Effects of non-planar hydrophobic cyclohexylidene moiety on the structure and stability of poly(arylene ether sulfone)s based anion exchange membranes

- DIm-CHPAES AEMs with high conductivity and improved chemical stability were prepared.
- 2-Dimethylimidazolium was much stable than 1-methylimidazolium pendant ionic group.
- Non-planar cyclohexylidene moiety promoted water retention and ionic transportation.
- AEMs with non-planar cyclohexylidene moiety exhibited higher backbone stability.

Anion exchange membranes from cyclohexylidene moiety containing poly(arylene ether sulfone)s with N-methylimidazolium and 1,2-dimethylimidazolium pendant ionic groups were prepared. For comparison, bisphenol A moiety and biphenyl moiety containing AEMs with 1-methylimidazolium and 1, 2-dimethylimidazolium pendant ionic groups were also prepared. The chemical structure of the polymers and corresponding AEMs obtained were characterized with 1H NMR and FT-IR spectroscopies. The surface morphology and hydrophilic-hydrophobic phase separation of the AEMs were studied by SEM and AFM. The thermal and mechanical properties, ion exchange capacity, water uptake, swelling ratio, hydroxide conductivity as well as long-term alkaline stability of the AEMs were also intensively investigated. It was confirmed that AEMs having pendant ionic groups of 1,2-dimethylimidazolium were much stable than those having 1-methylimidazolium pendant ionic groups. Results also showed that the existence of the non-planar hydrophobic cyclohexylidene moiety in the AEMs backbone could not only create steoric hindrance to facilitate dimensional and chemical stability, but also thwart the formation of large hydrophobic domains and provide additional free volume to facilitate water retention and ionic transportation. The hydroxide conductivity of cyclohexylidene moiety containing DIm-CHPAES AEM had a highest value of 90 mS cm−1 at 80 °C, and degraded only 12.4% after soaked in 1 M NaOH solution for 35 days at 60 °C, bearing a high potential for practical applications in alkaline anion exchange membranes fuel cells.

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