Copolymers, Polyblends, and Composites

27 Block Copolymers of Methyl Methacrylate 1

RAYMOND B. SEYMOUR, GLENN A. STAHL, DON R. OWEN, and HUBERT WOOD

Downloaded by GRIFFITH UNIV on October 25, 2017 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0142.ch027

University of Houston, Houston, Texas 77004

Polymerization in poor solvents is a two-step process in which the length of the precipitating macroradical coil is controlled by its solubility in the solvent. The length of the growing chain in the coils is diffusion-controlled. Hence, the molecular weight of poly(methyl methacrylate) prepared in hexane is essentially independent of the concentration of initiator. The following block copolymers were prepared by the addition of selected monomers to macroradicals formed by polymerizing methyl methacrylate (MMA) in poor solvents: poly(MMA-b-acrylic acid), poly(MMA -b-acrylonitrile), poly(MMA-b-ethyl methacrylate), poly(MMA-b -styrene), poly(MMA-b-vinyl acetate), poly(MMA-b-vinylpyrrolidone), poly(MMA-co-styrene-b-acrylonitrile), and poly(MMA-b -styrene). These block copolymers were characterized by yield data, solubility, pyrolysis gas chromatography, and turbidimetric titration.

I

t is g e n e r a l l y a c c e p t e d t h a t t h e m o s t v e r s a t i l e p r o c e d u r e f o r t h e p r e p a r a t i o n of b l o c k c o p o l y m e r s is t h e a d d i t i o n o f m o n o m e r s to l i v i n g i o n i c p o l y m e r s

(1) . A c c o r d i n g l y , p o l y ( m e t h y l methacrylate-Z?-alkyl acrylates) a n d the cor responding block alkyl methacrylates have been prepared b y anionic techniques (2) . H o w e v e r , a t t e m p t s t o p r e p a r e p o l y ( m e t h y l m e t h a c r y l a t e - Z ? - s t y r e n e ) b y anionic techniques were not successful (3).

P o l y ( m e t h y l m e t h a c r y l a t e - / > a c r y l o n i t r i l e ) h a s also b e e n r e a d i l y p r e p a r e d b y a d d i n g acrylonitrile to m e t h y l methacrylate ( M M A ) l i v i n g macroradicals (4, 5 ) , a n d t h i s t e c h n i q u e is also a v e r s a t i l e p r o c e d u r e f o r t h e p r e p a r a t i o n of m a n y other block copolymers (6). I n v e s t i g a t i o n s o f M M A m a c r o r a d i c a l s i n s o l v e n t s {7,8) a n d i n the vapor p h a s e ( 9 ) h a v e b e e n r e p o r t e d . It w a s s h o w n t h a t these M M A m a c r o r a d i c a l s are s t a b l e i n s o l v e n t s w h i c h h a v e s o l u b i l i t y p a r a m e t e r v a l u e s ( δ ) b e l o w 7.4 o r a b o v e 1 1 . 0 h i l d e b r a n d u n i t s ( H ) (10, 11). I n this investigation, block c o p o l y m e r s w e r e p r e p a r e d b y a d d i n g v i n y l m o n o m e r s t o m a c r o r a d i c a l s f o r m e d b y f r e e r a d i c a l i n i t i a t i o n o f M M A at t e m p e r a t u r e s b e l o w 5 0 ° C i n h e x a n e ( δ = 7.4 H ) a n d i n 1 - p r o p a n o l ( δ = 1 1 . 9 Η ) . A t t e m p t s to p r e p a r e blocks f r o m this m a c r o r a d i c a l b y a d d i n g i s o b u t y l 1

Present address: U n i v e r s i t y of Southern M i s s i s s i p p i , H a t t i e s b u r g , M i s s . 39401. 309

Platzer; Copolymers, Polyblends, and Composites Advances in Chemistry; American Chemical Society: Washington, DC, 1975.


310

COPOLYMERS,

POLYBLENDS,

A N D COMPOSITES

ι

I

I

I

I

0.5

1.0

1.5

2.0

2.5

AIBN, % Figure 1.

Yield of PMM A after 24 hrs at 50° C in hexane ( O ) and in benzene ( Δ )

m e t h a c r y l a t e , i s o p r e n e , o r v i n y l b r o m i d e at 5 0 ° C w e r e n o t s u c c e s s f u l . There was some e v i d e n c e of short blocks w h e n b u t y l acrylate, h y d r o x y e t h y l m e t h a crylate, a n d α-methylstyrene were a d d e d to M M A macroradicals i n 1-propanol at 5 0 ° C . H o m o b l o c k s of M M A were readily obtained w h e n M M A m o n o m e r w a s a d d e d t o M M A m a c r o r a d i c a l s i n h e x a n e o r 1 - p r o p a n o l at 5 0 ° C . B l o c k s o f s i g nificant size w e r e f o r m e d w h e n selected v i n y l m o n o m e r s w e r e a d d e d to M M A m a c r o r a d i c a l s i n h e x a n e o r 1 - p r o p a n o l at t e m p e r a t u r e s b e l o w 5 0 ° C . Experimental F r e s h l y d i s t i l l e d M M A w a s p o l y m e r i z e d at 2 5 ° C i n t h e a b s e n c e o f o x y g e n b y the ultraviolet light ( U V ) irradiation of a 1 0 % solution of M M A m o n o m e r i n h e x a n e w h i c h also c o n t a i n e d 1 % d i - f e r f - b u t y l p e r o x i d e ( b a s e d o n M M A ) . M M A m a c r o r a d i c a l s w e r e also p r e p a r e d b y h e a t i n g m o n o m e r s o l u t i o n s i n hexane or 1-propanol i n the presence of 2 . 5 % azobis(isobutyronitrile) ( A I B N ) f o r 4 8 h r s at 5 0 ° C . T h e r a t e o f p o l y m e r i z a t i o n w a s m o n i t o r e d b y gas c h r o m a t o g r a p h y ( G C ) of r e s i d u a l m o n o m e r a n d i n i t i a t o r , b y p r e c i s i o n d i l a t o m e t r y , a n d b y t h e y i e l d o f macroradicals i n aliquot samples. B l o c k copolymers were p r e p a r e d b y trans f e r r i n g t h e slurry of M M A macroradicals i n a n inert atmosphere to s m a l l bottles containing a d d i t i o n a l v i n y l m o n o m e r . These mixtures were heated i n sealed b o t t l e s at 5 0 ° C f o r 7 2 h r s . T h e e n d p r o d u c t s w e r e c h a r a c t e r i z e d b y G C analysis of residual m o n o m e r , y i e l d of solvent-washed p r o d u c t , pyrolysis G C ( P G C ) , a n d turbidimetric titration ( T T ) . V i s c o m e t r i c d a t a w e r e o b t a i n e d b y a v e r a g i n g five e f f l u e n t t i m e s m e a s u r e d t o ± 0 . 1 s e c at 2 5 . 0 0 ° C i n a n o . 1 U b b e l o h d e v i s c o m e t e r . G C r e t e n t i o n t i m e s were obtained o n a model A 1 0 0 C aerograph (Wilkens) equipped with a Servo-Ritter II recorder (Texas Instrument) a n d packed w i t h acid-washed C h r o m o s o r b W (Johns M a n v i l l e C o r p . ) a n d 2 0 % S E - 2 0 (General Electric C o . ) . T h i s e q u i p m e n t w a s also u s e d t o m e a s u r e t h e r e t e n t i o n t i m e s o f t h e o f f gases o f t h e p y r o l y z a t e . T h e l a t t e r w a s o b t a i n e d b y p l a c i n g a s o l u t i o n o f t h e sample o n a r h e n i u m tungsten code 13-002 coil ( G o w - M a c Instrument C o . ) ,


27.

SEYMOUR E T A L .

Block Copolymers

of Methyl

Methacrylate

311

e v a p o r a t i n g t h e s o l v e n t , a n d p y r o l y z i n g t h e r e s i d u a l f i l m f o r 5 sec. T h e r e l a t i v e a m o u n t s o f c o m p o n e n t s w e r e e s t i m a t e d b y c o m p a r i s o n w i t h t h e areas o f P G C peaks of samples of k n o w n composition. T u r b i d i t y data were obtained b y titrating a selected nonsolvent c o n t i n u ously using a microsyringe. T h e nonsolvent w a s injected into a magnetically s t i r r e d , e x t r e m e l y d i l u t e s o l u t i o n o f t h e p o l y m e r i n a s q u a r e glass c e l l . T h i s solution w a s i l l u m i n a t e d b y a parallel b e a m of light, a n d the intensity of t h e scattered light was measured b y a photoelectric cell a n d recorded continuously.


Results and

Discussion

Essentially quantitative yields of p o l y m e r ( P M M A ) were obtained w h e n M M A w a s p o l y m e r i z e d f o r 2 4 h r s at 5 0 ° C i n h e x a n e i n t h e p r e s e n c e o f 2 . 0 % A I B N ( F i g u r e 1 ) . Y i e l d s i n this heterogeneous p o l y m e r i z a t i o n system w e r e at least 8 0 % w h e n A I B N c o n c e n t r a t i o n e x c e e d e d 1 % . I n a h o m o g e n e o u s p o l y m e r i z a t i o n s y s t e m , h o w e v e r , y i e l d s w e r e less t h a n 8 0 % w i t h 2 % A I B N w h e n benzene w a s the solvent. Since the macroradicals precipitated w h e n their molecular weight ex c e e d e d t h e solubility l i m i t i n hexane, initiator concentration affected t h e rate of f o r m a t i o n b u t h a d l i t t l e effect o n t h e m o l e c u l a r w e i g h t o f t h e s e m a c r o r a d i c a l s ( F i g u r e 2 ) . I n b e n z e n e , m o l e c u l a r w e i g h t d e c r e a s e d as A I B N c o n c e n t r a t i o n increased. A l t h o u g h U V i n i t i a t i o n of M M A p o l y m e r i z a t i o n w a s d i s c o n t i n u e d after eight hours, p o l y m e r i z a t i o n c o n t i n u e d ( F i g u r e 3 ) . T h e increase i n m o l e c u l a r w e i g h t o f the p r o d u c t w i t h time after r e m o v a l of t h e U V source demonstrated that t h e increased y i e l d resulted f r o m a d d i t i o n of M M A m o n o m e r to t h e previously produced M M A macroradicals. H o m o b l o c k s of M M A were m a c r o r a d i c a l s at 5 0 ° C i n h e x a n e .

0.5

also p r o d u c e d f r o m A I B N - i n i t i a t e d M M A B o t h yield a n d reduced viscosity increased

1.0

1.5

AIBN,

2.0

2.5

%

Figure 2. Reduced viscosity of PMMA solutions after 24-hr polymerization of MMA at 50°C in hexane ( O ) and in ben zene ( Δ )


312

COPOLYMERS,

POLYBLENDS,

A N D COMPOSITES


25 J

Τ

1

8

20

•

1

1

— Γ

32

44

56

Time, hrs Figure 3.

Rate of UV-initiated polymerization of MMA in 1-propanol at 35°C UV radiation was discontinued after 8 hrs (*)

w i t h time (Figures 4 a n d 5 ) . Since the hexane slurry contained no residual A I B N , the increase i n w e i g h t resulted f r o m the a d d i t i o n of m o n o m e r to the M M A macroradicals. This conclusion was supported b y the findings f r o m viscometry a n d turbidimetry. T h e p o l y m e r i z a t i o n o f M M A i n a p o o r s o l v e n t o c c u r r e d i n t w o steps. T h e critical c h a i n length of the precipitated M M A m a c r o r a d i c a l w a s governed b y its s o l u b i l i t y i n t h e p o o r s o l v e n t , a n d t h e n u m b e r o f p r e c i p i t a t e d m a c r o r a d i c a l coils w a s a f u n c t i o n of initiator concentration. T h e rate of d i f f u s i o n of m o n o m e r into t h e p r e c i p i t a t e d coils i n the s e c o n d step w a s g o v e r n e d b y t h e ratio of

25

12

24

36

48

60

Time, hrs Figure

4.

Rate of formation of homoblocks of MMA macroradicals at 50°C



27.

Block Copolymers

SEYMOUR E T A L .

of Methyl

Methacrylate

313

Time, hrs Figure 5.

Effect of increasing size of MMA homoblock on reduced viscosity of MMA macroradicals

M M A m o n o m e r to t h e n u m b e r o f c o i l s a n d b y t h e d i i f u s i b i l i t y o f t h e m o n o m e r into the coils (11). P G C data ( F i g u r e 6) revealed that a block c o p o l y m e r i n w h i c h the block constituted 2 4 % of the m a c r o m o l e c u l e w a s o b t a i n e d w h e n acrylic a c i d ( A A ) was a d d e d to a M M A m a c r o r a d i c a l . T h e M M A m a c r o r a d i c a l w a s p r e p a r e d b y h e a t i n g M M A m o n o m e r w i t h 2 . 5 % A I B N i n h e x a n e 4 8 h r s at 5 0 ° C . T h e b l o c k copolymer was prepared b y heating the second monomer a n d the M M A macroradical i n hexane 96 hrs.

Λ MMA

Figure

6.

Gas chromatographic pyrogram poly(MMA-b-AA) (76:24)

of


314

COPOLYMERS,

POLYBLENDS,

,ΜΜΑ

MMA

'AN (10%)

AN (5%) MMA

JMMA

J MMA

MMA

AN (27%)

AN (22%)


MMA

Figure 7.

A N D COMPOSITES

ι MMA

Gas chromatographic pyrograms of

poly(MMA-h-AN)

Blocks 20 J

i — SCD ZJ

ίο Η

Figure 8.

Turbidimetric titration of poly(MMA-b-AN)

in DMF

MMA ( 72%)

MMA

Figure 9.

Gas chromatographic pyrogram of b-EMA)

poly(MMA-


27.

Block Copolymers

SEYMOUR E T A L .

A

of Methyl

315

Methacrylate

A

MMA

MMA

I MMA S (18%)


Figure 10.


poly(MMA-b-S)

T h e preparation of block copolymers of M M A a n d acrylonitrile ( A N ) was reported ( 1 2 ) . Findings from P G C (Figure 7) a n d T T (Figure 8) demon strated that p o l y ( M M A - f r - A N ) was p r e p a r e d b y heating A N a n d M M A macror a d i c a l s i n h e x a n e 9 6 h r s at 5 0 ° C ; t h e b l o c k s c o n s i s t e d o f 5 , 10, 2 2 , a n d 2 7 % copolymer. These block copolymers were soluble i n b o t h acetone a n d d i m e t h y l formamide ( D M F ) . B e c a u s e o f t h e l o w glass t r a n s i t i o n t e m p e r a t u r e ( T ^ ) of p o l y ( e t h y l m e t h a c r y l a t e ) ( Ρ Ε Μ Α ) , o n l y a short b l o c k ( 1 0 % ) w a s o b t a i n e d i n h e x a n e at 5 0 ° C ; t e r m i n a t i o n r e s u l t e d f r o m i n c r e a s e d s e g m e n t a l m o t i o n of t h e E M A b l o c k . H o w e v e r , a b l o c k w i t h a w e i g h t c o r r e s p o n d i n g t o 2 8 % c o p o l y m e r w a s o b t a i n e d at 4 0 ° C . P G C d a t a are p r e s e n t e d i n F i g u r e 9. P o l y ( M M A - Z ? - s t y r e n e ) f o r m e d i n b o t h h e x a n e a n d 1 - p r o p a n o l . T h e sty r e n e b l o c k ( S ) c o n s t i t u t e d 11 a n d 1 8 % of t h e c o p o l y m e r p r e p a r e d i n h e x a n e a n d i n 1-propanol, respectively ( F i g u r e s 10 a n d 1 1 ) . T h e Τ f o r p o l y ( v i n y l a c e t a t e ) ( P V A C ) is o n l y 2 8 ° C . H o w e v e r , as s h o w n b y the P G C data ( F i g u r e 1 2 ) , a c o p o l y m e r w i t h a V A C b l o c k e q u a l to 1 3 % of t h e m a c r o m o l e c u l e w a s o b t a i n e d i n 1 - p r o p a n o l . P G C ( F i g u r e 13) a n d T T ( F i g u r e 14) revealed that a block consisting of 14 w t % v i n y l p y r r o l i d o n e ( V P ) w a s o b t a i n e d w h e n V P w a s h e a t e d w i t h M M A m a c r o r a d i c a l i n 1 - p r o p a n o l 9 6 h r s at 5 0 ° C . A n A B C t y p e b l o c k c o p o l y m e r w a s o b t a i n e d b y a d d i n g A N to M Μ Α - V P b l o c k c o p o l y m e r ( F i g u r e 1 5 ) . It w a s s h o w n t h a t b l o c k s of s t y r e n e d i d n o t a d d t o A N m a c r o r a d i c a l s at m o d e r a t e temperatures unless s m a l l amounts of a solvent for p o l y a c r y l o n i t r i l e w e r e p r e s e n t ( 1 2 , 13). H o w e v e r , A N does f o r m a b l o c k w i t h s t y r e n e m a c r o r a d i c a l s , a n d , as s h o w n b y P G C ( F i g u r e 1 6 ) , p o l y ( M M A - c o - S - f r - A N ) g

Volume Fraction of Water Figure 11.

Turbidimetric

titration of poly(MMA-b-S)

in acetone


316

COPOLYMERS,

A MMA


Figure 12.

POLYBLENDS,

A N D COMPOSITES

(87%)

Gas chromatographic pyrogram of poly(MMA-b-VAC)

VP (14%)

Figure

13.

Gas chromatographic pyrogram of poly(MMA-b-VP)

30 CD +J > -r•r- Ό +-> -rr— SCD 3

20

10

Volume Fraction of Hexane Figure 14.

Turbidimetric titration of

poly(MMA-b-VP)


27.

Block Copolymers

SEYMOUR E T A L .

of Methyl

Methacrylate

317

MMA


VP

J Figure

15.

Gas chromatographic pyrogram of poly(MMA-b-VP-b-AN)

( 4 3 : 3 7 : 2 0 ) w a s o b t a i n e d w h e n A N w a s h e a t e d at 5 0 ° C w i t h p o l y ( M A A - c o - S ) ( 5 4 : 4 6 ) macroradicals i n hexane. PGC

( F i g u r e 1 7 ) also d e m o n s t r a t e d t h a t S f o r m e d b l o c k s w i t h c o p o l y m e r s

o f M M A a n d A N . T h e s i z e o f t h e S b l o c k i n c r e a s e d as t h e p r o p o r t i o n o f M M A i n the c o p o l y m e r m a c r o r a d i c a l increased; thus the S block constituted 12, 2 2 , a n d 3 5 % of the m a c r o m o l e c u l e AN

w h e n S was heated

at 5 0 ° C

i n hexane

with

c o p o l y m e r s c o n s i s t i n g of 5 0 , 6 6 , a n d 8 0 % M M A r e s p e c t i v e l y . L i k e w i s e , P G C ( F i g u r e 18) r e v e a l e d that a n S b l o c k e q u a l to 1 2 % of t h e

macromolecule b-AN)

was produced w h e n S was heated

at 5 0 ° C w i t h p o l y ( M M A -

( 7 2 : 2 8 ) i n 1-propanol i n the presence of s m a l l amounts of D M F ( w h i c h

was miscible w i t h 1-propanol)

as w e l l as i n its a b s e n c e .

o b t a i n e d w i t h this m a c r o r a d i c a l i n hexane e q u a l e d m o l e c u l e ; nevertheless,

H o w e v e r , the S block

only 6 %

of the macro-

a l a r g e r b l o c k of 1 5 % S w a s o b t a i n e d i n t h e p r e s e n c e

of r e l a t i v e l y s m a l l a m o u n t s o f D M F . D M F

was immiscible i n hexane,

a n d h e n c e it c o u l d p r e f e r e n t i a l l y

swell

the m a c r o r a d i c a l a n d t h e r e b y increase the rate of d i f f u s i o n of the S m o n o m e r . ^ MMA

(43%)

MMA

(20%)AN

S (37%)

Figure 16.

Gas chromatographic pyrogram of co-S-b-AN)

poly(MMA-


318

COPOLYMERS,

POLYBLENDS,


MMA (44%)

A N D COMPOSITES

MMA (52%)

MMA (52%)

X

y

AN (13%)

S (35%)

Figure 17.


poly(MMA-co-AN-b-S)

MMA (63%) i

Λ

MMA (63%) ι

AN (25%) MMA

(25%)

ι MMA

S (12%)

S (12%)

MMA (61%)

MMA (68%)

AN (24%) " MMA

AN (26%) " MMA

I Figure 18.

.AN

S (15%)


poly(MMA-h-AN-b-S)


27.

SEYMOUR E T A L .

Block Copolymers

of Methyl

Methacrylate

319

It w a s a n t i c i p a t e d t h a t S ( δ = 9 . 3 Η ) w o u l d d i f f u s e v e r y s l o w l y i n t o p o l y acrylonitrile macroradicals (δ = 12.5 Η ) a n d into macroradicals consisting of A N b l o c k s .


Conclusion Whereas the molecular weight of P M M A prepared i n homogeneous solu tion was inversely proportional to the concentration of initiator, the molecular w e i g h t of P M A p r e p a r e d i n poor solvents w a s essentially i n d e p e n d e n t of i n i tiator concentration. M M A h o m o p o l y m e r s w i t h increasing m o l e c u l a r weights were prepared b y a d d i n g M M A monomer to M M A macroradicals. T h e following block copolymers were prepared a n d characterized b y yield data, solubility, P G C , a n d T T : p o l y ( M M A - 6 - A A ) , p o l y ( M M A - & - A N ) , poly(MMA-fr-EMA), poly(MMA-fe-S), poly(MMA-fc-VAC), poly(MMA-fc-VP), p o l y ( M M A - f c - V P - 6 - A N ) , p o ! y ( M M A - c o - S - / > A N ) , a n d poly ( M M A - & - A N - & - S ) .

Literature Cited 1. Lenz, R. W., "Organic Chemistry of Synthetic High Polymers," p. 722, Interscience, New York, 1967. 2. Graham, R. K., Panchak, J. R., Kampf, M. J.,J.Polym. Sci. (1960) 44, 411. 3. Graham, R. K., Dunkelberger, D. L., Goode, W. E.,J.Amer. Chem. Soc. (1960) 82, 400. 4. Slavnitskaya, N. N., Semchikov, Y. D., Ryabov, Α., Bort, D. N., Vysomol. Soedin, Ser. A (1970) 12(18), 1956; Chem.Abstr.(1970) 73, 99240. 5. Seymour, R. B., Owen, D. R., Stahl, G. Α., Polymer (1973) 14, 324. 6. Seymour, R. B., Owen, D. R., Kincaid, P. D., Chem. Technol. (1973) 3(9), 549. 7. Norrish, R. G. W., Smith, R. R., Nature (1942) 150, 336. 8. Atkinson, B., Cotten, G. R., Trans. Faraday Soc. (1958) 54, 877. 9. Melville, H. W., J. Chem. Soc. (1941) 414. 10. Burrell, H., "Polymer Handbook," J. Brandrup, Ε. H. Immergut, Eds., chap. 4, Interscience, New York, 1965. 11. Seymour, R. B., Kincaid, P. D., Owen, D. R., J. Paint Technol. (1973) 45(580), 33. 12. Seymour, R. B., Owen, D. R., Stahl, G. Α., Wood, H., Tinnerman, W. N., Amer. Chem.Soc.,Div. Polym. Chem., Prepr. 14(2), 658 (Chicago, August, 1973). 13. Minoura, Y., Ogata, Y.,J.Polym. Sci. PartA-1(1969) 7, 2547. RECEIVED April 1, 1974. This investigation was supported in part by a grant from the Robert A. Welch Foundation.


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