Zwitterionization of Tertiary Amines in Nanoporous Block Copolymers: Toward Fouling-Resistant Ultrafiltration Membranes

Zwitterionization has emerged as a highly efficient strategy to diminish protein adsorption on separation membranes, and there is a strong need to develop new zwitterionic polymers for the preparation of nonfouling membranes. Herein, by the in situ formation of newly discovered trimethylamine N-oxide-derived zwitterionic polymers (PTMAO) on the surface of nanoporous block copolymers, we obtain ultrafiltration membranes exhibiting superior fouling resistance. Nanoporous membranes of (2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) are prepared by selective swelling-induced pore generation, which are subsequently soaked in H2O2 to oxidize the tertiary amine groups of PDMAEMA to form zwitterionic trimethylamine N-oxides. This oxidation takes place fast, and >70% conversion is achieved within 30 min. The thus-zwitterionized membranes exhibit strongly enhanced hydrophilicity and flexibly tunable permselectivity. Importantly, the membranes showed ultralow protein adsorption and exceptional fouling resistance, outperforming other membranes. This work demonstrates the high efficiency of PTMAO zwitterionization in mitigating membrane fouling and provides a new approach to prepare fouling-resistant membranes.