Copolymers, Polyblends, and Composites

21 Transparent Acrylic/PVC-Graft/Blend Copolymers, Polyblends, and Composites Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 02/02/16. For personal use only.

Polymers R. G. BAUER and M. S.

1

GUILLOD

Research Division, The Goodyear Tire & Rubber Co., Akron, Ohio 44316

Transparent graft/blend polymers were formed when acryloni trile and 2-ethylhexyl acrylate were polymerized in homogeneous solution in the presence ofpoly(vinylchloride).Physical proper ties of films cast from a solution blend of poly(vinyl chloride) and a copolymer of acrylonitrile and 2-ethylhexyl acrylate were gen erally inferior to those of the aforementioned graft/blends. A study of the morphology showed why the blend films were opaque while the graft/blends were transparent. Accelerated UV aging revealed that the graft/blend films remained service able approximately four times as long as the parent poly(vinyl chloride).

T

h i s s t u d y w a s i n i t i a t e d t o find g o o d a g i n g t r a n s p a r e n t films f o r o u t d o o r applications. P o l y ( v i n y l chloride) ( P V C ) has several excellent p h y s i c a l attributes, a n d , n o d o u b t for this reason, a n n u a l c o m m e r c i a l p r o d u c t i o n of P V C a n d copolymers has g r o w n to 4.29 b i l l i o n p o u n d s ( r a n k i n g 2 6 t h i n v o l u m e i n t h e c h e m i c a l i n d u s t r y ) (1). A s Grassie ( 2 ) has stated, h o w e v e r , "of a l l the h i g h t o n n a g e p o l y m e r s . . . P V C is b y f a r t h e least s t a b l e i n its p u r e s t a t e . " O n l y the use of various stabilizers has m a d e possible outdoor applications of P V C . O n the other h a n d , acrylic polymers have significantly better stability to U V degradation, a n d their a d d i t i o n to P V C to i m p r o v e outdoor w e a t h e r i n g has b e e n s u g g e s t e d ( 3 ) . F u r t h e r m o r e , c o p o l y m e r films o f a c r y l i c esters a n d acrylonitrile were s h o w n to have outstanding w e a t h e r i n g properties, a n d their p h y s i c a l b e h a v i o r is s i m i l a r t o t h a t o f p l a s t i c i z e d P V C (4).

T h e p r o s p e c t s o f c o m b i n i n g t h e a d v a n t a g e s o f b o t h p o l y m e r systems i n a single p o l y m e r l e d to solution a n d melt b l e n d studies. A l t h o u g h there w a s n o gross e v i d e n c e o f i n c o m p a t i b i l i t y w i t h t h e b l e n d p o l y m e r s , o p a q u e films were o b t a i n e d . T h i s w a s not u n e x p e c t e d since refractive indexes [acrylic c o polymer, n = 1.49; p o l y ( v i n y l c h l o r i d e ) , n = 1.54] were not matched, and solubility parameters [acrylic copolymer, δ (cale.) = 9.5; poly ( v i n y l chlo r i d e ) , δ = 9.7] differ slightly. D

2 0

D

2 0

B o t h t h e r m o d y n a m i c considerations (5) a n d microscopic evidence (6) suggest that w h e n t w o different h i g h - m o l e c u l a r - w e i g h t p o l y m e r s are b l e n d e d , a h e t e r o g e n e o u s m i x t u r e w i l l b e f o r m e d . It h a s b e e n s u g g e s t e d t h a t t h e u l t i m a t e 1

Present address: Alza Corp., 950 Page Mill Road, Palo Alto, Calif. 94304. 231

Copolymers, Polyblends, and Composites Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 02/02/16. For personal use only.

232

COPOLYMERS,

POLYBLENDS,

A N D COMPOSITES

state o f m o l e c u l a r m i x i n g , c h a r a c t e r i s t i c o f l i q u i d m i x t u r e s , is o n l y a p p r o a c h e d b y p o l y b l e n d s as a l i m i t ( 7 ) . S e v e r a l i n v e s t i g a t o r s h a v e l o o k e d at P V C b l e n d s w i t h n i t r i l e - b u t a d i e n e r u b b e r (6, 8), a n d , a l t h o u g h c o m p a t i b i l i t y i n c r e a s e d w i t h a c r y l o n i t r i l e c o n t e n t ( u p to about 4 0 w t % ) , micro-heterogeneity was still evident i n electron photomicrographs. W o u l d copolymerization of the acrylic monomers i n a homogeneous solut i o n of P V C l e a d to graft reactions that m i g h t enhance t h e c o m p a t i b i l i t y o f t h e two p o l y m e r systems? E v i d e n c e has been presented that substantial grafting occurs o n P V C i n emulsion (9) or homogeneous solution ( 1 0 ) , b u t not under h e t e r o g e n e o u s c o n d i t i o n s i n m e t h y l m e t h a c r y l a t e w h i c h is n o t a s u i t a b l e s o l v e n t for P V C ( I I ) . T h e p r e p a r a t i o n of graft copolymers o n P V C b y m e c h a n o c h e m i c a l r e a c t i o n s h a s b e e n d e s c r i b e d b y G u y o t et al. ( 1 2 , 1 3 , 14). These same investigators have s t u d i e d further the t h e r m a l d e g r a d a t i o n of these graft c o p o l y m e r s i n s o m e d e t a i l ( 1 5 , 16). M o r e recently, cationically polymerizable olefins w e r e g r a f t e d onto P V C a n d the t h e r m a l b e h a v i o r of t h e p r o d u c t has b e e n the subject of some controversy (17, 1 8 ) . T h e present investigation focuses o n p o l y m e r s p r e p a r e d b y t h e reaction of the monomers 2-ethylhexyl acrylate a n d acrylonitrile o n P V C i n a homogeneous solution using free r a d i c a l initiation. Experimental M o n o m e r Purification. A l l polymers were obtained from monomers purified b y p a s s i n g t h e m t h r o u g h R o h m a n d H a a s A m b e r l y s t e x c h a n g e resins (salt f o r m s ) . Polymer Preparation. P O L Y ( V I N Y L C H L O R I D E ) . T h e P V C polymers were all c o m m e r c i a l materials. Representative suspension grade P V C p o l y m e r s are Goodyear's P l i o v i c K 6 5 6 a n d K 9 0 6 a n d D o w ' s 144. K 6 5 6 ( I V = 0.77) w a s u s e d f o r t h e m e l t b l e n d s , a n d K 9 0 6 ( I V = 1 . 1 ) a n d 1 4 4 ( I V = 1.0) w e r e u s e d f o r t h e s o l u t i o n - c a s t films. ACRYLIC ESTER/ACRYLONITRILE COPOLYMERS. T h e p r e p a r a t i o n of these c o p o l y m e r s is d e s c r i b e d i n R e f . 4. G R A F T / B L E N D P O L Y M E R S . These polymers were prepared b y dissolving P V C i n either m e t h y l ethyl ketone or tetrahydrofuran, f o l l o w e d b y the appropriate 2-ethylhexyl acrylate/acrylonitrile m o n o m e r charge a n d the free r a d i a l i n i t i a t o r , e.g., L u p e r s o l 11 ( t e r i - b u t y l p e r o x y p i v a l a t e ) . T h i s s o l u t i o n w a s t h e n h e a t e d t o 5 0 ° - 7 0 ° C i n 4 - o z b o t t l e s , 2-1. glass r e a c t o r s , o r l a r g e r g l a s s - l i n e d autoclaves. P o l y m e r i z a t i o n times were n o r m a l l y 1 2 - 1 6 h r s ; a conversion check w a s t h e n m a d e , a n d , i f c o n v e r s i o n w a s c o m p l e t e , films w e r e cast f r o m t h e polymer solution. P h y s i c a l M e a s u r e m e n t s . I M P A C T S T R E N G T H . Impact strength w a s measu r e d b y t h e n o t c h e d I z o d t e c h n i q u e at 2 3 ° C . S a m p l e s w e r e c o n d i t i o n e d at t h e s e t e m p e r a t u r e s a f t e r n o t c h i n g , p r i o r to t e s t i n g . TRANSMISSION A N D H A Z E MEASUREMENTS. L i g h t transmission w a s measu r e d w i t h a G a r d n e r color difference meter, a n d haze w a s measured w i t h a H a z e m e t e r attachment o n the G a r d n e r colorimeter. Test pieces were films a p p r o x i m a t e l y 2 m i l s t h i c k . A l l m e a s u r e m e n t s w e r e m a d e at 2 3 ° C . DIFFERENTIAL T H E R M A L ANALYSIS ( D T A ) . These t h e r m a l profiles were obtained using a calorimeter cell w i t h a D u P o n t 900 D T A instrument. Samples w e r e c u t f r o m m o l d e d o r cast films o f these p o l y m e r s , a n d t h e y w e i g h e d 1 0 - 2 0 mg. A p r o g r a m m e d h e a t i n g rate of 1 0 ° C / m i n a n d a sensitivity of 0.2°/inch were used i n this study. A l l t h e r m a l profiles were o b t a i n e d w i t h t h e sample flushed w i t h a n N s t r e a m . 2


21.

BAUER

Transparent

A N D GuiLLOD

233

Polymers

G E L P E R M E A T I O N C H R O M A T O G R A P H Y ( G P C ) . T h e G P C data were o b tained w i t h a Waters Associates M o d e l 100 w h i c h was operated o n tetrahydrof u r a n at r o o m t e m p e r a t u r e . OPTICAL A N D E L E C T R O N MICROSCOPY. S a m p l e s o f film f o r o p t i c a l a n d electron microscopy were prepared b y m i c r o t o m i n g . T h e samples for optical phase contrast m i c r o s c o p y were a p p r o x i m a t e l y 1 5 - 2 0 μ thick whereas those for electron m i c r o s c o p y were ultra m i c r o t o m e d w i t h a d i a m o n d knife to about 0 . 0 5 - 0 . 1 μ thickness. A L e i t z O r t h o l u x microscope w a s used f o r the phase c o n t r a s t m i c r o s c o p y a n d a n R C A - E M U - 3 6 e l e c t r o n m i c r o s c o p e at 4 0 , 0 0 0 X magnification was used for the electron microscopy.

Results and

Discussion

P u r e l y physical p o l y m e r blends are most c o m m o n l y p r e p a r e d b y either m e c h a n i c a l m i x i n g (melt) or dissolution i n a c o m m o n solvent f o l l o w e d b y casting a n d solvent r e m o v a l . I n this study, b o t h techniques w e r e u s e d ; t h e l a t t e r m e t h o d w a s m o r e r e a d i l y a p p l i c a b l e f o r film f o r m a t i o n i n s m a l l - s c a l e laboratory batches. It w a s r e c o g n i z e d that certain m o r p h o l o g i c a l differences b e t w e e n melt- a n d solution-fabricated p o l y m e r s are often o b s e r v e d ; these i n c l u d e phase inversions a n d distortions, especially w i t h graft a n d b l o c k p o l y m e r s . H o w e v e r , casual observation b y optical a n d electron microscopy revealed n o d r a m a t i c d i f f e r e n c e s b e t w e e n t h e m e l t - a n d s o l u t i o n - c a s t films, a n d t h i s c a n n o t be r e a d i l y e x p l a i n e d . O n e n o t e w o r t h y aspect of t h e b l e n d study of p o l y m e r s m i x e d i n the melt pertained to o p t i m i z a t i o n of impact strength relative to acrylonitrile content i n t h e c o p o l y m e r . F o r this study, t h e p o l y m e r b l e n d s w e r e c o m p r e s s i o n - m o l d e d and tested w i t h a T i n i u s Olsen I z o d Tester. T h e composition of the acrylic copolymers a n d t h e b l e n d composition are given i n T a b l e I. T h e change i n T a b l e I.

B l e n d C o m p o s i t i o n of A c r y l i c E s t e r / A c r y l o n i t r i l e Copolymers with P V C

Constituent

Content, %

Pliovic K656 PVC Copolvmer« PVC stabilizer Lubricant

1

Total

83.7 12.5 1.84 1.96 100.00%

Acrylonitrile 2-ethylhexyl acrylate copolymers were of the following compositions, by wt ratio: 0/100, 10/90, 12/88, 15/85, 17 83, 20/80, 22/78. 25/75, and 30/70. α

i m p a c t s t r e n g t h w i t h a c r y l o n i t r i l e c o n t e n t is s h o w n i n F i g u r e 1 ; i t c a n b e seen t h a t i m p a c t s t r e n g t h is at a m a x i m u m at a b o u t 2 0 - 3 0 w t % a c r y l o n i t r i l e i n t h e copolymer. W i t h t h i s b a c k g r o u n d i n f o r m a t i o n , i t w a s d e c i d e d t o see h o w these b l e n d s w o u l d b e h a v e as films. I n T a b l e I I a r e t a b u l a t e d s o m e p h y s i c a l p r o p e r t i e s of e x t r u d e d films o f P V C / a c r y l i c c o p o l y m e r b l e n d s ( 9 / 1 , 1 / 1 , a n d 1 / 9 ) . I n T a b l e I I I a r e t a b u l a t e d p h y s i c a l p r o p e r t i e s o f s o l u t i o n - c a s t b l e n d films, cast f r o m t e t r a h y d r o f u r a n s o l u t i o n . T h e cast films c o n t a i n e d n o l u b r i c a n t s o r sta b i l i z e r s ( w h i c h w e r e p r e s e n t i n t h e e x t r u d e d films); n e v e r t h e l e s s , t h e i r o p t i c a l p r o p e r t y d e f i c i e n c i e s w e r e s i m i l a r t o t h o s e o f t h e e x t r u d e d films. T h e a d d i t i v e s u s e d w e r e : P V C s t a b i l i z e r (e.g., o r g a n o t i n c o m p o u n d s ) , l u b r i c a n t (e.g., m e tallic stéarates), a n d plasticizer (phthalate t y p e ) . T h e question t h e n arose: w h a t w o u l d b e t h e nature o f t h e p o l y b l e n d w h i c h could be prepared if the acrylic monomers were polymerized i n the

234

COPOLYMERS,


1.8

POLYBLENDS,

A N D COMPOSITES

r

0.4

0 . 2 \-

0

I

1

1

0

10

20

PERCENT

Figure 1.

ACRYLONITRILE

IN

» 30 COPOLYMER

Notched Izod of PVC / acrylic blends vs. concentration of acrylonitrile in the acrylic

p r e s e n c e o f P V C ? I t w a s n e c e s s a r y t o find a s u i t a b l e s o l v e n t m e d i u m f o r P V C a n d acrylic copolymer. B o t h m e t h y l ethyl ketone a n d tetrahydrofuran were f o u n d to be suitable for p r e p a r i n g 1 0 - 1 5 % solutions of P V C / a c r y l i c graft/ b l e n d a f t e r m o r e t h a n 1 0 h r s r e a c t i o n at 5 0 ° - 7 0 ° C , u s i n g 1 - 1 2 p a r t s o f a n o r g a n i c free r a d i c a l initiator (based o n 100 parts m o n o m e r c h a r g e ) . T y p i c a l l y , t h e w e i g h t r a t i o o f a c r y l i c m o n o m e r s to P V C w a s v a r i e d f r o m 1/1 t o 1/9 s i n c e i n s o l u b i l i z a t i o n i n v a r i a b l y o c c u r r e d w h e n t h e r a t i o o f a c r y l i c m o n o m e r exc e e d e d 1 / 1 . A l t h o u g h t h e w e i g h t r a t i o o f a c r y l i c ester ( 2 - e t h y l h e x y l a c r y l a t e ) t o a c r y l o n i t r i l e w a s v a r i e d f r o m 0 . 4 3 / 1 . 0 t o 2 . 3 4 / 1 . 0 , t h e o p t i m u m f r r film s t r e n g t h p r o p e r t i e s a p p e a r e d t o b e ca. 1 . 5 / 1 . 0 .

21.

BAUER

AND

GuiLLOD

T a b l e II.

Transparent

Polymers

235

Properties of E x t r u d e d F i l m of P V C / A c r y l i c Copolymer M e l t Blends Blend


Property Composition: PVC/(AN/2-EHA)« Lubricant Stabilizer Plasticizer Light transmission, % Haze, % Tensile strength, psi Ultimate elongation, % Drop height at - 2 0 ° F , in. Crescent tear, lbs/in. α

ΑΝ/2-ΕΗΑ:

2

3

1/1 0.5 1.7 5.0 83.2 52.9 3044 115 6 485

1/9 0.5 1.1 5.0 83.0 44.9 2254 120 20 183

1 9/1 0.1 2.05 10.0 88.7 19.9 2850 5.0 3 420

acrylonitrile/2-ethylhexyl acrylate, 1.0/1.5 wt % .

U n e x p e c t e d l y , w h e n films w e r e cast f r o m these p o l y ( v i n y l c h l o r i d e - g - 2 ethylhexyl acrylate/acrylonitrile ) solutions, they were crystal clear w i t h very l o w h a z e v a l u e s . T a b l e I V lists s o m e o f t h e p h y s i c a l p r o p e r t i e s o f these p o l y ( v i n y l c h l o r i d e - g - 2 - e t h y l h e x y l a c r y l a t e / a c r y l o n i t r i l e ) cast films; v a l u e s f o r a s o l u t i o n b l e n d o f t h e a c r y l i c c o p o l y m e r a n d P V C a r e also i n c l u d e d . W h i l e tensile strengths of the 1.0/1.5 a n d 1.0/4.0 a c r y l i c c o p o l y m e r / P V C - g r a f t / b l e n d films w e r e a b o u t 8 0 - 9 0 % t h a t o f t h e h o m o p o l y m e r P V C film, t h e y w e r e s i g nificantly higher t h a n that of the b l e n d p o l y m e r . F u r t h e r m o r e , t h e crescent tear s t r e n g t h s w e r e h i g h e r t h a n those o f t h e b l e n d a n d t h e P V C film. M o s t i m p o r t a n t l y , t h e h a z e v a l u e s o f t h e graft b l e n d films w e r e m u c h i m p r o v e d o v e r t h a t o f the b l e n d p o l y m e r , a n d they m o r e nearly a p p r o a c h e d that o f t h e h o m o polymer P V C . S i m i l a r p o l y m e r c o m p a t i b i l i z a t i o n effects w e r e o b s e r v e d b y W e l l o n s a n d co-workers ( 1 9 ) o n radiation graft copolymers o f cellulose acetate a n d p o l y s t y r e n e a n d b y R i e s s a n d h i s c o l l e a g u e s (20) o n v a r i o u s b l o c k c o p o l y m e r s . H u g h e s a n d B r o w n (21) also r e p o r t e d s o m e e v i d e n c e o f c o m p a t i b i l i z a t i o n i n a T a b l e III.

Properties of Solution-Cast P V C / A c r y l i c C o p o l y m e r Blends Blend

Property Composition: PVC/(AN/2-EHA) Tensile strength, psi Elongation, % Crescent tear, lbs/in. Light transmission, % Haze, % ° ΑΝ/2-ΕΗΑ:

a

1

2

3

9/1 3400 100 150 93 23

1/1 3300 100 425 93 40

1/9 1200 200 800 93 20

acrylonitrile/2-ethylhexyl acrylate, 1.0/1.5 wt % .

p o l y m e r solution study i n w h i c h a single h a z y phase existed f r o m a graft polymer whereas the physical mixture of homopolymers separated into t w o phases i n a c o m m o n solvent. W h a t is t h e e v i d e n c e f o r t h e o c c u r r e n c e o f g r a f t r e a c t i o n s o f these a c r y l i c m o n o m e r s o n t o P V C ? H o w w o u l d t h i s g r a f t i n g , i f i t o c c u r r e d , affect t h e c o m p a t i b i l i t y of the t w o p o l y m e r system? These a n d other p e r p l e x i n g questions l e d t o several experiments w h i c h were i n t e n d e d t o clear u p t h e uncertainty. A D T A thermogram between - 1 0 0 ° a n d + 1 4 0 ° C (Figure 2) of the 1.5/1.0-PVC/acrylic copolymer (1 . 5 / 1 . 0 - 2 E H A / A N ) graft/blend showed a

236

COPOLYMERS,

Table IV.

POLYBLENDS,

Tear Strength

Description*

psi

psi

%

1.5/1.0 PVC/acrylic copolymer solution blend 1.5/1.0 PVC/acrylic solution graft/blend 4.0/1.0 PVC/acrylic solution graft/blend PVC hompolymer Acrylic copolymer

4625

9

3640

60

—

—

5190

—

—

5760

— —

— —

%

Optical Properties

Cres Elmencent, dorf, Trans., Haze, lbs/in. g/mil % %

Break,

Yield,


COMPOSITES

Physical Properties of Cast F i l m s Tensile Properties

1

AND

159

10

93

49

5.5

192

11

93

4.0

6.0

228

20

93

1.0

6250 6.0 2530 300

104 105

18 137

93 93

1.5 2.1

« Acrylic copolymers were 1.5/1.0 (wt ratio) 2-ethylhexyl acrylate^crylordtrile charge. A l l films were 2.0 mils thick, cast on glass plates with a precision draw-down blade.

s i n g l e i n f l e c t i o n at a b o u t 8 5 ° C w h i c h p r e s u m a b l y w a s t h a t o f t h e g r a f t P V C . T h e r e w a s n o i n d i c a t i o n o f a n y i n f l e c t i o n , c h a r a c t e r i s t i c o f a glass t r a n s i t i o n f o r t h e a c r y l i c c o p o l y m e r , w h i c h w o u l d h a v e b e e n e x p e c t e d at a b o u t — 4 0 ° C if t h i s w e r e a b l e n d . F u r t h e r m o r e , a G P C c u r v e ( F i g u r e 3 ) , o b t a i n e d o n this 1 . 5 / 1 . 0 - P V C / acrylic copolymer ( 1 . 5 / 1 . 0 - 2 E H A / A N ) graft/blend s h o w e d o n l y a single peak, a l t h o u g h i t was considerably broader t h a n that of the parent h o m o p o l y m e r P V C w h i c h h a d a n M W D of 2 . 1 . Several o f these p o l y ( v i n y l c h l o r i d e - g - 2 - e t h y l h e x y l a c r y l a t e / a c r y l o n i t r i l e ) films w e r e e x a m i n e d b y p h a s e c o n t r a s t l i g h t m i c r o s c o p y , a n d n o n e s h o w e d e v i d e n c e o f t w o p h a s e s , i.e., t h e r e w e r e n o s u s p e n d e d p h a s e s l a r g e r t h a n 0.25-0.50^. N e x t , several o f these p o l y ( v i n y l c h l o r i d e - g - 2 - e t h y l h e x y l a c r y l a t e / a c r y l o nitrile) polymers a n d a solution b l e n d copolymer were examined b y electron m i c r o s c o p y (see F i g u r e s 4 , 5 , a n d 6 ) . A s w o u l d b e e x p e c t e d , t h e b l e n d p o l y m e r ( F i g u r e 4 ) s h o w e d gross i r r e g u l a r s h a p e d d o m a i n s m u c h l a r g e r t h a n 0.25μ. Figures 5 a n d 6 are electron photomicrographs of p o l y ( v i n y l chloride-g2 - e t h y l h e x y l a c r y l a t e / a c r y l o n i t r i l e ) w i t h e s s e n t i a l l y a l l o f t h e d o m a i n sizes s m a l l e r t h a n 0.25/x. C o n s e q u e n t l y , t h e g r a f t / b l e n d p o l y m e r s w o u l d b e e x p e c t e d to b e transparent whereas t h e solution b l e n d s w o u l d scatter l i g h t a n d appear turbid. R e c o g n i z i n g t h e difficulties w h i c h o n e c o u l d expect to have w i t h a frac t i o n a t i o n or extraction p r o c e d u r e f o r a n a l y z i n g these p o l y m e r s , w e searched for suitable solvent-nonsolvents f o r the P V C a n d acrylic copolymers. A p p l i c a -ΙΟΟ ^ • ^ ^

-80

-60

-40

-20

0

20

40

60

80 ΙΟΟ

Figure 2.

DTA thermogram of 1.5/1.0-PVC/acrylic

120

140

copolymer

graft/blend

21.

BAUER

A N D

—'

GuiLLOD

—

35

Transparent

1

1

1

1—

30

25

20

16


ELUTION

Figure 3.

237

Polymers

VOLUME,

COUNTS

Molecular weight distnbution curve for poly(vinyl chloride-g-2-ethylhexyl acrylate/acrylonitrile )

t i o n o f t h e f r a c t i o n a l s e p a r a t i o n p r o c e d u r e s o f S m e t s a n d C l a e s e n (11) w a s i n c o n c l u s i v e as t h e a d d i t i o n o f n o n s o l v e n t t o t h e g r a f t / b l e n d p o l y m e r s o l u t i o n l e d to the formation of a gelatinous mixture w h i c h was too w e l l emulsified to i s o l a t e . M o l a u (22) p o i n t e d o u t t h a t i s o l a t i o n o f g r a f t c o p o l y m e r s b y m e a n s of a f r a c t i o n a l p r e c i p i t a t i o n t e c h n i q u e f r o m a r e a c t i o n m i x t u r e c o n t a i n i n g t h e

Figure 4.

Electron photomicrograph of 1.5/1.0 blend of PVC and acrylic copolymer (1.5/1.0 2-EHA/AN)


238

COPOLYMERS,

Figure

5.

POLYBLENDS,

Electron photomicrograph of 1.0/4.0-acrylic (1.5/1.0 2-EHA/AN)/PVC-graft/blend

AND

COMPOSITES

copolymer

t w o p a r e n t h o m o p o l y m e r s is e x t r e m e l y l a b o r i o u s . I k a d a a n d c o - w o r k e r s (23) r e c e n t l y c o n f i r m e d t h i s w i t h g r a f t c o p o l y m e r s of p o l y ( v i n y l a l c o h o l - g - m e t h y l methacrylate) and poly (vinyl acetate-g-methyl methacrylate ) ; they observed that a stable c o l l o i d a l suspension was f o r m e d w h i c h resisted aggregation d u r i n g isolation. A Soxhlet-type extraction was partially successful i n separating the u n g r a f t e d p o l y m e r f r o m the g r a f t e d P V C . E x a m i n a t i o n of a l l c o n v e n t i o n a l solvents for the acrylic c o p o l y m e r w h i c h w e r e complete nonsolvents for P V C was not especially fruitful. C h l o r o f o r m c o m p l e t e l y dissolved the acrylic c o p o l y m e r , b u t it h a d o n l y l i m i t e d s o l u b i l i z a t i o n of t h e P V C ( 8 . 5 % at 2 3 ° C , 2 1 . 2 % s o l u b l e at r e f l u x t e m p e r a t u r e ) . A S o x h l e t e x t r a c t i o n , u n d e r N , o n a 1 . 5 / 1 . 0 P V C / a c r y l i c copolymer ( 1 . 5 / 1 . 0 - 2 E H A / A N ) graft/blend yielded an insoluble f r a c t i o n ( a b o u t 6 7 % of the g r a f t / b l e n d p o l y m e r ) w h i c h h a d I R a b s o r p t i o n b a n d s i n t h e ester c a r b o n y l r e g i o n ( 1 7 5 0 - 1 7 0 0 c m " ) ; t h i s m i g h t i n d i c a t e grafted 2-ethylhexyl acrylate. T h i s b a n d was absent f r o m a similarly treated h o m o p o l y m e r P V C s a m p l e . T h e p r e s e n c e o f ester o x y g e n i n t h e g r a f t / b l e n d 2

1

21.

BAUER

A N D

GuiLLOD

Transparent

239

Polymers


p o l y m e r w a s c o n f i r m e d b y oxygen analysis. T h e r e was no evidence f o r the presence of a — C = N nitrile g r o u p i n I R spectrum of the g r a f t / b l e n d sample. Since a n appreciable fraction of the P V C h o m o p o l y m e r was soluble i n refluxing c h l o r o f o r m , there c a n be no explanation for the absence of the nitrile group i n the insoluble fraction, n o r c a n there be a quantitative measure of graft efficiency. I n a n effort t o e x c l u d e t h e p o s s i b i l i t y t h a t c o n d i t i o n s p r e v a i l i n g d u r i n g t h e g r a f t i n g r e a c t i o n ( R e a c t i o n B ) w o u l d p r o d u c e ester o x y g e n sites o n t h e P V C backbone, control reactions were r u n i n a non-oxygen-containing solvent (1,2-dichloroethane) instead of m e t h y l e t h y l ketone ( R e a c t i o n C ) a n d i n t h e a b s e n c e o f t h e f r e e r a d i c a l i n i t i a t o r , terf-butyl p e r o x y p i v a l a t e ( R e a c t i o n A ) (see T a b l e V ) . E a c h o f t h e s e t r e a t e d P V C h o m o p o l y m e r s w a s t h e n S o x h l e t extracted w i t h chloroform, a n d the insoluble fraction was examined b y I R . T h e r e w a s n o a b s o r p t i o n i n t h e c a r b o n y l ester r e g i o n o r e v i d e n c e o f o t h e r f o r e i g n c o m p o u n d s ; h e n c e , t h e s o l v e n t a n d i n i t i a t o r w e r e r u l e d o u t as s o u r c e s of c a r b o n y l o x y g e n i n the P V C graft. O n e other e x p l a n a t i o n f o r t h e presence

Figure

6.

Electron photomicrograph of 1.0/1.5-acrylic (1.5/1.0 2-EHA/AN)/PVC-graft/blend

copolymer

240

COPOLYMERS,

Table V.

POLYBLENDS,

AND

COMPOSITES

Controls for O x y g e n Content of G r a f t / B l e n d P o l y m e r s

α

Reaction Material

A

Methyl ethyl ketone, reagent grade 1,2-Dichloroethane, reagent grade Pliovic K906 PVC Lupersol 11 (tert-butyl peroxypivalate, 75% act.)

110 — 7.5 —

B

C

110 — 7.5 0.95

— 130 7.5 0.95

A l l three expérimentais were prepared by first dissolving P V C in solvent at room temperature, then treating the solution under N at 6 0 ° C for 24 hrs. Finally, the treated P V C was isolated and Soxhlet extracted with chloroform under N for 36 hrs.


a

2

2

o f c a r b o n y l ester g r o u p s i n t h e S o x h l e t i n s o l u b l e s w h i c h c a n n o t b e p r e c l u d e d w o u l d b e e n t r a i n m e n t o f a c r y l i c ester c o p o l y m e r i n t h e P V C m a t r i x b e c a u s e of p o l y m e r e n t a n g l e m e n t s . It w a s o b s e r v e d t h a t t h e s e t r a n s p a r e n t 1 . 5 / 1 . 0 - P V C / a c r y l i c c o p o l y m e r ( 1 . 5 / 1 . 0 - 2 E H A / A N ) - g r a f t / b l e n d films w e r e s o m e w h a t m o r e r e s i s t a n t t o d e g r a d a t i o n f r o m U V e x p o s u r e t h a n u n s t a b i l i z e d h o m o p o l y m e r P V C (see T a b l e V I ) . T h e g r a f t / b l e n d films r e t a i n e d c l a r i t y a n d w e r e n o t i c e a b l y less p r o n e t o s h r i n k age i n t h e F a d e o m e t e r w h e r e t h e s e r v i c e l i f e w a s e x t e n d e d f r o m 5 0 0 h r s f o r t h e c o n t r o l t o 2 0 0 0 h r s f o r t h e g r a f t / b l e n d films. A D T A profile to 4 0 0 ° C of the transparent 1 . 5 / 1 . 0 - P V C / a e r y l i e c o p o l y m e r ( 1 . 5 / 1 . 0 - 2 E H A / A N ) indicated that w h i l e t h e decomposition m e c h a n i s m m a y be s o m e w h a t altered b y this graft p r o c e d u r e (there was n o strong e x o t h e r m ) , t h e onset o f d e g r a d a t i o n as i n d i c a t e d b y a n e n d o t h e r m o c c u r r e d at a b o u t t h e s a m e t e m p e r a t u r e as f o r t h e h o m o p o l y m e r (see F i g u r e 7 ) . T h i s a p p e a r s t o b e c o n t r a r y t o t h e o b s e r v a t i o n s o f G a y l o r d a n d T a k a h a s h i (17) a n d T h a m e et al. (18) o n c a t i o n i c g r a f t p o l y m e r s s i n c e t h e y o b s e r v e d a n i n c r e a s e i n t h e r m a l stability w i t h graft p o l y m e r s . P r e s u m a b l y , a free r a d i c a l graft reaction w o u l d o c c u r t o a lesser e x t e n t at t h e l a b i l e a l l y l i c a n d t e r t i a r y c h l o r i n e a t o m s t h a n w o u l d a c a t i o n i c a l k y l a t i o n o r g r a f t p o l y m e r i z a t i o n r e a c t i o n . I t is m o r e l i k e l y t h a t t h e α - h y d r o g e n o n t h e P V C b a c k b o n e is t h e p r e f e r r e d site f o r h y d r o g e n atom abstraction o c c u r r i n g w i t h t h e free r a d i c a l graft reaction. H e n c e , i n t h e f r e e r a d i c a l g r a f t p r o d u c t , g r a f t sites w o u l d b e m o r e p r e v a l e n t at t h e α - h y d r o g e n p o s i t i o n a n d less p r e v a l e n t at t h e t e r t i a r y o r a l l y l i c c a r b o n - c h l o r i n e site t h a n i n the ionic graft products. T h i s c o u l d account f o r differences i n t h e r m a l stability of t h e various graft p r o d u c t s . Table VI.

Effect of C a r b o n A r c Fadeometer Exposure o n Appearance of F i l m s Time of Exposure, hrs

Polymer

500

1500

transparent

white, opaque transparent

opaque, failed transparent

transparent

transparent

transparent

transparent

transparent

transparent

0

Dow 144 PVC

transparent

Dow 144 PVC (1 phr Cvasorb UV531 added) Dow 144 PVC/acrylic copolymer graft/blend Dow 144 PVC/acrylic copolymer graft/blend (1 phr Cvasorb UV531 added)

0

h

h

2000

transparent, failed" transparent, failed" transparent, failed"

Failure indicates that the film could not withstand a simple 9 0 ° flex test without fracture. The acrylic copolymer was a 1.5/1.0 2-ethylhexyl acrylate/acrylonitrile charged ratio, where P V C / a c r y l i c copolymer was i n the ratio of 1.5/1.0. a

b


21

BAUER

A N D

GuiLLOD

Transparent

241

Polymers

300 TEMPERATURE,

Figure 7.

Differential thermal analysis (10°C/min in N ) of PVC and chloride-g-2-ethylhexyl acrylate/acrylonitrile) t

polyvinyl

A m o r e t h o r o u g h e x a m i n a t i o n of the t h e r m a l b e h a v i o r of these p o l y ( v i n y l chloride-g-2-ethylhexyl acrylate/acrylonitrile) polymers w o u l d be appropriate to e l u c i d a t e f u r t h e r the m e c h a n i s m of P V C d e g r a d a t i o n . Conclusions A transparent P V C - a c r y l i c copolymer product c a n be f o r m e d b y p o l y m e r i z i n g 2-ethylhexyl acrylate a n d acrylonitrile i n the presence of a homogeneous solution of P V C u s i n g a free r a d i c a l initiator. I n contrast, p r o d u c t s f o r m e d b y the solution b l e n d i n g of P V C a n d a c o p o l y m e r of 2-ethylhexyl acrylate a n d acrylonitrile were translucent to opaque. T h e transparent P V C - a c r y l i c g r a f t / b l e n d products are s o m e w h a t m o r e resistant to U V d e g r a d a t i o n t h a n the parent P V C p o l y m e r a n d h a v e p h y s i c a l p r o p e r t i e s w h i c h a r e o f interest i n film a p p l i c a t i o n s . T h e s e p r o p e r t i e s i n c l u d e i m p r o v e d tear strength over the P V C parent p o l y m e r a n d s o m e w h a t h i g h e r tensiles t h a n a r e o b t a i n a b l e w i t h t h e a c r y l i c c o p o l y m e r . Acknowledgments T h e authors thank G o o d y e a r T i r e a n d R u b b e r C o . f o r permission to p u b l i s h t h i s p a p e r , a n d G o o d y e a r R e s e a r c h M i c r o s c o p y S e c t i o n f o r assistance i n the light a n d electron m i c r o s c o p y studies.

Literature Cited 1. Anderson, Ε. V., "Top 50 Chemicals Reflect Industry Recovery," Chem. Eng. News (1973) May 7, 8-10. 2. Grassie, N., "Polymer Science," A. D. Jenkins, Ed., Vol. 2, p. 1495, North Holland, Amsterdam and London, 1972.

242

COPOLYMERS,

POLYBLENDS,

A N D COMPOSITES

3. Deanin, R. O., Orroth, S. Α., Eliasen, R. W., Greer, T. N., Polym. Eng. Sci. (1970) 10 (4), 228. 4. Bauer, R.G.,Wathen, T. M., Mast, W.C.,Amer. Chem.Soc.,Div. Polym. Chem., Prepr. 14 (1), 606 (Detroit, May, 1973). 5. Hughes, L. J., Britt, G. E.,J.Appl. Polym. Sci. (1961) 5, 337. 6. Matsuo, M., Nozaki, C., Jyo, Y., Polym. Eng. Sci. (1969) 9, 197.


7. Yu, A. J., ADVAN. CHEM. SER. (1970) 99, 2.

8. Horvath, J. W., Wilson, W. Α., Lundstrom, H. S., Purdon, J. R., Appl. Polym. Symp. (1968) 7, 95-126. 9. Hayes, R. Α., J. Polym. Sci. (1953) 11 (6), 531. 10. Prabhakara Rao, S., Santappa, M.,J.Polym. Sci. Part A-l (1967) 5, 2681. 11. Smets,G.,Claesen, M.,J.Polym. Sci. (1952) 8, 289. 12. Guyot, Α., Michel, Α., J. Appl. Polym. Sci. (1969) 13, 911. 13. Michel, Α., Galin, M., Guyot, Α.,J.Appl. Polym. Sci. (1969) 13, 929. 14. Michel, Α., Bert, M., Guyot, Α.,J.Appl. Polym. Sci. (1969) 13, 945. 15. McNeill, I. C., Neil, D., Guyot, Α., Bert, M., Michel, Α., Eur. Polym. J. (1971) 7, 453. 16. Guyot, Α., Bert, M., Michel, Α., McNeill, I. C., Eur. Polym. J. (1971) 7, 471. 17. Gaylord, N.G.,Takahashi, Α., ADVAN. CHEM. SER. (1971) 99, 302. 18. Thame, N.G.,Lundberg, R. D., Kennedy, J. P.,J.Polym. Sci. PartA-1(1972) 10, 2507-2525. 19. Wellons, J. D., Williams, J. L., Stannett, V., J. Polym. Sci. PartA-1(1967)5, 1341. 20. Riess,G.,Kohler, J., Tournut,C.,Banderet, Α., Makromol. Chem. (1967) 101, 58. 21. Hughes, L. J., Brown, G. L.,J.Appl.Polym. Sci. (1963) 7, 59. 22. Molau, G. E., "Characterization of Macromolecular Structure," D.McIntire,Ed., p. 245, National Research Council, National Academy of Sciences, Washington, D.C., 1968. 23. Ikada, Y., Horii, F., Sakurada, I.,J.Polym. Sci. (1971) 11, 27. RECEIVED February 20, 1974. Work supported by Contribution #524 from the Goodyear Tire and Rubber Co. Research Laboratory.

Copolymers, Polyblends, and Composites

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