Structure, morphology, and properties of methyl-pendant poly(p-phenylene benzobisimidazole) and methyl-pendant poly(p-phenylene benzobisthiazole)

Monomethyl-pendant poly(p-phenylene benzobisimidazole) (MePBI) has been spu n into fiber and compared with an analogous methyl pendant poly(p-phenylene benzobisthiazole) (MePBZT). From FTIR and WAXD, the former system has been found to exhibit intermolecular hydrogen bonding, while the latter possess es only weak van der Waals interactions. The thermomechanical properties of both systems, as examined by TGA, TMA, and DMS, are presented and discusse d. A crystal structure of MePBI is proposed, which suggests intermolecular hydrogen bonding only between pairs of chains within the MePBI crystal. As compared to MePBZT and other rigid-rod polymers where the intermolecular hy drogen bond is not present, MePBI has higher compressive strength. The rela tively high compressive strength of MePBI is attributed to increased interm olecular association, as opposed to differences in morphology.