Synthesis and thermal properties of semi-rigid homo-, co- and terpolycarbonates comprising naphthalene ring

Semi-rigid homopolycarbonates comprising only naphthalene ring in the repeating unit, copolycarbonates composed of the naphthalene and dimethylsiloxane linkage and terpolycarbonates made up of the naphthalene, the dimethylsiloxane and biphenyl unit were prepared by melt polycondensation from a dioxydihexanol of the naphthalene, a diol of the dimethylsiloxane and/or a dioxydihexanol of biphenyl, and alkylene diphenyl dicarbonates having various alkylene spacer lengths. These polymers had good solubilities in chloroform. Thermal and liquid crystalline (LC) properties of the resulting polymers were evaluated by differential scanning calorimetry (DSC), polarizing microscope observation of optical textures and powder X-ray analyses at various temperatures. These measurements described that the homo- and copolycarbonates displayed thermotropic nematic plases in spite of low aspect ratio of the naphthalene ring. The terpolymers had no well-defined textures. Phase transition temperatures in the homo- and copolycarbonates decreased with increase of alkylene spacer lengths without showing odd-even fluctuation. The copolymers exhibited lower phase transition temperatures and wider LC temperature ranges than the homopolymers. All the polycarbonates possessed very low glass transition steps below room temperature.