(279c) Comb-Shaped Polybenzimidazole Positively Charged Membranes with Improved Ion Conductivity

Positively charged polybenzimidazole (PBI), with excellent mechanical, thermal and alkaline stabilities, has potential applications as separation membrane for food and bioprocessing. However, conventionalquaternization route for positively chargedPBI membrane fabrication suffers from extremely poor ion conductivity as compared with other membranematerials. In this study, it is evidenced through experimental data and molecular simulation that the poor conductivity is caused by an electrostatic interaction between the cationic quaternary reagents and imidazole anions on PBI backbone. It makes difficult covalent bonding of the quaternary reagents onto PBI and thus limits the aggregation of ionic clusters. Based on this analysis, a novel strategy is proposed to improve covalent bonding and ion conductivity. First removal of the negative charge of imidazole groups on PBI by grafting non-ionic side chains via N-substitution reaction, and then undergoing quaternization reaction. As a result, comb-shaped positively chargedpolybenzimidazole membranes are fabricated, using imidazolium, piperidine and trimethylamine as quaternary reagents, respectively. Transmission electron microscopy and small angle X-ray scattering exhibitlarger ion clusters in the comb-shaped PBI membranes. Higher ion conductivityof about 86.1mS cm^-1at 80 °C is achieved, about 90 % of which can be retained even after 2 M KOH immersion in 60 °C for 720 h. This work provides a universal promising method to prepare positively chargedPBI membranewith high ion conductivity.