SISV tetrablock terpolymers as a universal material platform for co-designing the mechanical and transport properties of membranes

Nonsolvent-induced phase separation (NIPS) is widely used to fabricate ultrafiltration membranes, but its nonequilibrium nature often produces disordered surfaces that limit transport performance. Amphiphilic block polymer self-assembly can promote surface ordering; however, most systems rely on brittle styrenic copolymers. Enhancing both transport and mechanical properties is essential for scalability. One strategy to toughen glassy polymers is incorporating a rubbery energy-dissipating block. This study examines how poly(isoprene) (PI) content influences the mechanical, fracture, and transport properties of amphiphilic tetrablock poly(styrene)-b-poly(isoprene)-b-poly(styrene)-b-poly(4-vinylpyridine) (SISV) membranes. Four SISV polymers with PI midblock contents from 0 to 36 wt% were synthesized while maintaining constant P4VP content and molecular weight. Copper-grid fracture tests and tensile experiments revealed a two-step transition—from brittle to rubber-toughened to thermoplastic elastomeric—as PI increased. This transition correlates with morphology changes quantified by TEM, SAXS, and supported by dynamic SCFT simulations. Membranes formed by self-assembly NIPS (SNIPS) showed a shift from ordered to disordered surfaces with more PI, altering MWCO and PEG rejection while maintaining high water permeance (~1,000 LMH bar⁻¹). These findings highlight the tradeoff between mechanical toughness and transport performance in advanced block polymer membranes.