Proton-Conducting Polymers Based on Benzimidazoles and Sulfonated Benzimidazoles

Abstract

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 10211 Scm21 for the undoped polymers to 1024 Scm21 (both at roomtemperature) for their acid-loaded derivativesm