Emulsifier-Free Emulsion Copolymerization of Styrene with

7 Emulsifier-Free Emulsion Copolymerization of Styrene with Acrylamide and Its Derivatives HARUMA KAWAGUCHI, YOSHISHIGE SUGI, and YASUJI OHTSUKA

Downloaded by UNIV OF MINNESOTA on October 14, 2014 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch007

Department of Applied Chemistry, Keio University, Yokohama, Japan

Emulsifier-free latices are useful not only for industrial purposes but also for studies on colloidal properties (1, 2) and medical applications (3, 4). Various methods have been tried to prepare characteristic emulsifier-free latices (5-8). Among them, copolymerization of hydrophobic monomers with hydrophilic comono mers has been the most applicable one (7, 8). There have been many studies on the effects of ionic comonomers on the kinetics of aqueous copolymerization and the properties of the resulting latices, but nonionic hydrophilic comonomers have rarely been used for these purposes. This paper deals with the copolymerization of styrene with acrylamide and its derivatives in emulsifier-free aqueous media. It is expected that the effects of acrylamides on the nucleation and stabilization of particles differ from those of ionic comono mers. The reaction mechanism, the characteristics of the latices prepared, and the effect of the properties of acrylamides on them are discussed. Experimental Materials. Ion-exchanged and distilled water was used in all the polymerizations. Four kinds of acrylamides were used as co monomers (M2). Acrylamide (ΑΑ, Wako Chemicals Co.) and methacrylamide (MA, Tokyo Kasei Co.) were recrystallized from benzene. N-(Hydroxymethyl)acrylamide (ΗΜΑ, Tokyo Kasei Co.) was recrystal lized from ethyl acetate. Ν,Ν-Dimethylacrylamide (DMA, Tokyo Kasei Co.) and styrene (St, Kashima Kagaku Yakuhin Co.) were dis tilled at 54°C/3.5 mmHg and 40°C/14.5 mmHg, respectively. In some copolymerizations cross-linking reagents were added to reduce the formation of water-soluble polymer. N,N-Methylenebisacrylamide (MBA, Nakarai Chemicals Co.) and N-allylacrylamide (AAA, Polysciences, Inc.) were used as received. Divinylbenzene (DVB, Tokyo Kasei Co.) was treated with 10 % sodium hydroxide and dried. Two kinds of initiators were used: Potassium persulfate (KPS, Taisei Kagaku Co.) was recrystallized from water and azobis(isopropylf

0097-6156/81/0165-0145$05.00/0 © 1981 American Chemical Society

In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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a m i d i n e h y d r o c h l o r i d e ) ( A I P A , Wako C h e m i c a l s Co.) was u s e d w i t h o u t further purification.


Procedures. A standard recipe f o r the l a t e x preparation i s shown b e l o w : ( S t + M2) 20 g, ( w a t e r + b u f f e r ) 160 g , and i n i t i a t o r 5 mmole/1. The w e i g h t f r a c t i o n o f M2 i n monomer c h a r g e ( f ) was v a r i e d f r o m 0.01 t o 0.50. P o l y m e r i z a t i o n s were c a r r i e d out a t 55°C o r 70°C and pH 2.5 o r 9.0 u n d e r n i t r o g e n . Samples w e r e w i t h drawn f r o m t h e r e a c t i o n m i x t u r e a t v a r i o u s t i m e i n t e r v a l s and t h e p o l y m e r was p r e c i p i t a t e d i n an e x c e s s o f a c e t o n e . The c o n v e r s i o n and p o l y m e r c o m p o s i t i o n were d e t e r m i n e d by g r a v i m e t r i c means a n d by e l e m e n t a l a n a l y s i s , r e s p e c t i v e l y . The M2 f r a c t i o n i n i n s t a n t a n e o u s l y - f o r m e d c o p o l y m e r ( F i ) was c a l c u l a t e d f r o m e q . 1: F i = Fc + c(dFc/dc)

(1 )

where F c = t h e M2 f r a c t i o n i n a c c u m u l a t e d c o p o l y m e r a t c o n v e r s i o n c. The d i a m e t e r o f l a t e x p a r t i c l e s was m e a s u r e d f r o m t h e i r t r a n s m i s s i o n e l e c t r o n m i c r o g r a p h s w h i c h w e r e o b t a i n e d by u s e o f a H i t a c h i e l e c t r o n m i c r o s c o p e HU-12AF. The u n i f o r m i t y r a t i o o f p a r t i c l e s i z e ( U ) was c a l c u l a t e d f r o m e q . 2: U = Dw / Dn 1

(2 )

3

where Dw = Σ N i D i * / Σ N i D i , Dn = Σ N i D i / Σ N i , and N i = t h e number o f p a r t i c l e s with diameter D i . Some p o l y m e r p r e c i p i t a t e s w e r e e x t r a c t e d w i t h w a t e r and b e n z e n e by u s e o f a S o x h l e t e x t r a c t o r f o r 72 h r s and t h e e x t r a c t s were e l e m e n t a l l y a n a l y z e d . A few l a t i c e s w e r e c e n t r i f u g e d w i t h a K o k u s a n H-502 c e n t r i f u g e a t 25000g f o r 1 h r t o d e t e r m i n e t h e amount and c o m p o s i t i o n o f t h e p o l y m e r w h i c h d i s s o l v e d i n t h e l a t e x serum. The p a r t i t i o n c o e f f i c i e n t , t h e r a t i o o f t h e M2 c o n c e n t r a t i o n i n S t t o t h a t i n w a t e r , was d e t e r m i n e d f r o m t h e a b s o r b a n c e ( a t 200 mp f o r DMA, 201 mp f o r AA, 203 mp f o r HMA, and 205 mp f o r MA) o f each phase e q u i l i b r a t e d a t 70°C. The s o l u b i l i t y o f S t i n t h e aqueous s o l u t i o n o f AA was d e t e r m i n e d f r o m t h e a b s o r b a n c e o f t h e s o l u t i o n a t 290 mp. R e s u l t s and D i s c u s s i o n The dependence o f t h e c o n v e r s i o n and p o l y m e r - c o m p o s i t i o n o n t h e r e a c t i o n t i m e i s shown i n F i g u r e 1 f o r t h e c o p o l y m e r i z a t i o n o f S t w i t h AA a t f = 0.4, pH 9.0 a n d 70°C. The p o l y m e r i z a t i o n c o u r s e was f o u n d t o c o n s i s t o f t h r e e s t a g e s : A t f i r s t AA p o l y m e r i z e s p r e f e r e n t i a l l y but the preference decreases r a p i d l y w i t h i n c r e a s i n g c o n v e r s i o n (0 - 1.0 h r ) ; S t p o l y m e r i z e s e x c l u s i v e l y ( 1 . 0 - 1.5 h r s ) ; and a g a i n AA p o l y m e r i z e s p r e f e r e n t i a l l y ( 1 . 5 h r s - e n d ) . A s i m i l a r c o p o l y m e r i z a t i o n mode was o b s e r v e d i n an aqueous c o p o l y m -



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Figure 1. Copolymerization of St with A A under the conditions of the weight fraction of acrylamide in monomer charge (f) = 0.9, pH = 9.0, and 70°C

American Chemical Society Library 1155 IGth St. I. W. Washington, 0. C. 2003S In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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e r i z a t i o n o f St with 4 - v i n y l p y r i d i n e (8). I n the f o l l o w i n g sect i o n s t h e d e t a i l s o f each r e a c t i o n stage a r e d i s c u s s e d n o t o n l y f o r t h e c o p o l y m e r i z a t i o n o f S t w i t h AA b u t a l s o f o r t h o s e w i t h HMA, DMA, and MA. The F i r s t S t a g e . The p r e f e r e n t i a l p o l y m e r i z a t i o n o f AA a t t h e i n i t i a l s t a g e o f c o p o l y m e r i z a t i o n means t h a t t h e m a i n r e a c t i o n l o c u s i s t h e aqueous p h a s e j u s t a s J u a n g and K r i e g e r p o i n t e d i t o u t f o r t h e aqueous c o p o l y m e r i z a t i o n o f S t w i t h s o d i u m s t y r e n e s u l f o n a t e ( SSS ) ( 9 ) . I n t h e S t - S S S s y s t e m , SSS p o l y m e r i z e d p r e f e r e n t i a l l y up t o a f e w p e r c e n t c o n v e r s i o n u n d e r t h e c o n d i t i o n o f SSS/St (w/w) = 0.014. C o p o l y m e r i z a t i o n o f h y d r o p h o b i c monomer w i t h a l a r g e amount o f h y d r o p h i l i c comonomer was c o n s i d e r e d t o y i e l d a g r e a t e r amount o f i n f o r m a t i o n w i t h r e s p e c t t o t h e r e a c t i o n mode. By u s e o f a r e l a t i v e l y l a r g e amount o f AA o r i t s d e r i v a t i v e s t h e c h a r a c t e r i s t i c r e a c t i o n mode o f t h e c o p o l y m e r i z a t i o n o f S t w i t h a c r y l a m i d e s c o u l d be c l a r i f i e d . Some p o l y m e r - c o m p o s i t i o n v s . c o n v e r s i o n c u r v e s were o b t a i n e d f o r t h e c o p o l y m e r i z a t i o n s w i t h d i f f e r e n t f s ( F i g u r e 2), a n d a l l o f them seem t o i n t e r s e c t t h e o r d i n a t e a t 1.0. From t h e i n i t i a l s l o p e o f t h e c u r v e s a n d t h e monomer r a t i o i n t h e aqueous p h a s e t h e monomer r e a c t i v i t y r a t i o was c a l c u l a t e d , b u t t h e c a l c u l a t i o n r e s u l t e d i n a n e g a t i v e r 2 . T h e r e f o r e , i t was c o n c l u d e d t h a t t h e c o p o l y m e r i z a t i o n c o u l d n o t be r e g a r d e d a s a homogeneous one e v e n j u s t a f t e r the b e g i n n i n g o f t h e r e a c t i o n . The f i r s t s t a g e was c o n s i d e r e d t o be a t r a n s i t i o n a l s t a g e t o e s t a b l i s h t h e p a r t i c l e f o r m a t i o n . A c c o r d i n g t o t h e homogeneous n u c l e a t i o n mechanism b y F i t c h (10), i n t h e e m u l s i f i e r - f r e e aqueous medium, t h e g r o w i n g o l i g o m e r s c o i l t o primary p a r t i c l e s and such p r i m a r y p a r t i c l e s agglomerate to f o r m s e c o n d a r y p a r t i c l e s w h i c h t h e n b e g i n t o i m b i b e S t monomer and c o n s e q u e n t l y p o l y m e r i z a t i o n o f S t i n t h e s e c o n d a r y p a r t i c l e s p r o c e e d s . A l m o s t t h e same p r o c e s s i s e x p e c t e d t o t a k e p l a c e i n St-AA c o p o l y m e r i z a t i o n s y s t e m . J u d g i n g f r o m t h e r a p i d d e c r e a s e i n t h e AA f r a c t i o n i n i n s t a n t a n e o u s l y - f o r m e d p o l y m e r ( F i g u r e 1) i n s p i t e o f t h e e x t r a o r d i n a r i l y l a r g e amount o f AA compared w i t h t h a t o f S t i n t h e aqueous p h a s e a n d no a p p r i c i a b l e p r e d o m i n a n c e o f S t i n c o p o l y m e r i z a b i l i t y (11), l o c a l i z a t i o n o f S t i n the v i c i n i t y o f the a c t i v e s i t e s might o c c u r e a r l i e r than e x p e c t e d , t h a t i s , even the growing o l i g o m e r s might g i v e f a v o r a b l e s i t e s f o r S t t o be l o c a l i z e d i nconcentrated state to accerelate the polymerization of S t and the p a r t i c l e n u c l e a t i o n . A c c o r d i n g t o t h e d a t a on t h e e x t r a c t i o n o f AA-St c o p o l y m e r , t h e c o p o l y m e r m o l e c u l e s c o n t a i n i n g more t h a n 15 % S t a r e i n s o l u b l e i n w a t e r . An a l t e r n a t i v e mechanism o f p a r t i c l e f o r m a t i o n , t h e m i c e l l i z a t i o n - t y p e one ( 1 2 ) , c a n n o t be neglected a t present. f

The g r a d u a l i n c r e a s e i n t h e number o f p a r t i c l e s must p l a y a n i m p o r t a n t r o l e t o d e c r e a s e t h e AA f r a c t i o n i n p o l y m e r r a p i d l y b e c a u s e a s t h e number o f p a r t i c l e s i n c r e a s e s t h e c o a l e s c e n c e o f a g r o w i n g r a d i c a l w i t h a p a r t i c l e becomes more f r e q u e n t and d e c r e a s e s t h e o c c a s i o n f o r t h e r a d i c a l t o r e a c t w i t h AA i n t h e aqueous p h a s e .


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The t o t a l c o n v e r s i o n where t h e l a t e x p a r t i c l e s came t o a p p e a r f i r s t o n t h e e l e c t r o n m i c r o g r a p h s w e r e more t h a n 20 % f o r t h e c o p o l y m e r i z a t i o n a t f = 0.5, 12 % a t f = 0.4, c a . 3 % a t f = 0.3, and l e s s t h a n 1.2 X a t f = 0.2. A common f a c t i n f o u r c o p o l y m e r i z a t i o n s i s t h a t t h e AA f r a c t i o n i n i n s t a n t a n e o u s l y - f o r m e d p o l y m e r d r o p s b e l o w 0.60 - 0.65 a t t h e p r e s e n t e d c o n v e r s i o n s . The f r a c t i o n c o n t i n u e s t o d e c r e a s e f u r t h e r t o l e s s t h a n 0.05. The Second S t a g e . The s e c o n d s t a g e i s d e f i n e d a s t h e s t a g e where S t p o l y m e r i z e s e x c l u s i v e l y . To c l a r i f y t h e m a i n r e a t i o n l o c u s a t t h i s s t a g e , some q u a n t i t a t i v e a n a l y s i s was done f o r t h e c o p o l y m e r i z a t i o n a t f = 0.4. U s i n g t h e AA c o n v e r s i o n a t w h i c h AA p o l y m e r i z a t i o n f i r s t l e v e l s o f f (35 % ) , t h e s o l u b i l i t y o f S t i n t h e aqueous s o l u t i o n o f AA (3.92 mmole/1), a n d t h e p a r t i t i o n c o e f f i c i e n t o f AA between S t a n d w a t e r (0.093), t h e m o l a r c o n c e n t r a t i o n r a t i o o f AA t o S t i n t h e aqueous p h a s e was c a l c u l a t e d t o b e a b o u t 120 w h e r e a s t h a t i n t h e p a r t i c l e s was c a l c u l a t e d t o be 0.008. From t h e monomer r e a c t i v i t y r a t i o r e p o r t e d b y M i n s k a n d h i s c o w o r k e r s (13), t h e AA f r a c t i o n i n t h e p o l y m e r i n s t a n t a n e o u s l y formed i n t h e p a r t i c l e s i s c a l c u l a t e d t o be 0.03, w h i c h i s v e r y c l o s e t o t h e experimental v a l u e . Therefore, i t i s concluded that during t h e s e c o n d s t a g e p o l y m e r i z a t i o n i n t h e aqueous p h a s e i s n e g l i g i b l e , o r the main r e a c t i o n l o c u s i s the p a r t i c l e s . T h i s must r e s u l t f r o m f a s t d i f f u s i o n o f r a d i c a l s i n t o t h e p r e e x i s t i n g p a r t i c l e s . The number o f p a r t i c l e s i n t h i s s t a g e was f o u n d t o b e a l m o s t c o n s t a n t as t h e s l o p e o f l i n e s i n F i g u r e 3 was a l m o s t 1/3 a l t h o u g h t h e c o p o l y m e r i z a t i o n s a t h i g h e r f s r e s u l t e d i n some d e c r e a s e i n t h e number o f p a r t i c l e s w i t h i n c r e a s e i n g c o n v e r s i o n . E x c l u s i v e p o l y m e r i z a t i o n o f S t c o n t i n u e s u n t i l the S t convers i o n a t t a i n s a b o u t 50 %. T h i s c r i t i c a l S t c o n v e r s i o n was c o n s t a n t r e g a r d l e s s o f f and i t corresponds t o the e q u i l i b r i u m concentration of p o l y - S t i n the p a r t i c l e . T h e r e f o r e , the second stage i s c o n s i d e r e d t o come t o end when a l l o f t h e S t d r o p l e t s d i s a p p e a r . f

The T h i r d S t a g e . The b e g i n n i n g o f t h e t h i r d s t a g e i s c h a r a c t e r i z e d b y g r a d u a l a c c e l e r a t i o n o f AA p o l y m e r i z a t i o n , a c c o m p a n i e d w i t h a n i n c r e a s e i n t h e l a t e x v i s c o s i t y a s shown i n F i g u r e 1. These phenomena must r e s u l t f r o m a l t e r a t i o n o f t h e m a i n r e a c t i o n l o c u s f r o m t h e p a r t i c l e s t o t h e aqueous p h a s e . Disappearance o f S t d r o p l e t s l e a d s t o a decrease i n the conc e n t r a t i o n o f S t i n t h e aqueous p h a s e a s w e l l a s i n t h e p a r t i c l e s . The d e c r e a s e i n t h e c o n c e n t r a t i o n o f S t i n t h e aqueous p h a s e causes growing r a d i c a l s t o keep t h e i r h y d r o p h i l i c i t y f o r a l o n g time. The r a d i c a l s c a n r e a c t w i t h many AA m o l e c u l e s b e f o r e t h e y d i f f u s e i n t o the p a r t i c l e s . Some r a d i c a l s w o u l d n o t l o s e t h e i r s o l u b i l i t y i n w a t e r even a f t e r t h e y p r o p a g a t e d t o b e p o l y m e r m o l e c u l e s and such k i n d o f molecules would cause an i n c r e a s e i n t h e latex viscosity. J u d g i n g f r o m t h e dependence o f t h e l a t e x v i s c o s i t y o n t h e r e a c t i o n t i m e , most o f t h e p o l y m e r d i s s o l v e d i n w a t e r i s c o n s i d e r e d t o form d u r i n g the t h i r d s t a g e . To r e d u c e t h e



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Figure 2. Dependence of polymer composition on conversion in copolymerization of St with AA at pH 9.0 and 70°C (Il

(O)

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Figure 3. Dependence of particle size on conversion in copolymerization of St with A A at pH 9.0 and 70° C (î: (0)0.2; (A) 0.3; Ο 0.4; ( V ) 0.5)


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f o r m a t i o n o f the polymer d i s s o l v e d i n water, a few c r o s s - l i n k i n g r e a g e n t s (MBA, AAA a n d DVB) were u s e d b u t no s u c c e s s f u l r e s u l t s w e r e o b t a i n e d : a d d i t i o n o f MBA o r AAA ( 5 wt % t o AA) i n c r e a s e d t h e amounts o f c o a g u l u m a n d u s e o f DVB ( a l s o 5 wt %) d i d n o t change t h e shape o f t i m e - c o n v e r s i o n c u r v e a n d d i s t r i b u t i o n o f AA units significantly. C o p o l y m e r i z a t i o n o f S t w i t h A c r y l a m i d e D e r i v a t i v e s . The d e p e n d e n c e o f t h e M2 f r a c t i o n i n i n s t a n t a n e o u s l y - f o r m e d p o l y m e r o n t h e t o t a l c o n v e r s i o n i s compared among f o u r k i n d s o f a c r y l a m i d e s S t c o p o l y m e r i z a t i o n s a t f = 0.4 ( F i g u r e 4) ( 1 4 ) . HMA a n d DMA r e s e m b l e AA c o n c e r n i n g t h e c o p o l y m e r i z a t i o n mode, t h a t i s , t h e i r r e a c t i o n course i s d i v i d e d i n t o three stages. On t h e o t h e r hand MA c o p o l y m e r i z e s i n a d i f f e r e n t mode. The p a r t i t i o n c o e f f i c i e n t s o f a c r y l a m i d e s b e t w e e n S t a n d w a t e r a t 70°C a r e shown b e l o w : AA (0.093); HMA (0.089); DMA ( 0 . 2 9 3 ) ; and MA (0.159). I t i s expected t h a t use o f an a c r y l a m i d e d e r i v a t i v e w h i c h has a l a r g e r p a r t i t i o n c o e f f i c i e n t c a u s e s s h o r t e r d u r a t i o n o f t h e f i r s t s t a g e i n i t s c o p o l y m e r i z a t i o n w i t h S t . DMA i s l e s s h y d r o p h i l i c t h a n AA a n d HMA a n d t h e f i r s t s t a g e o f St-DMA c o p o l y m e r i z a t i o n ends q u i c k l y compared w i t h o t h e r s . Consequently t h e DMA c o n v e r s i o n where t h e DMA p o l y m e r i z a t i o n l e v e l s o f f i s l o w e r t h a n t h e c o r r e s p o n d i n g v a l u e s f o r o t h e r a c r y l a m i d e s as shown i n F i g u r e 5 ( 1 4 ) . DMA u n i t s seem t o b e l e s s e f f e c t i v e f o r s t a b i l i z a t i o n o f t h e l a t e x p a r t i c l e s a n d t h e number o f p a r t i c l e s i n St-DMA c o p o l y m e r l a t e x i s much l e s s t h a n t h o s e i n St-AA o r St-HMA copolymer l a t i c e s . As m e n t i o n e d i n t h e p r e c e d i n g s e c t i o n t h e second stage resembles the steady stage i n u s u a l emulsion polyme r i z a t i o n from the v i e w p o i n t o f k i n e t i c s . T h e r e f o r e , the d u r a t i o n of the second s t a g e , t h a t i s , the d u r a t i o n o f l e v e l l i n g - o f f o f a c r y l a m i d e s c o n v e r s i o n i s expected t o be i n v e r s e l y p r o p o r t i o n a l to t h e number o f p a r t i c l e s . The r e s u l t s shown i n F i g u r e 5 s a t i s f y t h e e x p e c t a t i o n q u a l i t a t i v e l y . The l e v e l l i n g - o f f o f DMA c o n v e r s i o n a t t h e s e c o n d s t a g e m i g h t be s u r p r i z i n g b e c a u s e a n a p p r e c i a b l e amount o f DMA s h o u l d e x i s t i n t h e p a r t i c l e s . T h i s phenomenon c a n be e x p l a i n e d b y c o n s i d e r i n g l o w c o p o l y m e r i z a b i l i t y o f DMA w i t h S t . The r e a c t i v i t y r a t i o s o f S t a n d a c r y l a m i d e s o b t a i n e d b y S a i n i a n d h i s c o w o r k e r s (11) s u p p o r t t h i s c o n s i d e r a t i o n . The p a r t i t i o n c o e f f i c i e n t o f HMA i s v e r y c l o s e t o t h a t o f AA. B u t i t was f o u n d t h a t HMA u n i t s i n c o p o l y m e r i s l e s s e f f e c t i v e t o make t h e c o p o l y m e r w a t e r - s o l u b l e t h a n AA u n i t s , t h a t i s , St-HMA copolymer l o s e s i t s w a t e r - s o l u b i l i t y by c o n t a i n i n g a s m a l l e r amount o f S t t h a n St-AA c o p o l y m e r does ( F i g u r e 6 ) . The a v e r a g e m o l a r f r a c t i o n o f AA i n t h e w a t e r - s o l u b l e A A - S t c o p o l y m e r was 0.86 w h i l e t h e c o r r e s p o n d i n g v a l u e f o r HMA was 0.92. Such l o w e r a b i l i t y o f HMA t o make t h e c o p o l y m e r w a t e r - s o l u b l e may b e a t t r i b u t e d t o n e g l i g i b l e h y d r o g e n - b o n d i n g o f -NH- g r o u p s o f HMA due t o s t e r i c h i n d r a n c e a n d some l o s s o f h y d r o g e n - b o n d a b l e -OH g r o u p s due t o u n d e s i r a b l e s i d e - r e a c t i o n s . T h i s p r o p e r t y o f HMA w o u l d c a u s e t h e f i r s t s t a g e o f St-HMA c o p o l y m e r i z a t i o n t o e n d a t a s l i g h t l y l o w e r



152


Journal of Applied Polymer Science

Figure 4. Dependence of polymer composition on conversion in copolymerization of St with AA's at f = 0.4 (14) ((— · — j A A; ( ; HMA; ( ) DMA; (—' '—)ΜΛ)

100

1 Polymerization

2 Time

Journal of Applied Polymer Science

Figure 5.

Conversion of AA's as a function of time in copolymerization with St at f = 0.4 (U) ((O ) A A; (A) HMA; Ο DMA; (\J)MA)



7.

KAWAGUCHi ET AL.

Emulsifier-Free

Emulsion

Copolymerization

153

c o n v e r s i o n , a n d t h e amount o f t h e p o l y m e r d i s s o l v e d i n w a t e r t o d e c r e a s e . Under t h e same r e a c t i o n c o n d i t i o n s t h e number o f p a r t i c l e s formed i n St-HMA c o p o l y m e r i z a t i o n was a b o u t t h e same w i t h t h a t i n St-AA l a t e x b u t t h e d i s t r i b u t i o n o f p a r t i c l e - s i z e o f t h e f o r m e r was n a r r o w e r t h a n t h e l a t t e r . Some d i s c u s s i o n s f o r t h e p r e p a r a t i o n o f m o n o d i s p e r s e St-HMA l a t i c e s a r e p r e s e n t e d i n t h e following section. No c l e a r e v i d e n c e was o b t a i n e d a b o u t t h e a l t e r a t i o n o f t h e m a i n r e a c t i o n l o c u s f o r t h e c o p o l y m e r i z a t i o n o f S t w i t h MA. T h i s w o u l d be a t t r i b u t e d t o t h e d i f f e r e n c e i n t h e p a r t i t i o n c o e f f i c i e n t b e t w e e n MA a n d AA ( s e e a b o v e ) a n d t h e d i f f e r e n c e i n t h e number o f l a t e x p a r t i c l e s formed i n t h e i r c o p o l y m e r i z a t i o n s y s t e m s w i t h S t . (The number o f p a r t i c l e s In S t - A A c o p o l y m e r l a t e x was a b o u t a t h i r d of t h a t i n St-AA l a t e x . The s m a l l number f o r St-MA s y s t e m i s c o n s i d e r e d t o r e s u l t from the lower p a r t i c l e - s t a b i l i z i n g a b i l i t y o f MA due t o i t s l o w e r h y d r o p h i l i c i t y . ) These f a c t o r s would a l t e r t h e b a l a n c e o f t h e p o l y m e r i z a t i o n i n two r e a c t i o n l o c i , t h a t i s , t h e aqueous p h a s e a n d t h e p a r t i c l e s , a n d c o n s e q u e n t l y s e r v e t o change t h e r e a c t i o n mode. P r e p a r a t i o n o f Monodisperse and C l e a n L a t i c e s . I n the polym e r i z a t i o n d e s c r i b e d above, c o n d i t i o n s w i t h r e l a t i v e l y h i g h f s w e r e a d o p t e d t o make c l e a r t h e b e h a v i o r o f M2 i n t h e r e a c t i o n course. The r e s u l t i n g l a t i c e s c o n t a i n a f a i r l y l a r g e amount o f p o l y m e r d i s s o l v e d i n t h e serum. I t was a l s o c l a r i f i e d t h a t a d d i t i o n o f a n e x c e s s amount o f M2 monomers makes t h e p a r t i c l e - s i z e d i s t r i b u t i o n widespread. Some p o l y m e r i z a t i o n s o f S t w i t h a s m a l l amount o f HMA w e r e c a r r i e d o u t to o b t a i n m o n o d i s p e r s e l a t i c e s f r e e f r o m t h e p o l y m e r d i s s o l v e d i n t h e serum. The dependence o f t h e p a r t i c l e - s i z e a n d u n i f o r m i t y r a t i o o n t h e c h a r g e d amount o f HMA i s shown i n F i g u r e 7. J u d g i n g f r o m t h e r e s u l t s i n F i g u r e 7 t h e u n i f o r m i t y r a t i o w o u l d t a k e t h e minimum a t t h e f c l o s e t o 0.1. M o n o d i s p e r s e b u t much l a r g e r p a r t i c l e s w e r e o b t a i n e d a t t h e same monomer f e e d r a t i o b u t c h a n g i n g t h e mode o f monomer c h a r g e . The aqueous p r e p o l y m e r i z a t i o n o f HMA f o l l o w e d b y a d d i t i o n o f S t r e s u l t e d i n the f o r m a t i o n o f the l a t i c e s w i t h l a r g e p a r t i c l e s and w i t h o u t s i g n i f i c a n t b r o a d e n i n g o f the p a r t i c l e - s i z e distribution. I n t h e c a s e s shown i n F i g u r e 7 S t was c h a r g e d a f t e r 1 h r p o l y m e r i z a t i o n o f HMA whose c o n v e r s i o n a t t h i s t i m e was a b o u t 60 %. f

Conclusions Copolymerization o f styrene with acrylamides (acrylamide, N-(hydroxymethyl)acrylamide, Ν,Ν-dimethylacrylamide, a n d m e t h a c r y l a m i d e ) w e r e c a r r i e d o u t i n e m u l s i f i e r - f r e e aqueous m e d i a . When e i t h e r o f the former t h r e e a c r y l a m i d e s were used, the c o p o l y m e r i z a t i o n c o u r s e was d i v i d e d i n t o t h r e e s r a g e s o n t h e b a s i s o f t h e main r e a c t i o n l o c u s . A t f i r s t acrylamides polymerized preferen t i a l l y i n t h e aqueous p h a s e . A f t e r t h e p a r t i c l e f o r m a t i o n s t y r e n e


154


f

Water-Soluble F r a c t i o n (Fw)

Benzene-Soluble Fraction


r

Figure 6. Extraction of St-AA and StHMA copolymers (fractions are given in weight basis)

Figure 7. Dependence of particle size and uniformity on charged amount of HMA at pH 9.0 and 70°C (solid marks: St was charged after 1 h prepolymerization of HMA )

Charged

Amount

o f HMA

(g)



7. KAWAGUCHi ET AL.

Emulsifier-Free Emulsion Copolymerization

polymerized exclusively in the particles even if a significant amount of acrylamides remaining in the aqueous phase. The decrease in the concentration of styrene after disappearance of styrene droplets caused the transfer of the main reaction locus from the particles to the aqueous phase and consequently led to the forma tion of an appreciable amount of the polymer dissolved in the aqueous phase. In the copolymerization of styrene with methacrylamide no distinct alteration of the main reaction locus was detected. The hydrophilicity and reactivity of acrylamides affected the polymerization mode and also the latex properties, e. g., the particle size, the distribution of acrylamides units in the latex, etc. Polymerizations of styrene in the presence of a small amount of N-(hydroxymethyl)acrylamide gave monodisperse and clean latices with the diameter of 350 mp to 1100 mp, which depended on the mode of monomer charge. Acknowledgement The authors gratefully acknowledge the assistance of Mr. S. Nakata for elemental analysis and Mr. K. Fujita, Electron Micro scope Laboratory, for TEM work. Literature Cited 1. Vincent, B.; Young, C. A. Faraday Discuss. Chem. Soc., 1978, 65, 297 2. Healy, T. W.; Homola, Α.; James, R. O.; Hunter, R. J. Faraday Discuss. Chem. Soc., 1978, 65, 156 3. Rembaum, Α.; Yen, P. S.; Molday, R. S. J. Macromol. Sci-Chem., 1979, A13, 603 4. Norde, W.; Lyklema, J. J. Colloid & Interface Sci., 1979, 71, 350 5. Matsumoto, T.; Ochi, A. Kobunshi Kagaku, 1965, 22, 481 6. Goodall, A. R.; Hearn, J.; Wilkinson, M. C. Br. Polym. J., 1978, 10, 141 7. Liu, L-J.; Krieger, I. M. "Emulsions, Latices, and Disper sions" ed. by Becker, P.; Yudenfreund, M. N.; Decker: New York, 1978, p. 41 8. Ohtsuka, Y.; Kawaguchi, H.; Hayashi, S. Polymer, to be published. 9. Juang, M. S.; Krieger, I. M. J. Polym. Sci., Polym. Chem. Ed., 1976, 14, 2089 10. Fitch, R. M.; Prenosil, M. P.; Sprick, K. J. "New Concepts in Emulsion Polymerization" ed. by Hwa, J. C. H.; Vanderhoff, J. W.; Interscience, New York, 1969, p.95 11. Saini, G.; Leoni, Α.; Franco, S. Makromol. Chem., 1971, 144, 235; ibid., 146, 165; ibid., 147, 213 12. Goodall, A. R.; Wilkinson, M. C.; Hearn, J. J. Polym. Sci., Polym. Chem. Ed., 1977, 15, 2193


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13. Minsk, L. K.; Koflarchik, C.; Darlak, R. S. J. Polym. Sci., Polym. Chem. Ed., 1973, 11, 353 14. Kawaguchi, H.; Sugi, Y.; Ohtsuka, Y. J. Appl. Polym. Sci., to be published. April 6, 1981.


RECEIVED


Emulsifier-Free Emulsion Copolymerization of Styrene with

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