Poly(vinylidene fluoride) with grafted poly(ethylene glycol) side chains via the RAFT-mediated process and pore size control of the copolymer membranes

Abstract

Preparation of graft copolymers via living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with poly(vinylidene fluoride) (PVDF) in the reversible addition - fragmentation chain transfer (RAFT)-mediated process was carried out. The peroxides generated on the ozone-pretreated PVDF facilitated the thermally initiated graft copolymerization of PEGMA in the RAFT-mediated process. The chemical composition and structure of the copolymers were characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, and molecular weight measurements. The "living" character of the grafted PEGMA side chains was ascertained in the subsequent block copolymerization of styrene. Microfiltration (MF) membranes were fabricated from the PVDF-g-PEGMA comb copolymers by phase inversion in aqueous media. Surface composition analysis of the membranes by X-ray photoelectron spectroscopy (XPS) revealed a substantial surface enrichment of the PEGMA graft chains. The pore size distribution of the resulting membranes was found to be much more uniform than that of the corresponding membranes cast from PVDG-g-PEGMA prepared by the conventional radical polymerization process in the absence of the chain transfer agent. The morphology of the membranes was characterized by scanning electron microscopy. The pore size and distribution varied with the graft concentration and the density of graft points. The PVDF-g-PEGMA MF membranes displayed substantial resistance to γ-globulin fouling, in comparison to the pristine hydrophobic PVDF MF membranes.