Facile synthesis and the properties of novel cardo poly(arylene ether sulfone)s with pendent cycloaminium side chains as anion exchange membranes

To produce a highly anion-conductive and durable polymer electrolyte membrane for alkaline fuel cell applications, a series of novel cardo poly(arylene ether sulfone)s with different cycloaminium side chains were prepared, and the relationships between cycloaminium groups and the properties of the corresponding membranes were discussed in detail. It was found that the pendent alicyclic alkyl chain structure and higher alkalinity of alicyclic amine groups were responsible for the development of highly conductive ionic domains, as confirmed by TEM. The membranes with cycloaminium groups showed higher hydroxide conductivities than those bearing quaternary ammonium groups with similar IEC values, and their water uptakes and hydroxide conductivities were in accordance with the alkalinity of the alicyclic amine groups for each series. The highest conductivity (30 ms cm−1 at 25 °C and 59 ms cm−1 at 80 °C) was observed for the polymer with pyrrolidinium groups. The chemical stability of the membranes was evaluated under severe conditions (4 M NaOH at 80 °C), and degradation was investigated by measuring ion conductivity and 1H NMR changes during aging. By comparison with the 1H NMR data before and after aging, it was found that the degradation of poly(arylene ether sulfone)s with pendent cycloaminium side chains was mainly attributed to the SN2 reactions, and the methylene carbons which linked with the N atom were more sensitive than methyl carbons during aging.