Amphiphilic Poly(vinyl alcohol) Membranes Leaving Out Chemical Cross-Linkers: Design, Synthesis, and Function of Tailor-Made Poly(vinyl alcohol)-b-poly(styrene) Copolymers

Tailor-made poly(vinyl alcohol)-b-poly(styrene) copolymers (PVA-b-PS) for separation membranes are synthesized by the combination of reversible-deactivation radical polymerization techniques. The special features of these di-block copolymers are the high molecular weight (>70 kDa), the high PVA content (>80 wt%), and the good film-forming property. They are soluble only in hot dimethyl sulfoxide, but by the “solvent-switch” technique, they self-assemble in aqueous media to form micelles. When the self-assembled micelles are cast on a porous substrate, thin-film membranes with higher water permeance than that of PVA homopolymer are obtained. Thus, by using these tailor-made PVA-b-PS copolymers, it is demonstrated that chemical cross-linkers and acid catalysts can no longer be needed to produce PVA membranes, since the PS nanodomains within the PVA matrix act as cross-linking points. Lastly, subsequent thermal annealing of the thin film enhances the membrane selectivity due to the improved microphase separation.