Anionic Polymerization of Fluorocarbon Epoxides

19 Anionic Polymerization of Fluorocarbon Epoxides JAMES T. HILL and JOHN P. ERDMAN

Downloaded by UNIV LAVAL on June 18, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0059.ch019

Ε. I. du Pont de Nemours and Co., Inc., Elastomer Chemicals Department, Experimental Station, Wilmington, D E 19898

The o b j e c t i v e o f these. investigations was t o prepare p e r f l u o r i n a t e d polyether elastomers having b o t h good low temperature flexibility and h i g h thermal stability. The r i n g opening p o l y m e r i z a t i o n s o f h e x a f l u o r o p r o p y l e n e epoxide (HFPO) and o c t a f l u o r o i s o b u t y l e n e epoxide (OFIBO) were examined as a potential r o u t e t o such m a t e r i a l s . 0 /\ CF CF-CF 5

0 /\ (CF^) C-CF x

2

2

HFPO

2

OFIBO

A number o f n u c l e o p h i l e s a r e c a p a b l e o f opening t h e epoxide r i n g s in t h e s e monomers (1,2,3). F l u o r i d e i o n opens t h e r i n g s r a p i d l y w h i l e p r e s e r v i n g the p e r f l u o r i n a t e d nature o f the products. Nucleo philic a t t a c k o c c u r s e x c l u s i v e l y a t the more sub stituted c a r b o n f o r m i n g isolable p e r f l u o r o a l k o x i d e s .

CF CF CF Cf M 5

2

+

(CF^) CFCF Cf

2

2

2

M

+

Under some c o n d i t i o n s t h e salts l o s e t h e elements o f MF and form t h e c o r r e s p o n d i n g acyl fluorides. The s o u r c e o f t h e fluoride i o n and n a t u r e o f its g e g e n i o n a r e i m p o r t a n t b o t h in t h e ring opening r e a c t i o n and to the stability of the alkoxide product. Of more +

-

269

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

270

RING-OPENING POLYMERIZATION

than 40 fluoride s a l t s i n v e s t i g a t e d cesium f l u o r i d e was f o u n d t o be most effective for initiating ring opening and f o r m i n g s t a b l e a l k o x i d e s . The a l k o x i d e s can r e a c t w i t h additional epoxide t o form s t r a i g h t c h a i n o l i g o m e r s ( 4 ) .

ο

^

CP


CP^CPCPg + Ρ

—

• CFy3F CF 0 2

2

HFPO

CP

I

I

-

t> C F C F C F 0 ( C F C F 0 ) C F C F 0 5

2

2

2

n

2

A medium i s r e q u i r e d f o r cesium f l u o r i d e t o r e a c t w i t h e i t h e r HFPO o r OFIBO a t room t e m p e r a t u r e . T e t r a g l y m e (TG) was f o u n d t o be t h e b e s t o f a number of p o l a r and n o n - p o l a r media t e s t e d . I n i t i a t i o n or r i n g opening by cesium f l u o r i d e i n t e t r a g l y m e i s d i f f i c u l t because o f t h e low s o l u b i l i t y o f t h e s a l t i n e i t h e r t h e s o l v e n t o r t h e l i q u i d monomers. Poly m e r i z a t i o n i s slow t o i n i t i a t e , d i f f i c u l t t o c o n t r o l and i s accompanied by a c h a i n t r a n s f e r r e a c t i o n w h i c h y i e l d s o n l y low m o l e c u l a r weight o l i g o m e r s . From t h e r e a c t i o n o f HFPO we were a b l e t o i s o l a t e and c h a r a c t e r i z e o l i g o m e r s up t o t h e t e t r a d e c a m e r . H i g h e r o l i g o m e r s were n o t d e t e c t e d . As shown below the c h a i n t r a n s f e r r e a c t i o n f o r m a l l y can be r e p r e s e n t e d b y t h e e l i m i n a t i o n o f s o l v a t e d cesium f l u o r i d e from t h e growing a l k o x i d e f o l l o w e d by f l u o r i d e a t t a c k on epoxide t o g e n e r a t e new polymer c h a i n s . 0 - + R CF 0 Cs * R CF + 11

CsF

0 CsF|

+ C F ^ C F - C F ·> C F ^ C F ^ F ^ O Cs ·» new polymer 2

chains

To p r e p a r e h i g h m o l e c u l a r weight polymers r e q u i r e s t h e u s e o f s o l u b l e cesium p e r f l u o r o a l k o x i d e initiators. The p u r i f i e d a c y l f l u o r i d e o l i g o m e r s can be r e a c t e d w i t h cesium f l u o r i d e i n t e t r a g l y m e t o form w e l l d e f i n e d , s t a b l e , homogeneous i n i t i a t o r


19.

HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

271

solutions. I n t h e c a s e o f HFPO t h e s e i n i t i a t o r s a r e more u s e f u l t h a n f l u o r i d e s a l t s s i n c e t h e y a r e more c o m p a t i b l e w i t h t h e monomer, smoothly i n i t i a t e t h e p o l y m e r i z a t i o n , p e r m i t good temperature c o n t r o l and a l l o w t h e s y n t h e s i s o f f l u i d polymers c o n t a i n i n g up t o 100 monomer u n i t s . We have been a b l e t o demon s t r a t e p o l y m e r i z a t i o n s from t h e m o n o f u n c t i o n a l and difunctional initiators shown below.

ο (CP ) CPCF 0Cs/TG + 0ΡΙΒ0 * (CP^ÎgCPCPgOfciCP^ÎgCPgO^CiCP^JgCP


5

2

2

η = 99$· No u n r e a c t e d monomer i s f o u n d i n the r e c o v e r e d s o l v e n t i n d i c a t i n g t h a t c o n v e r s i o n s of HFPO a r e c l o s e t o 100$. Though q u a n t i t a t i v e r e c o v e r y o f the a c y l f l u o r i d e


HILL AND ERDMAN

19.

Polymerization

of Fluorocarbon

Epoxides

275

t e r m i n a t e d polymer i s p o s s i b l e i n most c a s e s i t i s more c o n v e n i e n t t o q u a n t i t a t i v e l y c o n v e r t t h e end groups t o t h e e t h y l e s t e r by quenching w i t h a b s o l u t e e t h a n o l and s u b s e q u e n t l y removing t h e s a l t and t e t r a glyme which s e p a r a t e s from t h e polymer. Polymer

Characterization


Number average

molecular weights

(M ) f o r t h e s e n

polymers c a n be determined b y a v a r i e t y o f methods; v a p o r phase osmometry, IR, UV and s a p o n i f i c a t i o n w i t h a l c o h o l i c potassium hydroxide. P u r i f i e d oligomers up t o t h e t e t r a d e c a m e r were used t o e s t a b l i s h IR e x t i n c t i o n c o e f f i c i e n t s f o r the a c i d f l u o r i d e (5.55 μπι) and t h e e t h y l e s t e r ( 5 . 6 μιη). Number average WW s up t o ~ 2 5 , 0 0 0 a r e a c c e s s i b l e w i t h t h e s e t e c h n i ques; a l l gave e q u i v a l e n t r e s u l t s . F o r polymers i n i t i a t e d by d i f u n c t i o n a l c a t a l y s t s t h e IR method a f f o r d s e q u i v a l e n t weights which a r e c o r r e c t e d t o number average m o l e c u l a r weights w i t h an NMR measure ment o f t h e average f u n c t i o n a l i t y . When c h a i n t r a n s f e r o c c u r s d u r i n g a d i f u n c t i o n a l p o l y m e r i z a t i o n m o n o f u n c t i o n a l polymers r e s u l t w h i c h have a t one end a p e r f l u o r o p r o p y 1 e t h e r group. 1

ι 3J> CF CFgCFgO — ~ C F C O E t s, 133.33 ppm 0CF„ I 3 EtOCCF

monofunctional

polymer

t , 1 3 1 . 5 6 ppm

CF. 1 V> CFCOEt

d i f u n c t i o n a l polymer

The amount o f c h a i n NMR. The secondary ppm (CFCI3) and t h e f i n d that these w e l l

t r a n s f e r can be measured by F f l u o r i n e s ( s ) absorb a t 1 3 3 . 3 3 t e r t i a r y ( t ) a t 1 3 1 . 5 6 ppm. We d e f i n e d , s e p a r a t e d , and easy t o


1 9


276

i n t e g r a t e peaks o c c u r i n t h e r a t i o 2 : 1 f o r monof u n c t i o n a l polymer and t h a t no s" absorbances e x i s t f o r p u r e l y d i f u n c t i o n a l polymers. The r e l a t i v e q u a n t i t i e s i n a m i x t u r e o f mono- and d i f u n c t i o n a l m a t e r i a l s c a n be d e t e r m i n e d from t h e i n t e g r a l r a t i o , t / s , by a p p l y i n g t h e e q u a t i o n : 11

t/s-1/2 ^^ ·^/2


mole f r a c t i o n d i f u n c t i o n a l polymer, D = Examples (bottom) trated i the M i weight. n

3+

o f s p e c t r a f o r a 33$ d i f u n c t i o n a l polymer and a 95$ d i f u n c t i o n a l polymer a r e i l l u s n F i g . 2. F o r any degree o f d i f u n c t i o n a l i t y s e q u a l t o 1 + D t i m e s t h e IR e q u i v a l e n t

Jv^, F u n c t i o n a l i t y , and Time One p o l y m e r i z a t i o n was conducted u s i n g a t e t r a glyme s o l u t i o n o f HFPO t r i m e r a l k o x i d e f o r i n i t i a t i o n and HFP as t h e d i l u e n t ; monomer was added s l o w l y and c o n t i n u o u s l y o v e r 50 h r s . Samples were removed d u r i n g t h e p o l y m e r i z a t i o n t o f o l l o w t h e M as a n

f u n c t i o n o f time and t h e amount o f monomer added. F i g u r e 3 shows t h i s r e l a t i o n s h i p and i l l u s t r a t e s t h e s e v e r e l i m i t a t i o n on M by c h a i n t r a n s f e r . A t t h e end o f 50 h r s t h e Mn was o n l y 5000 compared t o 59*4-00 M e x p e c t e d i f no c h a i n t r a n s f e r had o c c u r r e d . A t 7 h r s i n t o t h i s r u n t h e c h a i n t r a n s f e r parameter, MW theory/Μη, was 8 . 0 , i n d i c a t i n g t h a t each m o l e c u l e o f i n i t i a t o r had undergone an average o f 7 t r a n s f e r reactions. T h i s parameter i n c r e a s e d t o o n l y 1 1 . 9 a t the end o f 50 h r s s u g g e s t i n g t h a t most o f t h e c h a i n t r a n s f e r takes p l a c e e a r l y i n the p o l y m e r i z a t i o n perhaps even a t t h e onset o f p o l y m e r i z a t i o n . We f i n d also that the rate of chain t r a n s f e r increases with i n c r e a s i n g monomer a d d i t i o n r a t e s . Under r e a c t i o n c o n d i t i o n s i d e n t i c a l t o t h o s e u s e d i n t h e above exper iment t r i p l i n g t h e monomer a d d i t i o n r a t e r e s u l t s i n a n

n

5- f o l d i n c r e a s e i n t h e c h a i n t r a n s f e r r a t e w h i l e a 6- f o l d monomer r a t e i n c r e a s e r e s u l t s i n a 1 6 - f o l d



19. HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

277

Figure 1. NMR of the difunctional acyl fluoride and its corresponding cesium alkoxide 14

Figure 2. Partial expanded scale *'F NMR of 33% difunctional poly HFPO (bottom) and 95% difunctional poly HFPO (top)

1

10

j

1

1

20 30 40 TIME (hrs)

Γ

50

Figure 3. HFPO polymerization using cesium HFPO trimer alkoxide initiator



278

increase i n the t r a n s f e r rate. We o b t a i n e d more i n f o r m a t i o n from a s i m i l a r experiment u s i n g t h e d i f u n c t i o n a l i n i t i a t o r i n which b o t h f u n c t i o n a l i t y and Mn were f o l l o w e d as a f u n c t i o n of time. F i g u r e 4 shows t h e m o l e c u l a r weight response. I t i s o b v i o u s t h a t t h e r e i s an i n d u c t i o n p e r i o d f o r the polymerization. The M l a g s c o n s i d e r a b l y b e h i n d t h e t h e o r e t i c a l M up t o ~ 200 min and t h e n i t i n c r e a s e s , f o r a b r i e f p e r i o d f a s t e r than t h e r a t e o f monomer a d d i t i o n , i n d i c a t i n g t h a t t h e r e had been a l a r g e a c c u m u l a t i o n o f u n r e a c t e d monomer d u r i n g the i n d u c t i o n p e r i o d . T h i s slow i n i t i a t i o n i s p r o b a b l y caused by HFPO h a v i n g t o d i f f u s e t h r o u g h t h e mass o f v e r y v i s c o u s t e t r a g l y m e t o f i n d a l k o x i d e groups. Subsequent t h i n n i n g and d i s p e r s i o n o f t h e c a t a l y s t i n c r e a s e s t h e r a t e o f monomer r e a c t i o n . n


n

The o t h e r p o i n t t o observe i n t h i s f i g u r e i s t h e a p p a r e n t d i s c o n t i n u i t y a t 720 min. Here was one o f the p l a c e s t h a t t h e l i v i n g a n i o n i c n a t u r e o f t h e s e p o l y m e r i z a t i o n s was demonstrated. A f t e r 12 hours o f r e a c t i o n monomer a d d i t i o n was stopped and t h e p o l y m e r i z a t i o n m i x t u r e c o o l e d t o - 7 8 ° C and k e p t t h e r e f o r 8 h r . A f t e r rewarming t h e m i x t u r e t o -32°C, monomer a d d i t i o n was r e s t a r t e d and t h e p o l y m e r i z a t i o n continued. The d i s c o n t i n u i t y i s n o t u n u s u a l as a s l i g h t M i n c r e a s e was o b s e r v e d whenever a p o l y m e r i z a t i o n was shutdown and l a t e r r e s t a r t e d . The o b s e r v a t i o n s u g g e s t s t h a t r e l a t i v e t o t h e a l k o x i d e concent r a t i o n HFPO i s always p r e s e n t i n e x c e s s . Figure 5 i l l u s t r a t e s the d i f u n c t i o n a l i t y response f o r t h i s e x p e r i m e n t . The i n d u c t i o n p e r i o d and d i s c o n t i n u i t y a r e a l s o p r e s e n t . From t h e d i f u n c t i o n a l i t y measurements i t i s p o s s i b l e t o c a l c u l a t e a p s e u d o - f i r s t - o r d e r rate constant f o r chain t r a n s f e r , Kt. The average K t f o r t h i s r u n was 7 . 9 x 1 0 ~ s e c ~ . In t h e r a t e e x p r e s s i o n , t h e assumption t h a t t h e number o f a l k o x i d e ends i s c o n s t a n t a t a l l t i m e s l e a d s t o low v a l u e s f o r as c a l c u l a t e d from t h e f i r s t n

e

four points. T h i s might be e x p e c t e d f o r d u r i n g t h e i n d u c t i o n p e r i o d n o t a l l t h e a l k o x i d e ends a r e


l

Polymerization

of Fluorocarbon

Epoxides


19. HILL AND ERDMAN



280

a v a i l a b l e f o r propagation. L a t e r on as the i n i t i a t o r i s more e v e n l y d i s p e r s e d the assumption becomes v a l i d . C a l c u l a t i o n o f Kt from 20 o t h e r p o l y m e r i z a t i o n s r u n under s i m i l a r c o n d i t i o n s gave an average v a l u e o f 8.4 χ l O ^ s e c " . 1

Armed w i t h the c h a i n t r a n s f e r c o n s t a n t and t h e time dependence o f the m o l e c u l a r weight and d i f u n c t i o n a l i t y we d e v e l o p e d the a p p r o p r i a t e k i n e t i c expressions t o estimate the p s e u d o - f i r s t order r a t e c o n s t a n t f o r the r i n g opening p r o p a g a t i o n s t e p . We f i n d that a value o f 8 χ l O ^ s e c " g i v e s the best f i t t o a l l the d a t a . I t i s i n t e r e s t i n g t o note t h a t the v a l u e s we o b t a i n e d f o r K and K i n d i c a t e t h a t the maximum DP p o s s i b l e f o r a polymer i n i t i a t e d w i t h a m o n o f u n c t i o n a l a l k o x i d e i s about 100 (16,500 M ) . The d i f u n c t i o n a l m o l e c u l e s can be e x p e c t e d t o grow t o no more than DP 200 (33,000 M ) b u t t h i s m a t e r i a l would be contaminated w i t h a s u b s t a n t i a l f r a c t i o n o f lower DP m o n o f u n c t i o n a l polymer. U s i n g t h e k i n e t i c parameters d e r i v e d from our experiments we were a b l e to c a l c u l a t e r e a c t i o n t i m e s , monomer a d d i t i o n r a t e s and t h e c o r r e c t amount o f d i f u n c t i o n a l i n i t i a t o r t o use t o p r e p a r e moderate MW d i f u n c t i o n a l polymers c o n t a i n i n g no d e t e c t a b l e monof u n c t i o n a l contaminants. With c a r e f u l c o n t r o l we can r o u t i n e l y p r e p a r e 100$ d i f u n c t i o n a l polymers o f the s t r u c t u r e


1

p

t

n

n

0CP_

CF,

CF,

CF,

F C C F ( 0 C F C F ) -OCF^CF^O(CFCF^O) CFCF 2 m 2 2 2 n v

o

J

K

J

m + η a* 35 C h a i n Extended

Polymers

Because o f the c h a i n t r a n s f e r we were unable t o p r e p a r e e l a s t o m e r i c HFPO homopolymer. The h i g h e s t MW m a t e r i a l s p r e p a r e d were v e r y v i s c o u s l i q u i d s a t room temperature. The c h e m i c a l i n e r t n e s s o f t h e backbone and t h e h i g h r e a c t i v i t y o f t h e a c y l f l u o r i d e and e t h y l


19.

HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

281

e s t e r end groups e n a b l e s t h e c h a i n e x t e n s i o n w i t h a wide v a r i e t y o f r e a g e n t s . A few examples a r e shown below.


R

(J ) F

diols

^

polyesters

diamines

^

polyamides

P o l y e s t e r s were p r e p a r e d by c o n d e n s a t i o n o f t h e d i a c i d f l u o r i d e s w i t h a v a r i e t y o f f l u o r i n a t e d and non-fluorinated d i o l s . A l t e r n a t i v e l y t h e y c o u l d be prepared by metal c a t a l y z e d e s t e r interchange u s i n g the p o l y HFPO d i e s t e r s . Polyamides can be p r e p a r e d e i t h e r by s o l u t i o n o r i n t e r f a c i a l t e c h n i q u e s . These m a t e r i a l s were d e f i c i e n t i n b o t h t h e r m a l and hydrolytic stability. A r o m a t i c c h a i n e x t e n s i o n l i n k s were p r e p a r e d i n an e f f o r t t o i n c r e a s e t h e h i g h temperature s t a b i l i t y o f t h e polymer. B e n z i m i d a z o l e s were s y n t h e s i z e d by condensing e i t h e r the a c i d f l u o r i d e s o r e s t e r s with d i a m i n o b e n z i d i n e and s u b s e q u e n t l y d e h y d r a t i n g w i t h heat. For l,3*^-oxadiazoles the precursor polyh y d r a z i d e s c o u l d n o t be p r e p a r e d by the d i r e c t r e a c t i o n o f t h e a c y l f l u o r i d e s w i t h h y d r a z i n e as i n t r a c t a b l e u n s t a b l e c o r s s l i n k e d m a t e r i a l s were formed. They were b e s t p r e p a r e d by c o n v e r t i n g t h e p r e p o l y m e r end groups t o p h e n y l e s t e r s and then r e a c t i n g w i t h h y d r a z i n e t o form t h e d i h y d r a z i d e s . Subsequent r e a c t i o n w i t h a v a r i e t y o f d i a c i d h a l i d e s afforded a t t r a c t i v e elastomers. Dehydration with phosphorous p e n t o x i d e gave t h e c o - p o l y o x a d i a z o l e s b u t t h e s e were no l o n g e r rubbery.



282

Benzimidazole NH_ B (CF) . + N H


f

2

2

- ^ ) - ^ - N H

— * · —R

2

f

- CNH - ^ g )

Η 1*3*4 O x a d i a z o l e s R(C0P)

n

0

.

1 + C H 0 K -*R (COC H )

N

+

2

6

5

f

6

5

2 4

2

ρο

•

R.C^ f

CCI

» R (CNHNH )

H

f

2

2

^ C -/OV

μ Ν N-

il N ^ / Ν

I

diamine

CCI

1*3*4 t r i a z o l e crosslink

We were u n a b l e t o c h a i n e x t e n d t h e d i f u n c t i o n a l HPPO beyond DP = 10 ( 6 0 , 0 0 0 VL^). As p r e d i c t e d t h e polymers e x h i b i t e d T g s c l o s e t o - 5 0 ° C . The a r o m a t i c l i n k s e x h i b i t e d o n l y f a i r s t a b i l i t y a t 350°C. Though t h e f l u o r i n a t e d c h a i n s i m p a r t some r e s i s t a n c e t o aqueous bases we f i n d t h e m a t e r i a l s c h a i n extended w i t h 5 membered h e t e r o c y c l e s do n o t s u r v i v e such exposure. The s t r o n g e l e c t r o n w i t h d r a w i n g e f f e c t o f f


19. HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

283

the f l u o r i n a t e d s u b s t i t u e n t s r e n d e r t h e r i n g carbons very s u s c e p t i b l e to n u c l e o p h i l i c attack. I n aqueous base the polymers a r e degraded t o the o r i g i n a l molecular weights. The most i n t e r e s t i n g c h a i n extended polymers were t h e s - t r i a z i n e s . The d i e s t e r s can be c o n v e r t e d t o diamides w i t h ammonia and thence t o d i n i t r i l e s 0 • R (C0Et) f


0 ,

NH ^

2

V

C

N

Ρ ο *

V 2

R

f

C

(

s

N

)

2

V NH R

f

( c

S

N

)

2

— 3 +

R

f ( c

-NH ) 2

2

—

r •

4

3

AgO, Δ

j

f

f

Ν γ

γ * ^

N

R

N

f

X

w i t h phosphorous p e n t o x i d e . The n i t r i l e s can be c o n v e r t e d d i r e c t l y t o s - t r i a z i n e s a t h i g h tempera t u r e i n the presence o f s i l v e r oxide c a t a l y s t o r can be c o n v e r t e d t o b i s a m i d i n e s w i t h ammonia. When t h e s e f l u i d s a r e h e a t e d ammonia i s e v o l v e d and t h e t r i a z i n e networks form. L i k e t h e l i n e a r polymers these c r o s s l i n k e d m a t e r i a l s e x h i b i t g l a s s t r a n s i t i o n s i n t h e range - 5 0 t o - 6 0 ° C . They have good h y d r o l y t i c s t a b i l i t y and a r e v i r t u a l l y u n a f f e c t e d b y p r o l o n g e d h e a t i n g a t 350°C. The modulus, t e n s i l e s t r e n g t h , and e l o n g a t i o n a t b r e a k o f the b e s t t r i a z i n e polymers, however, a r e t o o low f o r g e n e r a l use i n molded goods. We b e l i e v e , however, t h a t t h e p o o r p h y s i c a l p r o p e r t i e s a r e n o t due t o i n h e r e n t weaknesses o f t h e HFPO backbone o r the t r i a z i n e l i n k s b u t r a t h e r t o l o o s e c h a i n ends and s h o r t d i s t a n c e s between t h e t r i functional crosslinks.


284


Literature Cited


1 Hill, J. T., J. Macromol. Sci.-Chem., (1974), A8(3), 499. 2 Eleuterio, H. S., U. S. Patent 3,358,003 (1967). 3 Sianesi, D., Pasetti, A. and Tarli, F., J. Org. Chem. (1966), 31, 2312 4 Moore, E. P., U. S. Patent 3,322,826 (1967) 5 Fritz, C. G. and Moore, E. P., U. S. Patent 3,250,807 (1966) 6 Hill, J. T., Eighth Int. Symp. Fluor. Chem., Kyoto, Japan, Aug. 24, 1976.


Anionic Polymerization of Fluorocarbon Epoxides

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