Effect of Viscosity and Solubility Parameter of a Nonreactive Liquid

19 Effect of Viscosity and Solubility Parameter of a Nonreactive L i q u i d Additive o n the Emulsion Polymerization of Styrene DONALD R. OWEN, DONALD McLEMORE and WAN-LI LIU Department of Polymer Science, University of Southern Mississippi, Hattiesburg, Miss. 39401 R. B. SEYMOUR and WILLIAM N. TINNERMAN Downloaded by FUDAN UNIV on March 8, 2017 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0024.ch019

Department of Chemistry, University of Houston, Houston, Tex. 77004

Monomers, such as styrene which are good solvents for their polymers do not retard the bulk polymeriza tion rate. However, this rate does not increase i n a viscous good solvent medium that is present toward the end of the polymerization. Heterogeneous solution polymerization i n nonviscous poor solvents (1) and i n viscous poor solvents i s faster than rates observed i n good solvents. Polymerization of styrene i n an emulsion polymeri zation has been shown to follow a kinetics scheme as first described by Smith and Ewart. When the v i n y l monomer i s not a good solvent for the polymer (i.e. a c r y l o n i t r i l e or vinyl acetate) large deviations from Smith-Ewart Theory kinetic predictions are observed. It i s the purpose of this investigation to attempt to modify a conventional styrene emulsion by the addi tion of a nonreactive oil soluble additive with d i f ferent combinations of viscosity and Hildebrand solu bility parameters. It was anticipated these additives would induce the same heterogeneous condition as i n a monomer system with poor polymer s o l u b i l i t y . Thus, this study was undertaken to study the effect of various good and poor viscous and nonviscous solvents on the rate of polymerization and the molec ular weight of the polymer obtained i n these emulsion systems. Experimental A l l polymerizations were conducted i n a 500 ml three-necked round bottom flask equipped with s t i r r e r , reflux condenser, and zero grade nitrogen i n l e t . The flask submerged i n a constant temperature bath at 50 ± 299

Piirma and Gardon; Emulsion Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

EMULSION

300

POLYMERIZATION

Downloaded by FUDAN UNIV on March 8, 2017 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0024.ch019

1 C. S t y r e n e monomer was washed w i t h 10$ sodium h y d r o x i d e s o l u t i o n and vacuum d i s t i l l e d . A l l ingre d i e n t s were o x y g e n - f r e e and t h e system was c o n t i n u o u s l y purged w i t h n i t r o g e n . The l i q u i d a d d i t i v e and monomer were added t o t h e aqueous s u r f a c t a n t s o l u t i o n p r i o r t o t h e a d d i t i o n o f t h e i n i t i a t i o n system. The f o r m u l a t i o n w h i c h c o n s i s t e d o f a h i g h s u r f a c t a n t c o n c e n t r a t i o n was as f o l l o w s : d i s t i l l e d water monomer T r i t o n X-405 sodium l a u r y l s u l f a t e potassium p e r s u l f a t e sodium b i s u l f i t e liquid additive

320 ml 40.0 g 2.0 g 0.60 g

0.100 g 0.030 g

varied

1-2 ml a l i q u o t samples were w i t h d r a w n from t h e p o l y m e r i z a t i o n system p e r i o d i c a l l y and t h e p o l y m e r i z a t i o n sam p l e was quenched by t h e a d d i t i o n o f 5 ml o f 2 p e r c e n t aqueous h y d r o q u i n o n e . The e m u l s i o n was creamed by t h e a d d i t i o n o f a s a t u r a t e d sodium c h l o r i d e s o l u t i o n and b r o k e n v i a a d d i t i o n o f 10 ml o f 0 . 1 Ν s u l f u r i c a c i d . The c o a g u l a t e d p o l y m e r was s u b j e c t e d t o a s e r i e s o f washings w i t h w a t e r , m e t h a n o l and f i n a l l y p e t r o l e u m ether. The sample was t h e n d r i e d t o c o n s t a n t w e i g h t i n a h e a t e d vacuum d e s i c c a t o r . I n t r i n s i c v i s c o s i t i e s were o b t a i n e d u s i n g a Cannon-Fenske v i s c o m e t e r and t h e u s u a l method o f e x t r a p o l a t i o n t o z e r o c o n c e n t r a t i o n by m e a s u r i n g t h e r e d u c e d v i s c o s i t i e s a t 0 . 1 $ , 0 . 0 5 $ and 0 . 0 2 5 $ by w e i g h t o f polymer i n benzene. The mean v i s c o s i t y average m o l e c u l a r w e i g h t s were d e t e r m i n e d u s i n g t h e MarkHouwink e q u a t i o n and an " a " v a l u e o f 0 . 7 2 and a K" value o f 12.3 x 1 0 ~ ( 2 ) . The g e l p e r m e a t i o n chromatography d a t a was o b t a i n e d u s i n g a Model 5 0 1 Waters G e l P e r m e a t i o n Chromatograph a t 75$ pump c a p a c i t y w i t h a t o t a l column composed o f 6 f e e t o f 5 x 10 S t y r a g e l , 4 f e e t o f 700°A pore s i z e CPG and 2 f e e t o f 3000°A p o r e s i z e CPG. 11

5

R e s u l t s and D i s c u s s i o n s As shown i n F i g u r e 1 , t h e a d d i t i o n o f 1 p a r t benzene t o 4 p a r t s o f s t y r e n e i n t h e e m u l s i o n formu l a t i o n caused a l a r g e r e d u c t i o n i n t h e r a t e o f p o l y merization. T h i s e f f e c t was i n c r e a s e d as t h e concen t r a t i o n o f t h e benzene was i n c r e a s e d . The c h a i n t r a n s f e r c o n s t a n t o f benzene i s n o t s i g n i f i c a n t enough t o account f o r t h i s e f f e c t b u t r a t h e r t h e s i m p l e f a c t t h a t



19.

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t h e benzene i s a n o n r e a c t a n t . Benzene i s termed a good s o l v e n t f o r p o l y s t y r e n e s i n c e i t s s o l u b i l i t y parameter (6=9.2H) i s w i t h i n a p r e v i o u s l y e s t a b l i s h e d range o f ± 1.8 (^) f o r p o l y s t y rene (δ=9.2H). When hexane (6=7.3H) was used a t t h e same c o n c e n t r a t i o n , v e r y l i t t l e p o l y m e r i z a t i o n r e t a r d a t i o n was o b s e r v e d . The i n t r i n s i c v i s c o s i t y and GPC e l u t i o n t i m e s o f t h e polymer r e s u l t i n g from t h e hexane m o d i f i e d e m u l s i o n i n d i c a t e d i t was s u b s t a n t i a l l y lower i n m o l e c u l a r w e i g h t t h a n the c o n t r o l . F i g u r e 1 a l s o shows t h e r e s u l t o f an a d d i t i v e t h a t i s a v i s c u o u s good s o l v e n t , d i b u t y l p h t h a l a t e (6=9.3H). Very l i t t l e e f f e c t on t h e r a t e o f p o l y m e r i z a t i o n was n o t e d . The 6 v a l u e o f t h i s a d d i t i v e i s w i t h i n 0.1H o f t h a t o f p o l y s t y r e n e and hence t h e d i f f e r e n c e i n r a t e s between t h i s s o l v e n t and benzene must be a t t r i b u t a b l e to t h e v i s c o s i t y o f t h i s a d d i t i v e (4_). As shown i n F i g u r e 1, t h e r a t e o f p o l y m e r i z a t i o n o f s t y r e n e i n the p r e s e n c e o f d i i s o c t y l p h t h a l a t e (6=7.4H) was much f a s t e r t h a n t h e c o n t r o l . The s m a l l c o n c e n t r a t i o n n e c e s s a r y t o cause an o b s e r v a b l e r a t e i n c r e a s e i s d i f f i c u l t t o e x p l a i n by a v i s c o s i t y i n c r e a s e o r s o l u b i l i t y p a r a m e t e r change o f the e n t i r e e m u l s i o n system. However, i f the v i s c o u s poor s o l v e n t a d d i t i v e i s c o n c e n t r a t e d on the s u r f a c e of the monomerpolymer e m u l s i o n p a r t i c l e , v e r y s m a l l amounts o f an a d d i t i v e c o u l d e x h i b i t a p r o f o u n d e f f e c t on p o l y m e r i z a t i o n r a t e and m o l e c u l a r w e i g h t o f t h e r e s u l t i n g p o l y mer. One can p o s t u l a t e a mechanism whereby the v i s cous p o o r s o l v e n t at low c o n c e n t r a t i o n s p l a y s a minor r o l e i n the i n i t i a l s t a g e o f the e m u l s i o n p o l y m e r i z a t i o n , s i n c e i t s c o n t r i b u t i o n t o the t o t a l s o l u b i l i t y p a r a m e t e r and v i s c o s i t y o f t h e system i s s l i g h t . As the p o l y m e r i z a t i o n r e a c h e s the s w o l l e n monomer-polymer p a r t i c l e stage, h i g h e r s u r f a c e c o n c e n t r a t i o n s of the v i s c o u s poor s o l v e n t a r i s e due t o t h e i m m i s c i b i l i t y o f a d d i t i v e with polystyrene r i c h core. This high surface c o n c e n t r a t i o n o f the a d d i t i v e can t h e n cause t h e p r o p a g a t i n g m a c r o r a d i c a l t o p o s s e s s a lower t r a n s l a t i o n a l d i f f u s i o n r a t e due t o t h e i n c r e a s e d v i s c o s i t y c o n t r i b u t i o n o f t h e a d d i t i v e . A l s o a l o w e r segmental d i f f u s i o n r a t e can be e x p e c t e d because o f the i n c r e a s e d s o l u b i l i t y p a r a m e t e r d i f f e r e n c e between t h e r e a c t i o n media and t h e p r o p a g a t i n g polymer s p e c i e s . T h i s enhancement o f p o l y m e r i z a t i o n r a t e i n t h e p r e s e n c e o f v i s c o u s poor s o l v e n t s has a l s o been o b s e r v e d i n t h e s o l u t i o n p o l y m e r i z a t i o n o f s t y r e n e (5) but at much h i g h e r concen trations . As can be seen from T a b l e 1, the d i i s o c t y l p h t h a l a t e systems p r o d u c e d p o l y m e r s w i t h a l o w e r My


302

EMULSION

POLYMERIZATION

and M t h a n t h e c o n t r o l . As e x p e c t e d t h e f a s t e r (1/0.25) system produced t h e l o w e s t m o l e c u l a r w e i g h t product. n

TABLE I


ADDITIVE none Nujol Nujol Nujol Nujol diisoctyl phthalate diisoctyl phthalate dibutyl phthalate

M xl0"

CONCENTRATION

6

M xl0 n

v

1: 1: 1: 1:

0.025 0.25 0.50 1

7.2 11.0 4.5 4.8 6.5

4.2 7.5 2.1 2.4 3.6

3.5 4.5 2.0 1.8 2.1

1:

0.025

5.8

3.1

2.5

1:

0.25

4.2

2.0

1.9

1:

0.25

6.8

3.8

3.5

— — —

As shown i n F i g u r e 2, r a p i d p o l y m e r i z a t i o n was a l s o o b s e r v e d when N u j o l (δ=6.4Η) was used as t h e v i s cous poor s o l v e n t . As i n t h e case o f d i i s o c t y l p h t h a l a t e , t h i s min e r a l o i l d e m o n s t r a t e d an a b i l i t y t o i n c r e a s e p o l y m e r i z a t i o n r a t e s and e i t h e r i n c r e a s e o r d e c r e a s e m o l e c u l a r w e i g h t s depending on t h e c o n c e n t r a t i o n as seen i n T a b l e 1. W i t h low c o n c e n t r a t i o n s o f N u j o l t h e r e s u l t i n g increased macroradical l i f e t i m e s should r e s u l t i n a l a r g e r p e r c e n t a g e o f h i g h m o l e c u l a r weight s p e c i e s . The (1/0.025) N u j o l system d e f i n i t e l y d e m o n s t r a t e d an i n c r e a s e d h i g h m o l e c u l a r w e i g h t f r a c t i o n as i n d i c a t e d by T a b l e 1 by t h e s u b s t a n t i a l i n c r e a s e i n M o v e r t h e c o n t r o l . At h i g h e r c o n c e n t r a t i o n s o f N u j o l , i n c r e a s e d r a t e s were o b s e r v e d as w e l l as l o w e r polymer m o l e c u l a r weights. One can p o s t u l a t e t h a t a t h i g h e r c o n c e n t r a t i o n s o f N u j o l a s i g n i f i c a n t i n c r e a s e i n t h e number o f p r o p a g a t i n g s p e c i e s p e r p a r t i c l e r e s u l t s i n more a c t i v e s i t e s competing f o r t h e same q u a n t i t y o f mono mer. T h e r e f o r e , a g r e a t e r number o f m a c r o m o l e c u l e s r e s u l t w i t h a c o r r e s p o n d i n g lower m o l e c u l a r w e i g h t . S i m i l a r r e s u l t s w i t h good and poor s o l v e n t s were a l s o noted f o r the p o l y m e r i z a t i o n of methyl methacrylate, a c r y l o n i t r i l e , and v i n y l a c e t a t e . I f indeed t h i s v i s c o u s poor s o l v e n t a d d i t i v e e f f e c t i s a r e s u l t o f a s u r f a c e p o l y m e r i z a t i o n phenom ena, one would expect t o see k i n e t i c d e v i a t i o n s from Smith-Ewart Theory. The c o n t r o l s t y r e n e e m u l s i o n v



OWEN

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Emulsion

15

30

Polymerization

45

of Styrene

60

75

90

303

105

120

MINUTES Figure 1. The rate of emulsion polymerization in the presence of various additives at a styrene-to-additive ratio of 1/0.25 by weight. O , styrene stand ard; Δ , benzene; ·, hexane; dibutyl phthalate; 0> Nujol; A , diisoctyl phthalate.


EMULSION

304

POLYMERIZATION

S t y r e n e / N u j o l System [ E ] P l o t t e d as 1.8 power


S t a n d a r d S t y r e n e System [ E ] P l o t t e d as 0.6 power

2.0 -1 .-2 [Ε] χ 10 moles 1 Figure 3. Comparison of the dependency of polymerization rate on surfactant concen tration of the standard styrene and styrene/Nujol (1:0.25) emulsion systems

l _

,

1

1.0

1

1

2.0

1

1

1—

3.0

S o l u b i l i t y Parameter D i f f e r e n c e Figure 4. The relationship of solvency to the retardation of emul sion polymerization in the presence of solvents. O, benzene; ψ , cyclohexane; ·, octane; Δ , heptane; O , Nujol; •, hexane.


19.

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ET AL.

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Polymerization

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305


p o l y m e r i z a t i o n r a t e (Rp) would be e x p e c t e d t o show a 0 . 6 power dependency on t h e t o t a l s u r f a c t a n t concen t r a t i o n [ E ] . I f t h e s u r f a c e o f t h e monomer-polymer p a r t i c l e becomes t h e l o c i o f p o l y m e r i z a t i o n and/or o c c l u s i o n phenomena become i m p o r t a n t a l a r g e d e v i a t i o n from t h e c o n t r o l c o u l d be e x p e c t e d . As shown i n F i g u r e 3 * t h e s t a n d a r d e m u l s i o n form u l a t i o n Rp e x h i b i t e d a 0 . 6 power dependency on [ E ] . Whereas, a t a s t y r e n e t o N u j o l r a t i o o f ( 1 / 0 . 0 2 5 ) a Rp dependency on [E] o f a p p r o x i m a t e l y 1 . 8 was observed. Conclusions As shown i n F i g u r e 4 , t h e r a t e o f p o l y m e r i z a t i o n o f s t y r e n e was r e t a r d e d by good n o n v i s c o u s s o l v e n t s such as benzene, c y c l o h e x a n e , and octane whose s o l u b i l i t y parameters (δ) were w i t h i n 1.5H o f t h a t o f p o l y s t y r e n e a t s t y r e n e t o a d d i t i v e r a t i o s o f 3 t o 1. The a b s o l u t e r a t e s were s l i g h t l y i n c r e a s e d i n p o o r e r n o n v i s c o u s s o l v e n t s such as heptane and hexane and were f a s t e s t i n v i s c o u s n o n s o l v e n t s such as d i i s o c t y l p h t h a l a t e and N u j o l . Rate s t u d i e s i n d i c a t e d a Rp dependency on [ E ] s u b s t a n t i a l l y g r e a t e r t h a n u n i t y f o r t h e s t y r e n e e m u l s i o n systems m o d i f i e d w i t h v i s c o u s poor s o l v e n t s .

Literature Cited (1) Seymour, R. B., Kincaid, P. D . , and Owen, D. R . , Jour. of Paint Technology, (1973), 45, (580) 33. (2) "Polymer Handbook", editors V. Brandrup and Ε. H. Immergut, IV-10, Ref. 51, Interscience, New York (1967). (3) Seymour, R. Β . , Kincaid, P. D . , and Owen, D. R., Advan. Chem. Ser., (1973), 129, 230. (4) Trommsdorff, E., Kohle, H., and Lagally, P . , Makromol. Chem., (1962), 51, 154. (5) Seymour, R. Β . , Stahl, G. Α., and Wood, Η., Polymer Preprints, 16 (in press).


Effect of Viscosity and Solubility Parameter of a Nonreactive Liquid

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