SAN-based block polymers as a platform for manufacturing strong isoporous membranes

Ultrafiltration (UF) membranes are widely used in water purification and bioprocessing, yet co-designing their mechanical and transport properties remains difficult due to broad pore size distributions formed during nonsolvent-induced phase separation (NIPS). These pore size distributions influence both transport through hydrodynamic resistance andmechanics through nucleating stress concentrations. Advancing UF membranes requires molecular designs that couple control of pore structure with mechanical robustness. Here, we introduce a design platform based on the solution self-assembly of block polymers bearing pendant polar groups. The polymers consist of a strong poly(styrene-co-acrylonitrile) (SAN) block and a hydrophilic poly(4-vinylpyridine) (P4VP) block that directs self-assembly. A series of SAN–P4VP polymers (Mn ≈ 115 kDa, 75 wt% SAN, 0–40 mol% acrylonitrile) demonstrate that (i) RAFT copolymerization provides a facile synthetic route, (ii) increasing acrylonitrile strengthens membranes through enhanced entanglement and dipole interactions, and (iii) acrylonitrile alters the balance between permeance and rejection without changing the surface pore ordering. These results establish molecular-level design rules for producing UF membranes that integrate mechanical durability with tunable transport performance, advancing materials for water and energy technologies.