Anion Exchange Membranes by Bromination of Benzylmethyl-Containing Poly(sulfone)s

Abstract

This report details the properties of anion-conducting membranes synthesized by halomethylation and quaternization of benzylmethyl-containing poly(sulfone)s. The benzylmethyl moieties, which serve as precursors to cationic sites, are introduced during polymer synthesis, thereby circumventing postmodification of the polymer by chloromethylation. By directing the distribution of ionic groups, the anion conductivity and water uptake of the membranes could be tuned over a wide range. For homogeneously distributed cationic groups, the water uptake and anionic conductivity were high relative to the material’s ion exchange capacity. When an unfunctionalizable comonomer was added, the water uptake decreased for a given ion content. A strong correlation between the water uptake and anion conductivity was observed for all materials. Interestingly, as the cation concentration in the membrane decreased due to an increase in water uptake, the anion conductivity increased. This unexpected relationship between the volumetric density of fixed charged sites and the anion conductivity underscores the importance of water uptake in these materials to promote fast anion transport.