Preparation and Characterization of Fibers Based on Poly(p-Phenylene Benzobisoxazole)s Containing Trifunctional Moiety as Chain Extender

Abstract: A series of poly( p-phenylene benzobisoxazole) (PBO)-based copolymers containing a trifunctional moiety in theirbackbones were prepared via polymerization of 4,6-diaminoresorcinol dihydrochloride (DAR) with terephthaloyl chloride(TPC) and 1,3,5-benzenetricarbonyl trichloride (BTC) in poly(phosphoric acid) (PPA). The concentration of trifunctionalBTC comonomer was controlled during polymerization to be 0.0-2.0 mol% of difunctional TPC concentration. The inherentviscosity and associated average molecular weight of PBO copolymers with different BTC contents were evaluated by usingsolution viscometry and the Mark-Houwink equation, respectively. In addition, single fibers based on neat PBO and its copol-ymers were prepared by in situ dry-jet wet spinning of anisotropic liquid crystalline polymerization products in PPA dopes.The molecular structure and morphology of the as-spun fibers were determined. The effects of BTC content on the thermalstability and tensile mechanical properties of the as-spun fibers were also investigated.Keywords: poly(p-phenylene benzobisoxazole) (PBO) fiber, dry-jet wet-spinning, thermal stability, mechanical property