Synthesis and properties of poly(arylene ether ketone)s with densely piperidinium-functionalized hexaphenylbenzene pendants for anion exchange membranes

Concentrated functionalization of the polymer side chain is widely considered as an effective structural strategy for improving the properties of anion exchange membranes (AEMs). However, the synthetic process typically involves highly toxic reagents. Herein, a series of poly(arylene ether ketone)s with densely benzyl-N-methylpiperidinium-functionalized hexaphenylbenzene pendants is synthesized, avoiding the demand of highly toxic reagents. The fabricated membranes present pronounced microphase separation resulting from the strong contrast in polarity between the hydrophobic polymer backbone and hydrophilic pendants. In contrast to analogous AEMs, the incorporation of bulky and rigid hexaphenylbenzene moieties enlarges the free volume within the membranes, which significantly enhances water absorption and inhibits dimensional change. Moreover, the presence of piperidinium-based cationic groups considerably enhances the alkaline stability of the membranes. One of the prepared membranes with an ion exchange capacity of 1.31 meq g−1 exhibits water uptake, swelling ratio, and hydroxide conductivity of 67.2%, 14.5%, and 49.2 mS cm−1 at 80 °C, respectively. The loss of conductivity is less than 6% after immersion in a 4 M KOH aqueous solution at 30 °C for 480 h. Additionally, a maximum power density of 340.1 mW cm−2 is achieved in the H2/O2 single-cell test, indicating promising application potential for the fabricated membranes.