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 syn thesized and their LC and other thermal properties were characterized. Thes e polymers consist of poly(oxy-1,4-phenyleneoxyterephthaloyl) backbone onto which the biphenylazophenyl mesogens are attached through the oxyoligometh yleneoxy spacers. The length of the oligomethylene units was varied from th e pentamethylene to the decamethylene group. The polymer containing the dod ecamethylene spacer was also included in this study. All of the polymers ar e found to be semicrystalline and they exhibit two thermal transitions befo re melting. The lower temperature transition occurs between 60 degrees C an d 85 degrees C, which decreases with increasing length of the spacers. In c ontrast, the high temperature transition occurring between 105 degrees C an d 117 degrees C depends on the length of spacers to a much less extent. All the polymers form nematic phases in melt. These polymers undergo an initia l thermal decomposition around 300 degrees C losing nitrogen gas.