Phenyltrimethylammonium Functionalized Polysulfone Anion Exchange Membranes

Anion exchange membrane (AEM) materials were prepared from commercial polysulfone (PSf) by functionalization with tertiary amines via lithiation chemistry. By optimizing the reaction conditions, a degree of substitution (DS) of 0.81 could be achieved without evident polymer decomposition or cross-linking. The PSf containing pendent bis(phenyldimethylamine) substituents were then quaternized with CH3I and ion exchange reaction to provide bis(phenyltrimethylammonium) (PTMA) polymer with hydroxide-conductive properties. Flexible and tough membranes with various ion exchange capacities (IEC)s could be prepared by casting the polymers from DMAc solutions. The ionomeric membranes showed considerably lower water uptake (less than 20%), and thus dimensional swelling in water, compared with many reported AEMs. The hydroxide conductivities of the membranes were above 10 mS/cm at room temperature. The unusually low water uptake and good hydroxide conductivity may be attributed to the “side-chain-type” structures of pendent functional groups, which facilitate ion transport. Although the PTMA substituents on the AEM were found to have insufficient long-term stability for alkaline fuel cell application, the investigation gives some insight and directions for polymeric designs by postfunctionalization.