The graft copolymerization of butyl acrylate (BA) onto chitosan was tried via a new protection-graftdeprotection procedure. About 6-0-maleoyl-N-phthaloylchitosan was synthesized and characterized b Fourier transform infrared spectra analysis (FT-IR) and H-NMR. Because the intermediate 6-0-maleoyl-N-phthaloyl-chitosan was soluble in organic solvents, the graft copolymerization was carried out in a homogeneous system. Grafting was initiated by gamma-irradiation. The graft extent was dependent on the irradiation dose and the concentration of BA monomer, and copolymers with grafting above 100% were readily prepared. (c) 2006 Wiley Periodicals, Inc.