Synthesis and characterization of benzimidazolium-functionalized polysulfones as anion-exchange membranes

Abstract

Anion-exchange membranes containing pendant benzimidazolium groups were synthesized from polysulfone by chrolomethylation followed by nucleophilic substitution reaction with 1-methylbenzimidazole. The structures of the polymers were characterized by H-1-NMR and FTIR analysis. The resulting membranes showed high thermal stability below 200 degrees C. The values of water uptake and swelling degree increased with the ion-exchange capacity of the polymeric membrane. The ionic conductivity was measured by means of impedance spectroscopy in aqueous solution of potassium hydroxide (10(-4)-10(-1) M). The results show not only a clear correlation between the membrane's electrochemical behavior with the electrolyte solution embedded in the membrane, but also with the degree of the polysulfone's chloromethylation.Thus, the ionic conductivity increased more than two orders of magnitude when the degree of chloromethylation increased from 40 to 140%. Benzimidazolium-functionalized polysulfones exhibited better thermal, mechanical, and electrochemical properties than the widely used polymeric membranes containing quaternary ammonium groups.