Synthesis and characterization of certain photocrosslinkable thermotropic liquid crystalline random copolyesters containing arylidene moiety

A new series of 12 thermotropic liquid crystalline and photocrosslinkable random copolyesters were synthesized from terephthalic acid, isophthalic acid and 4,4′-oxybis(benzoic acid) with four different arylidene diols and a common diol 1,2-bis(4-hydroxybenzoyloxy)ethane by direct polycondensation with diphenylchlorophosphate. The resulting polymers had inherent viscosities in the range 1.20-1.74 dl/g. Their structural features were investigated by Fourier transform infrared (FTIR), ¹H, and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The thermal behaviour of the copolyesters was investigated with differential scanning calorimetry and hot stage optical polarized microscopy. Our investigation on the effect of monomer structure on liquid crystalline behaviour shows that the copolymers containing bis(benzylidene)cycloalkanone exhibited higher melting and isotropization temperatures and extended liquid crystalline range. All of the copolymers showed some degree of crystallinity as evidenced by wide-angle X-ray diffraction and scanning electron microscopy. The photocrosslinkability of these polymers was established with UV irradiation/UV spectroscopy and scanning electron microscopy.