21 Effects of Solvents on Graft Copolymerization of Styrene withγ-IrradiatedCellulose
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YOSHIO NAKAMURA and MACHIKO SHIMADA Faculty of Technology, Gunma University, Kiryu, Gunma 376, Japan
Considerable works have been done on radiation-induced graft copolymerization of v i n y l monomers onto cellulose during past years. As many of them aimed the formation of graft copolymers with unique properties, few studies have been made on solvents effects for graft copolymerization. Sakurada et at (1 -5) have shown that the addition of small amount of water to reaction system markedly enhanced radiation-induced graft copolymerization of v i n y l monomers onto cellulose. Since then, many swelling agents to cellulose were used to aid diffusion of monomers into c e l l u l o s i c fibers. D i l l i and Garnett (6-13) reported that methanol i s p a r t i c u l a r l y attractive for the observat i o n of the Trommsdorff effect i n radiation-induced grafting of v i n y l monomers onto c e l l u l o s e . From the reports mentioned above, graft copolymerization of v i n y l monomers onto irradiated cellulose is considered to be affected by the diffusion of monomers into fibers, the swelling of trunk polymer, and the Trommsdorff effect of solvent on graft polymer radicals. In this paper, these effects of solvents on graft copolymerization of styrene onto irradiated cellulose will be discussed by investigating systematically weight increase after graft copolymerization, extent of grafting of graft polystyrene bonded chemically with irradiated c e l l u l o s e , amount of cellulose reacted with styrene, graft efficiency, molecular weight of graft polymer, number of reaction sites of graft copolymerization, and decay of cellulose radicals i n reaction system. Experimental Materials. Scoured cotton cellulose of Egyptian variety was purified by extracting with hot benzene -ethanol mixture (1/1 volume ratio) for 24 hr and washing with distilled water prior to a i r - d r y i n g . 298
Arthur; Cellulose Chemistry and Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
21. NAKAMURA AND
SHiMADA
Graft Polymerization of Styrene
299
S t y r e n e was p u r i f i e d b y p a s s i n g t h e monomer t h r o u g h a c o l u m n f i l l e d up w i t h a c t i v a t e d a l m i n a t o remove i n h i b itors of polymerization. M e t h a n o l was d i s t i l l e d b e f o r e u s e . O t h e r r e a g e n t s were r e a g e n t g r a d e , and were u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n . Irradiation. A f t e r p u r i f i e d c e l l u l o s e was d r i e d u n d e r v a c u u m a t 50 C f o r 20 h r , i t was i r r a d i a t e d u n d e r n i t r o g e n a t m o s p h e r e f o r l g h r b y Co-60 / - r a y s w i t h a n e x p o s u r e r a t e o f 1.0 χ 10 R / h r , f o r g r a f t i n g r e a c t i o n . Degree o f S w e l l i n g . Diameters o f c e l l u l o s i c f i b e r s a n d p o l y s t y r e n e t a b l e t were measured w i t h a m i c r o s c o p e o f 800 m a g n i f i c a t i o n s b e f o r e a n d a f t e r i m m e r s i o n i n v a r i o u s s o l v e n t s f o r 24 h r a t 30 C a n d averaged. D e g r e e o f s w e l l i n g ( D . S . ) was c a l c u l a t e d a s follows : D.S. = Da/Db
(a)
w h e r e Da s t a n d s f o r d i a m e t e r a f t e r i m m e r s i o n i n s o l v e n t a n d Db means d i a m e t e r b e f o r e i m m e r s i o n i n s o l v e n t . Graft Co-polymerization. Graft c o p o l y m e r i z a t i o n by s t y r e n e o n t o i r r a d i a t e d c e l l u l o s e was c a r r i e d o u t u n d e r n i t r o g e n a t m o s p h e r e a t 30 C. T h e l i q u o r r a t i o was 1 0 0 . A f t e r g r a f t c o p o l y m e r i z a t i o n , t h e samples were washed with methanol f o l l o w e d by washing with d i s t i l l e d water and a i r - d r y i n g . The samples were e x t r a c t e d w i t h h o t b e n z e n e t o remove homopolymer. The a p p a r e n t e x t e n t o f g r a f t i n g (A.E.G.) was d e t e r m i n e d a c c o r d i n g t o ( b ) : A.E.G. = (Wg-Wo)/Wo
(b)
w h e r e Wg d e s c r i b e s w e i g h t o f g r a f t c o p o l y m e r i z e d c e l l u l o s e a f t e r t h e b e n z e n e e x t r a c t i o n , a n d Wo means weight o f c e l l u l o s e before g r a f t c o p o l y m e r i z a t i o n . Fractionation. I n order t o separate t h e apparent g r a f t samples i n t o t h r e e p a r t s , namely, u n g r a f t e d c e l l u l o s e , i n s i d e homopolymer, and c h e m i c a l l y bonded g r a f t c o p o l y m e r , t h e samples were n i t r a t e d , o r a c e t y l a t e d . t h e p r o c e d u r e i s s h o w n i n F i g u r e 1. (i) Nitration. The g r a f t e d s a m p l e s w e r e n i t r a t e d a c c o r d i n g t o n o n d e g radative conditions reported by Alexander and M i t c h e l (14). To r e m o v e u n g r a f t e d c e l l u l o s e n i t r a t e s c o m p l e t e l y , t h e n i t r a t e d samples were e x t r a c t e d w i t h h o t a c e tone. After extraction, extracted cellulose nitrates w e r e w e i g h e d a n d t h e n i t r o g e n c o n t e n t was m e a s u r e d . The d e g r e e o f n i t r a t i o n was 2.4 p e r g l u c o s e " u n i t . T h e amount o f r e a c t e d c e l l u l o s e ( A . R . C . ) was c a l c u l a t e d a s follows : A.R.C. = ( 1 - W n / l . 6 7 ) / W o
(c)
Arthur; Cellulose Chemistry and Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
Arthur; Cellulose Chemistry and Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
Extraction^
Amount o f R e a c t e d Cellulose
Acetone Soluble Ungrafted Cellulose Nitrates
^Acetone
Apparent Graft Copolymer N i t r a t e d
Nitration
Graft
Figure 1.
Procedure of fractionation of apparent graft copolymer
True Extent of Grafting
Weight
Polystyrene j Molecular
Graft
£Hydrolysis
Benzenef I n s o l u b l e G r a f t Copolymer
Extraction
Benzene S o l u b l e I n s i d e Homopolymer
Benzene
Acetone I n s o l u b l e I n s i d e Homopolymer and Graft Copolymer
Extraction
Acetone Soluble Ungrafted Cellulose Acetates
Acetone
Apparent G r a f t Copolymer A c e t y l a t e d
Acetylation
Copolymer
Acetone I n s o l u b l e I n s i d e Homopolymer and G r a f t Copolymer_
Apparent
21.
NAKAMURA AND S H i M A D A
Graft
Polymerization
of
301
Styrene
w h e r e Wn means w e i g h t o f e x t r a c t e d c e l l u l o s e n i t r a t e s , (ii) Acetylation. A s s t y r e n e was a l s o n i t r a t e d a s c e l l u l o s e , a c e t y l a t i o n was c a r r i e d o u t t o s e p a r a t e i n s i d e homopolymer and t r u e g r a f t copolymer from apparent graft copolymer. The a p p a r e n t g r a f t e d s a m p l e s were acetylated i nt h emixture of acetic anhydride, g l a c i a l a c e t i c a c i d , a n d z i n c c h l o r i d e f o r 48 h r a t 60 C (15)· The a c e t y l a t e d s a m p l e s w e r e e x t r a c t e d c o m p l e t e l y w i t h hot a c e t o n e t o remove - u n g r a f t e d c e l l u l o s e a c e t a t e s . A f t e r i n s o l u b l e p a r t i n a c e t o n e was w e i g h e d , i t was e x t r a c t e d b y h o t b e n z e n e t o remove homopolymer w h i c h was n o t e x t r a c t e d b y t h e f i r s t b e n z e n e e x t r a c t i o n because o f entanglement. The t r u e e x t e n t o f g r a f t i n g ( T . E . G . ) was d e s i d e d a s f o l l o w s : T.E.G. = (Wg~Wo-Wh)/Wo
(d)
w h e r e Wh s t a n d s f o r w e i g h t o f i n s i d e h o m o p o l y m e r . Measurement o f M o l e c u l a r Weight. After the ace t y l a t e d t r u e g r a f t c o p o l y m e r was d i s s o l v e d i n m e t h y l e n e c h l o r i d e , t h e same v o l u m e o f a c e t o n e was a d d e d t o t h e solution. T h e c o n c e n t r a t e d h y d r o c h l o r i c a c i d was a d d e d t i l l t h e c o n c e n t r a t i o n o f h y d r o c h l o r i c a c i d was 3 N, a n d t h e s o l u t i o n was p o r e d i n t o m e t h a n o l a n d p r e c i p i t a t e d (JJL) · A f t e r t h e i s o l a t e d g r a f t p o l y s t y r e n e was p u r i f i e d , i t was d i s s o l v e d i n b e n z e n e a n d v i s c o s i t y a v e r a g e m o l e c u l a r w e i g h t was m e a s u r e d a c c o r d i n g t o ( e ) : Cn)= 2.4
x 10
β 4
0
Μ ·
6 5
(e)
Reaction Sites. Number o f r e a c t i o n s i t e s contributed t o grafting reaction i nirradiated c e l l u l o s i c f i b e r s was d e s i d e d a s f o l l o w s : N.R.S. = ( W t / M t ) / ( 1 0 0 / M c )
(N.R.S) 100 g
(f)
w h e r e Wt means t r u e e x t e n t o f g r a f t i n g e x p r e s s e d i n
