A sulfonated derivative of polybenzimidazole is reported, and its properties are analyzed in comparison with related polybenzimidazole proton‐conducting materials. Poly(2,5‐benzimidazole), poly(m‐phenylenebenzobisimidazole), and poly[m‐(5‐sulfo)‐phenylenebenzobisimidazole] were prepared by condensation of the corresponding monomers in polyphosphoric acid. Several adducts of these polymers with phosphoric acid were prepared. The resulting materials were characterized by chemical analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis; also, the dc conductivity of doped and undoped derivatives was measured. Similar to what has been observed for the commercial polybenzimidazole polymer (also examined here for comparison), the title polymers exhibit high thermal stability. Furthermore, their doping with phosphoric acid leads to a significant increase in conductivity from less than 10−11 Scm−1 for the undoped polymers to 10−4 Scm−1 (both at room temperature) for their acid‐loaded derivatives. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3703–3710, 2002

Preparation and characterization of membranes of poly͑2,5-benzimidazole͒ ͑ABPBI͒ ͑as thin as 20 m͒ for polymer electrolyte membrane fuel cells are reported. These membranes were prepared by solution casting and then impregnated in phosphoric acid baths. Their characterization included thermogravimetric analyses, conductivity measurements, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. These membranes have high thermal stability and good proton conductivity at temperatures up to 200°C (6.2 ϫ 10 Ϫ2 S cm Ϫ1 at 150°C and 30% relative humidity͒, similar to the well-known commercial polybenzimidazole ͑PBI͒. ABPBI membrane-electrode assemblies ͑MEAs͒ using commercially available E-TEK Pt/C electrodes were tested in H 2 /O 2 cells, obtaining power densities similar to those of PBI MEAs studied here as reference at temperatures of up to 180°C, humidifying the reactants at room temperature.

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