Synthesis and properties of combined type liquid crystalline polymers – aromatic polyesters bearing biphenylazophenyl mesogenic pendants connected to the backbone through polymethylene spacers

A series of new combined type liquid crystalline polyesters (LCPs) were synthesized and their LC and other thermal properties were characterized. These polymers consist of poly(oxy-1,4-phenyleneoxyterephthaloyl) backbone onto which the biphenylazophenyl mesogens are attached through the oxyoligomethyleneoxy spacers. The length of the oligomethylene units was varied from the pentamethylene to the decamethylene group. The polymer containing the dodecamethylene spacer was also included in this study. All of the polymers are found to be semicrystalline and they exhibit two thermal transitions before melting. The lower temperature transition occurs between 60°C and 85°C, which decreases with increasing length of the spacers. In contrast, the high temperature transition occurring between 105°C and 117°C depends on the length of spacers to a much less extent. All the polymers form nematic phases in melt. These polymers undergo an initial thermal decomposition around 300°C losing nitrogen gas.