A number of homo- and copolymer benzobisazole rigid-rod polymers have been synthesized, containing labile methyl pendants and benzocyclobutene groups for thermally induced crosslinking studies. Polycondensations of tetraamino, diaminodihydroxy and diaminodithio monomers with methyl, dimethyl and benzocyclobutene terephthalic acid derivatives in polyphosphoric acid (PPA) provided high molecular weight anisotropic liquid crystalline reaction mixtures. Selected benzobisthiazole polymers were dry-jet wet-spun into fibres from these PPA solutions. Depending on 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 benzobisazole rigid-rod polymer fibres. The highest axial compressive strength obtained from these fibres was 70 Ksi (480 MPa), a marginal improvement over that of unsubstituted rigid-rod polymer fibres.