Synthesis of highly sulfonated polybenzimidazoles by direct copolymerization and grafting

A series of highly sulfonated, ether-containing polybenzimidazoles (SOPBI) with controlled sulfonation degrees were synthesized from various stoichiometric ratio mixtures of sodium 6,6'-oxybis(3-carboxybenzenesulfonate) (SODBA), 4,4'-oxydibenzoic acid (ODBA), and 3,3'-diaminobenzidine (DAB) by solution copolycondensation in poly(phosphoric acid). The resulting sulfonated polymers were further sulfonated by grafting of pendant sulfonic acid chains via a reaction of 1,3-propane sultone with lithiated-N of the imidazole rings in the polymer backbone, yielding materials with high, absolute IEC values (3.42-4.15 meq g(-1)). Due to self-neutralization, the solid state polymers possessed free acid content of 1.40 to 2.15 meq g(-1), were soluble in organic solvents yet insoluble in aqueous solution, while displaying proton conductivites (11-47 mS cm(-1)) at elevated temperatures (80 degrees C, 95% RH). (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3654-3666