Synthesis and proton conductivity of sulfopropylated poly(benzimidazole) films

A novel proton-conducting polymer, sulfopropylated poly(benzimidazole) (PBI-PS), was synthesized by the ring-opening reaction of 1,3-propanesultone onto the reactive N–H groups of PBI. The equilibrium water uptake of PBI-PS films increased with increases in the relative humidity and sulfoalkylation level, and the maximum value of water uptake reached 11.3 H2O per sulfonic acid group (H2O/SO3H) at 90% R.H. and room temperature. The hydrous PBI-PS films showed a high proton conductivity of the order of 10−3 S cm−1 in the temperature range from 20°C to 140°C, which is superior to that of conventional proton-conducting polymers.