Polyacetylene properties

Much effort has been expended toward the improvement of the properties of polyacetylenes made by the direct polymerization of acetylene. Variation of the type of initiator systems (17—19), annealing or aging of the catalyst (20,21), and stretch orientation of the films (22,23) has resulted in increases in conductivity and improvement in the oxidative stabiHty of the material. The improvement in properties is likely the result of a polymer with fewer defects. 

Even with improvement in properties of polyacetylenes prepared from acetylene, the materials remained intractable. To avoid this problem, soluble precursor polymer methods for the production of polyacetylene have been developed. The most highly studied system utilizing this method, the Durham technique, is shown in equation 2. 

Copolymerizations of benzvalene with norhornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorhornene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymeriza tion of acetylene with other monomers (33—39), and various techniques for grafting polyacetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubiUty increases. 

L V. Krivoshei and V. M. Skorobogatov, Polyacetylene and Polyarylenes. Synthesis and Conductive Properties, Polymer Monographs Vol. 10, Gordon and Breach, Philadelphia, 1991. 

Masuda, T. and Higashimura, T. Polyacetylenes with Substituents Their Synthesis and Properties. Vol. 81, pp. 121-166. 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

All commodity polymers (that is those manufactured and sold in high volume) act as insulators because they have no free electrons to conduct electricity. Some low-volume polymers, such as polyacetylene, are conductive or semi-conductive, but their applications are specialized and their use limited. In this section, we shall concentrate on the properties of commodity polymers, because these materials represent the vast majority of polymers used in electrical applications. 

Nagels and Krikor143 studied the effect of y-irradiation on the electrical properties of fraws-polyacetylene. They reported a marked decrease of the conductivity and a slight increase of the thermopower after y-irradiation of 10 kGy (1 Mrad). Their study showed that no essential structural changes occur during irradiation. 

J.L. Bredas, R. Silbey, D.S. Boudreaux, and R.R. Chance, Chain-length dependence of electronic and electrochemical properties of conjugated systems polyacetylene, polyphenylene, polythiophene, and polypyrrole, J. Am. Chem. Soc., 105 6555-6559, 1983. 

These special properties, therefore, may be envisaged for hypothetical compounds such as polyacetylene, polydiacetylene, polyphenylene, (BN)V phases, etc. and... 

The first and most important event in the history of conducting polymers occurred in 1978 when it was announced that the electrical properties of polyacetylene could be dramatically changed by chemical treatment (Chiang et al, 1978). 

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