Fabrication of Cross‐Linked Anion Exchange Membranes Using a Pillar[5]arene Bearing Multiple Alkyl Bromide Head Groups as Cross‐Linker

Abstract A pillararene‐based macrocycle with up to 10 flexible chains bearing alkyl bromide head groups is synthesized and investigated for the first time as a multiarm cross‐linker for tertiary‐amine functionalized polyethersulfone. Different from any previously reported cross‐linker, this has a unique pillar‐shaped structure and abundant reactive sites to form multifunctional clusters in the conductive domain. This advantage enables cross‐linking to occur smoothly at the membrane‐casting stage and endows the cross‐linked membranes with improved performance. The cross‐linked anion exchange membranes are found to possess high conductivities and excellent alkaline stability. With a controllable swelling ratio of 19.5%, the maximum conductivity of a membrane can reach 155 mS cm –1 at 80 °C. Due to its local high‐density cross‐linked structure, a delay in degradation kinetics under alkaline condition can be observed, and the loss of conductivity is <10% after 400 h of alkaline stability test at 80 °C.