Micro-block poly(arylene ether sulfone)s with densely quaternized units for anion exchange membranes: Effects of benzyl N-methylpiperidinium and benzyl trimethyl ammonium cations

The piperidinium cation exhibited a substantial impact on the improvement of alkaline stability of anion exchange membranes (AEMs), yet the research regarding the micro-block polymer AEMs modified with it has not been conducted. Herein, we report two series of micro-block poly(arylene ether sulfone)s containing densely benzyl-N-methylpiperidinium (TTP-n-PIPPES) and benzyl-trimethyl-ammonium (TTP-n-QAPES) functionalized units for AMEs, respectively, where the n represents the molar ratio of monomer containing tri-tetraphenyl to the employed bisphenol monomers. The content and arrangement of the two types of cations in both polymer backbones were the same. The hydrophilic phases of TTP-n-PIPPES membranes exhibited isolated island states, wrapped with coherent hydrophobic phases. While the TTP-n-QAPES membranes formed continuous hydrophilic channels but fragmented hydrophobic phases. The discrepancy in the microscopic morphology of membranes and the intrinsic nature of cations thus rendered two types of AEMs with different advantages in macroscopic properties. The TTP-n-PIPPES membranes performed better dimensional stability and alkaline stability (low temperature). In contrast, the preferable capabilities of TTP-n-QAPES membranes were water affinity, hydroxide conductivity, and alkaline stability (high temperature). For instance, the TTP-18.2-PIPPES membrane was 11.7%, 11.4%, and 27.4% lower than the TTP-18.2-QAPES membrane at 80 °C in terms of dimensional change, water uptake, and hydroxide conductivity, respectively.