Poly acetylene stretching

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).

Orientation of the polymer chains can be obtained by different methods. Highly oriented films of poly acetylene have been made by performing polymerization in a liquid crystal 11,2]. It has also been shown that it is possible to attain highly oriented films of polyacetylene 13] and poly(p-phenylene vinylene) [4] by stretching their precursors. Kaneto et al. 15] have oriented polythiophene by stretching a film, prepared electrochemically on In-Sn oxide (ITO)-coated poly(ethyleneterephthalate) films. The processability of the recently developed poly(3-alkylthiophenes) [6-8] makes this class of polymers suitable for stretching. Yoshino et al. [9] have shown that it is possible to orient poly(3-alkylthiophene), both as free-standing films and in a blend with an elastomer. 

Theophilou (stretched poly acetylene), Dr Cosmo (modified polyacetylene), Dr Martinez (polythiophene). Dr Kallitsis (terphenylenes), Dr Lang/Dr Hmyene (verda-zyles, ferromagnetic materials) and Dr van Eyk/Dr Thelakat (substituted pyrroles and thiophenes). 

Special techniques were applied to orient the (CH) in order to attain high conductivities (i.e., values up to 100 000Scm [32] and parallel fibrils. Similarly, it is possible to make transparent (CH) films with a conductivity of over 5000 Scm The poly(acetylene) is produced on a plastic film and stretched together with the supporting material. Later it is complexed, e.g., with iodine, under standard conditions. 

Mechanical stretching can be performed after polymerization, e.g., in noncross-linked polymers. In the case of poly(acetylene)s prepared with aged Ziegler-Natta catalysts [34] stretching increases conductivity from 2500 S/cm to values as high as 10 S/cm. 

T e orientation process also produces an increase of the DC conductivity [20], with stretched films showing a room temperature conductivity parallel to the chains of 3 x 10" S/cm, similar to the value found for Shirakawa poly acetylene [47], and a temperature independent anistropy of about 40. Above 200K the conductivity appears activated with an energy of activation of 0.4eV. This temperature dei ndence will be determined by the most difficult hops these are likely to be between chains. Thus, the temperature independent anisotropy can be explained simply by the smaller number of interchain hops in the... 

Oriented thin films can be also obtained by stretching of poly acetylene, poly(alkyl)thiophene and some polydiacetylene isotropic thin films. In this case polymer chains align in the stretching direction. Some films like poly tiophene, polypyrrole can be obtained by electrochemical deposition. 

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]. 

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