and Copolymers

1

Production and Properties of 2-Cyano-1,3-butadiene Homo- and Copolymers

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E . M Ü L L E R , R. M A Y E R - M A D E R ,

and K. DINGES

Bayer, Leverkusen, West Germany

2-Cyano-l,3-butadiene cyano-1-cyclohexene

was synthesized and characterized

by pyrolysis of 1by physical

data.

Soluble homopolymers and copolymers with butadiene, isoprene, styrene, and chloroprene have been prepared solution

polymerization

Ziegler-Natta ethers or

by

under free-radical, anionic, and

initiation.

Radical

toluene/ether

mixtures

homopolymerization yielded

in

thermoplastic

polymers consisting mainly of 1,4- and 3,4-adducts in a ratio of 3:1. 10°C.

The polymers show glass stages of about

Anionic

initiation below 0°C with lithium alkyls,

metal phosphide, or metal amide catalysts gave thermoplastic

products

stages of about

with 57-70% of 1,2-linkages and glass 80°C.

Initiation with metal acetyl aceto-

nates and organoaluminum

compounds resulted in poly-

mers that in large part correspond to the radical-produced polymers.

Block

polymerization

was

carried

out

with

lithium alkyl compounds, as well as with alkali amides or alkali phosphides.

Cyanoprene polymerized onto polymer

ions formed of styrene, butadiene, or isoprene; the reverse reaction does not occur.

J ) o l y c h l o r o p r e n e has a n u m b e r o f d e s i r a b l e properties s u c h as w e a t h e r a n d o z o n e resistance, flame r e t a r d a n c e , a n d m e d i u m o i l resistance. Its s w e l l i n g b e h a v i o r t o w a r d a r o m a t i c oils, h o w e v e r , is m o d e r a t e , a n d i n f e r i o r t o that of b u t a d i e n e / a c r y l o n i t r i l e c o p o l y m e r s . synthesis b y a d d i n g H C N t o v i n y l a c e t y l e n e .

D u r i n g w o r k o n the

Instead, H C N addition

t i o n a n d c o p o l y m e r i z a t i o n b e h a v i o r o f c o m o n o m e r s s u i t a b l e f o r this purpose

was studied generally.

presence o f a n i t r i l e g r o u p ,

I n v i e w o f its c o n s t i t u t i o n a n d t h e

cyanoprene

(2-cyano-l,3-butadiene)

ap

p e a r e d s u i t a b l e a n d , o w i n g t o l i t t l e reference i n the l i t e r a t u r e , e s p e c i a l l y interesting. 1 Platzer; Polymerization Reactions and New Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

2

POLYMERIZATION REACTIONS A N D N E W POLYMERS

Monomer

Synthesis

2 - C y a n o b u t a d i e n e is n o t accessible a l o n g t h e lines o f c h l o r o p r e n e synthesis b y a d d i n g H C N t o v i n y l a c e t y l e n e .

Instead, H C N addition

results i n l - c y a n o - l , 3 - b u t a d i e n e . H C = CH - C = CH

2 HC = CH

2

HCN

HCI

H C=C-CH=CH 2

HC=CH-CH=CH. i CN

2

CI

T h e r e a r e t h r e e processes d e s c r i b e d i n t h e l i t e r a t u r e f o r s y n t h e s i z i n g cyanoprene

(1-5). CHq •

HCN

3

CH II CH,

CH,

CHo " . ^CN CH 3

CH II CH„

n

CH,

-CN

pyrolysis H C = C - C H = CH 2

2

CN .CN b)

2H C=CHCNV

c)

pyrolysis

2

" H C-C 3

6

Oo/NHq —

i

CH II CH

2

•

H C = C-CH = CH 2

CN

2

CN

h C - C N

i

CH II CH

2

I n Process a , v i n y l m e t h y l k e t o n e reacts w i t h h y d r o c y a n i c a c i d t o g i v e c y a n o h y d r i n , w h i c h is either d e h y d r a t e d b y s p r a y i n g w i t h

phos

p h o r i c a c i d a t 5 4 0 ° C ( y i e l d 74%) o r , after a c y l a t i o n w i t h acetic a n h y dride, pyrolized at 400°-550°C.

I n Process b , a c r y l o n i t r i l e is d i m e r i z e d

b y U V i r r a d i a t i o n t o give 1,2-dicyanocyclobutane; t r i l e is c o n v e r t e d after 84 hours.

8.5% o f t h e a c r y l o n i

T h e c y c l o b u t a n e d e r i v a t i v e reacts b y

c a t a l y t i c s p l i t t i n g at 4 5 5 ° C t o g i v e 2 - c y a n o b u t a d i e n e Process c i n v o l v e s a m m o n o x i d a t i o n o f isoprene.

( c o n v e r s i o n 20%).

O n e p e r cent b y v o l -

Platzer; Polymerization Reactions and New Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

1.

MULLER ET AL.

2-Cyano-l,3-Butadiene

3

Polymers

u m e of i s o p r e n e reacts w i t h a m m o n i a , steam, a n d a i r at 4 2 5 ° C o n z e o l i t e catalysts c o n t a i n i n g c o p p e r ( c o n v e r s i o n 30%, y i e l d 60%).

T h e process

u s e d b y us ( 6 ) is b a s e d o n t h e g e n e r a l r o u t e of s y n t h e s i z i n g 1,3-dienes b y r e t r o - d i e n e s p l i t t i n g of c y c l o h e x e n e d e r i v a t i v e s .

T h e synthesis goes f r o m c y c l o h e x a n o n e

via c y a n o h y d r i n t o

1-cyano-l-

cyclohexene, w h i c h is s p l i t b y p y r o l y s i s .

Pyrolyse *

H C = C-CH 2

= CH

2

CN T h e y i e l d of 2 - c y a n o b u t a d i e n e is 75%.

Properties

of

2-Cyano-l,3-butadiene

2 - C y a n o b u t a d i e n e is l i q u i d at r o o m t e m p e r a t u r e .

Its b o i l i n g p o i n t

at 760 t o r r c a n n o t b e m e a s u r e d d i r e c t l y b u t c a n b e e x t r a p o l a t e d f r o m the v a p o r pressure c u r v e : 9 0 ° C . d e n s i t y at

— 3 0 ° C is 0.89.

polymerize and dimerize.

A t 4 torr, its b o i l i n g p o i n t is 0 ° C .

T h e c o m p o u n d has a s t r o n g t e n d e n c y

to

P o l y m e r i z a t i o n , b u t not d i m e r i z a t i o n , c a n b e

prevented by adding phenothiazine. at r o o m

Its

D i m e r i z a t i o n takes p l a c e q u i c k l y

t e m p e r a t u r e , various k i n d s of

dimers

being

possible.

For

e x a m p l e , l , 4 - d i c y a n o - 4 - v i n y l c y c l o - l - h e x e n e forms i n a b o u t 86% y i e l d ( 7 ) . S t a b i l i z a t i o n of 2 - c y a n o b u t a d i e n e against d i m e r i z a t i o n c a n b e a c h i e v e d by

storage

at l o w

temperatures

and by

dilution w i t h benzene,

for

example. Homopolymerization

of

2-Cyano-l,3'butadiene

T a n a k a ( 8 ) r e p o r t e d p o l y m e r i z a t i o n experiments w i t h b e n z o y l p e r oxide.

H e o b s e r v e d t h e f o r m a t i o n of i n s o l u b l e p o l y m e r s i n a d d i t i o n to

dimer.

Wei

(9)

c a r r i e d out

organoaluminum compounds

polymerizations with

butyllithium

and

a n d obtained amorphous a n d partly crys

t a l l i n e p r o d u c t s w i t h t h e r m o p l a s t i c p r o p e r t i e s ; the m a t e r i a l s m e l t e d at 157°C

and

decomposed

at 3 3 6 ° C .

IR

spectroscopy

showed,

a

1,4-

trans s t r u c t u r e . I n our w o r k , the h o m o - a n d c o p o l y m e r i z a t i o n of

2-cyanobutadiene

were s t u d i e d f r o m the p o i n t of v i e w of t h e i n i t i a t i o n system ( r a d i c a l ,


4


ionic, and coordinate),

a n d t h e m i c r o s t r u c t u r e a n d properties of

the

products obtained were determined. Radical-Initiated H o m o p o l y m e r i z a t i o n .

W h e n this h o m o p o l y m e r i -

z a t i o n is c a r r i e d out w i t h b e n z o y l peroxides or other r a d i c a l formers i n a m a n n e r analogous

to e m u l s i o n p o l y m e r i z a t i o n of

c r o s s l i n k e d p o l y m e r s are f o r m e d . s u c h as toluene, b e n z e n e ,

chloroprene, highly

T h e y are i n s o l u b l e i n o r g a n i c solvents

or c h l o r o f o r m .

Radical polymerization i n

toluene, b e n z e n e , or hexane leads o n l y t o i n s o l u b l e p r o d u c t s . I n assessing these results, i t s h o u l d b e r e m e m b e r e d t h a t t h e t e m peratures i n most cases w e r e a b o v e 0 ° C so that d i m e r f o r m a t i o n has to be

t a k e n i n t o account.

O n t h e one h a n d , d i m e r i z a t i o n reduces

the

y i e l d a n d , o n the other h a n d , i t influences t h e course of p o l y m e r i z a t i o n t h r o u g h a r e g u l a t i n g effect.

Since w e wished to obtain soluble p o l y m

ers, w e h a d t o look f o r different routes.

I n d o i n g so, w e f o u n d that

s o l u b l e p o l y m e r s c a n b e o b t a i n e d w h e n t h e r e a c t i o n is c a r r i e d out i n p o l a r solvents s u c h as ethers or i n i n e r t solvents s u c h as t o l u e n e or hexane i n the p r e s e n c e of cocatalysts—ethers, p h o s p h i n e s , amines, or organoaluminum compounds.

T h e p o l y m e r s o b t a i n e d are t h e r m o p l a s t i c

a n d consist m a i n l y of 1,4-and 3,4-adducts i n a 3:1 r a t i o . CN

Besides the 1,4- a n d 3,4-adducts, c y c l i c structures are also present. Four

representative r a d i c a l p o l y m e r i z a t i o n s of

p a r e d i n T a b l e I.

cyanoprene

are

com

D i f f e r e n t i a l t h e r m a l anlysis shows, f o r t h e m a t e r i a l

m a d e f r o m toluene, a glass stage of a b o u t 10 ° C a n d a m e l t i n g r a n g e above 90°C.

T h e m a t e r i a l has m e d i u m c r y s t a l l i n i t y w h i l e t h e m a t e r i a l

m a d e i n T H F is l a r g e l y a m o r p h o u s . T h e d i s a d v a n t a g e of t h e s o l u b l e p o l y c y c a n o p r e n e s r a d i c a l r e a c t i o n was

obtained by a

that they have molecular weights b e l o w

a n d the y i e l d s w e r e not a l w a y s g o o d .

5000,

T h e r e f o r e , i t was necessary to

l o o k f o r different catalyst systems. Anionically Initiated Polymerization.

T h e disadvantages of r a d i c a l

p o l y m e r i z a t i o n of c y a n o p r e n e r e s u l t f r o m t h e o p e r a t i n g c o n d i t i o n s ( t e m p e r a t u r e s ) ; too

m a n y s i d e reactions, c h a i n - t e r m i n a t i n g reactions, a n d

c o n s e c u t i v e reactions occur.

B e c a u s e of this a n d t h e d i m e r i z a t i o n t e n

d e n c y of c y a n o p r e n e , catalysts h a d t o b e f o u n d that c o u l d f u l f i l l t w o contradictory requirements.

T h e y s h o u l d b e so reactive t h a t i t w o u l d

b e p o s s i b l e to w o r k at temperatures that e x c l u d e d i m e r i z a t i o n s as c o m -


1.

MULLER ET AL.

Table I.

Monomer (mole/l)

Solvent Emulsion in Water Toluene THF Toluene

10 0.29 0.29 0.8

2-Cyano-l,3-Butadiene

5

Polymers

Radical Polymerizations of Cyanoprene Ternperature (°C)

Catalyst (mmole/l) FAS

60

a

A I B N 14.5 AIBN14.5 (AIBN + TEA ) 8.7

6

ReacHon time Yield (h) (%)

50

5

50

50 50 50

24 24 5

50 50 20

Soluble in'

N Analysis (%)

—

17.1

f

— DMF D M F

d

17.9 16.9 16.9

C

° F A S = formamidine sulfinic acid A I B N = azodiisobutyronitrile T E A = triethylaluminum D M F = dimethylformamide • Theoretical nitrogen value = 17.7 The molecular weights of the soluble products were from 1000 to 5000. b

e

d

/

p e t i n g reactions, a n d t h e y s h o u l d b e s l o w e n o u g h to p r e v e n t c r o s s l i n k i n g a n d c y c l i z a t i o n reactions at l o w temperatures. I n v i e w of these p r e c o n d i t i o n s , i t was o b v i o u s to use a n i o n i c initiators. W i t h t h e l i t h i u m alkyls u s e d b y W e i — f o r e x a m p l e , b u t y l l i t h i u m or other organic

alkali compounds—only

insoluble thermoplastic products

are

o b t a i n e d , e v e n at — 80° C i n b o t h T H F a n d t o l u e n e b e c a u s e these i n i tiators are too reactive.

T h e reactions t h a t t a k e p l a c e i n c l u d e attack b y

the m e t a l l o - o r g a n i c c o m p o u n d

a n d the a l r e a d y m e t a l l i z e d c y a n o p r e n e

( o r the m e t a l l i z e d p o l y m e r ) o n t h e n i t r i l e groups of b o t h m o n o m e r a n d polymer. A n i o n i c catalysts of t h e t y p e s h o w n h e r e p r o v e d t o b e s u i t a b l e because t h e y react c o m p a r a t i v e l y s m o o t h l y a n d , u n l i k e o r g a n o - l i t h i u m c o m p o u n d s , t h e y d o not attack t h e C N g r o u p .

(Me=

Li, Na,

K)



I n c a r r y i n g out these experiments, a s o l u t i o n of t h e m o n o m e r is a d d e d d r o p w i s e i n t o a m i x t u r e of catalysts a n d solvents. is d e s t r o y e d , The

products

precipitated from

p l a s t i c i z i n g effect of the solvent. finally

T h e catalyst

a n d the p o l y m e r o b t a i n e d p r e c i p i t a t e d w i t h m e t h a n o l . m e t h a n o l are p l a s t i c , o w i n g t o

the

They swell on drying in vaccum, and

y i e l d t h e r m o p l a s t i c , porous

solids.

D e p e n d i n g on the experi

m e n t a l c o n d i t i o n s a n d t h e catalyst u s e d a n d its q u a n t i t y , the m o l e c u l a r w e i g h t s of the p r o d u c t s are a b o u t 10,000. T h e p r o d u c t s t u d i e d was p r o d u c e d i n T H F w i t h a d i p h e n y l p h o s p h i n e - l i t h i u m catalyst; i t h a d a m o l e c u l a r w e i g h t of 8300.

A f t e r shear

m o d u l u s p l o t t i n g over t e m p e r a t u r e , a glass stage of 81 ° C , a m o d u l u s of

elasticity of

strength of

32,000

661 k g / c m

kg/cm 2

2

(polystyrene^30,000),

(polystyrene^1000)

and a

were found.

flexural

The

glass

t e m p e r a t u r e was 2 0 ° C l o w e r t h a n t h a t of p o l y s t y r e n e , b u t t h e p o l y m e r is m o r e resistant to s w e l l i n g b y aromatics. Table II.

Cyanoprene Homopolymers Produced by Different Catalyst Systems a

Yield Catalyst

(%)

and Copolymers

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