Molecular simulations of neat, hydrated, and phosphoric acid-doped polybenzimidazoles. Part 1: Poly(2,2′-m-phenylene-5,5′-bibenzimidazole) (PBI), poly(2,5-benzimidazole) (ABPBI), and poly(p-phenylene benzobisimidazole) (PBDI)

Results of atomistic simulations of three polybenzimidazoles—poly(2,2′-m-phenylene-5,5′-bibenzimidazole) (PBI), poly(2,5-benzimidazole) (ABPBI), and poly(p-phenylene benzobisimidazole) (PBDI)—are reported in this communication. The effect of hydration and phosphoric acid (PA)-doping on the properties of these polybenzimidazoles have been studied. Densities and wide-angle X-ray diffraction (WAXD) patterns of the neat and PA-doped polybenzimidazoles agree well with available experimental results. Hydrogen bonding was examined in two ways. Radial distribution functions (RDFs) were used to measure bond lengths and the quantities of distinct types of bonds were counted. Both methods agree well with each other and indicate the strength of hydrogen bonding is mainly determined by the donor. Donor strength decreases in the order PA > water > polybenzimidazole. In the case that donors are the same, the hydroxyl oxygen atom in PA acting as acceptor forms the strongest hydrogen bond compared to other types of hydrogen acceptors. In addition, results suggest that PBI is less hydrophilic and has a lower affinity towards PA than either ABPBI or PBDI.