Synthesis and properties of novel polyimide fibers containing phosphorus groups in the main chain

Abstract

A series of polyamic acid copolymers (co-PAAs) containing phosphorous groups in the main chain were synthesized using different ratios of two diamines, i.e., bis(3-aminophenyl)methyl phosphine oxide (DAMPO) and 4,4′-oxydianiline (ODA), with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) by polycondensation in N,N′-dimethyacetamide (DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process, and then polyimide copolymer (co-PI) fibers were obtained by thermal imidization. ATR-FTIR spectra and elemental analysis confirmed the chemical structure of PAA and PI fibers. The as-prepared PI fibers have smooth and dense surface as well as uniform diameter. Compared with the blank PI-0, the T_g values of co-PI fibers increased considerably with the increase in DAMPO content. TGA results indicated that the co-PI fibers possessed good thermal stability up to 510 °C and a residual char yield of up to 61% at 850 °C. All co-PI fibers exhibited excellent elongation, and their tensile strength and modulus can reach 0.9 GPa and 14.97 GPa when the molar ratio of DAMPO/ODA was 6/4 and the draw ratio was 3.0. The relationship between microstructure and mechanical property is also discussed.