Modification of polyvinylidene fluoride through homogeneous reaction for preparation of hydrophilic membrane

Long-lasting anti-fouling membrane of polyvinylidene fluoride (PVDF) requires covalently bonded hydrophilic units, which faces challenges like multi-step treatments yet uneven modification due to heterogeneous reaction. For that, grafting hydrophilic polymer chains onto PVDF through homogeneous reaction was reported in this work. First, PVDF was dehydrofluorinated in solution by adding a small amount of ammonia water to generate C=C double bonds, and then vinyl-monomer of N-vinyl pyrrolidone (NVP) or vinyl acetate (VAc) was evenly grafted through heterogeneous reaction to provide hydrophilic side chains. The successful syntheses of the graft copolymers were confirmed using Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The grafting degrees have been controlled by the feeding amounts of the monomers. Moreover, the reaction mixture of PVDF-g-PVP was used as additive to prepare hydrophilic PVDF membrane, while the graft copolymer PVDF-g-PVAc was directly prepared into hydrophilic membrane. Water contact angles and bovine serum albumin adsorption capacities of the membranes were measured to evidence the improvements in their hydrophilicity and fouling resistance, and the porosities and water fluxes were determined to indicate their potential. The results suggest that the PVDF graft copolymers synthesized through the homogeneous reaction may find promising application in membrane field.

Graphical Abstract