Effect of polycondensation reaction conditions on the properties of thermotropic liquid-crystalline copolyester

Abstract

In this study a range of wholly aromatic copolyesters based on kink m-acetoxybenzoic acid (m-ABA) monomer (33mol%) and equimolar-linear p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67mol%) have been synthesized by melt polycondensation reaction process at 280C and 260C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), hot-stage polarized light microscopy, proton-nuclear magnetic resonance analysis (1H-NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280C in 5h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5-15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160C and 165C) in the nematic mesophase. The Tg values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93-126C. Fibers prepared by a hand-spinning technique from the polymer melt exhibit well-developed fibrillar structure parallel to the fiber axis.