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Side-chain-type imidazolium-functionalized anion exchange membranes: The effects of additional hydrophobic side chains and their hydrophobicity

Wei, Haibing, Li, Yan, Wang, Sheng, Tao, Guoqing, Wang, Tie, Cheng, Sheng, Yang, Shanzhong, Ding, Yunsheng
Journal of membrane science 2019 v.579 pp. 219-229
anion-exchange membranes, hydrophilicity, hydrophobicity, polymers, separation, water uptake
Ionic-conductive polymers with highly ordered, phase-separated structure are the promising materials used as anion exchange membranes (AEMs), thanks to their pronounced ion mobility. In this study, apart from imidazolium-functionalized hydrophilic pendants, additional octyl and perfluorooctyl-containing grafts were tethered to the polymer backbone and the resultant structure-morphology relationships were systemically investigated. The results revealed that the introduction of hydrophobic side chains as well as the corresponding hydrophobicity plays an important role in the formation of a phase-separated morphology in the membrane. AEMs containing perfluorooctyl-containing pendants (PPO-x-Imy8Fz) exhibited a pronounced microphase-separated morphology with ion clusters of about 2–5 nm size and a spacing of ∼6 nm, while the membranes with octyl pendants (PPO-x-Imy8Cz) or no additional hydrophobic side chains (PPO-x-Im) only showed indistinct or no phase separation. In addition, PPO-x-Imy8Fz AEMs showed better ion conductivity and suppressed water absorption, thereby exhibiting a good balance between water uptake and ion conductivity. The results of this study provide an efficient strategy to guide the architectural design of high-performance AEMs.