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Ether spaced N-spirocyclic quaternary ammonium functionalized crosslinked polysulfone for high alkaline stable anion exchange membranes

Zhang, Yang, Chen, Wanting, Yan, Xiaoming, Zhang, Fan, Wang, Xiaozhou, Wu, Xuemei, Pang, Bo, Wang, Jinyan, He, Gaohong
Journal of membrane science 2020 v.598 pp. 117650
anion-exchange membranes, aromatic compounds, cations, crosslinking, moieties, potassium hydroxide, quaternary ammonium compounds, tensile strength
N-spirocyclic cations containing anion exchange membranes (AEMs) possess excellent alkaline stability, but poor mechanical and conductive properties due to the rigid N-spirocyclic structure and lack of flexible side chain structural design. In this work, a flexible ether spaced N-spirocyclic quaternary ammonium functionalized side chain is proposed, in which hydroxyl substituted N-spirocyclic cation provides active grafting site with chloromethylated polysulfone through Williamson etherification. The flexible ether-oxygen spacer promotes aggregation of the rigid spirocyclic cations and thus significantly improves conductivity. The uniformly in-situ thermal crosslinking between benzene rings and the residue chloromethyl groups in polysulfone greatly enhances mechanical properties of the membranes. Constrained ring conformation of N-spirocyclic cation, ether spaced benzyl-free side chain, as well as the OH⁻ blocking crosslinked networks endow an excellent alkaline stability to the membranes. The ether spaced N-spirocyclic containing membranes exhibit well micro-phase separation structure, up to around 85.7 mS cm⁻¹ of hydroxide conductivity at 80 ᵒC, around 10.5 MPa of tensile strength in hydrated state and around 95.6% conductivity retention after immersion in 1 M KOH at 80 ᵒC for 720 h. The performance is among the best N-spirocyclic functionalized AEMs reported in the literature.