Simultaneous zwitterionization and selective swelling-induced pore generation of block copolymers for antifouling ultrafiltration membranes

Membranes with zwitterionic surfaces are highly desired in water-based separations for their distinguished fouling resistance. Herein, a facile strategy for the preparation of zwitterion-functionalized membranes is developed by coupling the pore-making and zwitterion functionalization in one step. We soaked thin films of poly (2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) in the mixture of ethanol and 1, 3-propanesultone (1, 3-PPST). In this mixture, PDMAEMA microdomains were selective swollen leading to nanoporous structures with PDMAEMA chains enriched on the surface. Simultaneously, the quaternization reaction between PDMAEMA and 1, 3-PPST took place. Unexpectedly, in addition to function as the zwitterionic agent, 1, 3-PPST also contributed to the selective swelling induced pore generation. It was found that the presence of 1, 3-PPST in ethanol slowed down the swelling process at the early stage, but evidently enhanced the swelling of PDMAEMA-b-PS films in longer duration. Thus-prepared zwitterion-functionalized membranes exhibited several times higher water permeance than non-zwitterionized counterparts, which should be attributed to increased pore size and strongly improved hydrophilicity as a result of zwitterion functionalization. Moreover, the membranes showed exceptional fouling resistance because of the presence of zwitterions.