Synthesis of Poly(2,5-benzimidazole) for Use as a Fuel-Cell Membrane

Poly(2,5‐benzimidazole) (ABPBI) was synthesized in a novel polymerization medium containing CH3SO3H and P2O5. 3,4‐Diaminobenzoic acid, a monomer for ABPBI, is soluble in the medium and the polymerization was therefore performed in a homogeneous state. It produced polymer fibers, thus simplifying the work‐up process. The membrane was cast directly from the polymerization mixture. Proton conductivities of the ABPBI membranes ranged from 0.02 to 0.06 S · cm−1 above 100 °C, without humidification, and the tensile strength of the membrane was approximately 100 MPa. Synthesis of ABPBI in a medium containing methanesulfonic acid and P2O5.