The graft copolymerization of methyl methacrylate (MMA) onto sodium salt of partially carboxymethylated guar gum (Na-PCMGG; degree of substitution = 0.497) with ceric ammonium nitrate as a redox initiator in an aqueous medium was studied. The optimized reaction conditions affording the maximum percentage of grafting of MMA onto Na-PCMGG were determined through the variation of the concentrations of nitric acid, ceric ammonium nitrate, MMA, and Na-PCMGG and of the temperature and time. The effects of these parameters on the grafting yields and the rates of polymerization, graft copolymerization, and homopolymerization were also studied, and the results were examined. The graft copolymer sample was characterized with IR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. (c) 2005 Wiley Periodicals, Inc.