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

Summary: 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.