Redox-Sensitive Microporous Membranes Prepared from Poly(vinylidene fluoride) Grafted with Viologen-Containing Polymer Side Chains

Abstract

A viologen-containing microfiltration membrane (VBV-g-PVDF) was prepared from 4-vinylbenzyl chloride (VBC), poly(vinylidene fluoride) (PVDF), and 4,4‘-bipyridine. The thermally induced graft copolymerization of VBC with ozone-preactivated PVDF was first carried out in N-methyl-2-pyrrolidone solution to produce VBC-g-PVDF copolymers. The resulting VBC-g-PVDF copolymers were cast into microfiltration membranes by phase inversion. Viologen was introduced by the reaction of 4,4‘-bipyridine with VBC-g-PVDF membranes followed by diquaternization of the bipyridine via a second reaction with VBC. The resulting VBV-g-PVDF membranes were characterized using X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and pore size distribution measurement. The VBV graft density has a profound effect on the structure and properties of the VBV-g-PVDF membranes. The permeability and flux of aqueous solutions through the membranes were investigated, and it was demonstrated that the viologen-containing membrane exhibited reversible permeability which can be regulated by redox reactions.