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 °C, 95% RH). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3654–3666
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