AN X-RAY INVESTIGATION ON CIS-TRANS POLYACETYLENES

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AN X-RAY INVESTIGATION ON CIS-TRANS POLYACETYLENES

G. Perego, G. Lugli, U. Pedretti, E. Cernia

To cite this version:

G. Perego, G. Lugli, U. Pedretti, E. Cernia. AN X-RAY INVESTIGATION ON CIS- TRANS POLYACETYLENES. Journal de Physique Colloques, 1983, 44 (C3), pp.C3-93-C3-96.

�10.1051/jphyscol:1983315�. �jpa-00222664�

AN X-RAY

INVESTIGATION ON CIS-TRANS POLYACETYLENES

G. Perego, G. Lugli, U. Pedretti and E. Cernia ASSORENI, 20097 S. Donato Milanese, Milano, I t a l y

R6sum6 - On d6montre,en partant de donn6es de diffraction de rayons X que le polyac6tylSne est form6 d'une phase cristalli- ne unique contenant soit l t i s o m P r e cis soit 1'isomPre trans.

Abstract

-

The formation of cis-trans mixed crystals in polya- cetylene is demonstrated by x-ray diffraction data.

Two crystalline modifications of polyacetylene

(PA)

are described in t h e literature, corresponding t o the all-cis/l-3/ and all-trans/4-8/

polymers respectively. On t h e contrary, no detailed informations exist about t h e crystallization o f cis-trans copolymers (c,t-PA), though t h e latters constitute t h e usual as-synthesized materials. We have therefore investigated a series of c,t-PA with compositions varying continuously from t h e all-cis t o the all-trans, by using wide-angle-x-ray diffraction

(WAXS)

technique. The composition of the m a t e r ~ a l s was controlled either by change o f t h e polymerization temperature or by appropriate thermal isomerization.

WAXS patterns of c,t-PA show:

- considerable line broadening but no detectable halo typical o f an amorphous phase, independent on the composition.

- A

unique set of hkO reflect ions with both

d

spacings and intensity distribution varying continuously with t h e composition (Fig. 1).

An equatorial pseudo-ortho-hexagonal cell with composition depen- dent parameters, intermediate between those o f t h e all-cis and all-trans respectively (see Tab. I ) , fits the experimental values o f (see Fig. 2).

-

Two sets of hkl reflections, which agree with the repeat lengths o f macromolecular chains with planar conformation in cis and trans configurations respectively. For each set, the intensity decreases and t h e l ine broadening increases with the decreasing of the concentration o f t h e related confiquration; the

-

001 reflections only are relatively sharp for all the composition range. On the contrary, both t h e intensity distribution and t h e d values are

-

practical

l

y independent on t h e composit ion with in each set of reflections.

The interpretation o f WAXS patterns allows t o exclude that c,t-PA contain separate crystals o f cis-PA and trans-PA, while suggesting

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983315

JOURNAL DE PHYSIQUE

t h e f o r m a t i o n o f m i xed c r y s l a l s . A mosa i c mode l i s p r o p o s e d , b u i l t up o f b l o c k s o f c h a i n segments i n c i s c o n f i g u r a t i o n a n d b l o c k s i n t r a n s c o n f i g u r a t i o n ( s c h e m a t i z e d i n F i g . 3 ) .

The m u t u a l a r r a n g e m e n t o f t h e b l o c k s i s o f n e m a t i c t y p e whi l e t h r e e d i m e n s i o n a l o r d e r e x i s t s w i t h i n t h e b l o c k , s i m i l a r t o t h a t o f t h e c o r r e s p o n d i n g p u r e f o r m . The b l o c k s i z e i s g e n e r a l l y r e l a t i v e l y l a r g e a l o n g t h e d i r e c t i o n o f t h e c h a i n a x i s b u t t h e a v e r a g e l a t e r a l s i ze d e c r e a s e s when d e c r e a s i n g t h e c o n c e n t r a t I o n o f t h e r e l a t e d c o n f i g u r a t i o n .

The model 9 i v e s c a l c u l a t e d i n t e n s i t i e s f o r hkO r e f l p c t i o n s i n good agreement w i t h t h e e x p e r i m e n t a l o n e s . A r e f i n e m e n t i s i n p r o g r e s s , b y t a k i n g i n t o a c c o u n t a l s o t h e h k l r e f l e c t i o n s . The d e t a i l s o f t h e s t r u c t u r a l c a l c u l a t i o n s w i l l b e r e p o r t e d e l s e w h e r e .

C o n c l u s i o n s

-

c,t-PA a r e a l m o s t c o m p l e t e l y c r y s t a l l i n e p o l y m e r s , t h e w h o l e c r i - s t a l l i n e phase b e i n g c o n s t i t u t e d b y c i s - t r a n s m i x e d c r y s t a l s , p a r a - c r y s t a l l i n e i n c h a r a c t e r . They a r e e s s e n t i a l l y one-phase m a t e r i a l s .

-

The f o r m a t i o n o f m i x e d c r y s t a l s p r o v i d e s f o r a c o n t i n u i t y i n t h e c r y s t a l s t r u c t u r e o f c,t-PA f o r t h e w h o l e c o m p o s i t i o n r a n g e . T h i s s u g g e s t s t h e c i s t o t r a n s i s o m e r i z a t i o n t o p r o c e e d t h r o u g h p r o g r e s - s i v e r e - a r r a n g e m e n t s o f t h e m a c r o m o l e c u l e s w i t h i n t h e m i x e d c r y - s t a l s . I n t h i s v i e w , i s o m e r i z a t i o n i s t o b e c o n s i d e r e d a s an

i n t r a c r y s t a l l i n e p r o c e s s .

E q p e r i m e n t a l

-

The i s o m e r c o n t e n t o f t h e samples was d e t e r m i n e d f r o m IR s p e c t r a a c c o r d i n g t o R e f . 9. WAXS p a t t e r n s o f s t r e t c h e d f i l m s were r e c o r d e d b y a s i n g l e c r y s t a l AED d i f f r a c t o m e t e r ; f o r u n s t r e t - ched m a t e r i a l s a s t a n d a r d s t e p s c a n n i n g d i f f r a c t o r n e t e r was u s e d . R e f e r e n c e s

1 ) Baughman R.H., Hsu S.L., Pez G.P., S i g n o r e l l i A.J., J. Chem. Phys.

@

( 1 9 7 8 ) 5405.

2 ) L i e s e r G., Wegner G., Mu l l e r W, Enke l mann V . , Makromol. Chem., R a p i d Commun.

1

( 1 9 8 0 ) 621.

3 ) C h i e n J.C., K a r a s z F.E., Shimamura K., M a c r o m o l e c u l e s

15

( 1 9 8 2 ) 1012.

4 ) L i e s e r G., Wegner G, M u l l e r W, Enkelmann V;

Makromol. Chem. R a p i d . Commun. 1_ ( 1 9 8 0 ) 627.

5 ) S h i m a m ~ ~ r a K., K a r a s z F.E., H i r s c h J.A., C h i e n J.C.W., Makromol. Chem. R a p i d Commun.

2

( 1 9 8 1 ) 473.

6 ) F i n c h e r C.R., Chen C.-E., Heeger A.J., Mac D l a r m l d A.G., H a s t i n g s J.B., Phys. Rev. L e t t .

48

( 1 9 8 2 ) 100.

7 ) A k a i s h i T., M i ~ a s a k a K . , l s h i k a w a K . , R e p o r t on P r o g r e s s P o l y . Phys. Japan X l l ( 1 9 7 9 ) 125.

8 )

Baughman R . H . , Hsu S.L., Anderson L.R., Pez G.P., S i g n o r e l l i A.J.,

' M o l e c u l a r M e t a l s , NATO C o n f e r e n c e S e r i e s , W . E . H a t f i e l d Ed. ( P l e - num P r e s s , 1 9 7 9 ) p . 187.

9 ) I t o T., S h i r a k a w a H., l k e d a S.,

J. Polym. S c i . Polym. Chem. Edn

12

( 1 9 7 4 ) 11.

fl

^{70% CIS}

XX.)

^,

F i g . 1 . E q u a t o r i a l ( e ) a n d m e r i d i o n a l (m) s c a t t e r i n g o f p o l y a c e t y l e - n e s w i t h d i f f e r e n t c o m p o s i t i o n s .

F i g . 2 . U n i t - c e l l p a r a m e t e r s , c a l c u l a t e d d e n s i t y a n d i n t e r p l a n a r spa- c i n g o f t h e most i n t e n s e r e f l e c t i o n a s a f u n c t i o n o f t h e c i s c o n t e n t .

JOURNAL DE PHYSIQUE

TABLE

1 - C r y s t a l

d a t a

A l I - c i s

P r e s e n t

w o r k R e f . 1 R e f .

2

R e f .

3 ( d l ( c ) ( c )

A I I - t r a n s

P r e s e n t

w o r k R e f .

5

R e f .

6

R e f .

7

R e f . 8

( c )

( d ( d ( e

a, A

7.38 7.32 7.32 7.37 7.41

b, A

4.09 4.24 4.25 4.065 4.08

c,A

2.457 2.46 2.46 2.45 2.46-2.48

a , "

_{- 3}

^{91.4 91.3}

P c a l c ' g S C m 1

. I 6 5 1.132 1.130 1.178 1.153-1.162

p,

⁰

^{5 5 24 55 5}

¹

( a )

A n g l e

between t h e

p l a n e o f

t h e c h a i n and

t h e

( 0 1 0 )

p l a n e o f

t h e

c r y s t a l

( s e t t i n g

a n g l e ) .

( b ) E x t r a p o l a t e d b y

a s s u m i n g an

o r t h o - h e x a g o n a l

c e l l

a n d f) =1.165.

( c ) F r o m e l e c t r o n

d i f f r a c - c a

c

t i o n .

( d )

F r o m x - r a y

d i f f r a c t t o n . ( e )

F r o m x - r a y

d i f f r a c t i o n and p a c k i n g

c a l c u l a t i o n s .

*

c i s t r a n s

F i g .

3. S c h e m a t i c model

o f

t h e

s t r u c t u r e o f

c,t-PA v i e w e d

a l o n g

c h a i n a x i s .

t h e