Poly(vinylidene fluoride) was grafted with maleic anhydride monomer via a free-radical mechanism in super-critical carbon dioxide medium. The free-radical initiator chosen for this study was benzoyl peroxide. The structure of the resultant copolymer pendant groups was determined by H-1 NMR spectroscopy to consist of individual succinyl anhydride functional groups. The degree of functionalization (graft level) was obtained by FTIR spectroscopy through the correlation of absorbance bands using standard samples. The FTIR analysis indicated increased graft level with monomer loading, reaction temperature, and treatment time; however, initiator loading and reaction temperature showed more-complex behavior. Graft levels increased at moderate benzoyl peroxide initiator loadings (5.0 wt%) and decreased at the highest initiator loadings (10.0 wt%). © 2005 Society of Plastics Engineers