Graft copolymerization of starch has been carried out onto preirradiated polypropylene (PP) in an aqueous medium using benzoyl peroxide (BPO) as the radical initiator. The maximum percentage of grafting (115%) of starch onto PP was obtained at optimum conditions of BPO concentration, 1.239 x 10(-3) moles; temperature, 65 degrees C; in 120 min. using 30 mL of water. Swelling studies were carried out in pure, binary, ternary and quaternary solvent systems comprising of water, ethanol (EtOH), dimethylsulphoxide (DMSO), and N,N-dimethylformamide (DMF) in different ratios. Maximum swelling is observed in DMSO and DMF, followed by EtOH and least in water for true graft. Water retention studies of pristine PP and PP-g-Starch (both composite and true graft) were investigated at different time periods, temperature and pH. The composite contains grafted PP, unreacted starch and unreacted PP whereas true graft is the product from which both unreacted polymers have been removed. Maximum % water retention of PP-g-Starch (composite) (110%) was observed in 8 h at 50 degrees C in neutral medium (pH 7). The graft copolymers were characterized by FTIR, DTG, DTA, TGA, and SEM. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 602-612, 2011