Anion exchange membranes containing no β-hydrogen atoms on ammonium groups: Synthesis, properties, and alkaline stability

Daniel Koronka, Kenji Miyatake

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Novel anion conductive polymer membranes have been designed and synthesized to investigate whether the absence of β-hydrogen atoms of ammonium groups affects the membranes' properties and chemical stability. The hydrophilic monomer, 2,2-bis(4-chlorobenzyl)-2-phenyl-ethylamine (3), was obtained via a two-step reaction with an overall yield of 98% under mild reaction conditions. Ni(0)-promoted copolymerization of 3 with 2,2-bis(4-chlorophenyl)hexafluoropropane (1) afforded high molecular weight copolymers (Mn = 12.8-19.6 kDa, Mw = 82.1-224.6 kDa). After quaternization with iodomethane, QBAF-BS polymers formed bendable, robust membranes from solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.50 to 2.44 mequiv. g-1. The membranes exhibited high hydroxide ion conductivity in water (up to 191 mS cm-1 at 80 °C for IEC = 2.25 mequiv. g-1), suggesting that the newly designed hydrophilic structure was effective in improving the ion conductivity. Based on small-angle X-ray scattering (SAXS) analyses and transmission electron microscopy (TEM) images, all membranes featured nano-phase separated morphology with a large dependence on the copolymer composition. The strain properties were improved on increasing the content of the hydrophilic component up to IEC = 2.25 mequiv. g-1, above which the strain became smaller due to the larger water absorption. The membranes were not stable under harsh alkaline conditions (in 8 M KOH at 80 °C) gradually losing the hydroxide ion conductivity. Compared to our previous AEMs which contained typical aliphatic ammonium groups, the lack of β-hydrogen atoms did not practically improve the alkaline stability of AEMs possibly due to the main chain degradation but contributed to higher ion conductivity. This journal is

Original languageEnglish
Pages (from-to)1030-1038
Number of pages9
JournalRSC Advances
Volume11
Issue number2
DOIs
Publication statusPublished - 2020 Dec 16

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)

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