A NEW FORM OF POLYACETYLENE

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A NEW FORM OF POLYACETYLENE

D. Bott, C. Chai, J. Edwards, W. Feast, R. Friend, M. Horton

To cite this version:

D. Bott, C. Chai, J. Edwards, W. Feast, R. Friend, et al.. A NEW FORM OF POLYACETYLENE.

Journal de Physique Colloques, 1983, 44 (C3), pp.C3-143-C3-146. �10.1051/jphyscol:1983327�. �jpa-

00222678�

JOURNAL DE PHYSIQUE

Colloque C3, supplément au n°6, Tome 44, juin 1983 page C3-143

A NEW FORM OF POLYACETYLENE

B.C. Bott \ C.K. Chai , J.H. Edwards , W.J. Feast , R.H. Friend

⁾

and M.E. HortonO)

(1) B.P. Research Centre, Chertsey Road, Sunbury-on-Thames, Middlesex TU16 7LN, U.K.

(2) Chemistry Department, Durham University, South Road, Durham DH1 3LE, U.K.

(3) Cavendish Laboratory, Madingley Road, Cambridge, U.K.

Résumé - Nous décrivons la préparation et la caractérisation d'une nouvelle forme de polyacétylène. Ce matériau semble avoir une très faible concentration en défauts et être principalement amorphe ; quelques aspects de ses propriétés, en particulier électriques (non dopé et dopé) sont discutés.

Abstract - We report the preparation and characterization of a new form of polyacetylene. This material appears to have a very low concentration of defects and to be largely amorphous; some aspects of its properties, in particular electrical behaviour (pristine and doped), are discussed.

We have previously described a novel approach to the synthesis of polyacetylene via a two stage eliminative process (Scheme 1 ) . As reported at that time, the

Scheme l

relatively low thermal stability of the polymer II led us to suppose that the sequence shown in Scheme 1 was unlikely to provide a satisfactory route to high quality polyacetylene. However, since our earlier report, we have refined the techniques required both for the purification of the precursor polymer II and for its conversion to a high purity form of polyacetylene. At the same time we have developed a second route in which the precursor polymer is significantly more

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983327

C3-144

JOURNAL

DE PHYSIQUE

stable (Scheme

2).

The syntheses of the monomers used in this work have been

Scheme

2

described previously, Compound

I2

and Compound

18.

The first step in both schemes involves ring opening polymerization at the cyclobutene ring, a reaction which is readily accomplished using a typical metathesis catalyst, such as that produced by reaction of tungsten hexachloride with tetramethyltin.* There are, of course, two

-CH=CH-

units in both monomers I and

IV

but only the cyclobutene unit will undergo ring opening since the other double bond is contained in a six membered ring and, for thermodynamic reasons, such systems do not undergo ring opening polymerization. The precursor polymers

I1

and

V

were purified by repeated dissolution-reprecipitation sequences in the conventional manner, they were then cast as films from solution and heated to complete the eliminati~n.~ The

elimination reactions involved in the conversions

I1 -+ 111

and

V -t VI

were studied by differential scanning calorimetry which showed that a significant rate of conversion commenced at z.

^310K

for polymer

11,

whereas for polymer

V

the onset of the conversion reaction occurs at E.

380K. It

is interesting to note that studies of the related precursor polymer

VII

(Scheme

3)

indicate a temperature of

Q @ v a

^{I _ )}

^{- +}

-

VII

+--+

Scheme

3

ca.

500K

for the onset of the anthracene elimination reaction. Thus, the polymers -

11, V

and

VII

show a progressive increase in thermal stability which mirrors the

progressive decrease in delocalization energy gained in the formation of the new

aromatic rings in the respective elimination reactions.

C a r e f u l r e g u l a t i o n of t h e p r e c u r s o r polymer's p u r i f i c a t i o n and t h e conversion s t e p 5 a l l o w s t h e p r o d u c t i o n of p o l y a c e t y l e n e of h i g h p u r i t y p o s s e s s i n g a novel morphology. The d a t a reviewed b r i e f l y below r e f e r s , f o r t h e most p a r t , t o t h i n f i l m s produced by t h e r o u t e o u t l i n e d i n Scheme 1.

S t r u c t u r e . I n c o n t r a s t t o Shirakawa6 and L u t t i n g e r p o l y a c e t y l e n e , t h i s new 7

m a t e r i a l shows v i r t u a l l y no evidence of c r y s t a l l i n i t y when examined by X-ray and e l e c t r o n d i f f r a c t i o n methods. Scanning and t r a n s m i s s i o n e l e c t r o n microscopy s t u d i e s r e v e a l e d no d e t e c t a b l e s t r u c t u r a

35 f i l m 11 um f i l m

Fig. 2. S. E.M. Micrographs of trans-pozyacety Zene produced by the route out Zined in Scheme 2

i X

2000). This shows a lack of fibrillar morphology.

Increasing magnification

to

X 20000 shows no structuraZ units.

-

3

o b t a i n e d a s a c o h e r e n t f i l m of h i g h d e n s i t y , p = 1.05 g.cm. (by f l o t a t i o n ) . Elemental a n a l y s i s i n d i c a t e s t h a t t o t a l e l i m i n a t i o n o f t h e aromatic u n i t can be achieved, and i . r . and n.m.r. spectroscopy g i v e no evidence f o r t h e p r e s e n c e of d e f e c t s a t t r i b u t a b l e t o sp3 carbons. The sample was examined by Resonance Raman Spectroscopy; when i r r a d i a t e d w i t h a l a s e r l i n e of 676.4 nm t h e sample gave a

-1 -1

C=C s t r e t c h i n g frequency a t 1480 cm.

,

t h i s compares w i t h a v a l u e of 1460 c m . f o r p o l y a c e t y l e n e prepared by c o n v e n t i o n a l t e c h n i q u e s , and i n d i c a t e s markedly s h o r t e r c o n j u g a t i o n l e n g t h s .

E l e c t r i c a l P r o p e r t i e s . P r i s t i n e p o l y a c e t y l e n e f i l m s produced by t h e r o u t e o u t l i n e d

-7 -1

i n Scheme 1 show a room temperature d . c . c o n d u c t i v i t y of

s.

1 0

(R

cm.)

,

t h i s i s a f a c t o r of 50 t o 100 times lower t h a n t y p i c a l v a l u e s r e p o r t e d f o r Shirakawa t r a n s - p o l y a c e t y l e n e . 8 This o b s e r v a t i o n probably i n d i c a t e s a lower d e f e c t

C3-146

JOURNAL DE PHYSIQUE

concentration in the sample described here, this hypothesis is supported by ammonia compensation experiments which reveal a decrease in conductivity by a factor of

z.

50 for our material compared with a change of more than four orders of magnitude for similarly compensated Shirakawa trans-polyacetylene.9 The temperature dependence of the conductivity is given by En5

a - -

1 for T > 300K and

TO % T

by Enu

a

-(; ) for T < 300K. The frequency dependence of the conductivity was measured up to lo5 Hz between room temperature and 10K; a relation of the form rs

a

T~u', where n > 1 and s < 1 was observed. Thls behaviour is characteristic of many amorphous semi-conductors, although it differs from that reported for

Shirakawa trans-polyacetylene.8 Doping of the films of this new material results in a rapid uptake of iodine, and for example at a composition represented by

(CH10.27)x, values of o (300K) of 10 (a cm.) -1 were recorded. Arsenic penta- fluoride has a rapid initial uptake but the rate of uptake falls sharply; at a

-1 Composition represented by ( C H [ A ~ F ~ ] ~ ~ ~ ~ ~ ) ~ values of 0 (300K) of 2 (a cm.) were recorded.

Conclusion. We have described a method of obtaining polyacetylene of high purity in an apparently amorphous, or at least very low crystallinity, form. Space does not allow a detailed presentation of the evidence in this communication but the various aspects of our investigations of this novel material will be thoroughly documented in a series of forthcoming publications.

References

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21,

(1980), 595.

-

LIU, R.S.H. and KRESPAN, C.G., J. Org. Chem.,

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PAQUETTE, L.A., KUKLA, M.J. and STOWELL, J.C., J. Amer. Chem. Soc.,

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BOTT, D.C., EDWARDS, J.H. and FEAST, W.J., European Patent Application Number 82306139*5,'18th November 1982.

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