J. Membr. Sci., 2014,  454, 351–358

A series of poly(imide benzimidazole) random copolymers (PIBIs) was synthesized by condensation polymerization of biphenyl-4,4’-diyldi(oxo)-4,4’-bis(1,8-naphthalenedicarboxylic anhydride) (BPNDA), (2-(4-aminophenyl)-5-aminobenzimidazole (APABI) and 4,4’diaminodiphenyl ether (ODA) in m-cresol in the presence of benzoic acid and isoquinoline at 180 °C for 20 h. The resulting PIBIs showed excellent thermo-oxidative as well as radical-oxidative resistance and, depending on the composition of the random copolymers, the PIBI membranes could be readily doped in polyphosphoric acid (PPA) or in 85 wt.% orthophosphoric acid under pressure at 180 °C to give acid uptakes as high as 780 wt.% and anhydrous proton conductivity of up to 0.26 S cm^-1 at elevated temperatures. The PIBI membrane with a 1:1 molar ratio between APABI:ODA (PIBI-1/1) and with an acid uptake of 300 wt.% showed an elastic modulus of 0.1 GPa at 160 °C, which an order of magnitude higher than that of the common polybenzimidazole membranes with similar acid contents. A preliminary H₂/air fuel cell test at 180 °C showed a peak power density of 350 mW cm^-2 of the fuel cell equipped with the phosphoric acid doped PIBI-1/1 membrane with a 300 wt.% acid uptake, demonstrating the technical feasibility of the novel electrolyte materials.

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