Graft copolymer of N-vinyl-2-pyrrolidone with guar gum was synthesized and its reaction conditions were optimized for better yield using potassium peroxymonosulfate (PMS) and glycolic acid (GA) as a redox initiator. The effect of PMS, GA, hydrogen ions, guar gum, and N-vinyl-2-pyrrolidone (NVP) along with reaction time and temperature were Studied by determining the grafting parameters: grafting ratio, efficiency, conversion, add-on, homopolymer, and rate of grafting. It was observed that the maximum yield Occurred at with a time of 120 min at a temperature of 45 degrees C and a guar gum concentration of 0.4 g/L concentration. The graft copolymer was characterized by infrared spectroscopy and thermal analysis. The activation energy for the grafted and ungrafted gum was calculated. It was observed that the graft copolymer was thermally more stable than the pure gum. The swelling and metal ion sorption behavior of guar gun-L and guar gum-g-N-vinyl-2-pyrrolidone also were studied. (c) 2006 Wiley Periodicals, Inc.