Polyacetylenes films

The resulting porous, fibrillar polyacetylene film is highly crystalline, so is therefore insoluble, infusible, and otherwise nonprocessible. It is also unstable in air in both the conducting and insulating form. 

Contrary to naive expectation, an extended ir-electron system snch as that in the original silvery polyacetylene film does not imply perfect bond conjngation or perfectly like bonds, or conduction along the chain It only implies a degree of charge-density delocalization. Such a material has the electronic structure of a... 

Shirakawa, H., The discovery of polyacetylene film the dawning of an era of conducting polymers, Nobel lecture, December 8, 2000. 

Fig. 8. Cyclic voltammograms of polyacetylene films on a platinum surface measured in acetonitrile containing 0.1 M Et4NBF4. Reproduced from [98],...

Dining doping of polyacetylene films, contact with the liquid tetrafluoride led to ignition of the film. 

Fig. 9.10 Cyclic voltammetry of a polyacetylene film electrode in the LiC104-propylene carbonate electrolyte. Scan rate 0.4 mV s. ...

Polyacetylene has good inert atmospheric thermal stability but oxidizes easily in the presence of air. The doped samples are even more susceptible to air. Polyacetylene films have a lustrous, silvery appearance and some flexibility. Other polymers have been found to be conductive. These include poly(p-phenylene) prepared by the Freidel-Crafts polymerization of benzene, polythiophene and derivatives, PPV, polypyrrole, and polyaniline. The first polymers commercialized as conductive polymers were polypyrrole and polythiophene because of their greater stability to air and the ability to directly produce these polymers in a doped form. While their conductivities (often on the order of 10" S/m) are lower than that of polyacetylene, this is sufficient for many applications. 

The conductivity of polyacetylene can be magnified by doping. Exposure of a polyacetylene film to dry ammonia gas leads to a dramatic increase in conductivity of 10 cm) Controlled addition of an acceptor, or /r-doping, agent such as AsFs, I2,... 

Figure 29.21 The upper portion shows the EPR lines recorded prior to exposing polyacetylene film to gaseous AsFs and the transformation of a symmetric EPR line shape to a dysonian line for conductive material. The ratio of the low-field to high-field amplitudes is shown in the inset as a function of the composition of the doped film. The lower portion of the curve shows a single line fit to the theoretical dysonian line shape (circles). 

Proton 1/Ti of heavily doped polyacetylene films with different dopants such as FSO3H, FICIO4, iodine, bromine and potassium was measured by Shimizu et al.113 and the behaviour expected for a quasi-ID metal was not found. Some of them showed a time dependence of 1/Ti. They have deduced the temperature dependence of resistivity from the 1/Ti and 1/Ti versus temperature shows T1 5 behaviour above 40 K and deviates from such behaviour below 40 K. Mizoguchi and Kuroda107 have given a comprehensive review of many investigations of NMR relaxation of both 1FI and 13C in undoped polyacetylene. 

In many laboratories that have access to a nuclear reactor, neutron activation is used for the chemical analysis of rocks, minerals, petroleum, biological tissues, alloys, etc., and the technique is well suited for the determination of the concentrations of trace elements in polymers. Neutron activation analysis was used by Given et al. (1) in their studies of water tree growth in polymeric insulation and by Wu and Chen (2) in their studies of dopant-polymer interactions in MoCl5-dcped polyacetylene films. In this work the principles of the method are described and the possibilities are illustrated by means of measurements carried out on polyethylene. 

Acetylene selectivity polymerizes in the presence of Ziegler catalysts whose components have low Lewis acidity [e.g., Ti(0-n-Bu)4—Et3Al(l 4)J. Cis-polyacetylene forms at low temperature, and trans-polyacetylene at high temperature (Eq. (1)). When doped, a polyacetylene film shows metallic conductivity, and hence the application of polyacetylene to polymer batteries and solar cells is now under intensive study 1-3). 

Fig. VI-1 shows the correlation between the electrical conductivity (a) and the draw ratio ( ) for iodine doped polyacetylene films the conductivity increases approximately linearly with the draw ratio [4]. The slope of a versus is approximately a factor of two larger for the thinner films (evidently the details of polymerization and/or doping result in more homogeneous, higher quality material for the thinner films).

An interesting composite material has been prepared by the electropolymerization of pyrrole on polyacetylene electrodes (45). Because oxidized polypyrrole is far more stable in air than polyacetylene, the resulting composite has the stability of polypyrrole. With different synthetic conditions, either a thin layer of polypyrrole was deposited over individual fibrils of the polyacetylene film or a dense polypyrrole film coated the entire film. When the dense polypyrrole film covered the entire polyacetylene film, the interior... 

Kyotani M et al (2010) Entanglement-free fibrils of aligned polyacetylene films that produce single nanofibers. Nanoscale 2(4) 509-514... 

Kijima, M. Mukai, S. Ohmura, K. Shirakawa, H. Kyotani, M. Synthesis of conjugated polymer with carbynoid structure by dehydrochlorination of chlorinated polyacetylene film. Synth. Met. 1999, 207(1-3), 59-60. 

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