Synthesis and Characterization of Certain Photocrosslinkablethermotropic Liquid Crystalline Random Copolyesters Containing Arylidene Moiety in the Main Chain

A new series of photocrosslinkable thermotropic liquid crystalline polyesters were synthesized by polycondensation with diphenylchlorophosphate, employing three dicarboxylic acids namely terephthalic acid, isophthalic acid and 4,4'-oxybis(benzoic acid). Four different arylidene mesogenic diols and 2-hydroxyethyl-4-hydroxybenzoate were used as comonomers. The structural features were investigated by viscosity measurements, FT-IR, ¹H and ¹³C NMR spectral studies. The thermal phase transitions and thermotropic liquid crystalline behaviour of these polyesters were studied by differential scanning calorimetry and hot stage optical polarized microscopy. The polyesters exhibited nematic or grainy texture on melting. The photocrosslinkability of the polyesters were established by scanning electron microscopy coupled with UV irradiation/UV spectroscopy. X-ray diffraction studies showed that 4-hydroxy(3-methoxybenzylidene) based polyesters have lesser degree of crystallinity than 4-hydroxy(benzylidene) based polyesters.