Wang, X.; Lin, C.; Gao, Y.; Lammertink, R.G.H.: Anion exchange membranes with twisted poly(terphenylene) backbone: Effect of the N-cyclic cations. Journal of Membrane Science 635 (2021), p. 119525/1-12
10.1016/j.memsci.2021.119525
Open Access Version
Abstract:
In order to investigate the relationship towards the cationic structures and ion exchange membrane performance, three kinds of twisted poly(terphenylene)-based anion exchange membranes (AEMs) with N-cyclic cations were prepared via facile Friedel-Crafts type polycondensation and quaternization. The steric hindrance of the N-cyclic cations is gradually increased from the small piperidinium to the sterically protected N-spirocyclic quaternary ammonium (QA). The twisted poly(terphenylene)s backbone promotes the self-assembly of the polymer chain and forms a microphase separated morphology, resulting in a highest conductivity of 68.7 mS cm−1 (80 °C) for the polymer tethered with piperidinium groups (m-TPNPiQA). The relative conductivity (conductivity/swelling ratio) of m-TPNPiQA is even higher than that of the commercial Fumapem FAA-3-50 membrane. Increasing the size of the QA is helpful to constrain water absorption and related swelling but has a negative effect on the chemical stability. β-Hofmann elimination degradation is observed for all of the AEMs during a stability test by 1H NMR analysis. The m-TPNPiQA demonstrates less than 6% ionic exchange capacity loss after 240 h in 5 M NaOH solution at 80 °C. The results demonstrated that the membrane performance is associated well with the features of the cationic groups. A high performance AEM can be achieved by grafting appropriate cations onto aryl ether-free backbone.