Graft copolymerization of vinyl monomers onto chitosan and other natural polymers using atom transfer radical polymerization has only recently attracted interest. This technique could potentially provide new ways to utilize this abundant natural polymer. It would enable a wide variety of molecular designs to afford novel types of tailored hybrid materials composed of natural polysaccharides and synthetic polymers. In this work, a chitosan macroinitiator was prepared by the reaction of chitosan with 2-bromo-isobutyryl bromide, after the chitosan amino group had been protected as the imine. The aqueous grafting of methoxy capped (PEG 350) methacrylate onto chitosan is described. The kinetic study revealed a first order polymerization reaction. Polydispersities of about 1.25 were obtained. (C) 2003 Wiley Periodicals, Inc.