Thermo-responsive graft copolymer PSf-g-PNIPM: Reducing the structure parameter via morphology control of forward osmosis membrane substrates

An amphiphilic graft copolymer, consisting of a polysulfone (PSf) main chain and poly(n-isopropylacrylamide) (PNIPM) grafts, was synthesized via a combination of atom transfer radical polymerization and click chemistry. The copolymer's structure characteristics (PNIPM length and content) substantially impacts membrane morphology and performance, and were optimized firstly. The resulting copolymer PSf-g-PNIPM with the best characteristics was used as an additive in the fabrication of PSf porous substrates by phase inversion. The effect of the graft copolymer on the physicochemical characteristics and performance of PSf substrate was thoroughly studied. The pure water permeability displays a temperature dependency for PSf substrates with 20 wt% PSf-g-PNIPM, with the maximum above the LCST of the PNIPM side chains. Thin film composite membranes formed on these substrates via interfacial polymerization show a significantly improved water flux during forward osmosis operation. The morphology and performance of the PSf-g-PNIPM modified substrate can be further tuned by the casting medium temperature. Membranes formed below the LCST show higher porosity and water flux.