Starch as one of the most abundant, renewable, low-cost, and biodegradable carbohydrate polymers worldwide suffers from some drawbacks: The most important one is that it lacks properties of synthetic polymers. So, modification of starch by graft copolymerization will provide a substantial modification route to alter physical and chemical properties of starch, thereby increasing its utilization, by attaching a flexible synthetic polymer onto the rigid natural polysaccharide backbone without greatly changing the latter. In addition to the main disadvantage of the above technique, the high percentage of homopolymer and low percentage of grafting are other disadvantages. At this point, our research team focused on how to maximize the graft yields and graft reaction efficiency percentage, minimize the homopolymer percentage, as well as enhance the water solubility of the prepared copolymers. Based on the results obtained, appropriate conditions for grafting methacrylic acid onto pregelled starch were established and the graft yield was higher under the following conditions: 10 mmol/L potassium persulfate (KPS); 8 mmol/L tetramethylethylene diamine (TMEDA) 50% methacrylic acid concentration (based on weight of substrate); liquor ratio, 10; reaction time, 60 min; and polymerization temperature, 60 degrees C. On the other hand, grafting was significantly enhanced by adding Fe3+, Cu2+, and Li+ in the grafting media and it follows the following order: Fe3+ > Cu2+ > Li+, in addition to the solubility percentage. Approximately 37.5% graft yield and 75% graft reaction efficiency as well as 25% homopolymerization were obtained when methacrylic acid was graft copolymerized onto pregelled starch as a reactive carbohydrate polymer using a new redox initiation system, namely KPS/TMEDA redox pair. Furthermore, a notable enhancement was observed in solubility percentage of grafted samples with lower graft yields than that of the higher one. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 138-149, 2011; View this article online at wileyonlinelibrary. com. DOI 10.1002/adv.20210