Amphiphilic poly(arylene ether sulfone) multiblock copolymers with quaternary ammonium groups for novel thin-film composite nanofiltration membranes

Abstract

Abstract Amphiphilic poly(arylene ether sulfone) (PAES) multiblock copolymers with quaternary ammonium groups were evaluated as tunable, size-selective barrier material in thin-film composite (TFC) nanofiltration membranes. Using a two-step synthesis, well-defined PAES multiblock copolymers with molecular weight (Mn) of at least 50\xa0kg/mol were obtained. Conversion to anion-exchange polymers was accomplished by block-selective bromination of methyl side groups at adjusted degree of functionalization and subsequent quantitative amination using triethanolamine. A library of copolymers with varied block length ratios and ion-exchange capacities (IEC; up to 2\xa0mmol/g) was obtained. PAES multiblock copolymers with suited hydrophilic/hydrophobic balance to yield films that are stable in water were further evaluated. Film casting of solutions of anion-exchange copolymers on a porous polyacrylonitrile support and solvent evaporation yielded TFC membranes with barrier layer thickness in the range of 1.5–1.9\xa0μm. Nanofiltration performance was measured with glycerine, glucose, sucrose, NaCl, MgCl2 and FeCl3 in water. While for a random copolymer with similar composition and same thickness, no water flux could be measured, the novel TFC membranes had permeances in the range of 1\xa0L\xa0m−2\xa0bar−1·h−1, at >99.9% rejection for glucose. Permeance increased and rejection (for glycerine and salt) decreased systematically with increasing IEC; an additional influence of block length ratio was identified. A membrane made from a block copolymer with longer hydrophobic block and moderate IEC of 0.9\xa0mmol/g showed the best “trade-off” between permeability and selectivity. Furthermore, the stability of the novel membranes under oxidative disinfection conditions was demonstrated.