Synthesis and properties of poly(arylene ether sulfone) anion exchange membranes with pendant benzyl-quaternary ammonium groups

Abstract

A series of side-chain type poly(arylene ether sulfone)s (sPAE) bearing pendant 3,5-dimethylphenyl groups are prepared via high temperature polycondensation reaction of 4,4’-biphenol, 4,4'-difluorodiphenyl sulfone, and new difluoro aromatic ketone monomer, (2,6-difluorophenyl) [3-[(3,5-dimethylphenyl)methyl]-5-methylphenyl] methanone. The sPAE-based anion exchange membranes (sQPAE(x/y)) containing pendant benzyl-quaternary ammonium groups are obtained by the corresponding bromomethylation of sPAE and subsequent quaternization. The obtained side-chain type membranes sQPAE(x/y) display anisotropic membrane swelling, high alkaline stability and good hydroxide conductivity in the range of 42.7–61.5 mS cm−1 at 80 °C, taking their low IECs of 0.97–1.29 mequiv g−1 into consideration. Their high hydroxide conductivity is attributed to the greater length and dense distribution of the pendant benzyl-quaternary ammonium groups. Besides, the crosslinked membrane sCQPAE(1/4) is prepared via quaternization reaction between brominated sPAE and crosslinker. Compared to the uncrosslinked membrane, sCQPAE(1/4) with same IEC shows lower membrane swelling, better oxidative stability, higher conductivity and chemical stability at 80 °C.