The Diels-Alder Reaction in Polymer Synthesis

'Tphe well-known 1,4-cycloaddition reaction of a 1,3-diene to a dieneo-. -** phile which .... 0 Obtained with a Hewlett-Packard high speed membrane os...
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41 The Diels-Alder Reaction in Polymer Synthesis J. K. S T I L L E , F. W . HARRIS, H . M U K A M A L , R. O. RAKUTIS, C. L . S C H I L L I N G , G. K. N O R E N , and J. A. R E E D University of Iowa, Iowa City, Iowa 52240

The synthesis of high molecular weight polymers through the Diels-Alder step-growth reaction has been investigated for the preparation of polyimides and polyphenylenes. The reaction of biscyclopentadienones with bismaleimides affords high molecular weight, soluble polyimides while the same reaction of the cyclopentadienones with diacetylenes produces colorless, soluble, phenylated polyphenylenes of high molecular weight and in quantitative conversions. The polymers are amorphous, form clear films, and are stable in air to 550°C. The reaction of bis-2-pyrones with the diacetylene dienophile also has been shown to give polyphenyls.

' T p h e well-known 1,4-cycloaddition reaction of a 1,3-diene to a dieneo-** phile which forms a six-membered adduct, commonly known as the Diels-Alder reaction, or diene synthesis, is established as a useful syn­ thetic organic reaction. Although this reaction provides a high yield of

adduct in certain cases, there are few reported syntheses of polymers which use it as a step-growth reaction (21). In theory, this polymeriza­ tion reaction should be successful if a monomer which contains both the diene and dienophilic portions were subjected to the polymerization conditions. Alternatively, high molecular weight polymer should be obtained from the reaction of equimolar amounts of a bisdiene with a bisdienophile. 628

41.

STILLE E T AL.

A A monomer

Diels-Alder

629

Reaction

BB monomer

N o t many h i g h molecular weight polymers have been obtained from this r e a c t i o n , h o w e v e r .

I n most cases, f a i l u r e c a n b e a t t r i b u t e d to the

r e v e r s a l of the d i e n e synthesis (23)

(Reaction 1), a h i g h frequency

side reactions, s u c h as c h a i n - g r o w t h p o l y m e r i z a t i o n of the d i e n e (23,

of 25),

or the i n s o l u b i l i t y of the r i g i d , r i n g - c o n t a i n i n g p o l y m e r w h i c h removes it f r o m the r e a c t i o n m e d i u m

(3).

T h e most successful p o l y m e r i z a t i o n s c a r r i e d out b y u s i n g a D i e l s A l d e r s t e p - g r o w t h r e a c t i o n are those w h i c h generate a h i g h l y r e a c t i v e A - B m o n o m e r in situ b y the r e a c t i o n of a b i s m a l e i m i d e w i t h c y c l o p e n t a dienone

(12),

2-pyrone

(6,

13),

or t h i o p h e n e d i o x i d e ( 5 )

derivatives.

T h e i n t e r m e d i a t e 1:1 a d d u c t loses c a r b o n m o n o x i d e , c a r b o n d i o x i d e , or sulfur d i o x i d e , r e s p e c t i v e l y , a l l to generate the same t y p e of r e a c t i v e A B m o n o m e r , w h i c h is c o n v e r t e d r a p i d l y to p o l y m e r . H i g h m o l e c u l a r w e i g h t p o l y m e r s are o b t a i n e d ( R e a c t i o n 4 ) . Cyclopentadienones C y c l o p e n t a d i e n o n e s c a n u n d e r g o a v a r i e t y of D i e l s - A l d e r reactions, d e p e n d i n g o n the s u b s t i t u t i o n o n the c y c l o p e n t a d i e n e r i n g , the d i e n o p h i l e , a n d the r e a c t i o n c o n d i t i o n s (17).

I n general,

cyclopentadienones

c o n t a i n i n g u p to t w o substituents, a n d i n c e r t a i n cases three substituents, are h i g h l y r e a c t i v e a n d spontaneously f o r m a " n o n d i s s o c i a t i n g " d i m e r (2)

t h r o u g h a s e l f - D i e l s - A l d e r r e a c t i o n . T h e r e f o r e , the reactions of these

cyclopentadienones

w i t h d i e n o p h i l e s are D i e l s - A l d e r reactions of

d i m e r w i t h the a c c o m p a n y i n g loss of c a r b o n m o n o x i d e ( R e a c t i o n 5 ) .

the

630

ADDITION

A N D CONDENSATION POLYMERIZATION

PROCESSES

O t h e r ^ s u b s t i t u t e d a n d c e r t a i n tetrasubstituted c y c l o p e n t a d i e n o n e s are n o t as self-reactive a n d f o r m " d i s s o c i a t i n g dinners" i n s o l u t i o n .

The

c y c l o a d d i t i o n c h e m i s t r y of these c y c l o p e n t a d i e n o n e s is that of the c y c l o -

41.

STILLE E T A L .

Diels-Alder

pentadienone monomer.

631

Reaction

O t h e r tetrasubstituted cyclopentadienones

exist

o n l y as m o n o m e r s a n d also e x h i b i t c y c l o a d d i t i o n reactions as s u c h .

The

difference i n r e a c t i v i t y of t h e t r i s u b s t i t u t e d ( " n o n d i s s o c i a t i n g " vs. "dissoc i a t i n g d i m e r " ) a n d the t e t r a s u b s t i t u t e d ( " d i s s o c i a t i n g d i m e r " vs. mer) cyclopentadienones t r o n i c effects.

mono-

c a n be a s c r i b e d u s u a l l y to steric a n d / o r elec-

T e t r a s u b s t i t u t e d " d i s s o c i a t i n g d i m e r s " are those

c o n t a i n s m a l l a l k y l groups i n the 2- a n d 5- positions ( I , R =

which

C H ) or 3

c o n t a i n a l k y l groups i n these positions w h i c h are not severely buttressed b y A r (e.g., b o t h A r groups i n I r e p r e s e n t e d b y the 1 , 8 - n a p h t h y l m o i e t y ) .

Ill

IV

632

ADDITION A N D CONDENSATION P O L Y M E R I Z A T I O N

PROCESSES

It is the r e a c t i o n of the " d i s s o c i a t i n g d i m e r " or m o n o m e r t h a t is of most interest i n p o l y m e r i z a t i o n . W h e t h e r or not R e a c t i o n 6 p r o c e e d s to afford p r o d u c t s I I , I I I , or I V d e p e n d s o n the d i e n o p h i l e , the d i e n e , a n d the r e a c t i o n c o n d i t i o n s .

Cyclopentadienones

which

are

"dissociating

d i m e r s " c a n b e d r i v e n to I V i n most cases b y t h e a p p r o p r i a t e d i e n o p h i l e at e l e v a t e d temperatures. T h i s is, i n fact, the course of t h e p o l y m e r i z a t i o n r e a c t i o n s h o w n i n R e a c t i o n 4.

M o n o m e r i c cyclopentadienones,

on the

other h a n d , w i l l often stop at the i n t e r m e d i a t e I I I , e v e n u n d e r q u i t e severe c o n d i t i o n s . I t is this r e a c t i o n stage t h a t is of p a r t i c u l a r interest to us for the s t u d y of D i e l s - A l d e r s t e p - g r o w t h p o l y m e r i z a t i o n s . Polyimides. T h e r e a c t i o n of t e t r a p h e n y l c y c l o p e n t a d i e n o n e ( V ) w i t h N-phenylmaleimide ( V I ) i n refluxing a-chloronaphthalene for 1.5 hours or r e f l u x i n g , 1,2,4-trichlorobenzene

(263°C.)

( 2 1 3 ° C . ) for 18 h o u r s

p r o v i d e s a q u a n t i t a t i v e y i e l d of a d d u c t V I I ( R e a c t i o n 7 ) . reacts w i t h N,N'-o-

(17)

Similarly, V

a n d p - p h e n y l e n e b i s m a l e i m i d e ( V I I I a , b ) ( 8 ) to afford

the d i a d d u c t s I X a , b ( R e a c t i o n 8 ) .

a,

o—C H

b,

p—C H

6

6

4

4

(8)

IX a,

o—C H 6

4

b, v—C H 6

4

41.

STILLE E T A L .

Diels-Alder

633

Reaction

T h e analogous reactions of V I I I a , b w i t h 3 , 3 ' - ( o x y d i - p - p h e n y l e n e ) bis(2,4,5-triphenylcyclopentadienone)

( X ) g i v e the c o r r e s p o n d i n g p o l y -

i m i d e s ( X I a , b ) i n q u a n t i t a t i v e conversions ( R e a c t i o n 9 ) .

Polymer X l b ,

o b t a i n e d f r o m the p - p h e n y l e n e b i s m a l e i m i d e ( V l l l b ) reaches a n i n t r i n s i c viscosity of 1.01 i n 4 hours i n r e f l u x i n g 1,2,4-trichlorobenzene, w h i l e X I a attains a n i n t r i n s i c v i s c o s i t y of o n l y 0.33 after 24 hours u n d e r the same c o n d i t i o n s . A p p a r e n t l y there is c o n s i d e r a b l e steric h i n d r a n c e i n the case of the o-isomer, a n d the result is a series of s h a r p k i n k s i n the p o l y m e r chain. films.

P o l y m e r X I is s o l u b l e i n D M F a n d forms clear, s l i g h t l y y e l l o w T h e p o l y m e r dehydrogenates s l o w l y at e l e v a t e d temperatures or

m o r e r a p i d l y w i t h c h e m i c a l d e h y d r o g e n a t i o n reagents to f o r m t h e t o t a l l y aromatic polyimide.

XI a, o - C H 6

b, p - C H G

4

4

Polyphenyls. A n o t h e r means of c a r r y i n g the c y c l o p e n t a d i e n o n e D i e l s A l d e r r e a c t i o n to the m o n o a d d u c t stage ( I I I , R e a c t i o n 6 ) is to use a n a c e t y l e n i c d i e n o p h i l e a n d o b t a i n a p r o d u c t w h i c h is n o longer a d i e n e b u t a n a r o m a t i c . T h e r e a c t i o n of t e t r a p h e n y l c y c l o p e n t a d i e n o n e ( V ) w i t h diphenylacetylene ( X I I )

affords h e x a p h e n y l b e n z e n e

( X I V ) b y loss of

c a r b o n m o n o x i d e f r o m the i n t e r m e d i a t e a d d u c t X I I I ( R e a c t i o n 1 0 ) .

In

c e r t a i n cases the i n t e r m e d i a t e a d d u c t X I I I c a n b e i s o l a t e d . T h e p r e f e r r e d r o u t e to the synthesis of t e t r a a r y l a t e d c y c l o p e n t a d i enones is the b a s e - c a t a l y z e d c o n d e n s a t i o n of b e n z i l s w i t h b e n z y l ketones ( R e a c t i o n 11) ( 1 7 ) .

634

^6H

ADDITION A N D CONDENSATION P O L Y M E R I Z A T I O N

C H 6

5

C H 6

5

5

XII C ;H (

C

c

H

5

^ S

Y

C H 0

5

C«H«

XIII

r)

- C

JOl

PROCESSES

6

H

5

+

(10)

CO

ArCOCOAr + Ar'CHoCOCHoAr'

(11) Ar

^Ar

O f p a r t i c u l a r interest to the f o r m a t i o n of p o l y m e r s is the fact t h a t m a n y bistetracyclones h a v e b e e n s y n t h e s i z e d b y this m e t h o d (17,

18).

T h e r e a c t i o n of bistetracyclones X , X V , a n d X V I w i t h m- a n d p - d i e t h y n y l b e n z e n e ( X V I I a n d X V I I I ) i n toluene at 225 ° C . for 24 h o u r s , afforded the p h e n y l a t e d p o l y p h e n y l s X I X a n d X X i n q u a n t i t a t i v e conversions (16,19,22). M o l e c u l a r w e i g h t s o f 30,000-60,000 c o u l d b e o b t a i n e d . T h e p o l y m e r s s h o w e d o u t s t a n d i n g t h e r m a l s t a b i l i t y ( T G A 5 5 0 ° C . b r e a k , a i r or n i t r o g e n ) , are a l l s o l u b l e i n c o m m o n o r g a n i c solvents ( u p to 15 w t . % ) , f o r m clear films,

are colorless, a n d a m o r p h o u s . T h e t h e r m a l d e c o m p o s i t i o n of these

p o l y m e r s has b e e n s h o w n to t a k e p l a c e b y the loss of p e n d a n t p h e n y l groups as p h e n y l r a d i c a l s . T h u s , the t h e r m a l t r e a t m e n t of a film u n d e r n i t r o g e n p r o d u c e s a c r o s s l i n k e d film w h i c h is s t i l l a m o r p h o u s b u t i n s o l u b l e ; n o a p p r e c i a b l e m a i n c h a i n d e g r a d a t i o n takes p l a c e . T o a c h i e v e p r o p e r m o n o m e r b a l a n c e , the m o n o m e r s w e r e p u r i f i e d w i t h great care. T h e s t o i c h i o m e t r y n e e d e d to a c h i e v e the h i g h e s t m o l e c u lar weight polymer ( T a b l e I)

required 1%

excess of b i s t e t r a c y c l o n e .

T h i s suggests either t h a t there w e r e i m p u r i t i e s i n t h e b i s t e t r a c y c l o n e t h a t

41.

STILLE E T A L .

Diels-Alder

635

Reaction

a. X = nil

b. x = o c.

C H G

5

C H 6

X= S

C H

5

6

5

a. X = nil XX

b. x = o c. X = S

e s c a p e d d e t e c t i o n i n c h r o m a t o g r a p h y or t h a t some side r e a c t i o n upset monomer balance. Severe p o l y m e r i z a t i o n c o n d i t i o n s ( 3 5 0 ° C , 48 h o u r s ) , i n fact, gave lower molecular weight polymers ([77] = 0 . 1 )

a n d a s m a l l a m o u n t of

b l a c k , i n s o l u b l e p r e c i p i t a t e . T h e s e results suggest t h a t there w a s c o n siderable degradation w h i c h interfered w i t h monomer

balance.

Such

636

ADDITION

A N D CONDENSATION

POLYMERIZATION

PROCESSES

d e g r a d a t i o n reactions at e l e v a t e d temperatures are k n o w n for tetracyclones

many

(17).

Table I.

Effect of Monomer Balance on Molecular Weight (Polymer X X b )

Mole Ratio X:XVIU

[77], dl/gram

M n X lOr*

6

1.02 1.01 1.00 0.98

0.61 0.64 0.58 0.38

0

3.6 4.1 2.9 1.9

d

At a concentration of 0.08M for each monomer. Taken at 25 °C. in toluene. Obtained with a Hewlett-Packard high speed membrane osmometer using a superdense membrane at 29.5°C. in toluene. When this reaction was run with a concentration of 0.01M for each monomer, the viscosity was 0.16.

0

6 0

d

The

p o l y m e r i z a t i o n r e a c t i o n is t y p i c a l of s t e p - g r o w t h reactions i n

that i t f o l l o w s second-order k i n e t i c s f o r t h e r e a c t i o n of t e t r a c y c l o n e ends w i t h acetylene ends ( F i g u r e s 1 a n d 2 ) .

5

10 Time,

Figure 1.

15

20

25

Hn.

Reaction of X and XVIII (time vs. DP)

41.

STILLE E T AL.

Diels-Alder

637

Reaction

I n a d d i t i o n , s e v e r a l bistetracyclones l i n k e d b y m e t h y l e n e units h a v e b e e n s y n t h e s i z e d a c c o r d i n g to the scheme s h o w n i n R e a c t i o n 14. O

O

O

ClC(CH ) _ CCl 2

n

2

C H C(CH ) _ CC H 6

A1CL '

(n = 10, 14)

O

5

2

n

2

6

5

Zn(Hg) HC1 Na

Br(CH ) Br + 2 C H Br 2

n

0

5

C H (CH ) C H 6

5

2

n

( 5

n

(n = 3, 4,6) C H CH CCl f i

5

2

A1CL,

e

H CH C 5

( C H ^ ^ ^ ^ C C H . C o H ,

2

Se0

2

oo

oo

C«H, (CH ); 2

(C(iH CH ) C 5

2

Cr.H-,

C H 6

5

2

XXI

a. n= b. n = c. n =

3 4 6

d. n = 10 e. n = 14

( ) 14

T h e p o l y m e r i z a t i o n reactions of b i s t e t r a c y c l o n e m o n o m e r s X X I a - e w i t h b o t h m- a n d p - d i e t h y n y l b e n z e n e ( X V I I a n d X V I I I ) p r o d u c e d a series of p o l y m e r s ( X X I I , R e a c t i o n 15) c o n t a i n i n g short b l o c k s of p h e n y l e n e units connected b y methylene chains. H i g h molecular weight polymers were o b t a i n e d ( T a b l e I I ) , a n d a r a n g e of p h y s i c a l properties w a s observed.

638

ADDITION

A N D CONDENSATION

POLYMERIZATION

PROCESSES

X X I a - e + X V I I or X V I I I

Table II. Polymer C

3

C4

C C C

6

1 0

w

m-

0.35

v-

0.55

59,000

771-

0.61

58,400

v-

0.77

42,600

m-

0.71

56,800

v-

1.51

63,400

m-

0.60

48,500

v-

1.30

50,500

0.48

31,300

0.77

32,700

771-

1 4

Polymer X X I I

46,500

Intrinsic viscosities in toluene at 25 °C. * Obtained with a Hewlett-Packard high speed membrane osmometer using a superdense membrane at 30°C. in toluene. 0

2-Pyrones The

D i e l s - A l d e r r e a c t i o n of 2-pyrones has b e e n u s e d i n p o l y m e r

syntheses ( 6 , 13)

(Reaction 4).

I n these reactions the 2 - p y r o n e is d i -

f u n c t i o n a l i n t h a t i t consumes t w o m o l e s of d i e n o p h i l e ( R e a c t i o n 1 6 ) . A p r a c t i c a l w a y of s t o p p i n g at t h e 1:1 a d d u c t is to use a n a c e t y l e n i c m o n o m e r (24) standing

(Reaction 17).

A l t h o u g h 2 - p y r o n e itself p o l y m e r i z e s o n

( J ) , p h e n y l - s u b s t i t u t e d 2-pyrones, i n c l u d i n g m o n o p h e n y l 2-

p y r o n e s , a r e stable at o r d i n a r y t e m p e r a t u r e s .

41.

STILLE

ET AL.

Co

Reo cti v e (moles/ I

Figure 2.

639

Diels-Alder Reaction

End s C H CH ) e

8

8

Reaction of X and XVIII (Co vs. DP)

640

ADDITION A N D CONDENSATION P O L Y M E R I Z A T I O N

PROCESSES

S i n c e the t h e r m a l d e g r a d a t i o n i n p h e n y l a t e d p o l y p h e n y l s of t h e t y p e X X a is c a u s e d b y t h e loss of p e n d a n t p h e n y l g r o u p s , a n d since t h e r e p o r t e d (4, 7, 9, 10, 11, 14, 15)

properties of p - p o l y p h e n y l e n e s are q u i t e

different f r o m those of X X a , the synthesis of a n u n p h e n y l a t e d

poly-

p h e n y l e n e b y this p a t h w a y w a s of c o n s i d e r a b l e significance. O n l y a f e w results e m p l o y i n g t h i s r e a c t i o n h a v e thus f a r b e e n o b t a i n e d .

[The p-poly-

p h e n y l e n e s r e p o r t e d are b l a c k or b r o w n , i n s o l u b l e , c r y s t a l l i n e m a t e r i a l s of l o w e r t h e r m a l s t a b i l i t y t h a n X X a . ] If the d i e n e f r a g m e n t of the 2 - p y r o n e a n d t h e acetylene d i e n o p h i l e are u n s y m m e t r i c a l l y s u b s t i t u t e d , the f o r m a t i o n of t w o i s o m e r i c

benzene

p r o d u c t s is possible. T h e m o d e l r e a c t i o n b e t w e e n 4 , 5 , 6 - t r i p h e n y l - 2 - p y r o n e (20)

( X X I I I ) a n d phenylacetylene yields approximately equal amounts

of 1, 2, 3, 4 - ( X X V ) a n d 1,2,3,5-tetraphenylbenzene

(XXVI).

Therefore,

this p o s i t i o n i s o m e r i s m w o u l d b e e x p e c t e d to m a t e r i a l i z e d u r i n g p o l y m e r formation

when

similar

bispyrone

monomers

are

polymerized

with

diethylnylbenzene.

XXIII

XXIV

XXV

XXVI

B i s - 2 - p y r o n e s X X X a n d X X X I w e r e p r e p a r e d b y u t i l i z i n g the basec a t a l y z e d M i c h a e l a d d i t i o n of bisdesoxybenzoins e t h y l p h e n y l p r o p i o l a t e ( X X I X ) (20) The

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

X X V I I a n d X X V I I I to

( R e a c t i o n s 19 a n d 2 0 ) .

the b i s p y r o n e s

X X X and X X X I

with

d i e t h y n y l - b e n z e n e ( X V I I I ) i n toluene at 2 2 5 ° - 3 0 0 ° C . for 2 0 - 4 8 p r o d u c e d b o t h s o l u b l e a n d i n s o l u b l e fractions of p o l y m e r s X X X I I

p-

hours and

X X X I I I ( R e a c t i o n s 21 a n d 2 2 ) . T h e s o l u b l e p o r t i o n s w e r e o n l y r e l a t i v e l y low molecular weight ( [97] = 0 . 1 ) .

T h e s e m a t e r i a l s d i d s h o w the same

excellent t h e r m a l s t a b i l i t y as e x h i b i t e d b y the p o l y p h e n y l s of t y p e X I X and X X .

41.

STILLE E T AL.

Diels-Alder

641

Reaction

C H 6

5

XXXII

X X X V I + XVIII

XXXIII H o p e f u l l y , this t y p e of synthesis w i l l p r o v i d e a p - p o l y p h e n y l e n e

of

u n q u e s t i o n a b l e structure so that its p h y s i c a l properties m i g h t be s t u d i e d . A l t h o u g h the u t i l i z a t i o n of the D i e l s - A l d e r synthesis as a s t e p - g r o w t h r e a c t i o n for p o l y m e r i z a t i o n r e q u i r e s , i n most cases, r a t h e r u n u s u a l m o n o mers, a n o c c a s i o n a l l e n g t h y a n d t r y i n g synthesis, torturous p u r i f i c a t i o n s , a n d , i n c e r t a i n cases, difficult r e a c t i o n c o n d i t i o n s , i t does afford

high

642

ADDITION A N D CONDENSATION POLYMERIZATION PROCESSES

molecular weight polymers with interesting and unusual structures which are not attainable by other means. Acknowledgment This work was supported by the U . S. Army Research Office, D u r ­ ham, N . C . Literature Cited (1) Albert, A., "Heterocyclic Chemistry," p. 268, Essential Books, Fair Lawn, N. J., 1959. (2) Allen, C. F. H., Van Allan, J. A.,J.Am. Chem. Soc. 72, 5165 (1950). (3) Bailey, W. J., Economy, J., Hermes, M. E., J. Org. Chem. 27, 3295 (1962). (4) Cassidy, P. E., Marvel, C. S., Ray, S., J. Polymer Sci. Pt. A , 3, 1553 (1965). (5) Chow, S-W., U. S. Patent 2,971,944 (Feb. 14, 1961). (6) Ibid., 3,074,915 (Jan. 22, 1963). (7) Frey, D. A., Hasegawa, M., Marvel, C. S., J. Polymer Sci. Pt. A, 1, 2057 (1963). (8) Kovacic, P., Hine, R. W.,J.Am. Chem. Soc. 81, 1187 (1959). (9) Kovacic, P., Hoppe, R. J., J. Polymer Sci. Pt. A-1, 4, 1445 (1966). (10) Kovacic, P., Itsu,L.C.,J.Polymer Sci. Pt. A-1, 4, 5 (1966). (11) Kovacic, P., Marchionna, V. J., Koch, F. W., Oziomek, J.,J.Org. Chem. 31, 2467 (1966). (12) Kraiman, E. A., U. S. Patent 2,890,206 (June 9, 1959). (13) Ibid., 2,890,207 (June 9, 1959). (14) Lefebvre, G., Dawans, F., J. Polymer Sci. Pt. A, 2, 3277 (1964). (15) Marvel, C. S., Hartzell, G. E., J. Am. Chem. Soc. 81, 448 (1959). (16) Mukamal, H., Harris, F. W., Stille, J. K.,J.Polymer Sci. Pt. A-1, 5, 2721 (1967). (17) Ogliaruso, M. A., Romanelli, M. G., Becker, E. I., Chem. Rev. 65, 261 (1965). (18) Ogliaruso, M. A., Shadoff, L. A., Becker, E. I., J. Org. Chem. 28, 2725 (1963). (19) Reid, W., Freitag, D., Naturwiss. 53, 306 (1966). (20) Ruheman, S.,J.Chem. Soc. 97, 459 (1910). (21) Stille, J. K., Fortschr. Hochpolym. Forsch. 3, (1), 48 (1961). (22) Stille, J. K., Harris, F. W., Rakutis, R. O., Mukamal, H., J. Polymer Sci. Pt. B, 4, 791 (1966). (23) Stille, J. K., Plummer, L., J. Org. Chem. 2, 4026 (1961). (24) Shusherina, U. P., Dmitrieva, U. D., Luk'ianets, E. A., Levina, R. A., Usp. Khim. 36, 437 (1967). (25) Upsom, R. W., U. S. Patent 2,776,232 (Dec. 6, 1955). RECEIVED April 8, 1968.