Polyacetylene and Styrene

Polymers in Electronics Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SANTA BARBARA on 09/03/15. For personal use only.

39 Ethylene-Propylene-Diene Terpolymer/Polyacetylene and Styrene-Diene Triblock Copolymer/ Polyacetylene Blends Characterization and Stability Studies KANGI. LEE and HARRIET JOPSON GTE Laboratories, Inc., Waltham, MA 00254 Two different blends, EPDM/polyacetylene and Kraton/polyacetylene have been prepared by various blending techniques. The characterization of two blends have been carried out by IR, X-ray and electron microscopic studies. Upon doping of the blends with various electron accepting agents, such as I and FeCl , conductivities of the blends were found to be i n the range of 10 - 100Ω cm-1. The conductivity stabilities of the blends have also been studied. 2

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The b u r g e o n i n g r e s e a r c h a c t i v i t y i n p o l y a c e t y l e n e i s a p p a r e n t upon p e r u s a l o f j o u r n a l s o f v a r i o u s s c i e n t i f i c d i s c i p l i n e s . U n f o r t u n a t e l y , p o l y a c e t y l e n e , because o f i t s unsaturated s t r u c t u r e , i s i n t r a c t a b l e and u n s t a b l e t o t h e environment. I n o r d e r t o c i r c u m v e n t t h e s e p r o b l e m s , some w o r k e r s Q.,2) attempted to copolymerize acetylenes w i t h s u b s t i t u t e d acetylenes. The r e s u l t i n g c o p o l y m e r s , h o w e v e r , w e r e f o u n d t o h a v e i n f e r i o r e l e c t r i c a l p r o p e r t i e s compared t o h o m o p o l y a c e t y l e n e s . As an a l t e r n a t i v e a p p r o a c h , Wnek a n d G a l v i n (3) p r e p a r e d a c o m p o s i t e o f p o l y a c e t y l e n e and p o l y e t h y l e n e f i l m . In order to introduce polyacetylene into the polyethylene m a t r i x , a high polymeriza t i o n t e m p e r a t u r e (100°C - 110°C) was e m p l o y e d t o b r e a k t h e c r y s t a l l i n i t y of polyethylene. Such h i g h p o l y m e r i z a t i o n t e m p e r a t u r e m i g h t l e a d t o s i d e r e a c t i o n s , s u c h a s c r o s s l i n k i n g and c h a i n scission. Furthermore, i n c e r t a i n a p p l i c a t i o n s , the blend o f p o l y e t h y l e n e and p o l y a c e t y l e n e i s s t i l l a r i g i d m a t e r i a l because the hose p o l y e t h y l e n e i s p a r t i a l l y c r y s t a l l i n e . In particular, the s t a b i l i t y o f p o l y a c e t y l e n e i s s t i l l p r o b l e m a t i c , a l t h o u g h t h e m e c h a n i c a l p r o p e r t i e s o f p o l y a c e t y l e n e w e r e i m p r o v e d some what b y b l e n d i n g w i t h a p r o c e s s a b l e p o l y m e r . I n t h i s p a p e r , we w i s h t o r e p o r t two d i f f e r e n t t y p e s o f elastomer blends, ethylene-propylene-diene terpolymer/polyacety lene and s t y r e n e - d i e n e t r i b l o c k c o p o l y m e r / p o l y a c e t y l e n e , i n the hope t h a t t h e s t a b i l i t y o f p o l y a c e t y l e n e m i g h t b e i m p r o v e d b y

0097-6156/84/0242-0497506.00/0 © 1984 American Chemical Society


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such blending techniques. Ethylene-propylene-diene (EPDM) rubber has been chosen since i t s highly saturated structure affords a material having resistance to attack by heat, l i g h t , oxygen, and ozone (4) · Furthermore, the presence of low level of unsaturation i n the EPDM rubber enables us to crosslink the blends subsequent to their preparation. Such crosslinked structures should lead to localization of polyacetylene chains by preventing molecular movement. It i s our hope that immobilization of polyacetylene in the hydrocarbon network of the polymer may contribute to the stabilization of polyacetylene. The styrene-diene triblock copolymer consists of individual chains of three blocks, an elastomeric diene block in the center and a thermoplastic styrene block on each end. This polymer i s called a thermoplastic elastomer. It exhibits some of the physi c a l properties of elastomers at use temperature and i s as processable as conventional plastics (_5) · The styrene/diene t r i block copolymer has the unique morphology of glassy polystyrene domains in the rubbery diene matrix. Therefore, such an elastomer does not require conventional vulcanization since the glassy polystyrene domains act as physical crosslinks. Experimental A l l solvents were purified according to the literature methods (6). Sulfur monochloride (Aldrich Chemical Co.) was used as received. Ethylene-propylene-diene terpolymers (Epcar 346 & 585) were obtained from Polysar Incorporated (7). The terpolymers have been purified by dissolving them i n heptane and then precipitating in methanol. Three different types of Kraton (a trade name of Shell Chemical Co.) thermoplastic elastomers, Kraton 1107 (styrene-isoprene-styrene triblock copolymer), Kraton 1101 (styrene-butadiene-styrene) and Kraton 4609 (styreneethylene-butylene-styrene) were obtained from Shell Chemical Co. (8). The polymers were purifed by dissolving i n toluene and precipitating i n methanol. IR spectra were obtained using a Perkin-Elmer Model 299B spectrophotometer. Electron micrographs were taken using a P h i l l i p s EM 400T instrument. Samples for transmission electron microscopes were either microtomed or casted from toluene. In a typical experiment , 2g of ethylene-propylene-diene terpolymer was dissolved i n freshly d i s t i l l e d toluene i n a 3-necked flask under an argon atmosphere. Two ml of Shirakawa catalyst (Ti(0Bu)^/ALEt ) (9) were added to the flask by means of a syringe. Subsequently, a l l solvents were slowly evaporated under vacuum by rotating the flask to ensure a uniform film of the polymer on the wall of the flask. Next, acetylene gas was introduced into the flask at room temperature. The polymerization of acetylene was evident from the color change of the film (brown ·> black). The flask was l e f t closed and f i l l e d with acetylene overnight at room temperature. Subsequently, the 3


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r e a c t i o n f l a s k was f l u s h e d w i t h a r g o n t o remove monomer r e s i d u e . The f i l m was washed w i t h f r e s h l y d e g a s s e d h e p t a n e a t l o w t e m p e r a ture. The f i l m was p e e l e d f r o m t h e s i d e o f t h e f l a s k , a n d s u b s e q u e n t l y d r i e d o v e r n i g h t u n d e r vacuum. As a n a l t e r n a t i v e p r o c e d u r e , t h e p o l y m e r i z a t i o n o f a c e t y l e n e was c a r r i e d o u t b y b u b b l i n g a c e t y l e n e g a s i n t h e t o l u e n e s o l u t i o n o f EPDM r u b b e r . In this way, t h e g e l f o r m o f t h e p o l y a c e t y l e n e / E P D M r u b b e r b l e n d was p r o d u c e d . A f t e r e v a p o r a t i n g t o l u e n e u n d e r vacuum, t h e g e l was p r e s s e d and d r i e d u n d e r vacuum. Upon d o p i n g t h e f i l m w i t h i o d i n e , t h e c o n d u c t i v i t y was m e a s u r e d b y s t a n d a r d f o u r - p o i n t p r o b e t e c h niques. The c r o s s l i n k i n g e x p e r i m e n t was c a r r i e d o u t b y i m m e r s i n g t h e b l e n d i n t o a 5% S C l 2 / t o l u e n e s o l u t i o n f o r 5 t o 30 m i n u t e s . For r a d i a t i o n c u r i n g , a s e a l e d tube c o n t a i n i n g t h e b l e n d f i l m was p l a c e d i n t h e γ-ray ( C o s o u r c e ) r a d i a t i o n chamber a t t h e d o s e r a t e o f 1.32 χ 10^ R/min. f o r 30 m i n u t e s . The e x p e r i m e n t a l 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 o f t h e ' p o l y a c e t y l e n e / s t y r e n e - d i e n e t r i b l o c k p o l y m e r b l e n d was e s s e n t i a l l y t h e same as t h a t o f t h e E P D M / p o l y a c e t y l e n e b l e n d . The p o l y a c e t y l e n e / s t y r e n e - d i e n e t r i b l o c k p o l y m e r was doped w i t h e i t h e r I ^ o r F e C l ^ i n nitromethane. 2

6 0

R e s u l t s and D i s c u s s i o n s EPDM/Polyacetylene Blends. EPDM t e r p o l y m e r u s e d h a s e t h y l i d e n e nobornene as a d i e n e u n i t . I t has a completely s a t u r a t e d hydro c a r b o n backbone, b u t w i t h d o u b l e bonds l o c a t e d on t h e s i d e c h a i n s . EPDM t e r p o l y m e r i s known t o h a v e e x c e l l e n t m i x i n g , e x t r u d i n g , and m o l d i n g c h a r a c t e r i s t i c s . T h u s , t h e E P D M / P o l y a c e t y l e n e (PA) b l e n d was f o u n d t o b e q u i t e a homogeneous f i l m h a v i n g e x c e l l e n t f l e x i b i l i t y a n d t o u g h n e s s . The d e g r e e o f e l a s t i c i t y i n t h e ma t e r i a l c o u l d be e a s i l y c o n t r o l l e d by a d j u s t i n g t h e r a t i o o f p o l y a c e t y l e n e t o EPDM p o l y m e r i n t h e b l e n d s . I R s p e c t r a o f t h e PA/EPDM b l e n d s i n d i c a t e d t h a t t h e b l e n d s c o n t a i n b o t h EPDM a n d p o l y a c e t y l e n e m o i e t i e s . I t was f o u n d t h a t t h e p o l y a c e t y l e n e was p r e s e n t i n p r e d o m i n a n t l y t r a n s - c o n f i g u r a t i o n , a s e v i d e n c e d b y a c h a r a c t e r i s t i c i n f r a r e d a b s o r p t i o n band a t 1015 cm"" ( 1 0 ) . F u r t h e r m o r e , t h e r e was no e v i d e n c e t h a t any p o l y a c e t y l e n e m o i e t i e s were g r a f t e d o n t o t h e u n s a t u r a t e d s i t e s o f EPDM r u b b e r . T h i s was c o r r o b o r a t e d b y an e x t e n s i v e e x t r a c t i o n e x p e r i m e n t . V i r t u a l l y q u a n t i t a t i v e amounts o f EPDM c o u l d be e x t r a c t e d f r o m t h e b l e n d w i t h t o l u e n e . IR s p e c t r a o f t h e f u l l y r e c o v e r e d EPDM w e r e i d e n t i c a l t o t h o s e o f t h e v i r g i n EPDM. Some e l e c t r o n m i c r o g r a p h s w e r e t a k e n o f PA/EPDM b l e n d s (5 w t . % PA) u s i n g OsO, a s a s t a i n i n g a g e n t f o r t h e p o l y a c e t y l e n e p h a s e . As shown i n F i g u r e 1, t h e p o l y a c e t y l e n e p h a s e a p p e a r s t o be d i s c o n t i n u o u s , w h i l e t h e e l a s t o m e r i c EPDM m a t e r i a l forms t h e continuous m a t r i x . Exposure o f t h e f i l m s t o vapor f o r 24 h o u r s r e s u l t e d i n u l t i m a t e c o n d u c t i v i t i e s o f 10 - 90 Ω " c m " , d e p e n d i n g upon p o l y a c e t y l e n e c o n t e n t s . I t 1

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Figure 1.


Transmission electron micrograph of the OsO^-stained EPDM Polyacetylene blend

0

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was i n t e r e s t i n g to note that the c o n d u c t i v i t i e s o f EPDM/PA blends were increased by s e v e r a l orders o f magnitude (10 Ω " cm" to 7 χ Ι Ο Ω"" cm" ) upon s t r e t c h i n g the sample (600% e l o n g a t i o n ) . Such an i n c r e a s e i n c o n d u c t i v i t y can be a t t r i b u t e d to the f a c t that p o l y a c e t y l e n e domains can be elongated and a l i g n e d upon s t r e t c h i n g the sample. Examination o f X-ray data c l e a r l y i n d i cated that the degree o f c r y s t a l l i n i t y was i n c r e a s e d as the f i l m of the blend was s t r e t c h e d . The blend o f EPDM and p o l y a c e t y l e n e was c r o s s l i n k e d u s i n g s u l f u r monochloride i n a toluene s o l u t i o n . I t should be noted that the c r o s s l i n k e d blend could not be doped with i o d i n e . Samples c o n t a i n i n g more than 2% o f s u l f u r d i d not p i c k up any i o d i n e even a f t e r a 72-hour p e r i o d . The completely saturated EPDM p o r t i o n s o f the blend seem t o prevent any i o d i n e molecules from permeating i n t o the p o l y a c e t y l e n e m o i e t i e s . In order to circumvent t h i s problem, we have doped the blend with i o d i n e p r i o r to the c r o s s l i n k i n g procedure. Subsequently, the doped m a t e r i a l having a c o n d u c t i v i t y o f 60 Ω " cm" was reacted w i t h s u l f u r monochloride i n a toluene s o l u t i o n f o r 10 minutes. The c o l o r of the s o l u t i o n turned from p a l e yellow to dark red while the polymer f i l m remained i n s o l u b l e i n the toluene s o l u t i o n . But the f i l m l o s t i t s c o n d u c t i v i t y ( l e s s than ΙΟ" Ω " cm" ) a f t e r the S 2 C I 2 treatment. The l o s s o f c o n d u c t i v i t y can be a t t r i b u t e d to the f a c t that s u l f u r monochloride e s s e n t i a l l y r e moves a l l i o d i n e from the blend. The complete absence o f i o d i n e i n the blend a f t e r S 2 C I 2 treatment was shown by elemental analysis. Since the chemical approach was too harsh t o prepare a c r o s s l i n k e d conducting blend, we turned our a t t e n t i o n to other methods o f c r o s s l i n k i n g . We found that γ-rays from C o can r e a d i l y c r o s s l i n k the blend w i t h i n a short p e r i o d o f time. Even a f t e r 30 minutes o f γ-radiation (dose r a t e * 1.32 χ 10 R/minutes) EPDM/PA blends became completely i n s o l u b l e i n almost a l l hydro carbon s o l v e n t s . However, u n l i k e the c h e m i c a l l y c r o s s l i n k e d m a t e r i a l , the i r r a d i a t e d blend can be doped with I 2 to produce a a m a t e r i a l having c o n d u c t i v i t y as high as 100 Ω " cm" . I t was found from i n f r a r e d data that only EPDM double bonds p a r t i c i p a t e d i n the c r o s s l i n k i n g r e a c t i o n . I t should be noted that c o n d u c t i v i t i e s o f the i r r a d i a t e d EPDM/PA blend upon doping were c o n s i s t e n t l y high (- 100 Ω " cm" ) r e g a r d l e s s o f the length of γ-ray r a d i a t i o n . The c o n d u c t i v i t y o f the m a t e r i a l d i d not change even a f t e r 8 days o f exposure to γ-ray r a d i a t i o n . The r a d i a t i o n does not appear to damage the p o l y a c e t y l e n e u n i t s o f the blend. We have compared the c o n d u c t i v i t y s t a b i l i t y o f the c r o s s l i n k e d EPDM/PA blend with the u n c r o s s l i n k e d blend and homopolya c e t y l e n e . As shown i n F i g u r e 2, the c o n d u c t i v i t y o f the I 2 doped EPDM/PA blend decays more slowly upon a i r exposure as compared to that o f homopolyacetylene. The i n c r e a s e i n s t a b i l i t y of the blend r e f l e c t s the high oxygen impermeability o f EPDM rubber due t o i t s h i g h l y s a t u r a t e d c h a r a c t e r . F i g u r e 2 a l s o 1


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TIME (Days) F i g u r e 2.

N o r m a l i z e d c o n d u c t i v i t y v s days o f a i r exposure f o r EPDM/Polyacetylene blends.

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shows t h e c o n d u c t i v i t y o f the c r o s s l i n k e d EPDM/PA blend decays even more s l o w l y than that o f the u n c r o s s l i n k e d b l e n d . Such s t a b i l i z a t i o n may be due to the f a c t t h a t p o l y a c e t y l e n e chains are immobilized by t i g h t l y c r o s s l i n k e d EPDM networks. Kraton/Polyacetylene Blends. As has been mentioned i n the p r e vious s e c t i o n , the s t a b i l i t y o f p o l y a c e t y l e n e can be somewhat improved when EPDM rubber i s blended w i t h p o l y a c e t y l e n e . The c r o s s l i n k i n g o f EPDM m o i e t i e s o f EPDM/PA blends c e r t a i n l y im proved the s t a b i l i t y f u r t h e r . However, most conventional elastomers such as EPDM may not be good host polymers f o r p o l y acetylene due t o the f a c t t h a t such polymers need p o s t - c u r i n g subsequent t o blend p r e p a r a t i o n . The heat and harsh chemicals a s s o c i a t e d w i t h t h e c u r i n g process would cause s c i s s i o n and/or c r o s s l i n k i n g o f the h i g h l y conjugated double bonds o f the p o l y a c e t y l e n e . F o r t h i s reason, we have turned our a t t e n t i o n on the t h e r m o p l a s t i c elastomer, styrene/diene t r i b l o c k copolymers. As was the case i n the EPDM/PA b l e n d , a l l of the r e s u l t i n g p o l y acetylene/Kraton t h e r m o p l a s t i c elastomer blends were found t o be f l e x i b l e and m e t a l l i c - l o o k i n g f i l m s . As shown i n F i g u r e 3, the s t r e s s - s t r a i n curve o f Kraton blends c o n t a i n i n g 4% p o l y a c e t y l e n e content behaved almost l i k e pure Kraton rubber. However, as one i n c o r p o r a t e s more p o l y a c e t y l e n e s i n t o the blends, the p r o p e r t i e s of the m a t e r i a l s become more t h e r m o p l a s t i c . The i n f r a r e d spec trum o f the blend i n d i c a t e s t h a t the m a t e r i a l d e f i n i t e l y contains both Kraton and p o l y a c e t y l e n e m o i e t i e s . P o l y a c e t y l e n e was p r e sent i n the predominantly t r a n s - c o n f i g u r a t i o n , as evidenced by e x h i b i t i n g a c h a r a c t e r i s t i c i n f r a r e d a b s o r p t i o n band a t 1015 cm" · Examination o f X-ray data c l e a r l y i n d i c a t e d t h a t p o l y a c e t y l e n e m o i e t i e s i n the blend r e t a i n high c r y s t a l l i n i t y by showing a sharp peak a t 29=23° t o 25° i n the X-ray d i f f r a c t i o n p a t t e r n (11). I n order t o i n v e s t i g a t e the d e t a i l e d morphology o f the b l e n d , a c o n s i d e r a b l e amount o f time has been devoted t o e l e c t r o n micro s c o p i c s t u d i e s . I t i s w e l l known t h a t , i n the ΑΒΑ-type t r i b l o c k copolymer, the outer g l a s s y A b l o c k s form s p h e r i c a l domains w h i l e the c e n t r a l rubbery b l o c k s a r e d i s p e r s e d as the m a t r i x . As shown i n F i g u r e 4, the p o l y a c e t y l e n e i s c l e a r l y i n c o r p o r a t e d i n to the rubbery m a t r i x r a t h e r than the g l a s s y p o l y s t y r e n e domain. Since the p o l y m e r i z a t i o n o f acetylene i n the presence o f the t r i b l o c k polymer was c a r r i e d out below t h e g l a s s t r a n s i t i o n temperature o f the p o l y s t y r e n e b l o c k , the above r e s u l t appears to be q u i t e reasonable. As i n the case o f the p o l y a c e t y l e n e / elastomer b l e n d s , the polyacetylene/Kraton blends become l e s s e l a s t i c w i t h i n c r e a s i n g p o l y a c e t y l e n e content. C u r r e n t l y , work i s i n progress t o i n c o r p o r a t e p o l y a c e t y l e n e i n the p o l y s t y r e n e domain o f the K r a t o n polymer. We have a l s o s t u d i e d the elonga t i o n behavior o f the blend m a t e r i a l upon doping. As shown i n Table 1, the undoped blend was found t o be extremely e l a s t i c and can be s t r e t c h e d up t o 1100% o f i t s o r i g i n a l l e n g t h . However, upon doping w i t h i o d i n e , the e l o n g a t i o n o f the m a t e r i a l was con1

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1200 A

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ELONGATION (%)

F i g u r e 3.

Figure 4 ·

S t r e s s - s t r a i n behavior of

SBS/Polyacetylene blends.

Transmission e l e c t r o n micrograph SBS/Polyacetylene

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s i d e r a b l y reduced. This corroborates the e l e c t r o n microscopic r e s u l t that polyacetylene moieties indeed i n c o r p o r a t e i n t o the r u b b e r y r e g i o n o f t h e t r i b l o c k p o l y m e r . The c o n d u c t i v i t y d e c a y o f K r a t o n / p o l y a c e t y l e n e i s much s l o w e r t h a n t h a t o f h o m o p o l y a c e tylene (Figure 5 ) .


Table I .

Effect of I

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D o p i n g on t h e E l o n g a t i o n o f SBS T r i b l o c k Copolymer/Polyacetylene Blends*

Time Doped (minutes)

Conductivities (Ω" cm" )

Elongation at B r e a k (%)

0 15 30 60 120 180

— 0.95 0.54 2.49 2.35 3.00

1127 335 314 300 255 167

1

1

*SBS T r i b l o c k C o p o l y m e r u s e d was K r a t o n D1101 R a t i o 30/70).

J 5

ι 10

I 15

I 20

I 25

Wt. % I Uptake

14.8 15 24.3 29.3 29.5 (Styrene/Butadiene

I 30

1 35

TIME (DAYS)

F i g u r e 5.

N o r m a l i z e d c o n d u c t i v i t y v s days o f a i r e x p o s u r e f o r Kraton/Polyacetylene blends.

506


Conclusion I n o r d e r t o improve the s t a b i l i t y o f p o l y a c e t y l e n e , polyacetylene was b l e n d e d w i t h e t h y l e n e - p r o p y l e n e - d i e n e terpolymer. Subsequent l y , t h e r e s u l t i n g EPDM/PA b l e n d was c r o s s l i n k e d w i t h γ - r a d i a t i o n . Upon d o p i n g w i t h i o d i n e , t h e c o n d u c t i v i t y o f t h e b l e n d was f o u n d t o b e i n t h e r a n g e 10-100 Ω" cm"" . I t was f o u n d t h a t t h e c o n d u c t i v i t y o f t h e c r o s s l i n k e d b l e n d d e c a y e d more s l o w l y compared to that o f e i t h e r the u n c r o s s l i n k e d blend o r homopolyacetylene. The t h e r m o p l a s t i c e l a s t o m e r / p Α b l e n d was a l s o p r e p a r e d i n o r d e r to avoid e x t r a c r o s s l i n k i n g s t e p s . Electron microscopic results i n d i c a t e d that polyacetylene moieties incorporated i n t o the rubbery m a t r i x r a t h e r than i n t o the p o l y s t r e n e g l a s s y domains.


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Acknowledgments

We would like to thank S. Tripathy for electron micrographs. Literature Cited 1. Deits, W.; Cukor, P.; Jopson, H. Synthetic Metals 1982, 4, 199. 2. Chien, J.C.W.; Wnek, G.E.; Karasz, F.E.; Hirsch, J.E. Macromolecules 1981, 14, 479. 3. Galvin, M.E.; Wnek, G.E. Polymer 1982, 23, 795. 4. Borg, E.L., in "Rubber Technology"; Morton, M., Ed.; Van Nostrand Reinhold. New York, 1983; p. 220. 5. Legge, N.R.; Holden, G.; Davison, S.; DeLaMare, H.E. in "Chemistry and Technology of Block Polymers"; Craver, J.K.; Tess, R.W., Ed.,; APPLIED POLYMER SCIENCE, Organic Coatings and Plastics Chemistry Division, American Chemical Society: Washington, D.C. 1975. 6. Riddick, J.A. "Organic Solvents; Physical Properties, Methods of Purification"; Wiley-Interscience: New York 1970. 7. "Epcar( ) EPM and EPDM Rubbers are Versatile," B.F. Goodrich Co., 1981. 8. "Kraton " Product Bulletin of Shell Chemical Co., 1980. 9. Ito, T.; Shirakawa, H.; Ideda, S. J. Polym. Sci., Polym. Chem. 1974, 12, 11. 10. Ito, T.; Shirakawa, H.; Ikeda, S. J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 1943. 11. Tsuchida, E.; Shih C.; Shinohara I . ; Kambara, S. J. Polym. Sci. 1964, A2, 3347. R

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RECEIVED December 19, 1983

Polyacetylene and Styrene

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