Self-Cross-Linkable Polyepoxides - American Chemical Society

14 Self-Cross-Linkable Polyepoxides YOSHIO TANAKA

Downloaded by CORNELL UNIV on October 8, 2016 | http://pubs.acs.org Publication Date: December 3, 1979 | doi: 10.1021/bk-1979-0114.ch014

Research Institute for Polymers & Textiles, 4 Sawatari, Kanagawa, Yokohama 221, Japan

The l i t e r a t u r e contains numerous references to the reactive copolymers of 2,3-epoxy-1-propyl esters such as 2,3-epoxy-1-propyl methacrylate, acrylate and v i n y l sulfonate with other v i n y l compounds l i k e p r o p i o n i t r i l e , methyl a c r y l a t e , and vinylbenzene (1), and to the addit i o n reaction of amino, carboxy, and hydroxy compounds with the epoxy ring of these copolymers (2). 2,3-Epoxy-1-propyl-2-propenyl ether i s found (2) to have a strong tendency to l i m i t the molecular weight of a polymer by chain transfer through the a l l y l portion of the molecule. Relatively little attention has been paid to the copolymers of 2 , 3 - e p o x y - 1 - p r o p y l e t h e r s such as 1ethenyl-4-(2,3-epoxy-1-propoxy) benzene, and to the s e l f - a d d i t i o n reaction of the epoxy group with c a t a l y t i c or reactive functional groups, being capable of opening or adding to the epoxy r i n g , in the copolymers. This paper, therefore, reports the r a d i c a l copolymerization of 2,3-epoxy-1-propyl methacrylate or 1-ethenyl-4-(2,3epoxy-1-propoxy)benzene with 4- and 2 - v i n y l p y r i d i n e s and with 5 - e t h y l - 2 - v i n y l p y r i d i n e , and the s e l f - c r o s s l i n k i n g reaction of these copolymers. Experimental Reagent-grade 2,3-epoxy-1-propyl methacrylate and v i n y l p y r i d i n e s were distilled at reduced pressure, and the middle fractions were collected for use. 1-Ethenyl-

4 - ( 2 , 3 - e p o x y - l - p r o p o x y ) b e n z e n e was p r e p a r e d f r o m 4 e t h e n y l p h e n o l and l - c h l o r o - 2 , 3 - e p o x y p r o p a n e by a twos t e p p r o c e s s (_1). 2, 2 - A z o i s o b u t y r o n i t r i l e was r e c r y s t a l l i z e d from i t s a l c o h o l i c s o l u t i o n . An epoxide and a v i n y l p y r id i n e were d i s s o l v e d i n 10 ml of d r y t e t r a h y d r o f u r a n f o l l o w e d by the a d d i t i o n of 0 . 5 mole-% of the i n i t i a t o r . The s o l u t i o n was t r a n s f e r e d t o a p o l y m e r i z a t i o n tube, c o o l e d i n a l i q u i d n i t r o g e n b a t h , degassed, and s e a l e d under vacuum a f t e r 1

0-8412-0525-6/79/47-114-197$05.00/0 © 1979 American Chemical Society

Bauer; Epoxy Resin Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


198

EPOXY RESIN CHEMISTRY

f l u s h i n g w i t h a stream of oxygen-free n i t r o g e n . The t u b e was t h e n p l a c e d i n a c o n s t a n t t e m p e r a t u r e bath a t 60.0 ± 0.2°C f o r s e v e r a l h o u r s . A t the end of the r e a c t i o n t i m e t h e t u b e was c o o l e d and o p e n e d . The r e a c t i o n m i x t u r e s was d i s s o l v e d i n a s m a l l amount o f the s o l v e n t and poured i n t o anhydrous p e t r o l e u m e t h e r . The i n s o l u b l e m a t e r i a l was c o l l e c t e d and washed w i t h c o l d petroleum e t h e r . A f l u f f y y e l l o w o r brown s o l i d was p u r i f i e d by r e d i s s o l v i n g twice and r e p r e c i p i t a t i n g i n a l a r g e e x c e s s of n o n s o l v e n t . I t was f i n a l l y d r i e d t o c o n s t a n t weight under vacuum a t a room temperature. Co polymer c o m p o s i t i o n s c a l c u l a t e d from carbon and n i t r o g e n analyses. The r e a c t i v i t y r a t i o s were c a l c u l a t e d by Mayo-Lewis t e c h n i q u e (3). V i s c o s i t i e s o f t h e p o l y m e r i c m a t e r i a l s were ob t a i n e d i n t e t r a h y d r o f u r a n w i t h an Ubbelohde-type v i s c o m e t e r a t 30.00 ± 0.02°C. The i n f r a r e d a b s o r p t i o n s p e c t r a i n the r e g i o n of 400-4000/cm were measured f o r the sam p l e by H i t a c h i Model EPI-G3 i n f r a r e d spectrophotometer. The samples were p r e p a r e d by the KBr p e l l e t t e c h n i q u e . The thermal b e h a v i o r of the specimens was observed w i t h a Rigakudenki DSC-TGA a p p a r a t u s . The X-ray d i f f r a c t i o n p a t t e r n of the powdered polymer was taken i n the r e g i o n o f 3-37° by a R i g a k u d e n k i M o d e l 3D-F X - r a y d i f f r a c tometer w i t h the use o f N i - f i l t e r e d copper Κ radiation. R e s u l t s and D i s c u s s i o n C o p o l y m e r i z a t i o n of the epoxides w i t h these v i n y l p y r i d i n e s i n t e t r a h y d r o f u r a n under reduced p r e s s u r e w i t h 2 , 2 ' - A z o i s o b u t y r o n i t r i l e a t 60°C gave s t a b l e y e l l o w or brownish p o l y m e r i c m a t e r i a l s . In F i g u r e 1-3, the con c e n t r a t i o n of M2 ( v i n y l p y r i d i n e ) i n the monomer m i x t u r e a r e p l o t t e d a g a i n s t the c o r r e s p o n d i n g mole f r a c t i o n M2 of v i n y l p y r i d i n e i n the copolymer. The l i n e s i n the f i g u r e s were c a l c u l a t e d from t h e monomer r e a c t i v i t y r a t i o s and the p o i n t s r e p r e s e n t e x p e r i m e n t a l d a t a . The r e a c t i v i t y r a t i o s f o r these epoxy compounds w i t h the p r e s e n t comonomers have not y e t been r e p o r t e d , but can be compared w i t h those p r e d i c t e d by the Q-e scheme. The Q-e v a l u e s f o r the i n d i v i d u a l v i n y l p y r i d i n e were c a l c u l a t e d by assuming Q=0.78 and e=-0.02, Q=0.85 and e=0.10, and Q=0.87 and e=0.40 f o r 2 , 3 - e p o x y - l - p r o p y l methacry l a t e ; these a r e g i v e n i n T a b l e I . Assuming Q=1.30 and e=-0.50 f o r 2 - v i n y l p y r i d i n e , and Q=1.37 and e=-0.74 f o r 5 - e t h y l - 2 - v i n y l p y r i d i n e , the Q-e v a l u e s f o r the epoxide were a l s o c a l c u l a t e d and are shown i n T a b l e I, compared with those o b t a i n e d from P r i c e ' s (£) or Tamikado's (!5) Q-e v a l u e s f o r t h e p y r i d i n e . The Q-e v a l u e s f o r 1ethenyl-4-(2,3-epoxy-l-propoxy) benzene were a l s o c a l c u l a t e d by assuming Q=0.82, e=-0.20 f o r 4 - v i n y l p y r i d i n e ,



14.

199

Self-Cross-Linkable Polyepoxides

TANAKA

0.0

0.2

0.4

0.6

0.8

1.0

VINYLPYRIDINE IN MONOMER ( MOLE FRACTION ) Journal of Polymer Science, Polymer Chemistry Edition

Figure 1. Monomer-copolymer composition curve for l-ethenyl-4-(2 3-epoxy-lpropoxy) benzene (Mi) with 4-vinylpyridine (M ): ( ) rj = 0.467 and r = 0.638 9

g

0.0

0.2

0.4

0.6

2

0.8

1.0


Figure 2. Monomer-copolymer composition curves for l-ethenyl-4-(2,3-epoxy-lpropoxy) benzene (Mj) or 2,3-epoxy-l-propyl methacrylate (M ) with 2-vinylpyridine (M ): ( ) l-ethenyl-4-(2,3-epoxy-l-prpoxy) benzene with rj = 0.556 and τ = 1-25; ( ) 2,3-epoxy-l-propyl methacrylate with r = 0.51 and r = 0.62 t

2

2

2


2



200

0.0

0.2

0.4

0.6

0.8

1,0


Figure 3. Monomer-copolymer composition curves for l-ethenyl-4-(2,3-epoxy-lpropoxy) benzene or 2,3-epoxy-l-propyl methacrulate (MJ with 5-ethyl-2-vinylpyridine (M ): ( ) l-ethenyl-4(2,3-epoxy-l-propoxy) benzene with T = 0.639 and τ = 1.38; ( ) 2,3-epoxy-l-propyl methacrylate with r = 0.57 and x = 0.62 2

2

t

2


2


e f g

b c d

2

a

c

d

b

b

-0.02 ' 0.10 ' 0.40b,e 0.54 -1.17 -1.67 -0.02b,c 0.10*>,d 0.40^,e 0.28

ei 2

b

b

d

d

-0.85 -0.73 -0.43 -0.50 > -0.lb,f -0.6b,g -1.04 -0.92 -0.62 -0.74 '

e b

d

e

b

e

b

b

d

b

0.78 'Ç 0.85 ' 0.87 ' 1.23 1.55 0.93 0.78*>,c 0.85 ' 0.87 ' 1.04

Qi

b

b

d

1.40 1.35 1.02 1.37*>,d

1.09 rg

b

1.15 1.14 0.91 1.30 ' 1.07 /f

Q2

Journal of Polymer Science, Polymer Chemistry Edition

P o l y m e r i z a t i o n c o n d i t i o n s : 0.02 mole o f monomers; p o l y m e r i z a t i o n i n t e t r a h y d r o f u r a n w i t h 0.5 mole-% o f 2 , 2 - a z o i s o b u t y r o n i t r i l e a t 60°C. R e f e r e n c e d a t a used f o r c a l c u l a t i o n o f Q-e v a l u e s , Data o f Young ( J . Polym. S c i . , 1961, 54, 4 1 1 ) . Data o f Young and Kennedy ( i n C o p o l y m e r i z a t i o n , G. E . Ham, Ed., I n t e r s c i e n c e , New York, 1964, Appendix B . ) . Data o f Iwakura e t a l . (Makromol. Chem., I960, 44/46, 570). Data o f P r i c e ( J . Polym. S c i . , 1948, 3, 7 7 2 ) . Data o f Tamikado ( J . Polym. S c i . , 1960, 43, 4 8 9 ) . 1

0.62

0.57

5-Ethyl-2-vinylpyridine

a

0.62

0.51

2-Vinylpyridine

2

r

2

rι

M

x

Table I Monomer R e a c t i v i t y R a t i o s and Q-e V a l u e s i n C o p o l y m e r i z a t i o n o f 2 , 3 - E p o x y - l - p r o p y l M e t h a c r y l a t e (M ) w i t h V i n y l p y r i d i n e s ( M )



202


Q=1.30, e=-0.50 f o r 2 - v i n y l p y r i d i n e , and Q=1.37, e=-0.74 f o r the other p y r i d i n e ; these a r e g i v e n i n T a b l e I I . The monomer-copolymer compostion curve c a l c u l a t e d from the monomer r e a c t i v i t y r a t i o s , ri=0.514 and r2=0.715, gave a p o o r e r f i t to the e x p e r i m e n t a l p o i n t s w i t h 4-vinylpyridine. To d e s c r i b e the d a t a o b t a i n e d w i t h 2 - v i n y l p y r i d i n e , the c a l c u l a t e d curve with Q=1.5 and e=-1.2 was p o o r e r f i t than t h a t w i t h Q=1.4 and e = - l . l , b u t b e t t e r t h a n t h a t w i t h Q=1.2 and e=-1.0 f o r 1e t h e n y l - 4 - ( 2 , 3 - e p o x y - l - p r opoxy)benzene. These calcul a t e d w i t h Q=1.5, e=-1.2; Q=1.3, e = - l . l ; and Q=1.2, e=-1.0 f o r l - e t h e n y l - 4 - ( 2 , 3 - e p o x y - l - p r o p o x y ) b e n z e n e gave an e x c e l l e n t f i t c o r r e s p o n d i n g c l o s e l y to the p o i n t s w i t h 5 - e t h y l - 2 - v i n y l p y r id i n e . The copolymers w i t h these p y r i d i n e s have a c h a r a c t e r i s t i c band due to an i n t e r m o l e c u l a r hydrogen bond i>(OH) of OH group of polymers about a t 3500/cm as shown i n F i g u r e 4. The bands a t 1660 t o 1640/cm a s s i g n e d t o the s t r e t c h i n g modes of the C=C bond of o l e f i n i c hydro carbons are not o b s e r v e d . The bands a s s i g n e d t o the i n - p l a n e and the o u t - o f - p l a n e bending modes f o r o l e f i n i c CH groups a r e a l s o not observed d i s t i n c t l y i n the 14501300/cm and 1000-800/cm r e g i o n s of the i n f r a r e d s p e c t r a of the copolymers. The s y m m e t r i c a l and the asymmetrical s t r e t c h i n g bands of the epoxy r i n g seem t o occur near 1250/cm and 910/cm, r e s p e c t i v e l y . The i n t e n s i t y of the band a t 910/cm d e c r e a s e d and d i s a p p e a r e d i n the s p e c t r a of the heated samples which became i n s o l u b l e and i n fusible. The homo- and copolymers of these e p o x i d e s w i t h the v i n y l p y r i d i n e s were h i g h l y amorphous as judged by the X-ray d i f f r a c t o g r a m s Under the e x p e r i m e n t a l c o n d i t i o n s , the r e s u l t i n g copolymers were s o l u b l e i n o r g a n i c s o l v e n t s s u c h a s t e t r a h y d r o f u r a n , c h l o r o f o r m , and Ν,Ν α imethylformamide, w h i l e i n a humid a t m o s p h e r e t h e copolymers, e s p e c i a l l y those w i t h 4 - v i n y l p y r i d i n e , were apt to be c o n v e r t e d t o the i n s o l u b l e m a t e r i a l s d u r i n g r e p r e c i p i t a t i o n or d r y i n g a t a room temperature. Dif f e r e n t i a l s c a n n i n g c a l o r i m e t r y and thermogravimetry s t u d i e s show t h e s e c o p o l y m e r s do n o t m e l t b u t r e a c t a u t o c a t a l y t i c a l l y a t 90-200°C and degrade e x t e n s i v e l y above 300°C. The p o l y m e r i c m a t e r i a l s were c r u s h e d , mixed w i t h KBr powder and p r e s s e d i n t o the form of a KBr d i s k . The samples were heated i n a f o r c e d d r a f t oven, taken out a t c o n v e n i e n t i n t e r v a l s , c o o l e d i n a d e s i c c a t o r , and the i n t e n s i t y of the band a t 910/cm was measured. The i n t e n s i t y of IR a b s o r p t i o n spectrum of the epoxy group a t 910/cm was found to d e c r e a s e i n p r o p o r t i o n to the de c r e a s e of the epoxy compound i n the r e a c t i o n system (2).


Bauer; Epoxy Resin Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1979. 1

c

d

2

-0.74

1.5 1.3 1.2

(

i n tetrahydro-

1.37

b


d

d

d

1.30 1.5 1.4 1.2

-0.50

d

0.82 d

1.6 1.4

-0.20

b

P o l y m e r i z a t i o n c o n d i t i o n s : 0.02 mole o f monomers; p o l y m e r i z a t i o n f u r a n w i t h 0.5 mole-% o f 2 , 2 - a z o i s o b u t y r o n i t r i l e a t 60OC. R e f e r e n c e d a t a used f o r c a l c u l a t i o n o f Q-e v a l u e s , C a l c u l a t e d v a l u e s from t h e assumed Q-e v a l u e s , Assumed v a l u e s used f o r c a l c u l a t i o n o f r i and r values.

0.675C

-1.2d -1.1 -1.0

d

1.28C 1.38 1.38

0.630c 0.639

d

d

2

Q*

-1.3 -1.2

1.25 1.39C

5-Ethy1-2-vinylpyridine

b c d

a

Qi

e

ei

-1.2 -1.1 -1.0

1.15C

0.531C 0.556 0.560C

2-Vinylpyridine

2

0.715C

r 0.638

ri 0.514c

2

0.467

M

4-Vinylpyridine

a

2

Monomer R e a c t i v i t y R a t i o s and Q-e V a l u e s i n C o p o l y m e r i z a t i o n o f 1 - E t h e n y l 4 - ( 2 , 3 - e p o x y - l - p r o p o x y ) b e n z e n e (Mi) w i t h V i n y l p y r i d i n e s ( M )

Table I I



3500

3000

2500

ΙΙΙΙΙΜΙΙΙΜΙΙ

2000

L 1900

ΙΙΚ0.172)

J 1800

L 1600

1500

WAVE NUMBER

1700

1200

1100 1000

900

800

700 650


( CM" )

1

WOO 1300

Figure 4. IR spectra of l-ethenyl-4-(2,3-epoxy-l-propoxy) benzene and its homopolymers and copolymers with 2-vinylpyridine. Number in parentheses shows the mole fraction of pyridine in the copolymer: (I) monomer; (II) homopolymer; (III) copolymer

4000

f


M

Κ) ο


14.

TANAKA


205

The c h a r a c t e r i s t i c bands of the methyl or methylene, and the p h e n y l groups a t 1440 and 1505/cm were used as s t a n d a r d s f o r copolymers o f these e p o x i d e s , r e s p e c t i v e l y , b e c a u s e t h e i r i n t e n s i t i e s d i d n o t change d u r i n g t h e reactions. The r e s u l t s of t y p i c a l e x p e r i m e n t s w i t h the copolymers of l - e t h e n y l - 4 - ( 2 , 3 - e p o x y - l - p r o p o x y ) b e n z e n e are p l o t t e d i n F i g u r e 5 , i n which the r e l a t i v e i n t e n s i t y changes of 910 t o 1505/cm are p l o t t e d a g a i n s t the r e a c t i o n time and f o l l o w , i n some c a s e s , s i g m o i d a l c u r v e s showing an i n d u c t i o n p e r i o d . The i n d u c t i o n p e r i o d was found to be dependent on the r e a c t i o n temperature and on the c o n t e n t of the v i n y l p y r i d i n e u n i t i n c o p o l y m e r s . The r e l a t i o n s h i p of the r a t e of consumption of the epoxy group, - ά ( Μ ] ^ t / l , o ) / ' w i t h the epoxy groups remaining M i , t / l O ' i n the copolymers o f 1 - e t h e n y l 4-(2,3-epoxy-l-propoxy)benzene i s shown in Figure 6. l , i ^ th c o n t e n t o f t h e epoxy g r o u p a t r e a c t i o n time i . The maximum r a t e o f consumption o f the epoxy group i n c r e a s e d as the mole f r a c t i o n o f the p y r i d i n e to the epoxy g r o u p i n c r e a s e d . A t t h e maximum r a t e o f r e a c t i o n t h e r a t e o f c o n s u m p t i o n o f t h e epoxy g r o u p r e a c h e d the s t a t i o n a r y s t a g e , i n d e p e n d e n t of the c o n t e n t of the epoxy group, the r e g i o n of which became l o n g e r as the f r a c t i o n of the p y r i d i n e i n c r e a s e d . The s l o p e of the l i n e a r p a r t of the c u r v e o b t a i n e d f o r the r e l a t i o n s h i p d e c r e a s e d w i t h i n c r e a s i n g the c o n t e n t of the p y r i d i n e u n i t e x c e p t i n the i n i t i a l s t a g e of the reaction. Then, the r a t e of d i s a p p e a r a n c e of the epoxy group v a r i e s w i t h the mole f r a c t i o n of the epoxy group and the o r d e r of r e a c t i o n w i t h r e s p e c t t o the c o n c e n t r a t i o n of the epoxy group cannot be determined by t h i s experiment. The t i m e - c o n v e r s i o n c u r v e s , however, are s i m i l a r to those observed i n the t e r t i a r y a m i n e - c a t a l y z e d o l i g o m e r i z a t i o n of epoxy compounds (2), i n which the r a t e i s f i r s t - o r d e r w i t h r e s p e c t t o the epoxy com pound e x c e p t i n t h e i n i t i a l stage of the r e a c t i o n . I f the r a t e of r e a c t i o n i s g i v e n as a f u n c t i o n of the c o n c e n t r a t i o n s of the epoxy and the p y r i d y l groups, the r a t e e q u a t i o n i s shown by: - dM]/dt = k f(Μχ) g(M ) and may be r e w r i t t e n a s : M

d t

M

f

M

s

e

2

- J d M i / f f M i ) = k g(M ) t i where f ( M j ) and g(M ) a r e f u n c t i o n s of the c o n c e n t r a t i o n s of the epoxide and the p y r i d i n e , k i s the r a t e c o n s t a n t , and t i i s the r e a c t i o n time when the c o n v e r s i o n of the epoxy group r e a c h e s i . Assuming t h a t g(M ) i s c o n s t a n t under the c o n d i t i o n , we can o b t a i n 2

2

2

g(M ) t i = K i where K i i s a c o n s t a n t shown by 2

-[/dM^/f(Μχ)]/k.



206

EPOXY

RESIN

CHEMISTRY

Figure 5. Time-conversion curves for the epoxy group of poly[l-ethenyl-4-(2,3epoxy-l-propoxy)benzene] in KBr pellet at 105°C for copolymers with various mole fractions of pyridine: (I) 0.274; (II) 0.399; (III) 0.584



14.

TANAKA


207

EPOXY GROUPS REMAINING ( % ) Journal of Polymer Science, Polymer Letters Edition

Figure 6. Dependence of the rate of consumption of the epoxy group at 130°C on the remaining epoxy group in copolymers obtained at reduced pressure with various mole fractions of pyridine: (I) 0.258; (II) 0.502; (III) 0.597


208


Thus, v a r i o u s r e c i p r o c a l v a l u e s of the r e a c t i o n t i m e t i , a t w h i c h t h e c o n v e r s i o n o f t h e epoxy g r o u p reaches i , a r e p l o t t e d a g a i n s t the mole f r a c t i o n o f the p y r i d i n e , M , as shown i n F i g u r e 7. The r e a c t i o n r a t e i n c r e a s e s with i n c r e a s i n g the c o n t e n t of the p y r i d y l group, reaches a maximum v a l u e about a t 0.5 or 0.6, and then d e c r e a s e s w i t h the f r a c t i o n of the p y r i d i n e . The r i n g - o p e n i n g r e a c t i o n of the epoxy group i n these c o p o l y m e r s may be c a r r i e d o u t i n t h e p r e s e n c e o f t h e p y r i d y l group by the c o c a t a l y t i c a c t i o n o f the h y d r o x y l group i n the polymer c h a i n . The mechanism o f t h i s s e l f c r o s s l i n k i n g r e a c t i o n o f t h e c o p o l y m e r s seems t o be s i m i l a r to those (2^) proposed f o r the o l i g o m e r i z a t i o n o f the epoxy compound and the c u r i n g of the epoxy r e s i n by a t e r t i a r y amine. The r e a c t i v i t y d i f f e r e n c e i n these self-crosslinking r e a c t i o n s between these copolymers seems to be d e s c r i b e d m a i n l y by t h e p o l a r e f f e c t o f any of the p o s s i b l e o r g a n i c m o i e t i e s of the copolymer e x c e p t the epoxy group. The r i n g - o p e n i n g r e a c t i o n o f the epoxy compound can be g e n e r a l l y e x p l a i n e d by the m o d i f i e d T a f t e q u a t i o n ( 6 ) . As a l i n e a r r e l a t i o n s h i p has been observed between the p o l a r s u b s t i t u e n t c o n s t a n t o* and the b a s i c i t y o f e t h e r s (2) t the r e a c t i v i t y towards n u c l e o p h i l i c s p e c i e s w i l l d e c r e a s e and t h a t towards e l e c t r o p h i l i c r e a g e n t s may i n c r e a s e as the b a s i c i t y o f the epoxy compound i n c r e a s e s , i . e . , as the σ* v a l u e d e c r e a s e s . The σ * v a l u e s f o r the s u b s t i t u e n t s R [R=CH CHC6H40CH and C H C ( C H 3 ) C 0 C H ] o f the epoxy compounds, OCH CHR, can not be found i n the l i t e r a t u r e , but t h e i r r e l a t i v e o r d e r may be e s t i m a t e d from those (σ*=0.600 and 1.9) (6>) f o r CgHs and CH3CO, σ * f o r 1,2-epoxypropane (R=CH3) being 0. T h e r e f o r e , the r e a c t i v i t y o f t h e epoxy group i n the copolymers o f 1ethenyl-4-(2,3-epoxy-l-propoxy)benzene can be c o n s i d e r e d to be h i g h e r towards e l e c t r o p h i l i c s p e c i e s and t o be lower towards n u c l e o p h i l i c compounds than t h a t i n the copolymers o f 2 , 3 - e p o x y - l - p r o p y l m e t h a c r y l a t e . In the self-crosslinking reaction, actually, the former was c o n v e r t e d to the i n s o l u b l e m a t e r i a l s f a s t e r and a t a lower temperature than the l a t t e r . The pKa v a l u e s o f u n s u b s t i t u t e d , 2 - v i n y l and 4v i n y l p r i d i n e s a r e 5.17, 4.92-4.98, and 5.62 ( 2 ) · A m e t h y l o r an e t h y l g r o u p i n 2- o r 6 - p o s i t i o n o f t h e p y r i d i n e n u c l e u s causes an i n c r e a s e i n b a s i c i t y as w e l l as t h a t i n 3- or 4 - p o s t i o n . Consequently, a similar i n c r e a s e i n r a t e would be a n t i c i p a t e d i f the r a t e was p r o p o r t i o n a l t o the b a s i c i t y o f t h e p y r i d y l group i n c o polymers. N e v e r t h e l e s s , the r a t e of r e a c t i o n c a t a l y z e d by 2 , 5 - d i s u b s t i t u t e d p y r i d y l group a r e n o t l a r g e r but s m a l l e r than 2- or 4 - s u b s t i t u t e d p y r i d y l group as shown


2

2

2

2

2


2

2

14. TANAKA

209



12

10

8

0.2

0.1

0.6

0.8

1.0

VINYLPYRIDINE IN COPOLYMER ( MOLE FRACTION )


Figure 7. Effect of the mole fraction of pyridine on the reaction at 130°C of the epoxy group in copolymers of l-ethenyl-4-(2,3-epoxy-l-propoxy) benzene (Φ, O, Φ) or 2,3-epoxy-l-propoxy methacrylate (O) with various vinytpyridines. Where 10/tj at 30% conversion of the epoxy group is plotted: (Q) copolymers with 2vinylpyridine; (%) copolymers with 4-vinylpyridine; ((D) and Ο copolymers with 5-ethyl-2-vinylpyridine.


210


i n F i g u r e 7. T h i s might be a t t r i b u t e d t o the s t e r i c e f f e c t o f any o f t h e p o s s i b l e o r g a n i c m o i e t i e s of the copolymer e x c e p t the p y r i d y l group. The s i m i l a r i d e n t i t y o f these r e s u l t s has been r e t a i n e d i n t h e r e a c t i o n of 2 , 3 - e p o x y - l - p r o p y l phenyl e i t h e r w i t h b e n z o i c a c i d c a t a l y z e d by s u b s t i t u t e d p y r i d i n e s and i n many o t h e r reactions (2).


Synopsis S o l u b l e and s e l f - c r o s s l i n k a b l e l i n e a r copolymers w i t h pendant epoxy and p y r i d y l groups were o b t a i n e d from l - e t h e n y l - 4 - ( 2 , 3 epoxy-l-propoxy) benzene or 2,3-epoxy-lp r o p y l m e t h a c r y l a t e and v i n y l p y r i d i n e s by t h e a c t i o n o f 2,2'-azoisobutyronitrile. The monomer r e a c t i v i t y r a t i o s were determined i n t e t r a h y d r o f u r a n a t 60°C, and the Q and e v a l u e s f o r these e p o x i d e s were c a l c u l a t e d w i t h t h e r e p o r t e d Q-e v a l u e s f o r these p y r i d i n e s . The i n t r i n s i c v i s c o s i t i e s o f t h e copolymers were found t o be 0.15-0.38 i n t e t r a h y d r o f uran a t 30°C and t o be dependent on the copolymer c o m p o s i t i o n . The copolymers were amorphous, had no c l e a r m e l t i n g p o i n t s , and became i n s o l u b l e c r o s s l i n k e d polymers under h e a t i n g w i t h o u t f u r t h e r a d d i t i o n o f any c u r i n g a g e n t s . The r e a c t i v i t y d i f f e r e n c e i n these s e l f - c r o s s l i n k i n g r e a c t i o n s among these copolymers was d e s c r i b e d by t h e s t e r i c as w e l l as t h e p o l a r e f f e c t of any o f t h e p o s s i b l e o r g a n i c m o i e t i e s o f t h e c o p o l y mers. Literature 1. 2.

3. 4. 5. 6.

7.

Cited

Tanka, Y; Okada, A; Tomizuka, I.,in "Epoxy Resins"; May, C. A., Tanaka, Y . , E d . ; Dekker: New York, 1973; Chap. 2. Tanaka, Y.; M i k a , T . F., i n "Epoxy R e s i n s " ; May, C. Α . , Tanaka, Y., E d . ; Dekker: New Y o r k , 1973; Chap. 3. Mayo, F . R . ; L e w i s , F . M . , J. Amer. Chem. S o c . , 1944, 66, 1594. P r i c e , C . C., J. Polym. Sci., 1948, 3, 772. Tamikado, T., J. Polym. Sci., 1960, 43, 489. T a f t , R. W. Jr., i n " S t e r i c E f f e c t s i n Organic Chemistry"; Newman, M. S . , E d . ; W i l e y : New Y o r k , 1956; Chap 13. P e r r i n , D. D. E d . , " D i s s o c i a t i o n Constants of Organic Bases in Aqueous Solution"; Butterworths: London, 1965.

RECEIVED May 21, 1979.


Self-Cross-Linkable Polyepoxides - American Chemical Society

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