Synthesis and properties of homopolyamide and copolyamides fibers based on 2,6-bis(p-aminophenyl)benzo[1,2-d;5,4-d′]bisoxazole

A novel aromatic homopolyamide with benzobisoxazole units in the main chain was synthesized with 2,6-bis(p-aminophenyl)benzo[1,2-d;5,4-d']bisoxazole and terephthaloyl chloride by low temperature solution polycondensation, the inherent viscosity of which was 1.98 dL/g. The diamine and p-phenylendiamine with terephthaloyl chloride were used to synthesize the copolyamides. The structures of homopolyamide and copolyamides were characterized by IR spectra, elemental analysis, and wide-angle X-ray diffraction. Wide-angle X-ray diffraction measurements showed that homopolyamide and copolyamides were predominantly crystallinity. The results of thermal analysis indicated that the thermal stabilities of the copolymer increased with an increase of the molar fraction of benzobisoxazole in the copolymers. The thermal stability of the copolyamides with decomposition temperatures (at 10% weight loss) above 570 degrees C was better than that of poly(p-phenylene terephthalamide) (PPTA). Fibers of homopolyamide and copolyterephthalamides were spun from lyotropic liquid crystal dope in 100% H2SO4. When compared with PPTA fibers prepared under the same conditions, the tensile strengths of copolyamides fibers improved by 20-33% with tensile strengths of 1.81 GPa, tensile moduli of 76 GPa, and elongations at break of 3.8-4.1%, which indicated that copolyamides fibers had outstanding mechanical properties. (C) 2008 Wiley Periodicals, Inc.