Polybenzoxazoles of relatively low molecular weight have been prepared from hexa-n-propylorthoisophthalate in DMSO at 100°C. Unlike the preparation of polybenzimidazoles via the same route which gave high molecular weight linear polybenzimidazoles, condensation of dihydroxy-diaminobiphenyl with bisorthoesters gave only polymers of low molecular weight. It has not been established but it is most likely that the formation of only low molecular weight polymers was caused by the low basicity of the aromatic amino groups. Benzimidazoles of low molecular weight had also been observed when aromatic tetramines of low basicity were used for the condensation with bisorthoesters.