Advancing Ultrafiltration: SAN-Based Block Copolymers for Strong, Selective, and Permeable Membranes

Ultrafiltration (UF) membranes are widely used in food production, water purification, and bioprocessing. However, co-designing their mechanical and transport properties remains challenging due to the highly non-equilibrium nature of the fabrication process: nonsolvent-induced phase separation (NIPS). This process offers membranes with pores that lead to numerous stress concentration points and broad rejection curves. Novel materials capable of stabilizing such stress concentrations while providing membranes with narrow rejection curves are critical for advancing separations conducted by UF.



This talk will introduce one class of such materials: SAN4VP, a block copolymer composed of a hydrophobic poly(styrene-co-acrylonitrile) block and a hydrophilic poly(4-vinyl pyridine) block. By considering a series of block copolymers of constant molecular weight, M_n ≈ 150 kDa, and varying acrylonitrile content (AN), the talk will show that the incorporation of AN into the styrenic block leads to stronger and tougher UF membranes, likely due to an increase in the entanglement density and a transition in the failure mode from crazing to crazing/shear banding. This improvement in mechanical properties, however, decreases water permeance and alters PEG rejection. Overall, this study introduces a molecular design for manufacturing mechanically robust membranes, while highlighting some of the challenges associated with co-designing the mechanical and transport properties of polymer membranes.