Synthesis and Properties of Highly Aligned Polyacetylene Prepared by using Smectic Liquid Crystal as a Solvent.

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Polymerization of acetylene has been carried out under anisotropic reaction field that is generated by equi-molar mixture of two kinds of smectic liquid crystals used as solvent for Ziegler-Natta type catalyst composed of tetra-n-butoxytitanium, Ti(O-n-Bu)_4, and triethylalumium, AlEt_3. The smectic liquid crystals have a cyclohexylphenoxy moiety as a mesogenic core, and alkyl chains as terminal groups, as shown below.As a result, we succeeded in a synthesis of as-grown directly aligned polyacetylene film in the smectic liquid crystal phase. Measurements of SEM (scanning electron microscope), however, indicated that the fibrils, bundles of polyene chains, are not uniformly aligned. Nevertheless, the microscopic alignment of fibrils enabled the iodine-doped film to attain high electrical conductivity of 1.4 x 10^4 S/cm, which is comparable to those of polyacetylene films prepared by nematic liquid crystal.Next, we have applied the solvent-free polymerization method recently developed for synthesis of highly tensile and stretchable polyacetylene film to the present liquid crystal method, in order to prepare as-grown aligned film with mechanical stretchability. The Ti(O-n- Bu)_4-AlEt_3 catalyst was first prepared without solvent at room temperature and aged at higher temperature of 150 ﾟC for 1 hour. Then to the catalyst was added an equi-molar mixture of nematic or smectic liquid crystals. The film obtained was indeed improved in fragility, but it showed no notable stretchability in spite of usage of high-temperature aged catalyst. This may be due to low concentration of the catalyst, which is an inevitable restriction to keep the liquid crystalline phase.