(496d) Strengthening Isoporous Ultrafiltration Membranes through Polymer Chain Entanglements

Ultrafiltration (UF) membranes are widespread in water purification and food production because they can separate solutes based on size through pore flow. However, despite being frequently used, their transport and mechanical properties remain challenging to co-design within their molecular structure. The reason relates to manufacturing, which involves nonsolvent-induced phase separation (NIPS) and the vitrification of pores. In this process, asymmetric structures with a selective surface layer positioned atop a porous substructure of negligible resistance to hydrodynamic flow form. These structures suffer from two significant issues: (i) broad surface pores that lead to diffuse rejection curves and (ii) the presence of numerous pores (i.e., defects or cracks) that concentrate stress and readily lead to fracture. Engineering polymers that can be manufactured by NIPS without presenting these issues is essential for developing advanced UF membranes.

In this talk, I will introduce poly[(styrene-co-acrylonitrile)-block-4-vinyl pyridine] as a platform for designing permeable, selective, and mechanically strong membranes. I will illustrate three crucial points by considering block copolymers of constant molecular weight, Mn ≈ 100 kDa, and acrylonitrile content from 0 to 40 wt%. The first is that self-assembling block copolymers in a selective solvent for the hydrophobic block affords polymer membranes with surface layers pervaded by narrowly dispersed pores. The second is that incorporating acrylonitrile in the hydrophobic block strengthens polymer membranes, decreasing the average packing length along the chains and enabling entanglements. The third is that these block copolymers are easy to synthesize, readily grown by the RAFT copolymerization of acrylonitrile and styrene using poly(4-vinyl pyridine) as a macromolecular chain transfer agent. These results pave the way for developing advanced UF membranes and improving separations in healthcare, energy, and water technologies.