Relationships between structures and liquid crystalline and optical properties in combined-type copolyisophthalates having nitro- and methoxyazobenzene units and aliphatic spacers in the side chain

Combined-type thermotropic liquid crystalline (LC) homo- and copolyisophthalates having nitro- and methoxyazobenzene units and three aliphatic spacers (hexamethylene, octamethylene and decamethylene) in the side chain and biphenyl unit in the main chain were prepared by melt polycondensation and relationships between polymer structures and LC and optical properties were discussed. Differential scanning calorimetry (DSC) measurements, optical texture observations using polarizing microscopy and powder X-Ray analyses indicated that the homopolyisophtalates with the nitroazobenzene unit form highly ordered smectic E phase and the other homo- and copolymers show less ordered smectic B or smectic C phase. The temperature ranges of smectic LC phases in the polymers decreased with increasing the methoxyazobenzene content. In these polymers, specific interaction such as electron donor-acceptor interaction between the nitro- and the methoxyazobenzene units plays no role in the formation and the stabilization of smectic LC phases. All the polymers displayed UV-vis absorption peak maxima on the basis of the azobenzenes or the biphenyl in solutions and in films, but no fluorescent properties were found, probably due to intra- and intermolecular quenching.