Polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzene dithiol dihydrochloride with bicycle [2.2.2] octane-1,4-dicarboxylic acid, as well as the corresponding dimethyl ester or diacid chloride, led to rigid-rod benzobisthiazole polymers. Colorless and soluble polymers with intrinsic viscosities as high as 30.6 dL/g( methanesulfonic acid, 30 degrees C) were obtained. The ultraviolet-visible spectrum of a polymer film cast from methanesulfonic acid under reduced pressure displayed no absorptions in the visible range (400-900 mu m). The polymer was thermooxidatively stable up to 420 degrees C in air as determined by thermogravimetric analysis. Fibers spun from a lyotropic polyphosphoric acid solution exhibited a tensile strength of 300-450 Ksi, a modulus of 26 Msi, and a compressive strength of 53 Ksi. Wide-angle Xray scattering patterns of polymer fibers indicated a 3-dimensional crystal structure rather than a nematic liquid crystal structure.