(613b) Fouling Resistant Triblock Polymer Ultrafiltration Membranes with Tunable Pore Surface Properties

Ultrafiltration (UF) plays an important role in a multitude of water treatment and industrial separations processes. Conventional UF polymeric membranes are typically made from homopolymer solutions using non-solvent induced phase separation. These membranes have high water permeability, but also broad pore size distributions. Modifying their surface chemistries can also be complicated, which limit their utility in challenging separations processes. Block polymers on the other hand, are emerging as promising membrane materials, as the self-assembled domains can be transformed into pores with uniform size distributions. The wide design space in block polymer chemistry also provides pathways to tune pore surface properties, which is key to developing membranes with improved fouling resistance and tailored selectivity.

Here, we present a triblock polymer platform for rationally tuning surface properties of UF membranes. The polymers are comprised of a short pore-lining midblock flanked by a styrene-based rigid matrix block and a poly(lactic acid) (PLA) etchable pore-forming block. The midblock, which will be exposed on the pore surface upon selective etching of the PLA block, functions as a handle to tune pore surface properties. As hydrophilic membrane surfaces are commonly desirable for fouling resistance, poly(oligo ethylene glycol methyl ether methacrylate) (POEGMA) was selected as the midblock. Materials with bicontinuous pores were obtained by heating the block polymer above the order-disorder transition temperature, trapping it in the fluctuating disordered state, followed by chemical etching of the polyester block to form pores. We demonstrate that the order-disorder transition is mainly influenced by the segregation strength of the end blocks, as POEGMA is miscible with PLA and a relatively short midblock was used. The triblock polymer phase space and structure-property-relationships were studied using rheology, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), nitrogen sorption, and contact angle measurements. Finally, composite membranes with thin hydrophilic block polymer selective layers on top of polysulfone support layers were fabricated. Overall, this work provides a strategy for achieving targeted pore surface properties in block polymer membranes through the incorporation of a pore surface-lining block.