Copolymers of Poly(2,5-benzimidazole) and Poly[2,2′-(p -phenylene)-5,5′-bibenzimidazole] for High-Temperature Fuel Cell Applications

Copolymers of poly(2,5-benzimidazole) (ABPBI) and poly[2,2'-(p -phenylene)-5,5'-bibenzimidazole] (pPBI) were synthesized for use as fuel cell membranes to take advantage of the properties of both constituents. The composition of the copolymers were controlled by changing the feed ratio of 3,4-diaminobenzoic acid and terephthalic acid with 3,3'-diaminobenzidine in the polycondensation reaction. The copolymer membranes showed higher conductivities, better mechanical properties, and larger acid absorbing abilities than commercial poly[2,2'-(m -phenylene)-5,5'-bibenzimidazole] membranes.