A previously unreported graft copolymer of xanthan gum (XOH) with acrylic acid was synthesized and the reaction conditions were optimized using a potassium monopersulfate (PMS)/Fe2+ redox pair. Grafting ratio, add on, and conversion increase with an increase in the ferrous ion concentration (2.0 x 10(-3) to 5.0 x 10(-3) mol dm(-3)) and PMS concentration (1.0 x 10(-3) to 4.0 x 10(-3) mol dm(-3)). It was observed that grafting takes place efficiently when the acrylic acid concentration and temperature were 5.0 x 10(-2) mol dm(-3) and 35degreesC, respectively. Samples of xanthan gum and xanthan gum-g-acrylic acid were subjected to thermogravimetric analysis with the objective of studying the effect of grafting of acrylic acid on the thermal stability of xanthan gum. The graft copolymer was found to be more thermally stable than xanthan gum. (C) 2003 Wiley Periodicals, Inc.