Poly(arylene ether sulfone) bearing multiple benzyl-type quaternary ammonium pendants: preparation, stability and conductivity

Abstract

A new difluoro aromatic ketone monomer, (2,6-difluorophenyl)[3,5-bis[(3,5-dimethylphenyl)methyl]phenyl]methanone, is developed to prepare a series of poly(arylene ether sulfone)s (PAES) bearing two pendant 3,5-dimethylphenyl groups via polycondensation reaction. The desired side-chain type PAESs containing multiple benzyl quaternary ammonium groups (QPAES(x/y)) are obtained by the corresponding bromomethylation and subsequent quaternization. Their properties, such as hydroxide conductivity, dimensional change, water uptake and alkaline stability, are investigated. Side-chain type membranes QPAES(x/y) with ion exchange capacities (IECs) of 0.96–1.22 mequiv. g⁻¹ display anisotropic membrane swelling and hydroxide conductivity of 39.9–49.8 mS cm⁻¹ at 80 °C. The greater length and dense distribution of the benzyl-type quaternary ammonium pendants are probably responsible for the good hydroxide conductivity and alkaline stability. Meanwhile, the corresponding crosslinked membrane (CQPAES(1/4)) shows higher conductivity, lower membrane swelling, better oxidative stability and higher chemical stability in hot alkali solution (80 °C) than the uncrosslinked one with a comparable IEC value.