclude that the propagation i n i t i a t e d by EtOSC^X proceeds mainly v i a an oxonium mechanism (Equation 5 ) . +

2

+

K i n e t i c s of the EtOS02CF3-Initiated P o l y m e r i z a t i o n of THF by and i ^ F Nmr Spectroscopy. I t has been pointed out i n s e v e r a l s t u d i e s (3> Jb 12* 23) that i n the THF polymerization.by a supera c i d e s t e r i n i t i a t o r , e.g., EtOSÛ2CF3, the propagating chain end may be i n the e q u i l i b r i u (Equation 9). Our previou Κ 0S0 CF " 2

I

3

=

0(CH ) 0S0 CF 2

4

2

(9)

3

II

p o l y m e r i z a t i o n i n i t i a t e d with superacid e s t e r s could be c a r r i e d out by % nmr spectroscopy alone ( 3 ) . However, i t was very d i f f i c u l t to v e r i f y d i r e c t l y the e q u i l i b r i u m of Equation 9 due to the l i m i t a t i o n of the s e n s i t i b i t y and r e s o l u t i o n of *H nmr spectroscopy. We d i s c l o s e d that l ^ F spectroscopy i s very powerful to abserve d i r e c t r y both the oxonium counteranion OSO2CF3- (I) and e s t e r species CH2OSO2CF3 ( I I ) . 19

F

nmr spectroscopy (11). F i g u r e 2 shows the ^F nmr spectrum of the THF p o l y m e r i z a t i o n system i n i t i a t e d by EtOS0 CF i n CCI4 a f t e r 48 min a t 13°C. The molar r a t i o of THF to i n i t i a t o r was 5 : 1 . Peak A at S -2.52 ( i n ppm r e l a t i v e to the e x t e r n a l standard of CF3CO2H c a p i l l a r y ) i s assigned to the i n i t i a t o r EtOS02CF3. Peak Β at 8 +0.46 i s due to the oxonium counteranion of I (OSO2CF3-) of the propagating s p e c i e s . F i n a l l y , peak C a t S -2.80is reasonably a s c r i b e d to the e s t e r species of I I (~~-CH OS02CF3). No other peaks were detected during a k i n e t i c run. Thus, the l ^ F spectroscopy provides w i t h a new method f o r the d i r e c t determination of the instantaneous concentrations of i n i t i a t o r and the oxonium and e s t e r species of propagation. F i g u r e 3 shows the v a r i a t i o n s of ([0+] + [E]) (curve A) and [ 0 ] (curve B) as a f u n c t i o n of time under the p o l y m e r i z a t i o n c o n d i t i o n s of F i g u r e 2, where [0+] and [E] denote the concentra­ t i o n s of the oxonium (I) and e s t e r (II) s p e c i e s , r e s p e c t i v e l y . At the end of the k i n e t i c run ( a f t e r 76 min) 28% of the charged i n i t i a t o r has been r e a c t e d . The molar r a t i o of [0+] to [E] reached to a constant v a l u e of 46 : 54 a t a l a t t e r stage of 2

2

Μ

+

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3

10.

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AND

155

Cyclic Ethers

KOBAYASHi

p o l y m e r i z a t i o n ( a f t e r about 30 min). This i n d i c a t e s that the e q u i l i b r i u m of Equation 9 i s a c t u a l l y present i n the THF p o l y m e r i z a t i o n i n i t i a t e d with Et0S0 CF3. S i m i l a r l y the THF polymerization was monitored by 19 nmr spectroscopy i n other four s o l v e n t s . In CHC1«, C ^ C ^ * and benzene s o l v e n t s the f r a c t i o n s of [ 0 ] were 85, 89, and 75% a t 0°C, r e s p e c t i v e l y , a f t e r the e q u i l i b r i u m was reached. In n i t r o benzene, however, the [E] f r a c t i o n was very small, e.g., below 2% a t 0°C throughout the p o l y m e r i z a t i o n . Kinetics. Based on the above nmr r e s u l t s the f o l l w i n g r e a c t i o n s w i l l e x p l a i n the course of the THF p o l y m e r i z a t i o n i n i t i a t e d with E t O S 0 C F (EtOTf). Initiation 2

F

+

2

EtOTf

oQ

+

3

—J

Et-0^_J- OTf" =

Et0(CH ) 0Tf

(10)

Propagation

+ ^^0Q-0Tf-

k

+

oQ

P(i)

+ /-^0(CH ) -0Q · 2

4

OtCH^-^OTf

OTf (11)

and

-0(CH ) 0Tf 2

4

+

W)

oQ

—0(CH ) -0Q · 2

4

0(CH ) ^0Tf 2

IXL

- [Ml

[M]

- [M]

l n

2 t

L

rt

=

k

[ p P

e

U

P

)

J

*

(12)

4

The i n t e g r a t e d form of the r a t e equation of propagation expressed as

OTf"

is

] d t

( 1 3 )

0

where kp^ p) i s the apparent r a t e constant of propagation and [P*] represents the t o t a l c o n c e n t r a t i o n of the propagating s p e c i e s , a

e

8

' "

[P*] = [0 ] +

+

[E]

(14)

The e s t e r species (II) i s not dead, but i s thought to be i n h e r e n t l y capable of propagation (Equation 12), s i n c e the e s t e r species EtOTf i n i t i a t e s the THF p o l y m e r i z a t i o n . [P*] was equal to the amount of the reacted i n i t i a t o r . Therefore, the f o l l o w i n g r e l a t i o n s h i p i s derived

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

156

POLY ETHERS

Time ( hr· * Bulletin of the Chemical Society of Japan Figure 1. Polymerization of THF by EtOSO F at 0°C. [P*]-time (curve A) and monomer conversion-time = 4. 8 X CH Cl soluiion (3). x

2

2

A

c -3

II

1 -2

-1

B

I

0(ppmf

1

Macromolecules Figure 2. F nmr spectrum of the THF po­ lymerization mixture by EtOSO^CFs initiator in CCl after 48 min at 13°C (11) 19

h

Time(min)

Macromolecules Figure 3. Polymerization of THF with EtOSO CF monitored by F nmr spectroscopy in CCl at 13°C. Rehtionships of ([0 ] + [E])-time (curve A) and of [0*)-time (curve B): [ M ] o = 5.30 mol/U U] ο = 1.05 mol/l. (11). r

S

19

k

+

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

SAEGUSA

AND

k

157

Cyclic Ethers

KOBAYASHi

p(ap) = p ( i )

* i

k

x

+

k

p(e)

· *

( )

x

15

where k p ( i ) and k p ( ) are the r a t e constants of propagation due r e s p e c t i v e l y to the oxonium i o n (I) a n d e s t e r (II) s p e c i e s , and X i and Xe a r e the molar f r a c t i o n s of [0 ] and [Ε], r e s p e c t i v e l y , i . e . , X i + Xe = 1. I t i s reasonable to assume that the magnitude of k p ( ) i s a t l e a s t smaller than that of k-^ which was about 140-280 times smaller than that of k ( i ) (Tables I I I and IV), i . e . , k p ( i ) » k p ( ) . Furthermore, Xe was not so l a r g e , i . e . , below 0.55 i n a l l cases (Tables I I I and I V ) . Therefore, Equation 15 becomes e

+

e

p

e

kp(ap) Consequently,

~

k p ( i ) · Xi

06)

Equation 13 i s converted to

In

[ML -

2

Ê [M] - [M] t

P V

e

U

0

+

The i n t e g r a t e d values of [P*] i n Equation 13 and [ 0 ] i n Equation 17 were obtained by g r a p h i c a l i n t e g r a t i o n on curves A and Β i n F i g u r e 3, r e s p e c t i v e l y . The monomer conversion was followed by % nmr spectroscopy (3) under the same r e a c t i o n c o n d i t i o n s as F i g u r e 3. Thus, p l o t s of Equations 13 and 17 could be made as shown i n F i g u r e 4 (A) and (Β), whose slopes gave values of kp(ap) = I . 6 X I O - and k p ^ ) = 3 . 6 *10"* 1/mol-sec at 13°C i n C C l ^ . S i m i l a r l y the k^(ap) *d k p ( i ) values were determined at 0 and 25°C (Table I I I ) . I t i s i n t e r e s t i n g to note that the [0 ] f r a c t i o n was not changed a t the r e a c t i o n temperatures 3

3

ai

+

+

Table I I I .

Rate Constants, A c t i v a t i o n Parameters, and the [ 0 ] F r a c t i o n i n the THF P o l y m e r i z a t i o n by E t 0 S 0 C F I n i t i a t o r i n CCI, ) 4 2

3

a

Temp

k

±

X 10

5

k

p(

a

p

)

Χ 10

3

k

p(

i

)

χ 10

3

[0+] Γ &

(°C)

(1/mol-sec)

(1/mol-sec)

(1/mol-sec)

0

0.80

0.84

2.2

45

13

2.1

1.6

3.6

46

25

3.9

3.0

5.7

47

16

13

-12

-24

ΔΗ* 20 (kcal/mol) AS^e.u.) a) b)

_5

(%)°

b

)

η

[M] = 5.30 mol/1, [I] = 1.05 mol/1. ο ο A f t e r the e q u i l i b r i u m was reached. Macromolecules (11).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

158

POLYETHERS

of 0, 13, and 25°C, a f t e r the e q u i l i b r i u m of Equation 9 has been reached. The r e s u l t s of s i m i l a r k i n e t i c s i n other four solvents a r e shown i n Table IV. The k^ values were increased with an i n c r e a s e

+

β

ο

ϋ

Ο

•Η U c0 Ν •Η

ch co oo σ> A

co

CO «4-1

lyme

M

ο

υ

rH

Φ

u 4-1 CJ CM

χ•Η ?Ο

ο CO

Γ*·*

Ο

CM

<Î-

te H P3 ου Ο

Φ 43 u 4-1 CO

β

•Η

η

4-1

α α ω ο > Η

•Η 4-»

Â

00

Ρ-τΗ

Φ

Ν-/

/-s ϋ

+

o

>

_

β

«—' TH

ω

μ

ο

43 4-1 4-1 CO

m

ΓΗ

β

«H

ω

H

β

c0 4J

α

m

te

u ω CM C Ο ο CO

ο 4οJ Φ w 4J

.

Ο

Ο

·

M

33 H

Φ

43

rH

50 β •Η

Ν-/

Φ Ο 43 Φ 4-1 V4

β

o

«4-4 4-1 Ο Χ

CO 4-J CO

co oo

co

CM

Ο

g

43 CM

00

CO ON

CM

co

β

ο

CO CO CO

o

43

CO

ϋ

T3

m

•Η U

φ

Ο

c0

II

υ φ

Ο rH

Γ-.

Φ

eu

42

U

43 •H Φ

CM

4J

β

CO

Φ

co H

II

CO co

Ο

ο oo

ω

4J

c0 4-»

Ο

χ-5 •πι

nd *H

Φ

•Η

Φ

ο

ιΗ

•Η

CO Ο

•H — · . Pu

Φ 43

ϋ

Ο CO

CO U

CO

β

co Ο /"Ν ιΗ Ο ν Φ ω

Ο

φ

.5


Ο CO

CM

rH u

CM

P3 U

Ο 55 m ffi

vD

U

of p o l a r i t y of the mixture. This phenomenon i s very f a m i l i a r with d i p o l e - d i p o l e S 2 r e a c t i o n s to produce i o n i c species such as N

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

SAEGUSA

AND

159

Cyclic Ethers

KOBAYASHI

the Menschutkin r e a c t i o n (21) and Equation 8 (22). In CCI. the v a l u e of k p ( p ) 2.6 times smaller than that of k p ( i ) . In a h i g h l y p o l a r solvent of nitrobenzene, however_, both the k p ( p ) and k p ( i ) values were i d e n t i c a l s i n c e the [0 ] f r a c t i o n was higher than 98% throughout the k i n e t i c run. I t should be noted that the k values i n Table I I correspond to the kp(ap) ^ because the phenoxyl end-capping method gives [P*] as the t o t a l propagating s p e c i e s , i . e . , [ 0 ] + [Ε] « [ P * ] . Therefore, i t i s q u i t e reasonable that both values of kp (Table II) and k ( ) (Table IV) were 1.7 x 10~ 1/mol-sec a t 0*C i n CH C1 . wore i n t e r e s t i n g l y , the k ( i ) values d i d not v a r y so much i n f i v e s o l v e n t s , being i n a narrow range of 2.0 - 4.4x10 1/mol-sec at 0°C, notwithstanding a b i g change of the d i e l e c t r i c constant of the system. The reason may be explained as f o l l o w s The propagating chain-end probabl i . e . , the f r e e i o n ( l a ) r e s p e c t i v e l y . T h i s i s very reasonable s i n c e Sangster and w

a

s

a

a

p

v a

u e s

+

3

p

a p

2

p

+ ~χ-ο(

ι + U

( l a )

oso cF " ir^--o; 2

3

=

0S0 CF 2

3

I b )

(18)

0(CH ) 0S0 CF 2

4

2

3

(II) Worsfold have r e c e n t l y reported that two kinds of the oxonium propagating s p e c i e s , the f r e e i o n and the i o n - p a i r , were i n v o l v e d i n the THF p o l y m e r i z a t i o n i n i t i a t e d by Et30+BF4~. Each of both species e x h i b i t e d a d i f f e r e n t r a t e constant of propagation (24). In Equation 18 the combined c o n c e n t r a t i o n of l a and l b corresponds to the [0+] v a l u e . I t i s l i k e l y , t h e r e f o r e , that the change of the solvent b r i n g s about the v a r i a t i o n not only i n the [ 0 ] / [ E ] r a t i o but a l s o i n the l a / l b r a t i o i n the [ 0 ] f r a c t i o n . In a d d i t i o n the r a t e constants of propagation due to l a and l b may be v a r i e d with the change of the s o l v e n t . The above r e s u l t s are q u i t e compatible with the proposed mechanism (Reactions 10-12). A l l the processes of the THF polymerization by EtOS02CF3 i n i t i a t o r can be given by Scheme 2. In the scheme the i n t e r c o n v e r s i o n between I and I I was a f a s t e r process than propagation, i . e . , the e q u i l i b r i u m of Equation 9 was a t t a i n e d during the p o l y m e r i z a t i o n . The k p ( ) v a l u e was estimated to be very small compared with the k p d ) v a l u e . The e s t e r type species (II) i s not dead, but i s i n h e r e n t l y able to r e a c t w i t h THF to produce oxonium s p e c i e s . In t h i s sense we propose to denote I I as a " s l e e p i n g " s p e c i e s . In the THF p o l y m e r i z a t i o n , the s o - c a l l e d "dormant" species ( I I I ) i s known, which i s produced by a c h a i n t r a n s f e r of the propagating oxonium to polymer a l k y l ether (15, 1£ 25). The a c y c l i c oxonium ( I I I ) i s a l s o not a dead s p e c i e s , and can regenerate a c y c l i c oxonium i o n by the r e a c t i o n w i t h THF. +

+

e

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

160

POLYETHERS

EtOS0 CF,

i — Et-θΓΊ · OTf" oG ^

Et0(CH ) 0Tf

k

9

2

3

2

4

k

p(ei

MO E t O ( C H ) - 0 ^ ] · OTf" 2

Et-t

4

2

4

2

OG

P(0

Et-tO(CH ) -^-oQ · Ο Τ Γ = : 2

-a

0(CH ) ^- 0Tf

4

y^2

P

1

Et-t0(CH ) ^0Tf 2

— 0 ( C H

2

)

4

4

0

III f!

However, I I I should be distingushed from a " s l e e p i n g s p e c i e s ( I I ) i n a sense that I I can awake i n t o a c y c l i c oxonium i o n of the propagating species (I) not only by the intermolecular r e a c t i o n with THF but a l s o by the intramolecular c y c l i z a t i o n of the socalled back-biting reaction. E f f e c t s of the counteranion on r a t e constants of propagation (kp(£))(13^It i s worth while to mention the e f f e c t of the counter­ anion on k p ( i ) i n the THF polymerization. There a r e s e v e r a l data a v a i l a b l e u n t i l now. Table V l i s t s the r a t e constants of propagation due to the oxonium species ( k p ( i ) ) by v a r i o u s i n i t i ­ a t o r s , a l l of which were r e c e n t l y determined i n our l a b o r a t o r y . I t was once thought that the value of kp(^) was not changed depending on the nature of the counteranion (23, 26). However, the kp(-Q values i n Table IV c l e a r l y i n d i c a t e that a wide v a r i e t y of counteranions brings about the change of the k p ( i ) value s i g n i f i c a n t l y . Such change i n kp(-Q values i s probably due to the change of the f r a c t i o n of f r e e ions and i o n - p a i r s i n the propagating s p e c i e s . Polymerization of BCMO (12) K i n e t i c s of the EtOSO^CF^-Initiated Polymerization of BCMO. The p o l y m e r i z a t i o n was monitored by % nmr spectroscopy. Figure 5 shows an example of the ^H nmr spectrum of the r e a c t i o n system. The molar feed r a t i o of BCMO to E t 0 S 0 C F was 6 : 1 . Figure 5 shows a -^H nmr spectrum a t a r e a c t i o n time of 180 min a t 63°C i n 2

3

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

SAEGUSA

AND

Table V.

161

Cyclic Ethers

KOBAYASHi

Rate Constants of Propagation I n i t i a t o r s a t 0°C k

Initiator

P ( i )

( k ( i ) ) by Various p

Xl()3

Method

e

&

Réf.

EtOS0 F

0.8

C

e

3

EtOS0 Cl

1.5

C

e

3

2

2

EtOS0 CF 2

2.0

3

C

EtOTn >

3.7

+

Et30 BF4~

4.I

b

4.6

d

7.8

d

3

BF -ECH ) 3

c

C

b

BF -ECH )

3, 11

e, f

0.70

a

e

e

13

g

19

g

18

g

18

g

18

b

SnCl4-ECH ) AlEtCl a) b) c) d) f)

2

Ethyl 2,4,6-trinitrobenzenesulfonate. ECH : e p i e h l o r o h y d r i n as a promotor. S o l u t i o n p o l y m e r i z a t i o n i n CH^C^. Bulk p o l y m e r i z a t i o n . e) By % nmr spectroscopy. By l ^ F nmr spectroscopy, g) By phenoxyl end-capping method.

CH C1

CH G1

0

EtOCH CCH OS0 CF 2

2

CH C1 2

IV

CH C1

9

l 2

2

3

9

, 2

ι i

EttOCHgGCHg^jOCHgÇCHgOSOgCFg CH C1

CH C1

2

V

2

(rè"2)

nitrobenzene s o l v e n t . C h a r a c t e r i s t i c peaks a t e ( S 4.80) and A ( S 4.83), which a r e assigned to o(-methylene protons (2H) o f -OSC^CF^ group i n e s t e r type species IV and V, r e s p e c t i v e l y . Other peaks assignments may be found i n F i g u r e 5. These r e s u l t s i n d i c a t e that the propagating species of the BCMD p o l y m e r i z a t i o n i s e s t e r type species given by IV and V. An a u t h e n t i c compound o f IV was prepared by the r e a c t i o n of EtOSOoCF^ with BCMO and i s o l a t e d by d i s t i l l a t i o n i n vacuo, bp, 45-46*0 10.04 mmHg). The chemical s h i f t of the methylene protons
1

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

162

POLYETHERS

The f o l l o w i n g scheme of r e a c t i o n s w i l l e x p l a i n the course of the BCMO p o l y m e r i z a t i o n . Initiation

EtOTf

+ 0

Cx

CH C1

CH C1

2

CH C1 2

2

"-°0< CH C1

slow

•OTf

2

VI CH C1 2

- Et0CH CCH 0Tf fast •ι CH C1 o

(19)

o

2

IV

{P*)

Propagation

CH C1 0

CH G1

Pi

CH C1

slow

2

EtOCH„CCH OTf 2| 2 CH C1 0

2

2

CH C1 2

Et0CH,CCH -

CH C1 2

o

CHgCl

CH C1

CH C1 2

OTf

fast

2

EtfOCHgCCH^OTf

(20)

CH C1 £

VII

VIII (P *) 2

Generally

^2^

ys. Qj^ ς-]

E«0CH ÇCH }- 0Tf 2

2

n

+

°ÇX

rH

QHpCl

κ

2

EtWcH^.OTf

IX (Pn*)

χ

( P n + 1

(21 )

*,

In the above r e a c t i o n s , 19-21, oxonium species V I , and V I I may be Involved as intermediates. However, these intermediates a r e not s t a b l e under r e a c t i o n c o n d i t i o n s and rearrange very r a p i d l y to the s t a b l e e s t e r s p e c i e s IV and V I I I , r e s p e c t i v e l y . The r a t e constant of i n i t i a t i o n (k^) was obtained by Equation 4. A f t e r the complete r e a c t i o n of i n i t i a t o r , the consumption r a t e of the f i r s t propagating species P^* i s given by

d[Pl*] ^ — "

k

P1

[Pl*][M]

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

(22)

10.

SAEGUSA

AND

Cyclic Ethers

KOBAYASHi

163

where k ^ i s the r a t e constant of the f i r s t propagation. f o r e , kp^ was c a l c u l a t e d according to

There­

p

In

! !_ = [Pi*]t

Γ

k

μ ι

2

Λ

1

[ ]dt

(23)

M

Ί

where the value of [ P i * ] t / [ P ^ * ] t was obtained by the i n t e g r a t i o n of peaks A j and A . In the above scheme, IV i s the smallest propagating s p e c i e s . Therefore, k i n e t i c s of the p o l y m e r i z a t i o n by IV as an i n i t i a t o r was a l s o c a r r i e d out a t elevated temperatures. In t h i s case, the r a t e of p o l y m e r i z a t i o n by IV i s given by 1

2

n

-

k

=

4f-

The t o t a l amount of [Pi*] and [ P * ] was found to be equal to the i n i t i a l c o n c e n t r a t i o n of IV throughout the k i n e t i c run, i . e . , [Pi*] + [P *]nè2 = [ I V ] On the assumption that k = k = =k i n t e g r a t i o n of Equation 24 gives n

n

0

p 2

[M]t, , n

r

^"S

t P l

t

*

] d t

r

9

+

p 3

?n

t

9

v^ "* [p

ldt

(25)

therefore

l n - ^ L [M]t

- k , f [P*]dt = k J t ! t 2

p

2

P

1

1

P

i' [P *]dt " t z

p

n

J

t

(26)

n

1

At 128°C i n nitrobenzene a l i n e a r p l o t of Equation 23 gave a value of k ^ = 1 . 8 1 0 * 1/mol-sec. Then, a p l o t of Equation 26 was made (Figure 6), which i s c o n s i s t of two s t r a i g h t l i n e s , A and B, of d i f f e r e n t slopes. The p l o t i n Figure 6 i s taken to i n d i c a t e kp > kpq— k ^. The s t r a i g h t l i n e A was u t i l i z e d to c a l c u l a t e k p s i n c e i t s period corresponds to the stage of the monomer consumpt i o n of the second to t h i r d propagation step. Thus, k was obtained as kp =5.7X 10"" l/mol«sec a t 128°C. From the slope of l i n e Β the r a t e constant was obtained as k =k ^=k n=2.5 χ 1 0 ~ l/mol*sec a t 128°C. At a higher temperature of 137°C k was found to be constant from n=3 to a t l e a s t n=5. These r e s u l t s a r e summarized i n Table VI. x

p

2

p

2

p 2

5

2

5

p3

p

D

p n

Reaction Mechanism. The above data are q u i t e compatible with the r e a c t i o n mechanism of 19-21. The e s t e r type propagating species were a c t u a l l y observed d i r e c t l y by nmr spectroscopy during the k i n e t i c run. In a d d i t i o n , the f i r s t propagating species IV

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

164

POLYETHERS

Macromolecules Figure 4. Plots of Equation 13 (A) and of Equation 17 (B) in the THF polymerization by EtOS0 CF in CCl at 13°C: [Αί] ο = 5.30 mol/l., [I]ο = 1.05 mol/l, [M]e = 2.3mol/l. (11) 2

3

h

Ô^ïj G E

F Π

Β

Cf^lJ F

F Π

X

Α RΛ χ

η

Επδ2)

c

H

2 Ρ

^ Γ.

CD

Bulletin of the Chemical Society of Japan Figure 5. H nmr spectrum of BCMO polymerization mixture by EtOS0 CF in nitrobenzene after 180 min at63°C (12) 1

2

3

-^J f[Pn]dt-10"

3

t

(molsec/i )

Bulletin of the Chemical Society of Japan Figure 6. Plots of Equation 25 in BCMO polymeriza­ tion initiated by IV in nitrobenzene at 128°C: [ M ] o = 3,5 mol/l, [IV] ο = 0.45 mol/l (12)

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

SAEGUSA

AND

Table VI.

Cyclic Ethers

KOBAYASHi

165

Rate Constants and A c t i v a t i o n Parameters i n the BCMG P o l y m e r i z a t i o n i n Nitrobenzene ) a

Temp.

kiXlO

(°C) 90

b

119

c

^χιο

3

(1/mol sec) 4.2

k

1 0 5

P n

xio

5

(1/mol·sec)

(Ι/mol·sec)

10

3.5

1.5

18

5.7

2.5

17

6.0

2.8

~30

8.0

4.0

d

3.7

c

137° ΛΗ*

V<

(1/mol ·sec)

128° 128

5

12.5

(kcal/mol) -36 (e. a)

-45

-46

-45

u.) [M] =3.50-3.90mo 1/1, 0

b) E t O S 0 C F 2

c) IV as an

3

[I] -0.37-0.56 mol/1. o

initiator. initiator.

d) Extrapolated value.

B u l l . Chem. Soc. Japan

(12).

was i s o l a t e d by vacuum d i s t i l l a t i o n , which induced the BGtO p o l y ­ m e r i z a t i o n d i r e c t l y from the f i r s t propagation. I t i s an important f i n d i n g s that the r a t e of propagation v a r i e d depending on the degree of p o l y m e r i z a t i o n , i . e . , kp-> kp2>kp3=*kp ( ώ 3 ) . These values were s u c c e s s f u l l y determined s i n c e ?χ* and P * (n£2) were d i r e c t l y observed by nmr spectroscopy. The d i f f e r e n c e i n kp i s due to d i f f e r e n t e l e c t r o p h i l i c r e a c t i v i t y of a l k y l groups toward BCMO monomer when n=l, 2, and £3 i n V. The b u l k i e r the a l k y l chain the l e s s the r e a c t i v i t y bacame. A c t i v a t i o n parameters (Table VI) a l s o support the mechanism 19-21. They are c h a r a c t e r i z e d by a general f e a t u r e of a c t i v a t i o n parameters of S 2 r e a c t i o n between two n e u t r a l molecules to produce an i o n i c s p e c i e s , i . e . , combination of low Δ Η ^ v a l u e (favorable f o r r a t e ) and low Δ value (unfavorable) i s seen i n every process. T h i s tendency i s already noted i n Reaction 8. The magnitude of k ^ i s about one-hundredth of that of k^. The small k ^ v a l u e i s a s c r i b e d to the lower AS* v a l u e ; Δ Η ^ being the same i n both cases. The r a t e d i f f e r e n c e between i n i t i a t i o n and the f i r s t propagation i s due to the d i f f e r e n t r e a c t i v i t y between CH^CH^- and EtOCH C(CH C1) CH - groups attached to -OSO^CF^. A s i m i l a r r e s u l t was reported by Buncel and n

p

p

2

2

2

2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

166

MLllington (27) i n the h y d r o l y s i s of primary a l k y l c h l o r o s u l f a t e s (XI) i n 85.3% aq. dioxane, i n which the r a t e of e t h y l group (XIa) R0S0 C1 2

(XIa)

R=CH CH

(Xlb)

R=(CH ) CCH

3

3

2

3

2

2 was

4.2x10 times as high as that o f neopentyl group (Xlb) . The t r a n s i t i o n s t a t e of the BCMO polymerization by E t O S 0 C F i s probably formulated as X I I , i n which two n e u t r a l molecules of 2

0

C F

r* w

R

c

3f°--" c~-- \/< c

. CH'jjCl

0

C H

Η

Η

XII

3

R=CH.

or

2

C 1

-0CH C o

-

CH C1 2

e s t e r species ( e l e c t r o p h i l e ) and BCMO monomer (nucleophile) a r e p o l a r i z e d . I t i s g e n e r a l l y accepted that the polymerization of oxetanes i n i t i a t e d by t y p i c a l Lewis a c i d s proceeds v i a an S^2 r e a c t i o n between the propagating oxonium and monomer (16, 2 5 ) . In t h i s case the t r a n s i t i o n s t a t e i s given by XEII.

, · A" Η

Η XIII

The mechanistic d i f f e r e n c e o f these two cases i s w e l l recognized by the observation that the t r a n s i t i o n s t a t e XII d i f f e r s much from X I I I s i n c e going from the i n i t i a l to t r a n s i t i o n s t a t e the charge i s developed a t XII whereas i t i s despersed a t X I I I . This was f u r t h e r supported by the examination of the solvent e f f e c t on the r a t e of BCMO p o l y m e r i z a t i o n (12). Conclusion New f i n d i n g s s p e c i f i c to the THF and BCMO polymerizations i n i t i a t e d by superacid e s t e r s are d e s c r i b e d . I n the THF p o l y m e r i z a t i o n the oxonium (I) and e s t e r (II) species of the propagating end were involved i n e q u i l i b r a t i o n , which were d i r e c t ­ l y observed by nmr spectroscopy. Thus, k ( a p ) and k p ( i ) were separately determined, i n which the c o n t r i b u t i o n of the propagation due t o the ester species (II) was estimated to be very small. In the BCMO polymerization, however, the e s t e r species (IV and V) were a c t u a l l y the propagating chain-ends. This provides p

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10.

SAEGUSA A N D

KOBAYASHi

Cyclic

Ethers

167

a new concept of the mechanism i n the c a t i o n i c ring-opening p o l y ­ m e r i z a t i o n of c y c l i c ethers, i . e . , the polymerization v i a the ester type (covalent) propagating s p e c i e s . The other examples of the covalent propagating species ever known a r e seen i n the p o l y m e r i z a t i o n of c y c l i c imino ethers ; a l k y l i o d i d e s being the s t a b l e propagating species (28). "Literature Cited" 1. 2.

G i l l e s p i e , R. J., Accounts Chem. Res. (1968) 1, 202. G i l l e s p i e , R. J., P e e l , Τ. Ε., Adv. Phys. Org. Chem. (1971)

3.

Kobayashi, S., Danda, Η., Saegusa, T., Bull. Chem. Soc. Japan (1973) 46, 3214. P e t t i t t , D. J., Helmkamp G. K., J. Org Chem (1964) 29, 2702. M u l l e r , M., Ber. (1873 Kobayashi, S., Yuki Gosei Kagaku Kyokai S h i (J. Syn. Org. Chem. Japan) (1973) 31, 935. Ahmed, M. G., A l d e r , R. W., James, G. H., Sinnott, M. L., Whiting, M. C., Chem. Commun. (1968) 1533. Saegusa, T., Kobayashi, S., Presented a t the 21st Annual Meeting of the Society of Polymer Science, Japan, May 1972. Smith, S., Hubin, A. J., "Polymer P r e p r i n t " (1972) 13, 66. Smith, S., Hubin, A. J., J. Macromol. Sci. Chem. (1973) A7, 1399. Kobayashi, S., Danda, Η., Saegusa, T., Macromolecules (1974) 415. Kobayashi, S., Danda, Η., Saegusa, T., Bull. Chem. Soc. Japan (1974) 47. (No. 11), in press. Kobayashi, S., Nakagawa, T., Danda, Η., Saegusa, T. B u l l . Chem. Soc. Japan, submitted. Kobayashi, S., Morikawa, Κ., Saegusa, T., to be reported. Saegusa, T., J. Macromol. Sci. Chem. (1972) A6, 997. Saegusa, T., Kobayashi, S., Prog. Polymer Sci. Japan (1973) 6, 107. Saegusa, T., Matsumoto, S., J. Polymer Sci. Part A-1 (1968) 6, 1559. Saegusa, T., Matsumoto, S., Macromolecules (1968) 1, 442. Saegusa, T., Matsumoto, S., J. Macromol. Sci. Chem. (1970) A4, 873. Saegusa, T., Kimura, Y., Fujii, Η., Kobayashi, S., Macromolecules (1973) 6, 657. Wiberg, Κ., " P h y s i c a l Organic Chemistry", p.379, John-Wiley & Sons, Inc., New York, 1966. Kobayashi, S., Ashida, T., Saegusa, T., Bull. Chem. Soc. Japan (1974) 47, 1233. Matyjaszewski, K., Kubisa, P., Penczek, S., Presented a t the I n t e r n a t i o n a l Symposium on C a t i o n i c Polymerization, September, 1973, Rouen, France.

9, 1.

4. 5. 6. 7. 8. 9. 10. 11. 7, 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

168

POLYETHERS

24. Sangster, J. Μ., Worsfold, D. J., Macromolecules (1972) 5, 229. 25. Dreyfuss, P., Dreyfuss, M. P., "Ring-Opening P o l y m e r i z a t i o n " F r i s c h , K. C., Reegen, S. L., Eds., Chapter 2, Marcel Dekker, New York, 1969. 26. Dreyfuss, P., Dreyfuss, M. P., Adv. Chem. Ser. (1969) 91, 335. 27. Bunsel, Ε., M i l l i n g t o n , J. P., Can. J. Chem. (1965) 43, 556. 28. Saegusa, T., Makromol. Chem. (1974) 175, 1199.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

11 Brominated Poly(Phenylene Oxide)s. I. Polymerization of Mono-, Di- and Tribromo-2,6-Dimethylphenol D W A I N M . W H I T E and H O W A R D J. K L O P F E R General Electric Research and Development Center, Schenectady, Ν. Y. 12301

The i n t r o d u c t i o n of the backbone o f poly(phenylene oxide)s i s o f i n t e r e s t because of the e f f e c t s the halogen can have on the flammability and on the s o l u t i o n and thermal p r o p e r t i e s o f the polymer. T h i s paper d e s c r i b e s poly(2,6-dimethyl-1,4-phenylene oxide)s which c o n t a i n monobromo and dibromo repeating u n i t s and have bromine contents ranging from approximately 5 t o over 50 wt. %. The general approach f o r the i n t r o d u c t i o n o f t h e bromine was via synthesis o f polymers utilizing di- and tribromophenols as monomers and comonomers. A second method, the d i r e c t bromination o f p o l y (­ phenylene oxide)s i n s o l u t i o n , and the p r o p e r t i e s o f the brominated polymers are described i n the f o l l o w i n g paper. Polymerization o f 3,4-dibromo-2,5-dimethylphenol (I) pro­ vided a route t o polymer in which the bromine was only on the aromatic r i n g s and not on the methyl groups ( r e a c t i o n 1 ) . The r e a c t i o n was found t o proceed under c o n d i t i o n s similar t o the r e a c t i o n described by S t a f f i n and Price f o r the p o l y m e r i z a t i o n of 4-bromo-2,6-dimethylphenol, I I I ( r e a c t i o n 2). Poly(3-bromo1

169

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

170 2,6-dimethyl-1,4-phenylene oxide), II, was formed in quantitative yield and with high molecular weight (intrinsic viscosities in chloroform

were

as

high

as

0.91

dl/g

and

correspond

to

molecular

weights up to M ca. 1.5 x 10 ). H nmr and elemental analyses 5

n

1

confirmed the presence of one bromine atom per repeating unit. The nmr analyses (both H nmr and C nmr) also showed that the 1

13

displacement of bromine had only occurred at C-4, i.e., the repeating unit was indeed the moiety shown in structure II. The infrared spectrum of the polymer was consistent with structure II except in one respect. In addition to a weak hydroxyl absorption at the normal end group frequency for unbrominated polymer (3610 cm in CS ), there was a slightly weaker absorption at -1

2

3525 cm . Both absorptions were more intense in lower molecular -1

weight polymers and absent in acetylated samples. One characteristic of 2,6-disubstituted polyphenylene oxides is the tendency to redistribute with phenols when heated in the presence of an initiator. The polymers are converted to low 2-4

molecular weight oligomers terminated at the non-phenolic end of the molecule with the aryl ether derived from the phenol. The application of this redistribution reaction to II (reaction 3) is

II summarized of

the

and a

the

Table

initiator

either

cited as

in

x

in

Table

yields

with

unbrominated

,

or

I)

low

With

polymer,

VII

at

normally yields II

were

8 0 °

(the

causes

of

milder

sate

for

caused

by

molecular The

chlorobenzene the

extensive

rates

high

II

phenolic

end

group

Possibly

the

3525

of

end

group

at

at

8 0 ° , more

1 3 0 ° ) may

atom.

polymer

indicate in

is

Even at

TPDQ,

in

less

When p o l y m e r i z a t i o n

a

for

reaction

(1)

which

corresponded to

molecular

basis

of

elemental

intractable

unbrominated

polymer

under

arise

forcing

weight and from

of

group

reaction.

proceed The to

represent

at

terminal proceed.

a

second

type

redistribution. applied

intractable

analysis

products

was

compenend

lower

amount

polymer.

toward

IV,

low

an

the

redistribution

reactive

4-chloroto

phenolic

only

and,

contrast,

conditions and

reactions

may

in

needed

the

moderate

group

bromo-2,6-dimethylphenol,

Similar

1 3 0 ° ,

unbrominated

required

been

of

redistribution

cm~^ h y d r o x y l is

(TMDQ)

conditions

Since,

forcing

have

potential

underwent

that

than

which

y i e l d ,

combination

redistribution

recovered polymer.

oxidation

bromine

weight

results

slower

higher

the

the

reaction

,

in

—

,

(3,3*,5,5 -tetraphenyl-4,4'-diphenoquinone, phenol

1/2,3

3 , 3 » , 5 , 5 - t e t r a m e t h y l - 4 , 4 - d i p h e n o q u i n o n e

phenol

result,

I.

=

to

product

3,4,5-triwas

homopolymer

infrared

the

spectrum.

exhaustive

conditions

produced

V on

(see

bromination the

of

following

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

11.

WHITE

Motio-, Di-, and

AND KLOPFER

Tribromo-2,6-Dimethylphenol

TABLE Redistribution [η]

of

of

171

I Phenols with

II Yield

I n i t i a l

(dl/g)

Initiator

0.35

TMDQ

0.35

TPDQ

Temperature

Phenol

p-chloro-

Polymer

80

75

130

55

80

86

VII

of

Recovered

Reaction

Polymer

(%)

phenol 0.91

TMDQ

0.91

TPD

paper). zation 2:1.

phenol

Soluble products of

IV

The

dibromo-

I

products and

repeating

the

with

random

even were

structure a

copolymers because

than

did

or

Phenols was

possible

bear (a

I

however, a

I

and by

VI.

ratio

The

random copolymer

unsuccessful either

obtained, the

however, of

copolymers which

were

VII,

were when

IV

to

by I

from III

1

contained

similarity

nmr

either

I

or

polymerized

as

the

IV

VI

Attempts with

a

as

oxide

spectrum o f

at

high

3,4was to

monomer

much

faster

III rate

IV.

IV

were

the to

C

structure.^

copolymerized with

employing oxidative

since

3

copolymeri-

was

3-bromo-2,6-dimethyl-l,4-phenylene

units,

consistent prepare

with

conditions

the

oxidative

cuprous halide/amine

catalyst;

2,6-dimethylphenpl

coupling

for

conditions.

polymerization

of

coupling conditions reaction

4).6-8

I for

This and

IV

VII

Polymerization

catalyst n

H O - O ^

+

n/2

0

t

2

H

^

-

VII of

of

^

H

+

H 0 2

(4)

VIII

4-bromo-2,6-dimethylphenol

quantity

^

a

base

and

a

requires

catalytic

at

amount

least

a

of

oxidizing

an

stoichiometric

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

agent.*

172

POLYETHERS

We found that when using the c a t a l y s t system f o r r e a c t i o n (4), the amine ( i n s u f f i c i e n t excess) functioned as base and the copper/amine complex functioned as i n i t i a t o r f o r r e a c t i o n (1) as w e l l as c a t a l y z i n g o x i d a t i v e c o u p l i n g . T h i s r e s u l t d i f f e r s from the r e p o r t by Blanchard and coworkers^ i n which r e a c t i o n (2) could not be i n i t i a t e d by a copper/amine ( p y r i d i n e ) c a t a l y s t . The suggested route f o r r e a c t i o n i s s i m i l a r to the proposed route f o r r e a c t i o n ( 2 ) and i n v o l v e s coupling between a phenoxy r a d i c a l and a monomer anion: 1

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

11.

WHITE

Additional

steps

redistribution leading

1

they y

were

are 0,

reactions

).

onto

rings

XII.

been

Copolymer with

lead

for dl/g;

II

serving

(a s a m p l e with

o f the product

structure

f o r the product.

did II

range

not redistribute I

shows II

VIII from

not arise

notoccur

χa n d

to the product

o f polymer

does

H nmr

and that

was XI where

T h ep r o d u c t

l i t t l e

prepared with

under

from

VII

the direct

o f a second until

that

mild

IV and

bromine

almost

a l l o f the

can be viewed

a mixture

f o r VII

o f I

and

andi n i t i a t o r

2,6-dimethylphenol.

Thephysical

(intrinsic

under

during

Since

i t

the mild

equilibration

methylene

with

stopper

chloride

suggested a block i s likely conditions with

that o f

monomer

as a monofunctional

co-equilibrate as a chain

viscosities as high

the other

by structure

XIII.

I.

phenol

a s0 . 6 8 complex-

copolymer

polymer

II

polymerization

even

a t8 0 ° ) ,

component oligomers.

f o r reaction

VII f o r

wasused a s a

nmre f f e c t s )

can be represented

from

[ η ]0.35 dl/g)

was f u n c t i o n i n g

not readily

product

random c o p o l y m e r s .

structure

as oxidant

o f VIII

no long

(Table

extensive

monobrominated.

no f r a c t i o n a t i o n

polymer

does

eventually

and V I I ,

copolymers d i d form,

the introduction

unit

a t i o n ; H did

I

t h e normal

anion

XI was i d e n t i c a l

product

since

copolymerization

properties

produce

paper).

XI wasa l s o

dioxide

Polymer

monomers

bromination

This

o f VIII

involve

of halide

the general

Polymer

a repeating

have

would

the direct

structure

atom

With

( s e ef o l l o w i n g

bromination

sequence

andloss

0

suggested that

(i.e.,

2

from

conditions

1

polymers.

random 1,

resulted had

i n the reaction

C nmr s p e c t r a

3

173

3

reactions

to high

crosscoupling and

Μ οπό-, Di-, and Tribromo-2 6-Dimethylphenol

A N D KLOPFER

which Polymer

(4) a n d t h e

Colorless,

XIII

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

hazy

POLYETHERS

174 films

resulted

composed With

of

after

equal

an i n i t i a l

product

were

The Table were

solution

molar

2:1

ratio

of

Both

found

VII

of

of

to

short

type

C H OBr 8

w h i c h was

of

repeating

units,

7

on both

the bromopolymers

Chemical

and longer

range

the aryl

and methyl

protons.

Shifts

films

of

unit. the

ο

i n

Υ

of

in

bromine

the Polymer

Ζ

Segment

Ζ

_ 0 . ο - ^ . ο - ^ - ο - ^ Α

Α Chemical

Polymer Br

summarized

effects

II

f o r Protons

Υ

^

are

range

TABLE

Structure

a polymer

each

homogeneous. nmr s p e c t r a o f

II.

casting

quantities

Aryl

VIII

None

II

Y,Z

XI

Y

Η with

m-H

Location

Shift

a

( δ )

Methyl

Η with

an

o-Br

o-H

m-Br

2.08

6.50 6.07 6.40

6.12

2.00

2.32

2.08

2.35

(3

& 4)

2.02 (1 XII

A,Y

2)

6.42(4)

2.07(4)

2.30(1)

6.30(3)

1.93(3)

2.23(2)

1.98

2.20

6.02(4)

Α , Υ , Ζ

VI

&

5.83(3) (a)

Number

i n parenthesis

methyl

i s

When the

same

an aromatic ring,

additional ring

the

proton

ring

was o r i e n t e d

t h e r e s o n a n c e was s h i f t e d

upfield

shift

shielded an aryl

bromine.

specifies

on which

the Η or

located.

The e f f e c t

was n o t e d

proton

when

meta

a bromine

on the adjacent

was p r o n o u n c e d

to

upfield

(ranging

a bromine 0.4

ppm.

atom

1

2

i n An

i n one

ring

ortho

from

0.1

to

to

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

the

0 . 3 ppm)

11.

in

WHITE

polymers

bromine

containing

atoms

on

adjacent

ring

long

short

and

proton

at

relative

The

methyl

The bromines the

ppm) in

of

and

adjacent

accounted

The in

3

were

para

for

the

two

an

when

relative

samples

was

the

VI

the

two

above both

peak

shifted

the

the

for

the

upfield

0.7

VIII. in

several

(0.1

ppm)

rings.

ortho

pronounced u p f i e l d

allowed

occurred

in

of

polymer

II)

upfield

methyl

one

directly

p o s s i b l e and

(Table

dibrominated an

lie

For

affected

shifted

since

to

175

In

methyl

upfield

methyl

ways by

addition,

downfield

(<0.1

peaks

by

bromine.

shielding a

(0.2

ppm) .

bromine to

This

between

2.0

0.3

latter

and

2.1

ppm

XI. shift

estimation

copolymers VI

The

were

proton

shifted a

unit had

effects.

ring

aryl

were

shifted

always

effects

Β on

protons

ring

polymer

ring

steric

the

peaks

same

effect

to

range

methyl

dibromo

ring

due

to

the

each

location

ppm

in

Mono-, Di-, and Tribromo-2,6-Dimethylphenol

AND KLOPFER

and

the

of

of

the

the

dibrominated

distribution

of

adjacent

repeating

units

peaks

a l l

XI

dibrom

intensities

indicated

a

of

shifted

random

and

unshifted

for

distribution.

Acknowledgements The

authors

technical

would

like

to

thank

Mrs.

C.

E.

Billington

for

assistance.

Experimental All

v i s c o s i t i e s were

mono-,

d i -

direct

bromination

the

and

polymers

data

are

were

Preparation m)

ously

stirred

phenol

was

(I)

solution phere.

was off,

Torr.

0.91 m

T

c

r

The in

an

tion an the

170

were

s

of

0.01

a

over in

the

intrinsic

a

g

at

(100%

by

manner.

500

Tg

292°;

of

mixtures

one

ferricyanide

was

synthesis of

block

no

0.35

and a

layer then

was

with

dried

of

The

once.

at The

the

2%

and

The

polymer

hours

at

was

2 5 °

and

viscosity: indicative

of

calorimetry.

4-bromophenols

added (see

separated

20

scanning

aq.

atmos­

water.

transitions

of

copolymers

g,

vigor­

150 ml

Intrinsic

instance d l / g .

(0.329 a

nitrogen

methanol.

and

differential

to

3,4-dibromo-2,6-dimethyl­

yield).

In

viscosity of

ml

of

nmr

TMS).

period

benzene

benzene

to

the

analyses

ferricyanide

2 5 ° under and

The

by

structures?

vs.

minute

of

2 5 ° .

Elemental

CDCI3

ml

methanol,

2 5 ° ) .

noted

27

at

prepared

suggested

in

150

the

copolymerizations I,

(run

solution

m)

dropwise 2.0

at

were

1 3

Aqueous potassium

washed w i t h

identical of

II.

II

minutes,

added

(CHCI3 y

chloroform

the

hydrochloric acid

Weight:

dl/g

or

g,

10%

solution

T

of

Table

mixture

After

filtered 12

in

with

potassium hydroxide

washed w i t h

in

2,6-dimethylphenol.

added dropwise

(2.80 of

of

consistent

reported

0.001

measured

tribromodimethylphenols

were

run

homopolymerizaThe

polymer

polymer

was

useful

below).

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

had for

POLYETHERS

176 Copolymerization 0.04

m)

and

stirred

I

of

g,

(Vibromixer)

(0.072

0.0005

g,

benzene

at

2 5 °

temperature minutes,

washed w i t h Intrinsic

and m)

to

I.

in

water

3 8 . 5 ° ,

and

solution

spectrum

poly(phenylene

to

and

form

a

units

10

to

Weight: The

clear,

elemental

oxide)

0.02

was

6.54

g

50

ml

120

methanol

(96%

cast

flexible a

conoff,

yield).

c o u l d be

indicated

a

the

filtered

transparent

analysis

to

in

After

ml

g,

to

bromide m)

minutes,

750

polymer

(4.88

added

cuprous g,

The polymer

d l / g .

VII

was

decreased.

dropwise

dried.

0.51

of

After

slowly

added

of

benzene

(2.58

bath).

then

was

solution

ml

solution

hydrochloric acid. methanol

A 50

dibutylamine

(stirred

viscosity:

chloroform nmr

and

solution

5 ml

VII

0.01

oxygenated

m)

rose

the

taining

The

(2.80

4:1

from

film.

ratio

poly(monobromophenylene

of

oxide)

units. A of

similar

VII

and

centration tion

was

(0.0144

g,

was

g

cast

film

(94%

The from

a

g,

the

be

(1.40

of

from

Dioxide

stirred

at

2 5 ° .

After

F i l t e r

form

With 83%

yield

yield hot

in

a 9:1

and this

benzene

to

was used

20 55

g

adding 2.6

to

g

the

4:1

ratio

formed

of a

c a s e was remove

VII

to

and

prepare high

a

block

isolated

of

dioxide the

then

dl/g

molecular in

mixture

and

c o u l d be film.

copolymer

91%

and

films. 0.02

benzene

was

m), was

filtered

benzene) and

cast

The

product

yield

g,

ml

washing

A

hazy.

weight

(2.44 100

washed w i t h After

polymer

transparent

VII in

and

drying,

from

nmr

the

chloro-

spectrum

was

ratio. I,

the

polymer

flexible

transparent

probably

due

the

in

the

slightly

flexible,

flexible

monomer

m)

(CHCI3).

slurry

yield)

0.002

Weight:

methanol.

(76%

g,

an

0.50

into

was

to

bromide

example.

minutes,

(which

added

cuprous

II

units)

previous

was

A

polymer

minutes,

to

lead

of

70

The

dl/g)

was

of

(0.258

After

flexible

II.

transparent,

with a

and

Cell

form

consistent

polymerizations

m repeating

benzene

viscosity:

Oxidations.

through

to

to

0.01

solution

the

chloroform

m)

weighed

of

0.68

0.005

polymer

other

solution

g,

in

ml).

was

VII

g,

by

m)

Intrinsic

viscosity:

precipitated

64

chloroform)

ratio

A

1.99

dibutylamine

of

manner

yield).

cast

0.01

and

same p r o c e d u r e 2:1

Lead I

in

and VII. d l / g ,

(Vibromixer)

volume

(from

(intrinsic could

(1.22

0 . 0 0 0 1 m)

isolated

3.02

II

0.35

stirred

(total

the

substantiall

viscosity

2,6-xylenol

for

proportionately.

Copolymers of

oxygenated,

used

or

differed

Block

benzene

I

changed

(intrinsic and

p r o c e d u r e was

either

polymer

to

from

was

film.

extensive the

lead

isolated The

washing salt

in

higher with

residue.

Summary Highly have

brominated

been prepared

by

poly(2,6-dimethy1-1,4-phenylene polymerization

of

bromophenols

oxide)s and

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

by

11,

WHITE

Μοπο-,

AND KLOPFER

copolymerization

of

Di-, and Tribromo-2,6-Dimethylphenol

bromophenols

Dibromo-2,6-dimethylphenol

(I)

and

has

111

2,6-dimethylphenol.

been

3,4-

homopolymerized

poly(3-bromo-2,6-dimethyl-l,4-phenylene

oxide)

to

form

(II):

I and a

copolymerized

random

bromophenols under

have

oxidative

unbrominated ing

units.

produced was

3,4,5-tribromo-2,6-dimethylphenol

with been

mono-

and

dibromo

copolymerized

coupling

repeating

with

conditions

to

to

form

units.

Both

2,6-dimethylphenol

form

copolymers

with

repeating Co-oxidatio

predominantly

supported

slow

with

copolymer

rate

of

by

a

block

spectral

and

redistribution

copolymer. chemical

of

II

The

block

evidence

with

structure

(e.g.,

phenols)

and

the

very

fractionation

data. Spectral

analysis

bromophenols

and

structures.

-^H n m r

range

effects

shifts

on

in

aryl

of

the

copolymers

2,6-dimethylphenol spectra

which

protons

of

the

bromine in

of

bromophenols

indicated

random

copolymers

atoms

adjacent

and

of

copolymer

displayed

caused pronounced

long upfield

rings.

Literature Cited 1.

Staffin, 82,

G.

C.

and

Price,

C.

C.,

J.

Am.

Chem.

Soc.

(1960),

3632.

2.

White,

3.

White,

D. D.

4.

White,

D.

5.

The

13

C

M.,

J.

M.,J. M. nmr

Org.

Chem.

Polymer and

Klopfer,

spectra

(1960),

Sci.

of

A-1 H.

the

34,

297.

(1971),

J.,

ibid.

polymers

9,

663.

(1972),

were

10,

complex

1565.

and

will

be

described in detail elsewhere. 6. W., 7.

Hay, J.

A.

S.,

Am.

Hay,

Blanchard,

Chem.

A.

S.,

H.

Soc.

U.S.

S.,

Endres,

G.

81,

6335.

(1959),

Patent

3,306,874

F.,

(February

and

28,

Eustance, 1967).

8. Hay, A. S., U.S. Patent 3,306,875 (February 28, 1967). 9.

Blanchard, J.

10.

H.

Polymer

Hay,

A.

S., Sci.

S.,

Finkbeiner, (1962),

Advances

in

H.

58,

L.

and

Russell,

G.

Α.,

469.

Polymer

Sci.

(1967),

4,

496.

11. Factor, Α., Heinsohn, G. E. and Vogt, L. Η., Polymer Letters (1969), 7, 205. 12.

A

similar

shift

(0.35

ppm)

was

found

in

3-bromo-2,6-dimethyl­

-4(2,6-dimethylphenoxy)phenol; Hamilton, S. B. and Blanchard, H.

S., 13.

J.

Org.

Auwers,

K.

Chem. and

(1970), Markovitz,

T.,

35,

3348.

Chem.

Berichte

(1908),

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

41,

2332.

12 Brominated Poly(Phenylene Oxide)s. II. Bromination of Poly(2,6-Dimethyl-1,4-Phenylene Oxide) D W A I N M . W H I T E and C H A R L E S M . O R L A N D O General Electric Research and Development Center, Schenectady, Ν. Y. 12301

The p r e p a r a t i o n o by m o d i f i c a t i o n o f Price's p o l y m e r i z a t i o n o f bromophenols was described in the preceding paper. An a l t e r n a t e route t o these polymers is the d i r e c t bromination o f polyphenylene oxides. The bromination o f poly(2,6-dimethyl-1,4-phenylene oxide),2-5 I, t o prepare I I , I I I and IV and combinations o f the r e p e a t i n g u n i t s in I and I I I and in I I I and IV is described in t h i s paper. The p r o p e r t i e s o f these products a r e compared with the corresponding polymers d e r i v e d from p o l y m e r i z a t i o n s o f bromophenols.

The i n t r o d u c t i o n o f a s i n g l e bromine atom onto the aromatic r i n g and/or onto the methyl group o f I has been i n v e s t i g a t e d . In our l a b o r a t o r y , H a l l found t h a t 0.5 mole bromine p e r mole o f r e p e a t i n g u n i t o f I a t 15° in chloroform under i o n i c c o n d i t i o n s introduced one bromine per two r e p e a t i n g u n i t s . Recently, Cabasso e t al i n v e s t i g a t e d s e v e r a l routes to I I and III, Free r a d i c a l c o n d i t i o n s (e.g., N-bromosuccinimide ( N BS) and l i g h t ) 7

178

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

12.

WHITE

A N D ORLANDO

Poly(2,6-Dimethyl-l,4-Phenylene

Oxide)

179

a f f o r d e d methyl bromination while i o n i c c o n d i t i o n s l e d t o as much as one aryl bromine p e r ring. The i n t r o d u c t i o n o f two bromine atoms onto a s i n g l e aromatic r i n g o f I has not been r e p o r t e d . We have found t h a t the i n t r o d u c t i o n o f more than one bromine t o form u n i t s such as in IV d i d occur when the bromination was c a r r i e d out a t high bromine concentrations. Furthermore, the r e a c t i o n c o n d i t i o n s which favored the formation o f dibrominated r i n g s over mono-brominated r i n g s were found t o be very c o n c e n t r a t i o n dependent. Under m i l d c o n d i t i o n s (15°, d i l u t e s o l u t i o n i n t r i c h l o r o ethylene) and with one mole o f bromine p e r r e p e a t i n g u n i t I , the product contained 0.9 B r / u n i t and had predominantly s t r u c t u r e III. With excess bromine, the value c o u l d be r a i s e d r e a d i l y t o 1.0 B r / u n i t but d i d not exceed 1.1 B r / u n i t even a t r e l a t i v e l y h i g h s o l u t i o n concentrations (2.4 g I added t o 6 g Br2 i n 4 ml c h l o r o form) o r a t 80° with Lewis a c i d c a t a l y s t s . Dibromo u n i t s were formed with e i t h e r I o bromine concentration The bromine contents o f these polymers u s u a l l y contained between 1.6 and 1.85 B r / u n i t . Above t h i s bromine l e v e l the products were p a r t i a l l y i n s o l u b l e . In an extreme case, the a d d i t i o n o f I t o l i q u i d bromine produced an almost completely i n s o l u b l e s o l i d which corresponds t o the homopolymer IV. The nmr and i r s p e c t r a o f the products from d i r e c t bromina t i o n showed t h a t only r i n g bromination had occurred and t h a t there was no methyl group bromination. The s p e c t r a were almost i d e n t i c a l t o the spectra o f the corresponding homopolymers and copolymers from combinations o f 2,6-dimethylphenol, 3,4-dibromo2,6-dimethylphenol and 3,4,5-tribromo-2,6-dimethylphenol. A d e t a i l e d d e s c r i p t i o n o f the s p e c t r a o f these brominated polymers i s presented i n the preceding paper. The conversion o f I t o I I I and IV by the d i r e c t bromination of I r e s u l t e d i n a decrease i n i n t r i n s i c v i s c o s i t y o f the polymer. Since the i n t r o d u c t i o n o f bromine i n c r e a s e d the u n i t molecular weight o f the polymer without a f f e c t i n g the l e n g t h o f the u n i t and s i n c e the i n t r i n s i c v i s c o s i t y measurement was based on weight percent c o n c e n t r a t i o n s , an i n c r e a s e i n r e p e a t i n g u n i t weight r e s u l t e d i n a p r o p o r t i o n a l decrease i n molar c o n c e n t r a t i o n o f polymer. The a c t u a l decrease i n v i s c o s i t y was compared with the estimated decrease based on the change i n r e p e a t i n g u n i t weight due t o bromination (Table I ) . Bromination i n d i l u t e s o l u t i o n produced no abnormal v a r i a t i o n i n v i s c o s i t y while bromination a t higher bromine concentrations r e s u l t e d i n a decrease i n v i s c o s i t y which was as much as 30% g r e a t e r than expected. Chain cleavage r e a c t i o n s i n v o l v i n g hydrogen bromide may have c o n t r i b u t e d t o the a d d i t i o n a l decrease. Methyl brominated polymers (II) were prepared f o r comparison with the r i n g brominated m a t e r i a l s . Under the c o n d i t i o n s used (NBS, l i g h t , C C I 4 a t r e f l u x , 3 hrs) with 0.5 mole NBS/repeating u n i t , the product contained 0.41 B r / u n i t by bromine a n a l y s i s . A four hour r e a c t i o n with 1.0 NBS/unit introduced 0.88 B r / u n i t .

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

180

POLYETHERS

TABLE Decrease

in

Intrinsic

I

V i s c o s i t y Upon R i n g Bromine

Br/Unit 0

%

(initial

1-1

Dilute

0.35

0.34

0.29

0.34

0.21

0.29

1-1

Concentrated

1.6

Concentrate

1.7

Concentrated

spectra sample

the

The

had

been

are Tg,

was

differential

raised

lowered

by

by

for

in

III

from

to

the

onto

the

change the

III

from

higher

rings

were

transitions

bromine

insoluble, The the

and

bromo

could of

the oxide

dibromo-

same w e i g h t

bromo

units

and

(with

twice

as

of

bromine

thermal onto

ring

d l / g Br/

brominated (Table

I)

occurring

methyl

I

from

or

on

units. not

Above by

be

rings

the

prepared

for

of

aryl

of

T h u s when bromine

the

two

but

other

contained

dibromo

many

bromo

repeating

units)

was

due

bromine to

as

of

85%

level

polymers

no were

measurements. units same

on for

contained

units, had

for

appear

copolymers

one

the

not much

Br/unit

TOA

of

observed

probably

these

bromo

approximately

moieties.

as

1.85

Since

values

polymer

polymerization

did

when

The

of

Tg

and

the

introduction

DSC.

presence was

the even

rings

value

reaction

Further

The

groups.

the

higher

TOA,

8

II).

whether

of

transition

a n a l y s i s ,

(Table

aromatic

similar

displacement sites

DSC

properties

glass

optical

the

the

the

The

were

appreciably

percentage

0.39 0.88

reaction

on

III.

slightly

weight.

discernible

films

effect

Tg

dibromo

polyphenylene

monothe

of

the

to

for

conditions

cleavage

and

onto

290°) The

remaining

were

of II

bromine

bromination the

value

chain

dl/g

for

mild

intrinsic dl/g

bromination.

(ca.

molecular

single

the

0.29

than

under

measured by

introducing

prepared

a

to

The 0.49

scanning calorimetry,

3,4-dibromo-2,6-xylenol. polymer

of

Tables

introducing

polymer

greater

introduction

shown

i n i t i a l and

prepared

photo-catalyzed of

an

Br/unit

likelihood

effects

temperature,

was

0.41

bromination.

from

d e c r e a s e s were the

polymer

and/or

ring

decreased with

which

suggest

during

showed no

had

These

Tg

0.50 0.39

unit.

of

Calculated

0.41

polymers

was

Found

(dl/<

Dilute

the

the

Concentration

Viscosity

0.66

nmr

and

Intrinsic

polymer)

viscosities for

Bromination

the

the

the

Tg

both

of

the

contained monoformer

higher

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Tg.

12.

W H I T E A N D ORLANDO

Poly(2,6-Dimethyl-l,4-Phenylene

TABLE Glass

Transition Analysis

Polymer

8

Source

%

I I

+

B r

9

Temperatures

and

II Measured by

Differential

Br

181

Oxide)

Br/Unit

Scanning

Thermal

Optical

Calorimetry

DSC

TOA

0

0

214

221

30.1

0.65

250

238

37.1

0.88

280

53.1

1.69

290

55.5

1.85

293

19.6

0.37

201

21.5

0.41

197

38.4

0.92

190

40.2

1.00

289

10.0

0.17

234

5.4

0.08

222

9.3

0.16

223

12.2

0.22

223

30.7

0.67

237

32.4

0.70

242

41.

I

+

NBS

DBX

292

(homopolymer)

(a)

DBX

+

X

TBX

+

X

Abbreviations:

DBX =

X

and

in

described

248

3,4-dibromo-2,6-xylenol;

tribromo-2,6-xylenol; TBX a r e

221

=

2,6-xylenol. the

preceding

TBX =

Polymers

from

paper.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3,4,5DBX

182

POLYETHERS

The to

the

oxygen

bromine

relatively

index^

(Table

content

unaffected

of by

III)

the the

was,

and

structure

of

TABLE Oxygen %

Indices

Br

in

polymer

the

proportional to

be

polymer.

III

of

y

general, appeared

Polymer

Bromo

Polymers Oxygen

Source

:

28

0

Polymer

I

5

TBX

+

X

37

10

TBX

+

X

36

30 40

I

+

Br

2

52

42

I

+

B r

2

55

Experimental All

viscosities

contents

were

corroborated third

scans

imeter

based by

on

a

analysis

g,

0.02

added

over

0.056

m)

ously. then

in

gradually and

precipitated 4.7

structure form

a

there

less

(2.4 a

period

The

g

clear

polymer

was

less

to

loss

products

of

from

2 5 ° . was

measured

Bromine

Br

the

and

when

by

were

second

scanning

and

calor-

the

DSC

thermo-optical

the

washed

of

two

hours,

ml

500

methanol

(9

the

50

to

dl/g)

was

characteristic

The

polymer

could

vigor-

addition, chloroform

ml

and

was

g,

stirred

3 5 ° during

dropwise with

was

oxide)*

0.5

bromine

mixture

2 5 ° to

After

spectrum

viscosity

solution

added

Br/unit.

methanol.

dried. of

be

a case

to

film. (6

g)

1.1

added

period

a

while

was

nmr

aryl

bromine

minute

25°C. and

for

particularly

was

intrinsic

to

rose

polymer

contained

5

polymeric

units;

solution

1.6

flexible,

product

ation over

g.

averages

H

Poly(2,6-dimethyl-l,4-phenylene

chloroform,

the

with

With meric

I.

dropped

The

Weight:

of

ml

added

at

C,

8

temperature

was

Tg

for

differential

cases,

the

chloroform

are

DSC-2

several

5 minute 4

in

analyses

values

weak,

m repeating

a

The

In very

Bromination (2.4

Tg

Perkin-Elmer

were

(TOA).

measured

elemental

^-H n m r .

( 4 0 ° / m i n ) .

transitions

were on

in

the

above

Br/unit. to

4.5

followed bromine

contained

by due

from

g

procedure,

With bromine

the to 1.7

a

the

two-stage in

addition

4

ml

chloroform

of

4.5

vaporization

and

to

1.85

poly-

broming

bromine),

the

Br/unit.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

12.

WHITE

AND ORLANDO

Poly(2,6-Dimethyl-l,4-Phenylene

Oxide)

183

Brominations o f I i n d i l u t e s o l u t i o n (10%) were c a r r i e d out a t 10 to 25° i n t r i c h l o r o e t h y l e n e . With 0.6 t o 1.0 moles B r p e r repeating u n i t , r i n g bromination was n e a r l y q u a n t i t a t i v e . With F e B r 3 o r A I C I 3 (5 wt % based on I) and temperatures ranging from 25° to 80° and 2.0 moles B r 2 per repeating u n i t , only up to 1.1 B r / u n i t was found. 2

Bromination o f I I . To a s o l u t i o n o f I I I (2 g, 1 Br/unit) i n 2 ml chloroform was added bromine (3 g, pure l i q u i d ) with s t i r r i n g over a 5 minute p e r i o d . A f t e r 2 hours, 20 ml chloroform was added, nitrogen was passed through the mixture to remove unreacted bromine and r e s i d u a l HBr. The s o l u t i o n was f i l t e r e d t o remove a tan s o l i d , 0.75 g when dry, and then added dropwise to methanol. The p r e c i p i t a t e d polymer, when washed and d r i e d , weighed 1.75 g, 1.7 B r / u n i t . Addition of I to phenylene oxide) (1.5 g, i n t r i n s i c v i s c o s i t y 0.49 dl/g) was slowly added t o a f l a s k c o n t a i n i n g 15 ml o f bromine. The polymer d i s s o l v e d immediately, HBr was v i g o r o u s l y evolved and the r e a c t i o n mixture became v i s c o u s . The r e a c t i o n mixture was s t i r r e d f o r 30 minutes and the excess bromine was evaporated with a n i t r o g e n stream. The residue was suspended i n 50 ml o f benzene, f i l t e r e d , thoroughly washed with methanol and d r i e d under vacuum. The brominated product (3.2 g) was i n s o l u b l e i n acetone, benzene, a c e t o n i t r i l e , chlorobenzene, chloroform, hot DMF and hot DMSO. P r e p a r a t i o n o f I I . To a s o l u t i o n o f poly(2,6-dimethyl-l,4phenylene oxide-) (48 g, 0.40 m repeating u n i t s , i n t r i n s i c v i s c o s i t y 0.49 dl/g) i n 500 ml carbon t e t r a c h l o r i d e a t r e f l u x was added N-bromosuccinimide (35.6 g, 0.20 m) over a t e n minute p e r i o d while the s o l u t i o n was i r r a d i a t e d with a 150 watt f l o o d lamp a t a distance o f 10 cm. A f t e r three hours the mixture was f i l t e r e d t o remove c r y s t a l s o f succinimide. The f i l t r a t e was added t o 1000 ml methanol which was being s t i r r e d v i g o r o u s l y i n a blender. A f t e r f i l t e r i n g , the polymer was s t i r r e d i n methanol, f i l t e r e d and d r i e d . Weight: 59.6 g, 0.41 B r / u n i t . Intrinsic viscosity: 0.39 d l / g . For a s i m i l a r r e a c t i o n with an i r r a d i a t i o n time o f one hour, the polymer contained 0.37 B r / u n i t . With twice as much NBS (71.2 g) and a four hour r e a c t i o n time, the product weighed 78 g and contained 0.88 B r / u n i t . Intrinsic viscosity: 0.29 d l / g . % nmr (CDCI3 v s . TMS): 6 1.88 ( C H 3 ) , 4.35 (CH Br), 6.48 and 6.67 (Ar H»s) . 2

Summary D i r e c t bromination o f poly(2,6-dimethyl-l,4-phenylene oxide) (I) a t high bromine concentrations introduced two bromine atoms onto the a r y l r i n g s o f a m a j o r i t y o f the repeating u n i t s while at lower concentrations mainly monobromo u n i t s were formed. No

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

184

POLYETHERS

bromination

of

the

average

of

1.8

soluble

in

liquids

polymer, Free

solid,

radical

viscosities under

mild

of

as

was

per

observed.

repeating

chloroform

prepared

methyl

the

and

with

and

unit

Polymers

with

or

were

lower

benzene.

during

I

The

to

upon both

and

with

of

from

the

but

NBS.

introduced

methyl did

and

not

aryl

occur

detectable

Spectral,

polymers

an bromine.

intrinsic

was

bromophenol

from

at

f lamdirect

polymerization

similar.

Literature Cited 1. Staffin, G. C. and Price, C. C., J. Am. Chem, Soc. (1960), 82, 2. W.,

Hay, J.

3632. A.

S.,

Am.

Blanchard, Chem.

H.

Soc.

S.,

Endres,

(1959),

81,

G.

F.,

and

Eustance,

6335.

3. Hay, A. S., U.S. Patent 3,306,874 (February 28, 1967). 4. Hay, A. S., U.S. Patent 3,306,875 (February 28, 1967). 5. Hay, A. S., Adv. Polymer Sci. (1967), 4, 496. 6. Hall, W. L., personal communication. 7. Cabasso, I., Jagur-Grodzinski, J. and Vofsi, D., personal communication from Dr. Cabasso. 8. Kovacs, A. J. and Hobbs, S. Y., J. Applied Polymer Sci. (1972) 16, 301. 9.

Fenimore,

C.

P.

and

Martin,

F.

J.,

Mod.

an

homo-

liquid (NBS)

The

bromination

conditions,

properties polymers

of

exclusively.

decreased

cleavage

bromination

the

addition

N-bromosuccinimide

concentrations

thermal and

by

groups

polymers

Chain

ionic

bromination were

was

the

bromine

mability

such

bromination

onto

bromination. higher

groups

atoms

poly(3,5-dibromo-2,6-dimethylphenylene-l,4-oxide),

insoluble bromine

methyl

bromine

Plast.

(1966),

141; ASTM D-2863.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

44,

13 Polyperfluoroalkylene Ethers as High-Temperature Sealants R. W. ROSSER and J. A. PARKER Ames Research Center, NASA, Moffett Field, Calif. R. J.

DEPASQUALE

94035

and E. C. STUMP JR.

PCR Inc., Gainesville, Fla.

32601

Although the o b j e c t i v f o r h i s c o n t r i b u t i o n s t o polyether chemistry, our i n t e r e s t s take a t a n g e n t i a l course in that we d e a l with p o l y p e r f l u o r o a l k y l e n e e t h e r s . A f t e r reviewing some o f the literature to p o i n t out l i m i t a t i o n s in f l u o r o e t h e r s y n t h e s i s , we d i s c u s s current work that is designed to alleviate d e f i c i e n c i e s in o b t a i n i n g high molecular weights and then give our p r o j e c t i o n s on some of the challenges f o r f u t u r e work in t h i s area. Figure 1 r e f l e c t s Dr. P r i c e ' s work on propylene oxide p o l y m e r i z a t i o n . You will recall that the base c a t a l y z e d , room temperature p o l y m e r i z a t i o n o f propylene oxide shown in the first equation l e d t o only low molecular weight dihydroxy terminated species (1). The second equation shows that a ferric c h l o r i d e propylene oxide complex (2) a t 80° C y i e l d e d polymers o f very high molecular weights. Both amorphous and crystalline polymers were i s o l a t e d from t h i s experiment. I n other s t u d i e s (3), Dr. P r i c e utilized a variety o f complexes such as aluminum i s o p r o p o x i d e - z i n c c h l o r i d e , which a l s o produced high molecular weight p o l y e t h e r s . As a r e s u l t o f some o f Dr. P r i c e ' s important d i s c o v e r i e s in h i g h molecular weight p o l y e t h e r s , a whole spectrum of commercially s i g n i f i c a n t m a t e r i a l s has been developed. As an example, the chain extension o f p o l y e t h e r s with d i i s o c y a n a t e has l e d to a host o f polyurethane a p p l i c a t i o n s . These achievements prompted us t o consider the possibility of b u i l d i n g long-chain p e r f l u o r o a l k y l e n e ethers that would y i e l d a combination o f p r o p e r t i e s f o r severe environmental a p p l i c a t i o n s that would not be p o s s i b l e with any other polymer system. Our goal, then, was t o o b t a i n high molecular weight elastomers that have good low-temperature mechanical p r o p e r t i e s , high thermal stability, and high chemical r e s i s t a n c e , w h i l e maintaining sufficient flexibility over a wide temperature range. I t should be mentioned here that, until now, p e r f l u o r o e t h e r s y n t h e s i s has been l i m i t e d by inadequate molecular weights. Perhaps more research in catalysis will overcome t h i s problem and open another important door, as Dr. P r i c e and others have done with the 185

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

186

POLYETHERS

propylene oxide p o l y m e r i z a t i o n . Table 1 shows a l i s t of fluoro-elastomers. The unusual r e s i s t a n c e of h i g h l y f l u o r i n a t e d m a t e r i a l s to high temperatures, o x i d a t i o n , and a v a r i e t y of organic solvents has been known s i n c e Plunkett's discovery of T e f l o n i n 1938. E f f o r t s s i n c e then have

TABLE 1. FLUORINATED POLYMERS CONTINUED SERVICE TEMPERATURE,°C

FLUOROCARBON BACKBONE ÇF 2

2

2

-(CF -CF ) 2

0CF

2

DIAMINE

200

n

-

n

CROSS-LINK

3

CH -CF -CF -CF>

i

Tg,°C

270

127

250

-12

C F 0 R CN

180

-50

PENDANT COOH

220

-65

3

-(-CF-CF -CF -CF 2

2

2

f

n

6

5

260

CF

3

-f N - 0 - C F CH

2

f

2

-S, - 0 I

CH

- C F

n

CH -CH CF

3

I

L

2

I

— S, — 0

2

3

VINYL-SILANE

I

3

CH

3

centered on the synthesis of p a r t i a l l y and completely f l u o r i n a t e d polymers designed to r e t a i n the thermo-oxidative and chemical s t a b i l i t y of p o l y t e t r a f l u o r o e t h y l e n e , while adding elastomeric character, low-temperature f l e x i b i l i t y , p r o c e s s a b i l i t y , e t c . Note that the high glass t r a n s i s t i o n temperature of T e f l o n i s lowered by going to a V i t o n system (4). However, V i t o n s l i m i t a t i o n s o f chemical and solvent r e s i s t a n c e and s e r v i c e l i f e at higher temperatures are a r e s u l t of the presence of C-H bonds s i n g u l a r l y and a l t e r n a t i n g -CF-CH- bonds c o o p e r a t i v e l y l e a d i n g to hydrogen f l u o r i d e e l i m i n a t i o n . In the cases of V i t o n , fluorocarbon t r i a z i n e (_4 ), and a new duPont elastomer (4) 1

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

13.

ROSSER E T A L .

187

Polyperfluoroalkylene Ethers

(ECD 006), the glass t r a n s i t i o n temperatures are near -10° C, with an i n c r e a s e i n thermal s t a b i l i t y of ECD 006 c h i e f l y because of i t s perfluoroearbon backbone. M a t e r i a l s at the top of the t a b l e b a s i c a l l y have a T e f l o n backbone, which appears to l i m i t t h e i r usefulness f o r very low temperature a p p l i c a t i o n s . I t can be r e a d i l y seen that only by i n c o r p o r a t i n g ether backbones can one design m a t e r i a l s that w i l l maintain f l e x i b i l i t y below -30° C. For example, the n i t r o s o rubber has a Τ of -50° C, but i t s high-temperature s t a b i l i t y i s l i m i t e d . T h e f l u o r o s i l i c o n e comes nearest to meeting the requirements of a high-temperature s e a l a n t . I t has e x c e l l e n t low- and h i g h temperature p r o p e r t i e s , but i t tends to undergo r e v e r s i o n and has low t e a r s t r e n g t h . Because these m a t e r i a l s s t i l l f a l l somewhat short of a n t i c i p a t e d requirements, l e t us turn our a t t e n t i o n to the p e r f l u o r o a l k y l e n e ethers and examine t h e i r potentialities. Before we discus f l u o r o e t h e r s that have d i f u n c t i o n a l termination, l e t us b r i e f l y consider some of the f l u o r o e t h e r work i n the l i t e r a t u r e . Although much work has been done with t e t r a f l u o r o e t h y l e n e oxide, i t i s q u i t e unstable and t h e r e f o r e d i f f i c u l t to handle experimentally. Consequently, e f f o r t s have been centered on hexafluor©propylene oxide p o l y m e r i z a t i o n . The mechanism of hexafluoropropylene oxide polymerization i s shown i n Figure 2. Hexafluoropropylene oxide i s f i r s t prepared by t r e a t i n g hexafluoropropylene with hydrogen peroxide i n the presence of base. Charcoal and f l u o r i d e i o n have both been used as c a t a l y s t s , but the f l u o r i d e i o n i s the p r e f e r r e d n u c l e o p h i l e . Ring-opening a t t a c k i s apparently at the most hindered carbon atom, and the r e s u l t i n g n-perfluoropropoxide i o n reacts with more hexafluoropropylene oxide to give e q u i l i b r i u m mixtures of alkoxide and a c i d f l u o r i d e (_5). A n i o n i c p o l y m e r i z a t i o n of hexaf l u o r o ­ propylene oxide i s reported to behave l i k e a " l i v i n g polymer." Continued chain growth i s achieved by using a s o l v a t i n g system of glymes f o r emulsion. Polymers up to 4000 molecular weight were synthesized, but, by using hexafluoropropylene d i l u e n t to minimize v i s c o s i t y b u i l d u p , the molecular weight could be increased somewhat. The r e s u l t i n g polymers are l i q u i d s that y i e l d only monofunctional m a t e r i a l s that are incapable of e i t h e r chain-extension or c r o s s - l i n k i n g . This i s i n marked c o n t r a s t to the a l i p h a t i c s e r i e s of p o l y e t h e r s , which have dihydroxy termination and thus can be f u r t h e r modified. Figure 3 r e f l e c t s s t a b i l i z a t i o n or end-capping of the r e a c t i v e a c y l f l u o r i d e end group, which may be c a r r i e d out i n s e v e r a l ways as shown. Antimony f l u o r i d e adds a f l u o r i n e atom to the chain while e l i m i n a t i n g carbon monoxide (5). Base treatment of the a c y l f l u o r i d e gives r i s e to an a d d i t i o n a l hydrogen atom, and i r r a d i a t i o n approximately doubles the molecular weight with the e l i m i n a t i o n of two gas s p e c i e s . This l a s t mechanism i s u t i l i z e d i n our work. The m a t e r i a l s shown i n g

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

0H~> HO-CH-CHO—HO-CH-CH^NOCH CH CH CH CH^ 0Θ CH 17 /C = 0.129-0.141 / \ 'SP CH-CH CH _ /OR 80 C \ /OCH-CH 2

2

/ÏÎc

2

3

2

3

3

N U 2

3

8

E

X

2

><

V

X

CH

3

CH —ÇH

/Fe

2

X

1

77'SP/C~3-4

CH

/

./OR ''CH

^Η -0Η-OCH -CK 2

2

3

I CH

0

1

3

A. AMORPHOUS, T7/C = 2.23 B. CRYSTALLINE, 77 /C= 10.60 SP

SP

Figure

~

C F

H0 BASE 2

2

2

OA c e »

= CF

CF

3-CF - C F

CF CF CF 0"3

2

2

2

CF-CF 0" ^ r F - ( C F - C F - 0

N

2

)

2

CF

3

CFCF CF + F" 0 3

3

CF

|t

+

-CF -CF-CF

{CF-CF -0)-

-

2

V δ

F" 2

n

CF

3

CF

3

2

" C F - C F I 3

M = ~4000 N

Figure 2.

Hexafluoropropylene oxide polymerization

^

F(CF-CF -0)η -CF -CF , CF 2

2

3

3

Il

F{CF-CF -0 } CF - CF 2

CF

3

N

CF

3

KOH , H0 2

F(CF-CF -0) -CHF - CF I CF 2

N

3

3

[(CF -CF -CF -0) -CF] 3

2

2

N

CF, + COF + CO 2

Figure 3.

Krytox fluids—end capping

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2

+ F

13.

ROSSER E T A L .

Polyperfluoroalkylene

Ethers

189

Figure 3 have found commercial use as p o l y m e r i z a t i o n solvents and i n e r t h y d r a u l i c f l u i d s . Note that these uses r e f l e c t the molecular weight l i m i t a t i o n s which preclude t h e i r c o n s i d e r a t i o n f o r high-temperature s e a l a n t a p p l i c a t i o n s . Figure 4 d e p i c t s recent e f f o r t s by European workers (6). In t h i s case, hexafluoropropylene oxide i s not i s o l a t e d , but hexafluoropropylene i s i r r a d i a t e d with oxygen d i r e c t l y . In the gas phase, hexafluoropropylene y i e l d s a c y l f l u o r i d e s of low molecular weights, and i n the l i q u i d phase, i t produces peroxides of up to 7000 molecular weight, as shown i n l i n e 2. Even though we have an i n i t i a l l y high average molecular weight, the peroxides are not s t a b l e . The chains are s t a b i l i z e d by heat or r a d i a t i o n , which f i r s t destroys the peroxide, and then they are t r e a t e d with elemental f l u o r i n e to end-cap the polymer. Unfortunately, t h i s process e f f e c t s a lowering of the molecular weight and r e s u l t s i n a polymer that i s inadequat Figure 5 shows a s e r i e d i f u n c t i o n a l or m u l t i f u n c t i o n a l oligomers. The d i i o d i d e shown on l i n e 1 was i r r a d i a t e d to give an o i l of low molecular weight. Line 2 describes the i r r a d i a t i o n of p e r f l u o r o - o x y d i p r o p i o n y l f l u o r i d e (POPF) i n FC-75 s o l u t i o n which gives a d i f u n c t i o n a l a c i d f l u o r i d e terminated poly(perfluorotetramethylene oxide) (7) at an of 1000 or more. I n v e s t i g a t o r s turned t h e i r a t t e n t i o n to end-group m o d i f i c a t i o n by forming d i a l c o h o l s and d i n i t r i l e s from the low molecular weight p o l y f u n c t i o n a l a c y l f l u o r i d e s . Elastomers were made through chain extension r e a c t i o n s of the d i a l c o h o l s with diisocyanates to give polyurethanes (7); t r i a z i n e s were prepared by analogous routes. However, urethanes have l i m i t e d thermal s t a b i l i t y , and, although t r i a z i n e s are adequate thermally, the f l u o r o e t h e r chains between aromatic groups are too s h o r t to allow a Tg that i s adequate f o r lowtemperature compliance a p p l i c a t i o n s . Figure 6 i n d i c a t e s attempts to b u i l d elastomeric p r o p e r t i e s i n t o a polymer by i n c o r p o r a t i n g a f l u o r o e t h e r chain i n t o a polyimide system (8). L i n e 1 shows an a r y l diamine polymer intermediate prepared i n a lengthy s e r i e s of synthesis steps from a p e r f l u o r o a l k y l e n e ether d i c a r b o x y l i c a c i d . The polymer i s prepared from the r e a c t i o n of the diamine with p e r f l u o r o hexamethylene-bis(phthalic anhydride). As expected, the polymer had e x c e l l e n t thermal s t a b i l i t y , but, again, i t s low-temperature p r o p e r t i e s were d e f i c i e n t . For example, when X + y = 0, the T was 130° C; when χ + y = 1, the Τ was 110° C; and when χ + y = 3, the Τ was 80° C. With t h i s system, we are unable to achieve r e q u i s i t e chain f l e x i b i l i t y because of a preponderance of r i g i d aromatic groups that i n h i b i t e l a s t i c i t y and cause a r a i s i n g of the T^ beyond p r a c t i c a l l i m i t s f o r our intended purpose as a s e a l a n t m a t e r i a l . The f l u o r o e t h e r segment i s simply too short to y i e l d a u s e f u l low-temperature elastomer. I f a high molecular weight d i f u n c t i o n a l f l u o r o e t h e r had been synthesized by some unique c a t a l y s t system, many of the problems g

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

hi/

C F , - CF = C F + 0 ?

CF3-O ( C F - 0 )

2

2

hi/

C F , - C F = C F + Oo ?

Il - 0 ( C F 0 ) - CF 3

6

CF

2

CF

-0(C F 0) -(C F -0-0 3

LIQUID PHASE

6

M Δ OR hi/

N

n

n

3

6

)

r

UP TO 7 0 0 0

F? • -fo-CF-CF OF ) — STABILIZES \ ' CF

{0-CF} I CF

2

n

K

3

n

+ CF 0

3

LUBRICANT Figure 4.

I CF CF 0 - C F 2

2

2

hv

CF - I

-fCF

2

0

Fomblin fluids

CF CF CF θ )

2

2

0

FC-CF -CF -0-CF 2

2

η

- OILS

2

N

°NH C

3

DINITRILES

Figure 5.

0

FC -£ C F C F 0 - C F C F ) CF

2

DIALCOHOLS

CF

2

0

CF -CF

2

2

2

2

2

n

M > 1000 n

POLYURETHANES

POLYTRIAZINE

Polyether through photolysis

CF

3

3

- C F - C F - 0 - ( 2) - • 0 - C F - C F 2

CF

-

2

5

X x + y= 3

CF Δ , -H 0l 2

3

ÇF

'

0

f

3

- C F - C F - 0 - "(CF ) - • 0 - C F - C F 2

Figure 6.

2

X

2

5

Imide-linked

perfluoroalkylene ether

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2

13.

ROSSER ET AL.

Polyperfluoroalkylene

Ethers

191

i n the above systems would be obviated. Other i n v e s t i g a t o r s have a l s o prepared d i f u n c t i o n a l f l u o r o e t h e r n i t r i l e s , notably through the use of t e t r a f l u o r o e t h y l e n e oxide (9). We at NASA reopened the question of l e a r n i n g to chain extend these f l u o r o e t h e r systems i n consort with s c i e n t i s t s at PCR Inc. The o b j e c t i v e was to prepare long-chain d i f u n c t i o n a l p o l y p e r f l u o r o e t h e r s and i n v e s t i g a t e chain extension mechanisms, as w e l l as to convert these materials to s t a b l e c r o s s - l i n k e d polymers f o r sealant a p p l i c a t i o n s . The n i t r i l e , acetylene, and isocyanate groups were considered. Each of these i s capable of both t r i m e r i z a t i o n r e a c t i o n s and d i p o l a r c y c l o a d d i t i o n s . From t h i s base l i n e , one could then evoke both chain extension and c r o s s - l i n k i n g with a v a r i e t y of r e a c t i o n schemes. One can see i n Figure 7 that we are s t i l l using a f l u o r i d e i o n c a t a l y s t as i n the o r i g i n a l work on hexafluoropropylene oxide polymerization. Ou work i n that we emphasiz Reasonably high molecular weight d i a c i d f l u o r i d e s were prepared by the c o - o l i g o m e r i z a t i o n of h e x a f l u o r o g l u t a r y l f l u o r i d e and HFPO i n i t i a t e d by CsF i n tetraglyme. The r e a c t i o n c o n s i s t s of converting h e x a f l u o r o g l u t a r y l f l u o r i d e to a p e r f l u o r o a l k o x y anion, which then reacts w i t h HFPO to a f f o r d the d e s i r e d d i a c i d f l u o r i d e s . HFPO was gradually added and the progress of product appearance was monitored by GLC. The fluorocarbon l a y e r was c a r e f u l l y d i s t i l l e d and samples of 60% m + η = 5 (7-EDAF) ether d i a c i d f l u o r i d e and 30% m + η = 6 (8-EDAF) were obtained as w e l l as various other f r a c t i o n s c o n t a i n i n g d i a c i d f l u o r i d e mixtures. P h o t o l y t i c d i m e r i z a t i o n of 7-EDAF with a 450 W Hanovia lamp f o r 650 hours at r e f l u x gave an 89% conversion of s t a r t i n g m a t e r i a l to 7-EDAF dimer, bp 224-235°C/l mm. As the dimer formed i n the vapor phase, i t p r e c i p i t a t e d on the w a l l s of the v e s s e l . In Figure 8, conversion of a c y l f l u o r i d e s to d i n i t r i l e s where m + η = 6 (8-EDAF) and a l s o the dimer of m + η = 5 (7-EDAF dimer) gave us two molecular weights f o r a d d i t i o n a l study. The conversion procedure c a l l s f o r the use of ammonia i n Freon 113 followed by d i s t i l l a t i o n from P2O5. This presents the background f o r the work reported below. I t was hypothesized that by using long-chain polyether d i n i t r i l e s from t r i a z i n e precursers, the r e s u l t i n g m a t e r i a l s would be u s e f u l as s e a l a n t s . The 8-EDAF d i n i t r i l e and the 7-EDAF dimer d i n i t r i l e p r e v i o u s l y prepared were polymerized i n separate experiments to three-dimensional matrixed p o l y t r i a z i n e s by t r e a t i n g them with c a t a l y t i c amounts of ammonia at 225° C. These polymers were g e l - l i k e m a t e r i a l s which maintained the shape of the tubes from which they were prepared. They possessed e x c e l l e n t thermal p r o p e r t i e s but were d e f i c i e n t i n mechanical p r o p e r t i e s . We then turned our a t t e n t i o n to a l t e r n a t e chain extension and c r o s s - l i n k i n g r e a c t i o n s to overcome the obvious molecular weight d e f i c i e n c i e s . The f i r s t s e r i e s of r e a c t i o n s u t i l i z e unsaturated f u n c t i o n a l i t i e s as extension p o i n t s . N i t r i l e was

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

0 0 Il II FC(CF ) -CF 2

ο

C F -

II _ C F FC-(CF ) -CF 0

S

3

OF C (CF )

s

2

3

2

2

2

A 0 / \ Β + CF -CF-CF 3

2

0 CF CF CF CF 0 -F" Il I , I \ A » I II — — F C - C F - ( 0 C F C F ) - 0 - ( C F ) " 0 ( C F - C F - 0 ) CF - C F 3

2

CF 0

3

Β 3

2

3

m

2

3

5

2

,

n

m + η = 4 -6

/ hi/ " 0 CF CF Il I , I F C - C F - (0CF - C F - )

CF

3

CF, Ί

3

2

-"2 m+n = 5 ( 7 - E D A F DIMER) M

Figure 7.

0 Il

Preparation of long-chain perfluoroether

CF

CF

3

I

F C - C F - ( 0 CF

CF 1, 2.

NH P 0 2

ÇF

3

0 (CF )

2

2

CF

3

i

3

NsC - C F - ( 0 CF -CF 2

5

~ 3 0 0 0 , bp 224 - 2 3 5 ° C / Imm

n

5

ÇF

3

3

-0-fCF-CF -0) -CF| 2

ÇF

3

n

ÇF

3

3

}_0-(CF ) -0-fCF-CF -0) -CF42

5

2

n

R = PERFLUOROALKYLENE ETHER f

Figure 8.

Cross-linked triazine

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

13.

ROSSER E T A L .

Polyperfluorocilkylene Ethers

193

chosen as the p r i n c i p a l d i p o l a r o p h i l e to study, but any unsaturated system such as acetylene might be u t i l i z e d . D i f u n c t i o n a l n i t r i l e s were mixed with r e a c t i v e d i p o l a r , d i f u n c t i o n a l n i t r i l e oxide moieties, as shown on l i n e 1 of Figure 9. Thus, long-chain f l u o r o e t h e r d i n i t r i l e s combine conveniently with terephthalonitrile,Ν,Ν'-dioxide i n a 1,3-dipolar c y c l o a d d i t i o n to y i e l d poly (1,2,4-oxadiazolyl f l u o r o e t h e r ) , a five-membered r i n g h e t e r o c y c l e - f l u o r o e t h e r system. Polymerization was followed by disappearance of n i t r i l e oxide (2300 cm"*) and n i t r i l e (2220 cnT*) i n f r a r e d absorptions. New bands appeared at 1560 and 915 cm~l, presumably owing to the 1,2,4-oxadiazole s t r u c t u r e . That we have s i g n i f i c a n t l y increased the molecular weight i s demonstrated by the r e s u l t that the 8-EDAF d i n i t r i l e / TPNO r e a c t i o n gave a l i g h t - y e l l o w "snappy" rubber of considerable strength and e l a s t i c i t y . I t must be kept i n mind that d i a c e t y lenes can a l s o react wit On l i n e 2, we have anothe w i l l react with n i t r i l e s to give poly 1 , 2 , 4 - t r i a z o l e s . Finally, on l i n e 3, we show a r e a c t i o n scheme f o r s y n t h e s i z i n g poly (1,3,4-oxadiazoly1 f l u o r o e t h e r s ) . These same pathways may be used f o r achieving s t a b l e c r o s s - l i n k s , as w i l l be shown p r e s e n t l y . Let us b r i e f l y examine the f l u o r o e t h e r polymers which have been synthesized. From Figure 10, i t can be seen that both s t r u c t u r e s are e s s e n t i a l l y long f l u o r o e t h e r chains separated by thermally s t a b l e anchor p o i n t s . These "hard domains" are expected to improve high-temperature mechanical p r o p e r t i e s , as w e l l as provide c r o s s - l i n k s i t e s and molecular weight c o n t r o l . You w i l l r e c a l l that our goal was to reduce the number of branch points i n the f l u o r o e t h e r system by more e f f e c t i v e chain extension of the o r i g i n a l f l u o r o e t h e r . With the p h o t o l y t i c d i m e r i z a t i o n , we have probably reached the upper molecular weight l i m i t s with f l u o r i d e i o n c a t a l y s i s . However, we have demonstrated that, by i n c r e a s i n g the molecular weight of the f l u o r o e t h e r backbone to 3000 through t h i s awkward process, i t i s p o s s i b l e to obtain a Τ (-50° C) c o n s i s t e n t with the chain extension that was r e q u i r e d . One of the p o s s i b i l i t i e s f o r overcoming the disadvantages of low molecular weights i n current s t a t e - o f - t h e - a r t p e r f l u o r o ether systems i s to i n c r e a s e the weights by the use of p o l y functionality. Figure 11 shows p e r f l u o r o 1,5-hexadiene d i o x i d e , which i s c u r r e n t l y being copolymerized i n the HFPO c o - o l i g o m e r i z a t i o n scheme. T h i s , then, provides us with the opportunity of securing high branch f u n c t i o n a l i t i e s i n l i n e a r polyfluoroethers. Therefore, lower extents of r e a c t i o n with respect to the n i t r i l e group may now become reasonable i n terms of achieving a w e l l - v u l c a n i z e d , e f f e c t i v e l y c r o s s - l i n k e d elastomer f o r a sealant a p p l i c a t i o n . In a d d i t i o n , we are addressing ourselves to a s i m i l a r mechanism through the c r o s s l i n k i n g agent ( t r i f u n c t i o n a l n i t r i l e ) which contains a branch p o i n t as w e l l .

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

194

O ^ N

a Ν —·- • / R f - ^ I ^ O - | Λ Ί 4

- C s Ν — 0 + Ν m C - Rf R f —C

s C-

\

f Ν

FC - R " - C F

C-Rf'

—

f

0 - N

N-N

• Rf' — '

V

N - 0 /

W

Ν —Ν - R,"-'

X

n

λ

-

Rf = PERFLUOROALKYLENE ETHER

Figure 9.

Chain extension reactions

CONTINUED SERVICE TEMPERATURE,*C

FLUOROETHER BACKBONE

CF

-ifV

ÇF

3

CF (CF- C F

2

2

*e

CROSS-LINK

ÇF,-

3

5

- C F - f 0 C F C F 4- 0 ( C F L O

Tg,

2

0 f

CF —

n

Ν —0

230

-43

CN

260

-50

C F OR CN

X ÇF3

— f V- C F {

ÇF

ÇF 0 (CF- C F

ÇF -

3

3

0 CF2CF) O(CF ) m

2

5

3

2

0} CFn

X

Figure 10.

I.

Heterocyclic-perfluoroalkylene

INCORPORATE

ο / \

C F - CF - ( C F ) 2

2

ether copolymers

ο / \

2

- CF - C F

2

INTO FLUOROETHER SYNTHESIS

CF 2.

INCORPORATE

NC — ^

(

3

_

J^—C—^^—CH

CN

INTO TRIMERIZATION OF FLUOROETHER DINITRILE

Figure

11.

Poly functionality

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

6

5

13.

ROSSER

ET

AL.

Polyperfluoroalkylene Ethers

195

A t o t a l l y d i f f e r e n t approach to enhancing the l i n e a r i t y of the f l u o r o e t h e r s i s based on the p r e p a r a t i o n of p o l y ( i m i d o y l amidine). In the f i r s t step of Figure 12, the d i n i t r i l e i s f i r s t converted to an amidine which i s i s o l a t e d and p u r i f i e d . More d i n i t r i l e i s then added to the amidine to give a linear p o l y ( i m i d o y l amidine). Ring c l o s u r e to t r i a z i n e can be accomplished with an a c i d f l u o r i d e or an anhydride. For example, a low-molecular weight, l i n e a r p o l y ( i m i d o y l amidine) derived from 8-EDAF d i n i t r i l e was prepared and converted to the p o l y t r i a z i n e by (CF CO) 0 treatment. In p r e l i m i n a r y experiments, the corresponding t r i a z i n e was prepared with pendant -(CF2) CN groups by p a r t i a l treatment of the p o l y ( i m i d o y l amidine) with (NECCF CF CF CO) 0. Mole-ratios of 85:15 and 70:30 of (CF CO) 0 : [ N C ( C F ) C 0 ] 0 , r e s p e c t i v e l y , were used. V o l a t i l e s were removed, and the residues were viscous l i q u i d s which containe the i n f r a r e d . It is significan of p e r f l u o r o s e b a c o y l n i t r i l e to t r i a z i n e , a hard p l a s t i c with a T of 110° C r e s u l t s . However, by evoking the stepwise l i n e a r growth of p o l y ( i m i d o y l amidine) a s u b s t a n t i a l lowering of the Tg was reported. Thus, we can take advantage of the chemistry learned i n chain extensions shown i n the previous f i g u r e s and introduce pendant groups to c r o s s - l i n k with a 1,3-dipolar c y c l o a d d i t i o n of n i t r i l e oxide to e i t h e r n i t r i l e or acetylene; t h i s gives us a low-temperature c u r i n g mechanism, as shown i n Figure 13. One can a l s o v i s u a l i z e , although i t i s not shown, a t r i m e r i z a t i o n of the pendant n i t r i l e by using a c a t a l y s t such as t e t r a p h e n y l t i n to give a c r o s s - l i n k e d system where three chains are t i e d together. Another approach i s shown i n F i g u r e 14. Here, we have an a r y l ether c r o s s - l i n k r e s u l t i n g from a p-fluoroaromatic pendant group which undergoes f a c i l e n u c l e o p h i l i c s u b s t i t u t i o n with the dipotassium s a l t of hexafluoroacetone bisphenol. Of course, η i s much greater than m and can be c o n t r o l l e d by a l t e r i n g stoichiometry. I t has been documented (10) that p o l y t r i a z i n e s d e r i v e d from p e r f l u o r o a l i p h a t i c d i n i t r i l e s are tough and, i n some cases, brittle. Thus, i t i s conceivable that, by mixing a f l u o r o a l i p h a t i c d i n i t r i l e with a long-chain f l u o r o e t h e r d i n i t r i l e and subsequently polymerizing to a p o l y t r i a z i n e , the r e s u l t i n g m a t e r i a l would d i s p l a y p r o p e r t i e s intermediate between the p o l y t r i a z i n e s derived from homopolymerization of the n i t r i l e s . This approach i s c u r r e n t l y under i n v e s t i g a t i o n . Various r a t i o s of 7-EDAF dimer d i n i t r i l e and p e r f l u o r o s e b a c o n i t r i l e have been polymerized with c a t a l y t i c q u a n t i t i e s of ammonia at 225° C. P r e l i m i n a r y r e s u l t s are shown i n Figure 15 which c l e a r l y demonstrates the p r i n c i p l e s t a t e d . In summary, we b e l i e v e the long-chain p e r f l u o r o e t h e r polymers a f f o r d e x c e l l e n t o p p o r t u n i t i e s f o r a p p l i c a t i o n i n the 3

2

3

2

3

2

2

2

2

3

2

2

g

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

-

R f

'_CN +

NH

H N [J R 2

NH

2

I

'

C

S

^ N

C

f s

l! NH

NH N H

II /

/

II

^ R " " f

C

/

2

2

FC ( C F ) X

I

^ N ^

C

2

^ R "

FC-CF

f

3

3

Ο

ΝγΝ

OR H y ^ - F

N ^ N

X

CF

Figure 12.

R = PERFLUOROALKYLENE ETHER SEGMENT

3

f

Chain extension—polyimidoyl

if V CF

amidine

Rf "

3

R = PERFLUOROALKYLENE ETHER f

Figure 13.

Heterocyclic

cross-link

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ROSSER

Polyperfluoroalkylene

ET AL.

Ethers

- Î *T-< R

CF

3

F3C-Ç-CF3

Figure 14.

Aryl ether cross-link

40 \

30 - \

5 6 2 3 4 FLUOROETHER CHAIN , BY WEIGHT FLUOROALIPHATIC CHAIN

Figure 15.

Effect of copolymer ratios on T

g

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

198

area of high-temperature elastomers and, i n p a r t i c u l a r , as a supersonic f u e l tank sealant. The accomplishments to date c l e a r l y p o i n t out the importance of o b t a i n i n g both low- and high-temperature p r o p e r t i e s that have s u f f i c i e n t molecular weight to achieve mechanical form. The d e f i c i e n c i e s i n applying a 1:1 a p p l i c a t i o n of Dr. P r i c e ' s mechanism i n achieving high molecular weights have yet to be overcome i n these systems. However, we b e l i e v e the i n c r e a s i n g use of f l u o r o e t h e r s f o r other a p p l i c a t i o n s w i l l lead to s i m p l i f i c a t i o n of the chemistry that i s involved i n a t t a i n i n g high molecular weight polymers. Literature Cited St. P i e r r e , L. E. and P r i c e , (1956) 78, 3432.

2.

P r i c e , C. C. and Osgan

3.

Osgan, M. and P r i c e , C. C.: J. p. 153, Nottingham Symposium.

4.

A r n o l d , R. G., Barney, A. L. and Thompson, Chemistry

and

Technology

S.:

J.

(July

Macromol

C.:

Polym.

1973)

Sci.

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Eleuterio, 1027.

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S i a n e s i , D., P a s e t t i , Α., F o n t a n e l l i , R., B e r n a r d i , G. C. and C a p o r i c c i o , G.: La Chimica E L'Industria (1973) 55(2), 208.

7.

Z o l l i n g e r , J. L., Throckmorton, J. R., Ting, S. T. and Mitsch, R. Α.: "Polymers i n Space Research," C. L. Segal, ed., p. 409, Marcel Decker Inc., Ν. Y., 1970.

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Webster, J. Α., NASA Report, NAS-8-21401, (Monsanto Res. Corp., Ohio), Mar 1972.

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F r i t z , C. A. and Warnell, J. L.: U.S. (1967).

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Dorfman, Ε., Emerson, W. E. and Lemper, Chemistry

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(1972) A6(6),

Pat. 3,317,484

A.

I.:

Rubber

1175.

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

INDEX

C

A Activation, chain 33 Activation parameters in polymerization .156, 165 Addition, monomer 22, 28, 35 Addition, sequential 26 A G E (allyl glycidyl ether) 101 elastomers, T M O 106,112, 114 Aged Parel elastomer 123, 124 Aging, heat 126 Air aging of T M O - A G E vulcanizate Alkylene copolymers, arylene1 Allyl glycidyl ether (AGE) 101,120 copolymer, propylene oxide48, 101 Amorphous catalyst sites 11 polymer 10 poly (propylene oxide) 146 Angles, bond 90, 92 Anionic polymerization 3 Applied crystallization kinetics 70 Aryl ether cross-link 197 Arylene-alkylene copolymers 15 Asymmetric catalytic sites 139 Atactic poly (propylene oxide) 137 Avrami theory and plots 44, 67 Β

Backbone, ether linkage in polymer 1 Barriers, torsional 92 Base catalysis 3,21 B C M O (3,3-bis(chloromethyl) oxetane) 150 polymerization 160, 162, 164, 165 Biorefrigence changes from heating 49 3,3,-Bis (chloromethyl) oxetane (BCMO) 150 Block copolymers .173, 176 Bond angles 90, 92 lengths 90 stretching 92 Bonding, hydrogen 92 Brominated poly(phenylene oxide) 169, 178 Bromination of poly (phenylene oxides), direct 178 Bromination, ring 180 Bromophenols, polymerization and copolymerization of 169 Bromopolymers, H NMR spectra of .... 174 Bromopolymers, oxygen indices of 182 4-Bromo-2,6-xylenol 12 f-Butylethylene oxide 4 f-Butyl hydroperoxide (TBHP) 124 n-Butyllithium cleavage of poly(propylene oxide) 142 l

C~C coupling C - O coupling Calculated intensity Calculated structure factors Calorimetry, differential scanning Carbon-13 NMR analysis Catalysis, base Catalysis, potassium hydroxide Catalyst chelate

13 13 97 97 60,181 140 ..... 3, 21 31 104

different 43 Et Al-0.5 H 0-acetyl acetone 108,109 sites amorphous 11 asymmetric 139 chiral 9 control of 9 isotactic 11 stereoelective coordination 10 stereoselective coordination 9 systems .38,102 zinc hexacyanocobaltate complex 20 Cationic polymerization 7,150 Chain activation 33 end control 9 extension of polyethers 185, 194, 196 process, Markov 40 propagation 27, 33 scission 128 structure, up and down 39 termination 26 Characterization, polymer 105 Chelate catalysts 104 Chelation 5 Chemical shifts for protons 174 Chiral catalyst sites 9 Chromatogram, gas 143 Chromatogram, gel permeation ...25, 28, 32, 35 Cleavage of dechlorinated H E R C L O R Η elastomer 142 extent of 144 mixtures 140, 143 of poly (propylene oxide) 140, 142 Commercial poly(propylene ether) diol 32 Comonomer 46 Complex catalyst, zinc hexacyanocobaltate 20 Composites 60 Compression set 127,128,129 Configuration triads 39 Contour map, energy 94 3

2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

202 Coordination catalysts 101 for polymerizing epoxides 102 stereoelective 10 stereoselective 9 Coordination polymerization of epoxides 9, 101 Copolymer arylene-alkylene 15 block , 176 elastomers, P O - A G E 101 heterocyclic-perfluoroalkylene ether 194 propylene oxide . 4 6 , 51, 53 and allyl glycidal ether of 48 ratios on glass transition temperature, effect of 197 stress optical coefficient of 51 structure, block 173 Copolymerization 176 of bromophenols and 2,6-dimethylphenol ....... . 169 relative reactivity of monomer of T M O with coordination catalysts 101 with saturated epoxides 110 with unsaturated epoxides and oxetanes Ill Coulombic potential 94 Counteranion 160 Coupling C-C 13 C-O 13 oxidative 12, 171 Cross-coupling reactions 172 Cross-link aryl ether 197 heterocyclic 196 scission 128 sulfur 120 triazine 192 Crystal structure defects of polymer 87 models 90,92 multi-state 87 Crystalline fractions of propylene oxide polymers 43 polyepichlorohydrin 148 family of 81 microscopic and dilatometric melting temperatures of .. 75 typical 73 polymers, structural refinement of 95 polymers, x-ray structural analysis of 86 poly (propylene oxide) 146 Crystallization heterogeneous nucleation of isotactic poly (propylene oxide) 58 isotherms 44, 64, 65 kinetics .42,45,70 parameters for poly (propylene oxide) 46 primary .... 63 rate of polyepichlorohydrin 80 rates of spherulites 78 stress-induced 47 temperature 65 Cure systems, sulfur 120 Cure time 106 Cyclic ethers, cationic polymerization of 150

D

Data, treatment of unobserved 96 Dechlorinated H E R C L O R H elastomer 142, 143 Dechlorination with L A H 148 Dechlorination of polyepichlorohydrin .... 139 Decomposers, stabilization and hydroperoxide 123 Dibromo-2,6-dimethylphenol 169 Differential scanning calorimetry 60, 181 Diffraction techniques, x-ray 86 Dihedral angles 93 Dilatometric melting curve 77 Dilatometry 60,62,71 Dilaurylthiodipropionate (LTDP) 124 Dimensional order, limited long range three 86 Dimer units 137 2,6-Dimethylphenol, copolymerization of bromophenols and 169 Poly(propylene ether) diol) Diphenyl ether 11 Dipropylene glycols 142, 143 Displacement, S 2 2 Distribution narrow molecular weight 26 sequence 41 stereosequence 38 triad 41 Disulfides 120 DMSO (dimethylsulfoxide) 6 Dormant species 159 Downfield shift of hydrogen 7 Dynamic modulus 51, 53, 54, 132 Dynamic properties 129 N

Ε Elastomers 47 aged Parel 123, 124 dechlorinated H E R C L O R 142,143 fluoro186 high-temperature 198 neoprene 126 oxetane 115, 116 Parel , 122 P O - A G E copolymer 101 polyetherurethane 21, 102 studies, early polyether 101 TMO-AGE 106, 112, 113, 114 T M O and PO 115 vulcanizates 103 vulcanized Parel 121, 122, 127 E elimination 2 Enantiomer 83 End capping 151, 188 Energetic constraints for crystal structure models 92 Energies, packing 92 Energy contour map 94 epoxide-silica interfacial 62 filler-polymer interaction 59 pair wise potential 94 Epichlorohydrin homopolymer 139 Episulfide polymerization 10 2

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

203

INDEX Epoxides anionic polymerization of 3 cationic polymerization of 7 coordination catalysts for polymerizing 102 coordination polymerization of 9 silica interfacial energy 62 substituted ... 136 T M O copolymerization with 110, 111 1,2-Epoxides 20 Erythro isomers 11 Esters, superacid 150 Et
F NMR spectroscopy Filler content for silica fillers Filler-polymer interaction energy First-order rate plots Fluids, Fomblin Fluids, Krytox Fluorinated polymers Fluoro-elastomers Foam rubber, polyurethane Foams and elastomers, polyurethane Fomblin fluids Force changes from heating Formulation for Parel elastomer, vulcanization Four-parameter model Frequency for propylene oxide copolymer Fuel tank sealant, supersonic Functionality determination Functionality, hydroxyl 1 9

154 64 59 25 190 188 186 186 1 21 190 49 122 40 51,53 198 22, 29 30

G Gas chromatogram 143 Gas chromatographic analysis of cleavage mixtures 140 Gel permeation chromatogram 25, 28, 32, 35 Geometric constraints for crystal structure models 90 Glass transition temperatures 130, 181, 186, 197 Glycols, dipropylene 142 Growth rates of spherulites 78 Gum vulcanizate properties of T M O - A G E elastomer 114 H *H NMR spectra of B C M O polymerization

164

Ή NMR (Continued) spectra of the bromopolymers 174 spectroscopy 154 Head-to-head linkages 136 Heat aging 126 Heating, force and biorefrigence changes from 49 Helical conformation 91 Helix, hypothetical three-atom 93 H E R C L O R Η elastomer 142, 143 Heterocyclic cross-link 196 Heterocyclie-perfluoroalkylene ether copolymers 194 Heterogeneous nucleation of isotactic poly (propylene oxide) crystalliza­ tion 58 Heterogeneous nucleation theory 61 Heterotactic triads 39 Hexafluoropropylene oxide polymerization 188 Homopolymerization, T M O Homopolymers Hydrogen bonding Hydrogen, downfield shift of Hydroperoxide decomposers, stabilization and Hydroxyl functionality Hypothetical three-atom helix

.101, 107 47, 139 92 7 123 30 93

Imaginary component of dynamic modulus 53 Imide-linked perfluoroalkylene ether 190 Incremental monomer addition 28 Index, residual 98 Induction time 65 Initiation of BCMO polymerization 162 Initiators 157, 161 Insoluble fractions of copolymers, stereoregular 48 Intensity, calculated 97 Intensity, threshold 96 Interaction energy, filler-polymer 59 Interactions, non-bonded 92 Interactions, polar 92 Interfacial energy 62 Intrinsic viscosity from ring bromination 180 Irregular structures in polyepichlorohydrin 136 Isolation, polymer 104 Isomers, erythro and threo 11 Isosyn sequences 6 Isotactic catalyst sites 11 poly (propylene oxide) 38, 88, 137 crystallization, heterogeneous nucleation of 58 crystallization isotherms of pure .64, 65 system, silica58 sequences 5, 82 triads 39 Isotherms, crystallization 44, 64, 65 Isotherms, sigmoidal 63

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

FOLYETHERS

204

Κ

Kinetic studies 21, 23 Kinetics crystallization 42, 45, 70 of the EtOS0 CF -inirJated polymerization 154, 160 of the T H F polymerization by phenoxyI end-capping method ... 151 Krytox fluids—end capping 188 2

3

L L A H , dechlorination with L A H treatment Lead dioxide oxidations Least squares analysis Least squares residue Lengths, bond Line search minimization Linear polymers Linkage in polymer backbone, ether Linkages head-to-head head-to-tail tail-to-tail Long-chain perfluoroether Long range three dimensional order, limited L T D P (dilaurylthiodipropionate)

148 144 176 89 98 90 95 1 1 13 13 136 192 86 124

M

Map, energy contour 94 Markov chain process 40 Mechanical properties of rubber vulcanizates 46 Mechanism, polymerization 31 Mechanism, S 2 151 Melting curve, dilatometric 77 of spherulites 76 temperatures of polymers 43, 75 Microscopic melting temperatures 75 Microscopy ... 70 Microstructure, polymer 137, 139 Minimization, line search 95 Modulus, dynamic (see Dynamic modulus) Molecular weight characterization 22 Molecular weight for poly ( propylene ether) diols 26, 30 Monobromo-2,6-dimethylphenol, polymerization of 169 Monomers 104 addition 22, 28, 35 relative reactivity of 105 Monopole approximation 94 Morpnology of propylene oxide polymers 42 Morphology, spherulite 72 Multi-state structure in crystals 87 N

Ν Narrow molecular weight distribution ... NBC (nickel dibutyldithiocarbamate) .... Neo-pentyl effect Neoprene elastomers Nickel dibutyldithiocarbamate (NBC) .... NMR analysis of polyepichlorohydrin, carbon-13

26 123 7 126 123 140

NMR (Continued) shift, upfield 7 spectra of B C M O polymerization, *H 164 spectra of the bromopolymers, *H 174 spectroscopy, H and F 154 Non-bonded interactions 92 Non-crystalline material 88 Nucleation heterogeneous 58, 61 of spherulites 78 X

1 9

Ο [ 0 ] fraction in the T H F polymerization 156 Observed structure factors 97 Optical analysis, thermal 181 Optical coefficient, stress 51 Order, limited long range three dimensional 86 Oxetane elastomers 115, 116 +

Oxidations, lead dioxide Oxidative coupling Oxonium species Oxygen indices

176 12,171 159 182

Ρ Packing energies 92 Pairwise potential energy 94 Parameter model, a four 40 Parel elastomer compression set of vulcanized 127 effect of stabilizer on aged vulcanized 124 physical properties of aged 123, 126 stress relaxation of vulcanized 121 vulcanizates 103, 122 vulcanization formulation for 122 1,5-Pentanediol 21 Perfluoroalkylene ether copolymers, heterocyclic194 Perfluoroalkylene ether, imide-linked .... 190 Perfluoroether, long-chain 192 Phenols, redistribution of 171 Phenoxyl end-capping method 151 Photolysis, polyether through 190 Plasticity, Williams 32 PO (propylene oxide) elastomers 101, 115 Polar interactions 92 Poly (f-butylethylene oxide) 4 Poly ( 2,6-dimethyl-l,4-phenylene oxide) 169,178 Polyepichlorohydrin carbon-13 analysis of 140 crystalline 73,81,148 crystallization rate of 80 dechlorination of 139 irregular structures in 136 microscopic and dilatometric melting temperatures of 75 spherulites 72 stereoregularity of 70 Polyepoxides 2 Polyethers 1 chain extension 185 elastomer studies 101 through photolysis 190

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

205

INDEX

Polyetherurethane elastomers 102 Polyfunctionality 194 Polyimidoyl amidine 196 Polymer amorphous 10 backbone, ether linkage in 1 bromo 182 characterization 105 crystalline 86,87,95 fluorinated 186 interaction energy, filler59 isolation 104 linear 1 microstructure on physical properties, influence of 137 propylene oxide (see Propylene oxide polymers and Poly (propylene oxide) ) radicals 172 segment, protons in the 174 Polymerization BCMO 160,162 bromophenols 169 catalysts for 102 of cyclic ethers, cationic 150 different extents of 25 episulfide 10 of 1,2-epoxides 20 of epoxides 3, 7, 9 hexafluoropropylene oxide 188 mechanism 31 of mono-, di-, and tribromo-2,6dimethylphenol 169 of oxetanes 109, 111 seeded 24 studies 103,107 of tetrahydrofuran 150, 151,154,156,157, 164 of trimethylene oxide (TMO) 101, 108 Polyols, poly (propylene ether) 20 Polyphenylene oxides 11 Poly (propylene ether) diol 21 commercial 32 formation 24,25,28,30 hydroxyl functionality vs. molecular weight for 30 molecular weight of 26 polyurethanes prepared from 32 prepared by incremental monomer addition 28 Poly (propylene ether) oxide 64,65 Poly (propylene ether) polyols 20 Poly (propylene ether) triols 34 Poly (propylene oxide) (see also Propylene oxide polymer) 1, 3 atactic 137 cleavage of 140, 142 crystalline and amorphous 146 crystallization 46, 58 from dechlorination with L A H 148 isotactic 38,88, 137 rubber 20 spherulites of 42 system, silica-isotactic 58 Polyperfluoroalkylene ethers 185 Polysulfides 120,121

Polyurethane 31,185 foam rubber 1 foams and elastomers 21 prepared from poly (propylene ether) diols 32 Potassium hydroxide catalysis 31 Potential, 6-12 94 Potential, Coulombic 94 Potential energy, pairwise 94 Primary crystallization 63 Propagation of B C M O polymerization 162 chain 27,33 rate constant of 152, 160, 161 rate during poly (propylene ether) diol formation .28,30 Propylene oxide (PO) 3,136 -allyl glycidyl ether copolymers 48, 101 catalyst systems for polymerizing 102 copolymers 51,53,54 crystallization kinetics of melting temperature of morphology of percent crystallinity of stereosequence distribution of stereosequence length of texture of rubber sequential addition of Protons in the polymer segment

42, 45 43 42 43 38 43 49 46,120 26 174

R Racemic mixtures 83 Radicals, polymer 172 Rate constant in the B C M O polymerization 165 of propagation 152,160, 161 in the T H F polymerization 156 Reaction mechanism 163 Reactivity of monomers in copolymerization 105 Real component of dynamic modulus .... 51 Redistribution of phenols 171 Redistribution reactions 170 Relaxation, stress 121, 130, 131 Residual index 97,98 Resolution of the dipropylene glycols .... 143 Rigidity, torsional 115 Ring bromination 180 Ring opening polymerization 8, 20,150 Rubber natural 126 poly (propylene oxide) 20, 46, 120 polyurethane foam 1

S S 2 reaction Saturated epoxides Scanning calorimetry, differential Scission, chain or cross-link Sealants, high-temperature Sealants, supersonic fuel tank Seeded polymerizations Sequence distribution N

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2, 20, 151 110 60, 181 128 185 198 24 41

POLYETHERS

206 Sequence (Continued) isosyn 6 isotactic 5, 82 syndiotactic 5, 10 Sequential addition of propylene oxide 26 Sigmoidal isotherms 63 Silica 60 fillers . 64 interfacial energy, epoxide62 -isotactic poly (propylene oxide) system 59 Skeletal conformation 91 Sleeping species 159 Spectra of the bromopolymers, *H NMR 174 Spectroscopy *H and F NMR 154 Spherulites crystallization rates of 78 growth rates of 78 melting of 76 morphology 72 nucleation of 7 polyepichlorohydrin 7 of poly (propylene oxide) 4 Stabilization 120, 123, 124 Stereochemistry for ring opening 8 Stereoelective coordination catalyst 10 Stereoregularity 35, 48, 49, 70 Stereoselection 5 Stereoselective coordination catalysts 9 Stereosequence distribution 38 Stereosequence length of polymers 43 Stress-induced crystallization 47 Stress optical coefficient 51 Stress relaxation 121, 130, 131 Stretching, bond 92 Structural analysis of crystalline polymers, x-ray 86 defects of polymer crystals 87 refinement of crystalline polymers 95 Structure block copolymer 173 in crystals, multistate 87 factors, observed and calculated 97 models, constraints for crystal 90, 92 in polyepichlorohydrin, irregular 136 trial 94 up and down chain 39 Substituted epoxides 136 Sulfur compounds, decomposition of T B H P by 125 cross-linking 120 cure systems 120 Superacid esters by 150 Supersonic fuel tank sealant 198 Syndiotactic sequences 5, 10 Syndiotactic triads 39 1 9

Τ Tail-to-tail linkages Tank sealant, supersonic fuel TBHP (ί-butyl hydroperoxide) decomposition . . . . Teflon Temperature on compression set, effect of crystallization

136 198 124 125 186 127 65

Temperature (Continued) on the crystallization rate, effect of .... 80 dynamic modulus vs 53, 54, 132 glass transition 130, 181, 186, 197 of polymers, melting 43,75 on propagation rate, effect of 28 torsional rigidity vs. 115 Termination reaction, chain 26 Tetrahydrofuran (see T H F ) Tetramethylene oxide 2 Texture of propylene oxide polymers .... 49 Thermal optical analysis 181 T H F (tetrahydrofuran) 150 polymerization of 150, 156 by E t O S 0 C F , 154, 157, 164 by EtOSO.F .' 157 by phenoxy end-capping method .... 151 Three-atom helix, hypothetical 93 Three dimensional order, limited long range 86 Threo isomers 11 2

on compression set, effect of 127 cure 106 induction 65 T M O (Trimethylene oxide) - A G E elastomers 112 effect of cure time on 106 gum vulcanizate properties of 114 torsional rigidity vs. temperature for 115 vulcanizate properties of 113 - A G E vulcanizate 114 effect of air aging on 114 coordination polymerization of 101 copolymerization 110, 111 homopolymerization 101, 107 polymerization of 108 2,4, Tolylene diisocyanate 32 Torsional barriers 92 Torsional rigidity 115 Transition probabilities 40 Treated silica fillers 64 Triads configuration 39 distribution of 41 heterotactic 39 isotactic 39 syndiotactic 39 Trial structures 94 Triazine, cross-linked 192 Tribromo-2,6-dimethylphenol 169 Trimethylene oxide ( T M O ) 101 Triols, poly(propylene ether) 34 Triphenylphosphine 121

U Unobserved data, treatment of Unsaturated epoxides and oxetanes Untreated silica fillers Up and down chain structure Upfield shift

96 111 64 39 7, 174

V Viscosity, intrinsic Vulcanizate oxetane elastomers

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

180 116

INDEX

Vulcanizate (Continued) Pare! elastomer properties, gum rubber studies Vulcanization formula Vulcanization studies Vulcanized Parel elastomer 121, 122,

W 113,

106, 105, 124,

103 114 46 112 122 120 127

Williams plasticity

X X-ray diffraction techniques X-ray structural analysis 2,6-Xylenol Ζ

Zinc hexacyanocobaltate complex catalyst

In Polyethers; Vandenberg, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.