SAN-Based Block Polymers as a Platform for Manufacturing Strong Isoporous Membranes

Abstract

Ultrafiltration (UF) membranes are ubiquitous in water purification and bioprocessing. However, their mechanical and transport properties remain challenging to codesign because of the broad pore size distributions at the surface and within the bulk that result from nonsolvent-induced phase separation (NIPS)─their typical manufacturing process. These distributions influence the hydrodynamic resistance to water flow and the stress concentrations around pores. Thus, developing advanced UF membranes requires innovative molecular designs that offer control over the surface and bulk pores, as well as the mechanical properties of the load-bearing polymer. We introduce a platform for manufacturing UF membranes by leveraging solution self-assembly of block polymers and chain architectures with pendant polar groups. The block polymers consist of a poly(styrene-co-acrylonitrile) hydrophobic block, which is known for its strength, and a poly(4-vinylpyridine) hydrophilic block, which drives solution self-assembly. We focus on a series of block polymers with constant molecular weight, M_n ≈ 115 kDa, SAN fraction, 75 wt %, and varying acrylonitrile content, 0 to 40 mol %, to demonstrate that (i) RAFT dispersion copolymerization of acrylonitrile and styrene provides a facile route to synthesize strong block polymers, (ii) incorporation of acrylonitrile into the hydrophobic block enhances membrane strength by facilitating chain entanglements and dipole–dipole interactions, and (iii) acrylonitrile alters the balance between membrane permeance and rejection, even when the membranes feature similar surface and bulk pores. Overall, our results provide insights into the molecular design of UF membranes with enhanced mechanical and separation properties, contributing to the development of advanced materials for water and energy technologies.