Novel intrinsic piperidine-based zwitterionic sulfobetaine polyimide copolymers for high-performance ultrafiltration membranes with balanced permeability and antifouling properties

High-performance ultrafiltration (UF) membranes as the essential supporting layer are required to meet the increasing demand for water treatment, while membrane fouling, especially irreversible pollution caused by water flux reduction and poor rejection rate, limits membrane effectiveness and lifespan. A novel piperidine-based diamine monomer (PIP-DA) was successfully synthesized to provide a reactive tertiary amine site and subsequently copolymerized with 4,4′-oxydianiline (ODA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), followed by quaternization with 1,3-propanesultone, to fabricate a series of intrinsic zwitterionic sulfobetaine polyimide copolymers (ZPIP-CoPI-x) with varying zwitterionic contents. The zwitterionic polyimide copolymer UF membranes were prepared via traditional and convenient non-solvent induced phase separation (NIPS). The incorporated zwitterions drastically enhanced the ZPIP-CoPI-0.4 UF membranes surface hydrophilicity as evidenced by a remarkably low water contact angle of 48° and a high water absorption rate of 91.28%, and achieved an outstanding balance between permeability and selectivity with a high pure water flux of 276 L/m 2 ·h and an exceptional bovine serum albumin (BSA) rejection rate of 98.2% at 0.10 MPa. Compared to non-zwitterionized ODA-6FDA, all ZPIP-CoPI-x UF membranes demonstrated excellent comprehensive antifouling performance, including dramatic reduction in BSA adsorption, high flux recovery ratios (FRR >90% over three cycles), and minimized irreversible fouling, attributable to the formation of a stable hydration layer and electrostatic repulsion. Furthermore, the membranes exhibited good antibacterial adhesion properties against both E. coli and S. aureus , along with excellent long-term operational stability, reusability, and chemical resistance across a broad pH range, presenting a promising solution for water treatment applications.