7 Biologically Active Modification of Polyvinyl Alcohol: The Reaction of Phenyl Isocyanate with Polyvinyl Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 12, 2016 | http://pubs.acs.org Publication Date: June 10, 1980 | doi: 10.1021/bk-1980-0121.ch007
Alcohol CHARLES G. GEBELEIN and KEITH E. BURNFIELD Department of Chemistry, Youngstown State University, Youngstown, OH 44555 Numerous papers have appeared in the literature describing the reactions of various compounds with polymers in order to change the properties of the polymers (1-5). Often these reactions have resulted in significant changes in such properties as flammability, solubility, thermal degradation, photodegradation, strength and biological activity. In this present paper, we will briefly review some of the reactions that have been run on poly(vinyl alcohol), especially in regards to their potential biomedical activity, and then we will describe the reaction of phenyl isocyanate with poly(vinyl alcohol) and consider some of the potential utility of this modified polymer. PVA Formation Reaction. Poly(vinyl alcohol) is itself a modified polymer being made by the alcoholysis of poly(vinyl acetate) under acid or base catalysis as shown in Equation 1 (6,7). This polymer cannot be made by a direct polymerization because the vinyl alcohol monomer only exists in the tautomeric form of acetaldehyde. This saponification reaction can also be run on vinyl acetate copolymers and this affords a means of making vinyl alcohol copolymers. The homopolymer is water soluble and softens with decomposition at about 200°C while the properties of the copolymers would vary widely. Poly(vinyl alcohol) has been widely utilized in polymer modification because: (1) it is readily available, (2) it is inexpensive and (3) it has the readily reacted hydroxyl group present. -f-CH Cfr->^| 0 CH~C=0 0
3
n
CH0H J v H+ or OH" o
?
-f-CH CH->- + n CHC00CH z| n J J OH (Equation 1) 0
o
Q
Esterification Reactions. Possibly the simplest reaction on poly(vinyl alcohol) would be the acetylation to regenerate the poly(vinyl acetate), Equation 2. While this reaction occurs readily, with acetic anhydride in pyridine solution, the result0-8412-0540-X/80/47-121-083$05.00/0 © 1980 American Chemical Society In Modification of Polymers; Carraher, Charles E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
MODIFICATION O F POLYMERS
84
i n g p o l y ( v i n y l a c e t a t e ) o f t e n has a s t r u c t u r e (and p r o p e r t i e s ) d i f f e r e n t f r o m t h e o r g i n a l v i n y l a c e t a t e p o l y m e r . T h i s change o c c u r s because the o r i g i n a l p o l y ( v i n y l a c e t a t e ) o f t e n has c h a i n b r a n c h i n g o c c u r r i n g from the a c e t a t e group a s w e l l as the polymer b a c k b o n e c h a i n . On a l c o h o l y s i s , t h e s e b r a n c h e s a r e c l e a v e d a n d the polymer decreases both i n m o l e c u l a r weight and the e x t e n t o f branching (8-12). O t h e r p o l y m e r i c e s t e r s c a n b e made f r o m p o l y ( v i n y l a l c o h o l ) and t h i s i s i l l u s t r a t e d i n Equation 3 which shows t h e f o r m a t i o n o f p o l y ( v i n y l b u t y r a t e ) .
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 12, 2016 | http://pubs.acs.org Publication Date: June 10, 1980 | doi: 10.1021/bk-1980-0121.ch007
-f-CH CHH>0
OH
( E q u a t i o n 2)
(CH CO) 0 3
2
pyridine
0
1 0=C-CH„
(CH CH CH CO) 0 3
OH
2
pyridine
2
2
2| 0
( E q u a t i o n 3)
n
1
0=CCH CH CH 2
2
3
R a d i a t i o n Induced R e a c t i o n s . G r a f t polymers have been p r e pared from p o l y ( v i n y l a l c o h o l ) by the i r r a d i a t i o n o f the polymermonomer s y s t e m a n d some o t h e r m e t h o d s . The g r a f t e d s i d e c h a i n s reported include: acrylamide, a c r y l i c acid, a c r y l o n i t r i l e , ethyl a c r y l a t e , ethylene, e t h y l methacrylate, methyl methacrylate, s t y r e n e , v i n y l a c e t a t e , v i n y l c h l o r i d e , v i n y l p y r i d i n e and v i n y l p y r r o l i d o n e ( 1 3 ) . P o l y ( v i n y l a l c o h o l s ) w i t h g r a f t e d m e t h y l metha c r y l a t e a n d sometimes m e t h y l a c r y l a t e h a v e b e e n s t u d i e d a s memb r a n e s f o r h e m o d i a l y s i s (1£J. G r a f t polymers c o n s i s t i n g o f 50% p o l y ( v i n y l a l c o h o l ) , 25% p o l y ( v i n y l a c e t a t e ) a n d 25% g r a f t e d e t h y l e n e o x i d e u n i t s can be used t o prepare c a p s u l e cases f o r d r u g s w h i c h do n o t r e q u i r e a n y a d d i t i o n a l p l a s t i c i z e r s ( 1 5 ) . When p o l y ( v i n y l a l c o h o l ) i s i r r a d i a t e d w i t h a n e l e c t r o n beam a b o v e i t s Tg, a c r o s s l i n k e d h y d r o g e l f o r m s QL6). Poly(vinyl a l c o h o l ) h y d r o g e l s have been found t o be e f f e c t i v e eye l e n s s u b s t i t u t e s i n a l b i n o r a b b i t s s i n c e t h e i r p r o p e r t i e s were v e r y s i m i l a r to the i n t a c t eye l e n s (17). P o l y ( v i n y l a l c o h o l ) ointments cont a i n i n g p i l o c a r p i n e h a v e b e e n shown t o b e e f f e c t i v e s u s t a i n e d r e l e a s e a g e n t s w h i c h l a s t 4-5 h o u r s l o n g e r t h a n t h e u s u a l s o l u t i o n s o f p i l o c a r p i n e and a r e n e a r l y f r e e o f s i d e e f f e c t s such a s eye i r r i t a t i o n ( 1 8 ) . A n o t h e r h y d r o g e l a p p l i c a t i o n i n v o l v e s c r o s s l i n k i n g p o l y ( v i n y l a l c o h o l ) and h e p a r i n t o g e t h e r w i t h g l u t a r a l d e hyde and formaldehyde. These h y d r o g e l s a r e c l a i m e d t o have l o w t h r o m b o g e n i c i t y a n d h a v e b e e n e v a l u a t e d a s a h e m o d i a l y s i s membrane. They show p r o m i s e i n t h i s l a t t e r a p p l i c a t i o n s i n c e t h e y a r e more p e r m e a b l e t o m o l e c u l e s s u c h a s i n s u l i n t h a n a r e t h e u s u a l c e l l o p h a n e membranes. R a d i a t i o n c r o s s l i n k e d p o l y ( v i n y l a l c o h o l ) g e l s have been proposed a s s y n t h e t i c c a r t i l a g e i n s y n o v i a l j o i n t s (19).
In Modification of Polymers; Carraher, Charles E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
7.
GEBELEIN AND BURNFIELD
Polyvinyl
85
Alcohol
A c e t a l Formation Reactions. Like other alcohols, p o l y ( v i n y l a l c o h o l ) u n d e r g o e s an a c i d c a t a l y z e d r e a c t i o n w i t h v a r i o u s a l d e h y d e s t o f o r m a c e t a l s . Two o f t h e s e p r o d u c t s , t h e f o r m a l and t h e b u t y r a l , a r e o f i m p o r t a n c e i n d u s t r i a l l y and t h e r e a c t i o n s a r e shown i n E q u a t i o n s 4 and 5, r e s p e c t i v e l y . P o l y ( v i n y l b u t y r a l ) has b e e n known s i n c e t h e 4 0 s and i s u s e d as a p l a s t i c i n t e r l a y e r i n safety glass. I n t h i s case, the r e a c t i o n i s stopped w i t h about 25% o f t h e OH g r o u p s r e m a i n i n g , t o p r o m o t e good a d h e s i o n t o t h e g l a s s , and t h e p o l y m e r i s u s u a l l y p l a s t i c i z e d w i t h a b o u t 30% d i b u t y l sebacate (20). T h i s a c e t a l r e a c t i o n w i l l not proceed b e y o n d a b o u t 87.5% c o n v e r s i o n o f t h e OH g r o u p s s i n c e some o f t h e s e g r o u p s become i s o l a t e d and c a n n o t u n d e r g o a c e t a l f o r m a t i o n .
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 12, 2016 | http://pubs.acs.org Publication Date: June 10, 1980 | doi: 10.1021/bk-1980-0121.ch007
f
OH OH OH • X -f-CH CHCH CHCH CIf->1
2
1
2
CH
2
0,H
+
-f-CH
>
—±
-CH 1
CH-CH
|
I X
C
H
z
2
-CH-H I CH,
(crosslinked p o l y ( v i n y l formal) (Equation OH OH - f - C H CHCH CH->0
0
CH CH CH Q
0
0
CHO
4)
-
