POLYBENZOBISTHIAZOLES WITH CROSS-LINKING SITES FOR IMPROVED FIBER AXIAL COMPRESSIVE STRENGTH

A number of homo- and copolymer benzobisazole rigid-rod polymers have been synthesized, containing labile methyl pendants and benzocyclobute ne groups for thermally induced crosslinking studies. Polycondensation s of tetraamino, diaminodihydroxy and diaminodithio monomers with meth yl, dimethyl and benzocyclobutene terephthalic acid derivatives in pol yphosphoric acid (PPA) provided high molecular weight anisotropic liqu id crystalline reaction mixtures. Selected benzobisthiazole polymers w ere dry-jet wet-spun into fibres from these PPA solutions. Depending o n their thermal treatment conditions, the fibres showed Young's moduli from 18 to 43 Msi (124-296 GPa) and tensile strengths from 240 to 460 Ksi (1650-3170 MPa), comparable to those of unsubstituted benzobisazo le rigid-rod polymer fibres. The highest axial compressive strength ob tained from these fibres was 70 Ksi (480 MPa), a marginal improvement over that of unsubstituted rigid-rod polymer fibres. (C) 1997 Elsevier Science Ltd.