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.
