Amino-Functional Polybenzimidazole Blends with Enhanced Phosphoric Acid Mediated Proton Conductivity as Fuel Cell Electrolytes

A new amino‐functional polybenzimidazole copolymer is synthesized by homogeneous solution condensation polymerization from a novel monomer, N,N′‐bis(2,4‐diaminophenyl)‐1,3‐diaminopropane. The copolymer readily dissolves in organic solvents and shows good film forming characteristics. To balance the phosphoric acid uptake and to obtain mechanically robust membranes, the amino‐functional polybenzimidazole derivative is blended with high molecular weight poly[2,2′‐(m‐phenylene)‐5,5′‐bisbenzimidazole] at different ratios. Due to the high acid uptake, the homogenous blend membranes show enhanced proton conductivity at temperatures well above 100 °C as also confirmed by the fuel cell polarization data. A novel amino‐functional polybenzimidazole copolymer is synthesized from isophthalic acid, 3,3′‐diaminobenzidine, and new a multifunctional monomer, obtained by coupling of 2,4‐dinitrophenyl with 1,3‐diaminopropane followed by mild and clean reduction with hydrazine hydrate. Blends of the new polymer with conventional polybenzimidazole afford mechanically robust membranes showing enhanced phosphoric acid uptake, increased proton conductivity, and improved fuel cell performance.