Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containing m-hydroxybenzoic acid units

Fibers of fully aromatic thermotropic copolyesters based on p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m-acetoxybenzoic acid (m-ABA) were prepared by a high-temperature melt-spinning technique. Two types of the copolyesters were prepared by a high-temperature melt polycondensation reaction using 33 mol % of kink (m-ABA) and 67 mol % linear monomer units (p-ABA, TPA, HQDA), and characterized by differential scanning calorimetry (DSC), polarized optical microscopy, wide-angle X-ray diffraction (WAXD), and intrinsic viscosity measurements. The mechanical properties and the morphology of the fibers were also determined by tensile tester, WAXD, and scanning electron microscopy (SEM). The copolyesters exhibited phase-separated nematic liquid crystalline morphology within a broad temperature range in an isotropic matrix. DSC analysis of the copolyesters revealed broad endotherms associated with the nematic phases. The melting and spinning temperatures were in a processable region. Fibers exhibit well-developed fibrillar structure parallel to the fiber axis. The highly oriented morphology of the fibrils is slightly dependent on the type of the linear monomer. The strength and modulus values determined for the fibers that contain equal molar composition of the linear p-ABA, HQDA/TPA units are comparable to other reported rigid systems containing fully aromatic species. (C) 2002 Wiley Periodicals, Inc.