Imide Hydrolytic Stability of - American Chemical Society

Chapter 21

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Imide Hydrolytic Stability of N-Substituted Dimethacrylamide Cyclopolymers: Poly [N-(4-sulfophenyl) dimethacrylamide] Joseph J. Kozakiewics, Sun-Yi Huang, Daniel R. Draney, and JoAnn L. Villamizar American Cyanamid Company, Stamford, CT 06904-0060 The hydrolytic stability of water soluble poly[N-(4-sulfo phenyl) dimethacrylamide] (PSPDM) was studied at 90°C in aqueous solutions at pH 7, pH 1.2 (0.1M HCl), and pH 12.3 (0.1M NaOH). PSPDM, which possesses predominantly 5-mem bered ring imides, was prepared by the cyclopolymerization and subsequent sulfonation of N-phenyldimethacrylamide. No detectable PSPDM imide hydrolysis occurred after 30 days at pH 7 or pH 1.2. Under basic conditions, however, complete hydrolysis to amic acid occurred after one day. The re sulting Nsubstituted amide was extremely stable to further basic hydrolysis. C y c l o p o l y m e r i z a t i o n o f s u b s t i t u t e d d i m e t h a c r y l a m i d e s i s w e l l known and has r e c e n t l y been employed as a possilple^ r o u t e f o r the s y n t h e s i s o f head-to-head p o l y ( m e t h a c r y l i c e s t e r s ) . ' Unexpectedly, the r e s u l t i n g backbone 5-membered r i n g i m i d e s were found t o be n e a r l y imp o s s i b l e t o h y d r o l y z e . X i and V o g l found t h a t p o l y ( N - p h e n y l d i m e t h a c r y l a m i d e ) c o u l d n o t be h y d r o l y z e d i n v e r y c o n c e n t r a t e d sodium h y droxide or potassium hydroxide s o l u t i o n s . Additionally, hydrazino l y s i s w i t h b o t h anhydrous h y d r a z i n e and h y d r a z i n e monohydrate was u n s u c c e s s f u l . A l l attempts t o h y d r o l y z e p o l y ( N - p h e n y l d i m e t h a c r y l amide) were u n s u c c e s s f u l . O t s u and Ohya attempted t o h y d r o l y z e p o l y ( N m e t h y l d i m e t h a c r y l a m i d e ) and p o l y ( N - p r o p y l d i m e t h a c r y l a m i d e ) i n b o t h v e r y s t r o n g a c i d i c and v e r y s t r o n g b a s i c aqueous s o l u t i o n s . No h y d r o l y s i s was o b s e r v e d w i t h t h e p o s s i b l e e x c e p t i o n o f t h e r e a c t i o n o f p o l y ( N - p r o p y l d i m e t h a c r y l a m i d e ) i n 60% aqueous KOH a t 100 C f o r 14 days. The h y d r o l y z e d polymer, however, was n o t i s o l a t e d . Otsu and Ohya c o n c l u d e d t h a t t h e i r i m i d e - c o n t a i n i n g polymers were n o t h y d r o l y z e d under a c i d i c o r b a s i c c o n d i t i o n s . The extreme r e s i s t a n c e o f t h e s e i m i d e groups t o h y d r o l y s i s i s s u r prising. Imides a r e w e l l known t o be r e a d i l y h y d r o l y z e d under b o t h

0097-6156/88/0364-0291 $06.00/0 © 1988 American Chemical Society

Benham and Kinstle; Chemical Reactions on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

a c i d i c and b a s i c c o n d i t i o n s . 5-membered r i n g s u c c i n i m i d e s and 6membered r i n g g l u t a r i m i d e s a j e ^ h y d r o l y z e d under m i l d l y a l k a l i n e c o n d i t i o n s a t room t e m p e r a t u r e . Herd e t a l . have shown, however, t h a t a l k y l s u b s t i t u t i o n a t t h e second and t h i r d p o s i t i o n o^ N-phenyl succinimides can s i g n i f i c a n t l y e f f e c t the h y d r o l y s i s r a t e . Np h e n y l s u c c i n i m i d e h y d r o l y z e d 83 times f a s t e r t h a n N-phenyl-2,2,3,3tetramethylsuccinimide. Imide groups i n polymers have a l s o been shown t o be r e a d i l y h y d r o l y z e d . H y d r o l y s i s o f t h e 5-membered r i g g ^ imides o f a n h y d r o p o l y a s p a r t i c a c i d has been s t u d i e d e x t e n s i v e l y . There i s no r e a s o n t o e x p e c t t h e i m i d e groups o f N - s u b s t i t u t e d d i methacrylamide copolymers t o be u n u s u a l l y h y d r o l y t i c a l l y s t a b l e based on these s t u d i e s .

To s t u d y the f a c t o r s l e a d i n g t o t h e u n u s u a l h y d r o l y t i c s t a b i l i t y of p o l y d i m e t h a c r y l a m i d e s , we s y n t h e s i z e d poly[N-(4-sulfophenyl)dim e t h a c r y l a m i d e ] (PSPDM) ( I V ) . PSPDM ^s water s o l u b l e , i n c o n t r a s t t o the p r e v i o u s l y s t u d i e d p o l y m e r s . ' The h y d r o l y t i c s t a b i l i t y o f PSPDM was s t u d i e d i n a c i d i c , n e u t r a l , and b a s i c aqueous s o l u t i o n s a t 90 C and above. The r e s u l t s o f t h e s e e x p e r i m e n t s w i l l be d e s c r i b e d . EXPERIMENTAL N - p h e n y l d i m e t h a c r y ^ m i d e (PDMA) was s y n t h e s i z e d by t h e method o f B u t l e r and Meyers. P o l y ( N - p h e n y l d i m e t h a c r y l a m i d e ) (PPDMA) was p r e p a r e d by f r e e r a d i c a l c y c l o p o l y m e r i z a t i o n o f PDMA. AIBN (0.050g., 0.3 mmoles) and PDMA (5.00 g., 21.8 mmoles) were d i s s o l v e d i n 8.0 g . d r y DMF. The s o l u t i o n was purged w i t h n i t r o g e n f o r 30 minutes and t h e n h e a t e d t o 50 C. A f t e r 19 h o u r s , a d d i t i o n a l AIBN (0.050 g., 0.3 mmoles) was added and t h e h e a t i n g c o n t i n u e d f o r a t o t a l o f four days. The s o l u t i o n was then poured i n t o 400 m l . methanol. The w h i t e p r e c i p i t a t e d polymer was f i l t e r e d , washed w i t h methanol, and d r i e d under vacuum a t 50 C t o g i v e 3.78 g . (76% y i e l d ) of polymer w i t h i n h 0.23 (0.5% polymer i n DMF, 3 0 ° C ) . Poly[N( 4 - s u l f o p h e n y l ) d i m e t h a c r y l a m i d e ] (PSPDM) was p r e p a r e d by s u l f o n a t i o n of PPDMA. PPDMA (1.50 g.) was s l o w l y d i s s o l v e d i n fuming s u l f u r i c a c i d (40 g., 18-24% SO^) a t room t e m p e r a t u r e . The s o l u t i o n was then poured i n t o two l i t e r s s a t u r a t e d sodium c h l o r i d e . The p r e c i p i t a t e was f i l t e r e d , d i s s o l v e d i n 200 ml d e i o n i z e d water, d i a l y z e d a g a i n s t d e i o n i z e d water f o r two days and f r e e z e d r i e d . The r e s u l t i n g p o l y mer (1.40 g.) was s o l u b l e i n water and DMSO. H y d r o l y t i c s t a b i l i t y s t u d i e s were p e r f o r m e d by p r e p a r i n g one wt.-% aqueous s o l u t i o n s i n c u l t u r e t u b e s , a d j u s t i n g t h e s o l u t i o n s t o the d e s i r e d pH and p l a c i n g t h e s e a l e d tubes i n an oven a t t h e d e s i r e d temperature. The tubes were removed a t v a r i o u s times, c o o l e d to roo^m t e m p e r a t u r e , d i a l y z e d and f r e e z e - d r i e d . The C NMR s p e c t r a were o b t a i n e d a t 50.3 MHz on a V a r i a n XL200 spectrometer. IR s p e c t r a were o b t a i n e d on a D i g i l a b F75-15 FTIR and P e r k i n - E l m e r 1310 i n f r a r e d s p e c t r o p h o t o m e t e r .


21.

KOZAKIEWICS ET AL.

Imide Hydrolytic Stability

293

RESULTS AND DISCUSSION F r e e r a d i c a l c y c l o p o l y m e r i z a t i o n o f N - p h e n y l d i m e t h a c r y l a m i d e (PDMA) (I) y i e l d e d PPDMA p o s s e s s i n g p r e d o m i n a n t l y 5-membered r i n g i m i d e s ^ ( I I ) ( F i g u r e 1) as d e t e r m i n e d by C NMR and IR ( F i g u r e 2 ) . The C NMR peak a t 50.0 i n d i c a t e s t h a t PPDMA a l s o c o n t a i n s a s m a l l amount of 6-membered r i n g imide ( I I I ) . No pendant v i n y l groups y e r e f o u n d . T h i s i s i n agreement w i t h PPDMA p r e p a r e d by X i and V o g e l . PPDMA was s o l u b l e i n DMF, DMSO and c h l o r o f o r m , b u t was i n s o l u b l e i n w a t e r . S u l f o n a t i o n o f PPDMA p r o c e e d e d q u i c k l y a t room temperature t o g i v e PSPDM (IV) ( F i g u r e 3 ) . S u l f o n a t i o n o f t h e a r o m a t i c r i n g s wegt t o n e a r l y 100% c o m p l e t i o n i n t h e p a r a p o s i t i o n as d e t e r m i n e d by C NMR and IR ( F i g u r e 4a and b ) . The s m a l l peaks between 128 and 133 ppm a r e a t t r i b u t a b l e t o a s m a l l f r a c t i o n o f PPDMA r i n g s which were not s u l f o n a t e d . PSPDM, i n c o n t r a s t t o PPDMA, i s v e r y s o l u b l e i n water. The h y d r o l y t i c s t a b i l i t y o f PSPDM was s t u d i e d i n i t i a l l y a t 90°C i n aqueous s o l u t i o n a t pH 1.2 (0.1M HCI), pH 7 and pH 12.3 (0.1 M NaOH). A t b o t h pH 1.2 a n ^ pH 7, no d e t e c t a b l e h y d r o l y s i s o c c u r r e d a f t e r t h i r t y days. The C NMR s p e c t r a o f t h e s e samples were unchanged. Under a c i d i c and n e u t r a l c o n d i t i o n s , t h e h y d r o l y t i c s t a b i l i t y o f t h e i m i d e was e x c e l l e n t . A f t e r o n l y one day a t pH 12.3, however, t h e i m i d e r i n g s were n e a r l y q u a n t i t a t i v e l y o p e n e ^ t o amic a c i d (V) ( F i g u r e 5 ) . The a r o matic carbon r e g i o n of the C NMR spectrum shows t h r e e new major a r o m a t i c c a r b o n peaks from t h e N - s u l f o p h e n y l a m i d e group a t 127.9, 134.1 and 144.6 ppm and t h e d i s a p p e a r a n c e o f t h e c o r r e s p o n d i n g i m i d e a r o m a t i c peaks ( F i g u r e 6 ) . New c a r b o n y l peaks a l s o appear a t 178 and 182 ppm a t t r i b u t a b l e t o t h e amide c a r b o n y l c a r b o n and t h e c a r b o x y l a t e c a r b o n y l carbon, r e s p e c t i v e l y . Under b a s i c c o n d i t i o n s , t h e i m i d e r i n g s a r e r e a d i l y h y d r o l y z e d t o t h e r e s p e c t i v e c a r b o x y l a t e and amide. S u r p r i s i n g l y , however, no f u r t h e r h y d r o l y s i s o f t h e amide o c c u r r e d on h e a t i n g f o r an a d d i t i o n a l 29 d a y s . The amide, u n l i k e the s t a r t i n g i m i d e , i s h y d r o l y t i c a l l y s t a b l e a t pH 12.3 and 90 C. In an a t t e m p t t o h y d r o l y z e PSPDM c o m p l e t e l y t o head-to-head p o l y ( m e t h a c r y l i c a c i d ) , h i g h e r temperature, and more s t r o n g l y b a s i c c o n d i t i o n s were employed. PSPDM was h e a t e d a t 125 C f o r f o u r days i n 5M NaOH. L i k e t h e 0.1M NaOH e x p e r i m e n t s , t h e i m i d e was h y d r o l y z e d t o t h e amic a c i d and no f u r t h e r . The amide o f t h e r i n g opened i m i d e (V) i s e x t r e m e l y r e s i s t a n t t o b a s i c h y d r o l y s i s . The amide h y d r o l y t i c s t a b i l i t y may be a t t r i b u t a b l e t o s e v e r a l factors. The amide i s l o c a t e d r i g h t n e x t t o t h e c a r b o x y l a t e group which i s formed d u r i n g i m i d e h y d r o l y s i s . Under b a s i c c o n d i t i o n s , t h i s c a r b o x y l a t e group may s c r e e n t h e amide group from i n c o m i n g h y d r o x i d e ions· The c a r b o x y l group o f t h e amide i s a l s o q u i t e crowded by t h e polymer c h a i n and n e i g h b o r i n g pendant g r o u p s . This


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CHEMICAL REACTIONS O N POLYMERS

ÇH

ÇH

3

CH =C *c N

o=c

-f CH C

2

=o

3

l>H 2

.c

o=c

O = C L

= o

, r~

2

(II)

1.

2

CCH f- -tCH -C

2

(D Figure

CH I

3

C=CH

2

ÇH I

3

_c

=

(III)

Free R a d i c a l P o l y m e r i z a t i o n

o f PDMA t o PPDMA.

(a)

π 180

(b)

ι

1

1

1

1

1

1

I

Γ

160

140

120

100

80

60

40

20

0

10EL

WAVENUMBERS Figure

2.

13„ (a) C NMR

(50.3 MHz, CDC1 , TMS); (b) IR o f PPDMA. 3


o

21.

CH

I

•f C H

CH

3

I

3

H S 0 , S0 2

- C — CH 2

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KOZAKIEWICS ET AL.

2

-)

4

3

»

CH,

- C

I

,c = o

S0 H 3

ai) Figure

(IV)

3.

S u l f o n a t i o n o f PPDMA t o PSPDM.


296



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297

(IV) F i g u r e 5.

(V)

A l k a l i n e h y d r o l y s i s o f PS PSPDM a f t e r one day a t 90°C and pH 12.3 (0.1M NaOH).

Jul 180

160

F i g u r e 6.

140

120

100

" Γ 80

60

40

20

1 3

C NMR (50.3MHz, D O ) o f PSPDM a f t e r h e a t i n g a t 90°C f o r one day a t pH 12.3 (0.1 M NaOH).


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crowding may r e s t r i c t t h e a c c e s s i b i l i t y o f t h e amide group t o incom ing hydroxide i o n s . I t i s a l s o p o s s i b l e t h a t t h e p o l y m e r i c amide i s i n h e r e n t l y r e s i s t a n t t o h y d r o l y s i s under t h e c o n d i t i o n s employed. F u r t h e r attempts w i l l be made t o h y d r o l y z e t h i s amide t o e n a b l e t h e p r e p a r a t i o n o f head-to-head p o l y ( m e t h a c r y l i c a c i d ) . An i m p o r t a n t d i f f e r e n c e between PSPDM and t h e p r e v i o u s l y s t u d i e d N s u b s t i t u t e d d i m e t h a c r y l a m i d e c y c l o p o l y m e r s i s t h e water s o l u b i l i t y of PSPDM. H y d r o x i d e i o n p r o b a b l y had l i m i t e d a c c e s s t o a l a r g e f r a c t i o n o f t h e i m i d e groups i n t h e s e o t h e r d i m e t h a c r y l a m i d e c y c l o polymers owing t o t h e i r l i m i t e d s o l u b i l i t y i n w a t e r . T h e i r h y d r o l y t i c s t a b i l i t y under b a s i c c o n d i t i o n s may have been governed s o l e l y by s o l u b i l i t y . With t h e aqueous s o l u b l e PSPDM, however, h y d r o x i d e i o n has g r e a t e r a c c e s s i b i l i t y t o t h e imide g r o u p s . I t i s a l s o pos s i b l e t h a t any i m i d e r i n g s h y d r o l y z e d i n t h e p r e v i o u s s t u d i e s were i n a d v e r t e n t l y r i n g c l o s e d d u r i n g polymer i s o l a t i o n and a n a l y s i s . H s i e h e t a l . have r e c e n t l y r e p o r t e d t h a t a c i d i f i c a t i o n o f h y d r o l y z e d p o l y a c r y l a m i d e s c a n cause i m i d i z a t i o n between n e i g h b o r i n g amides and a c i d s under r e l a t i v e l y m i l d c o n d i t i o n s . The h y d r o l y s i s o f PSPDM under t h e b a s i c c o n d i t i o n s s t u d i e d was unanticipated i n l i g h t of the h y d r o l y t i c s t a b i l i t y of N-substituted p o l y ( d i m e t h a c r y l a m i d e s ) s t u d i e d by V o g l , Otsu, and c o - y o r k e r s . The m i l d e l e c t r o n - w i t h d r a w i n g s u l f o n a t e group ( = 0 . 0 9 ) is e x p e c t e d t o make t h e imide s l i g h t l y l e s s r e s i s t a n t t o h y d r o l y s i s . E l e c t r o n w i t h d r a w i n g s u b s t i t u e n t s on t h e p h e n y l r i n g o f N-phenyl s u c c ^ i m i d e have been shown t o i n c r e a s e t h e r a t e o f i m i d e h y d r o l y sis. E l e c t r o n d o n a t i n g groups d e c r e a s e t h e r a t e o f imide h y d r o l ysis. C o n s e q u e n t l y , PSPDM would be p r e d i c t e d t o h y d r o l y z e m a r g i n a l l y f a s t e r t h a n PPDMA. The e f f e c t i s n o t e x p e c t e d t o be l a r g e enough t o be t h e s o l e f a c t o r d e t e r m i n i n g whether t h e i m i d e groups o f p o l y ( N - s u b s t i t u t e d d i m e t h a c r y l a m i d e s ) h y d r o l y z e under t h e c o n d i t i o n s studied. 1

Five-membered r i n g i m i d e s i n c y c l o p o l y m e r s o f N - s u b s t i t u t e d d i m e t h a c r y l a m i d e s such as PSPDM c a n be h y d r o l y z e d t o amic a c i d s under m o d e r a t e l y b a s i c c o n d i t i o n s . The r e s u l t i n g N - s u b s t i t u t e d amide i s e x t r e m e l y r e s i s t a n t t o b a s i c h y d r o l y s i s . Consequently, t h i s b a s i c h y d r o l y s i s approach c a n s t i l l n o t be employed f o r t h e p r e p a r a t i o n o f head-to-head p o l y ( m e t h a c r y l i c a c i d ) . CONCLUSION S u l f o n a t i o n o f PPDMA o c c u r s r e a d i l y t o y i e l d t h e water s o l u b l e PSPDM. PSPDM i s s t a b l e a t n e u t r a l and m o d e r a t e l y a c i d i c c o n d i t i o n s , but i s r e a d i l y h y d r o l y z e d t o amic a c i d ( V ) i n 0.1 Ν NaOH a t 90 C. The amide o f t h e h y d r o l y z e d i m i d e , however, i s e x t r e m e l y r e s i s t a n t t o f u r t h e r h y d r o l y s i s under b a s i c c o n d i t i o n s .

REFERENCES 1. 2.

Xi, F. and Vogl, O., J. Macromol. Sci.-Chem., A20 (3), 321 (1983). Otsu, T. and Ohya, T., J. Macromol. Sci.-Chem., A21 (1), 1 (1984).


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Hargreaves, M.K., Pritchard, J.G., and Dave, H.R., Chem. Rev., 70 (40), 439 (1970). Sircar, S.S.G., J. Chem. Soc., 600 (1927). Sircar, S.S.G., J. Chem. Soc., 1252 (1927). Edward, J.T. and Terry, K.A., J. Chem. Soc., 3527 (1957). Herd, A.K., Eberson, L., and Higuchi, T., J. Pharm. Sci., 55, 162 (1966). Vegotsky, Α., Harada, K., and Fox, S.W., J. Am. Chem. Soc., 80, 3361 (1958). Harada, K., J. Org. Chem., 24, 1662 (1959). Kovacs, J . , Nagy Kovacs, H., Konyves, I., Csaszar, J . , Vajda, T., and Mix, H., J. Org. Chem., 26, 1084 (1961). Gordon, A.J., and Ford, R.A., "The Chemists Companion", J. Wiley & Sons, NY, NY, p. 147 (1972). Tirouflet, J. and le Trouit, E., C.R. Acad. Sci., Paris, 241, 1053 (1955). Hsieh, E.T., Westerman, I.J., and Moradi-Araghi, Α., Poly. Mat. Sci. Eng. Prepr., 55, 700 (1986). Butler, G.B., and Meyers, G.R., J. Macromol. Sci.-Chem., A5, 105 (1971).

RECEIVED August 27, 1987


Imide Hydrolytic Stability of - American Chemical Society

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