Herein we report the surface modification of poly(vinylidene fluoride) (PVDF) microporous membrane via thermally induced graft copolymerization with maleic anhydride (Man)/styrene (St) in supercritical carbon dioxide (SC CO2). SC CO2, as a solvent and carrier agent, could accelerate mass transfer of monomers inside polymer matrixes and then facilitate the graft copolymerization on the surface of the membrane and within membrane pores, which were confirmed by FF-IR/ATR and XPS spectra together with SEM photographs. The effects Of SC CO2 pressure and temperature and the monomer concentration on the graft copolymerization were investigated. The modified PVDF membranes containing from 0 to 7 wt.% of grafted St-Man copolymer (SMA) were prepared and analysed in terms of surface microstructure, composition, hydrophilicity and biocompatibility. Solid-state C-13 CP/MAS NMR and DSC indicated that the grafted SMA on the PVDF membrane had the alternative sequence structure and formed the different phases in the modified membrane, where the grafted SMA was associated with T-g of 122.8 degrees C and the PVDF matrix with T-m of 161.2 degrees C. The static contact angle measurements revealed that remarkable and permanent hydrophilicity was obtained upon grafting SMA. The experiments of BSA adsorption and cell growth also showed that the surface of SMA-based PVDF membrane has excellent biocompatibility. (C) 2008 Elsevier B.V. All rights reserved.