Poly acetylene iodine-doped

As discussed earlier, substitution onto the polyacetylene chain invariably has a deleterious effect on dopability and conduction properties. At the same time the stability tends to improve. Masuda et al.583) studied a large range of substituted polyacetylenes and found that stability increased with the number and bulkiness of the substituents, so that the polymers of aromatic disubstituted acetylenes were very stable, showing no reaction with air after 20 h at 160 °C. Unfortunately, none of these polymers is conducting. Deitz et al.584) studied copolymers of acetylene and phenylacetylene they found that poly(phenylacetylene) degrades even more rapidly than does polyacetylene and that the behaviour of copolymers is intermediate. Encapsulation of the iodine-doped polymers had little effect on the degradation, which is presumably at least in part due to iodination of the chain. 

Figure 4.8-5 Raman spectra of poly(acetylene), degraded by exposure to ambient conditions. The numbers refer to the exposure time in hours, according to Knoll and Kuzmany, 1984 (a), and to the conductivity of the samples after iodine doping with different concentrations of defects, characterized by the ratio R of the satellite peak intensity to the primary- peak intensity of the C=C stretching mode, according to Schaefer-Siebert et al. 1987 (b).

M. Kyotani, S. Matsushita, T. Nagai, Y. Matsui, M. Shimomura, A. Kaito, and K. Akagi, Helical carbon and graphitic films were prepared from iodine-doped helical Poly(acetylene)... 

Another widely used approach is the in situ polymerization of an intractable polymer such as polypyrrole onto a polymer matrix with some degree of processibil-ity. Bjorklund [30] reported the formation of polypyrrole on methylcellulose and studied the kinetics of the in situ polymerization. Likewise, Gregory et al. [31] reported that conductive fabrics can be prepared by the in situ polymerization of either pyrrole or aniline onto textile substrates. The fabrics obtained by this process maintain the mechanical properties of the substrate and have reasonable surface conductivities. In situ polymerization of acetylene within swollen matrices such as polyethylene, polybutadiene, block copolymers of styrene and diene, and ethylene-propylene-diene terpolymers have also been investigated [32,33]. For example, when a stretched polyacetylene-polybutadiene composite prepared by this approach was iodine-doped, it had a conductivity of around 575 S/cm and excellent environmental stability due to the encapsulation of the ICP [34]. Likewise, composites of polypyrrole and polythiophene prepared by in situ polymerization in matrices such as poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidine chloride-( o-trifluoroethylene), and brominated poly(vi-nyl carbazole) have also been reported. The conductivity of these composites can reach up to 60 S/cm when they are doped with appropriate species [10]. 

The properties of such apparently soluble materials differed greatly from those containing stabilized polyacetylene crystallites. Attempts to dope the soluble copolymers yielded materials with low conductivities, and chemistry typical of solution chemistry (bromination) was observed rather than the formation of a stable bromine-doped polyacetylene phase. A poly(isoprene-fo-acetylene) copolymer oxidized with iodine gave conductivities as high as 1-10 S/cm, but the characterization of the copolymer was insufiScient to unambiguously identify it as a soluble copolymer. On the basis of previously reported work, this material is likely to correspond to a stabilized suspension rather than a solution. 

However, these polymers were found to be very poor conductors, even after doping with iodine. Another type of acetylenic polymer, poly(silylenediethynylene), (SiR2C=C—C ),j (10), can be synthesized by condensation of Cl2SiR R (R, R = CH3, C2H5, or CeHs) and l,4-dilithio-l,3-butadiyne prepared from 1,4-bistrimethylsilylbut-l,3-diyne and methyllithium (eq. 10) (75). 

---