This article reports the synthesis of the block and graft copolymers using peroxygen-containing poly(methyl methacrylate) (poly-MMA) as a macroinitiator that was prepared from the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in the presence of bis(4,4'-bromomethyl benzoyl peroxide) (BBP). The effects of reaction temperatures on the ATRP system were studied in detail. Kinetic studies were carried out to investigate controlled ATRP for BBP/CuBr/bpy initiating system with MMA at 40 degrees C and free radical polymerization of styrene (S) at 80 degrees C. The plots of In ([M-o]/[M-t]) versus reaction time are linear, corresponding to first-order kinetics. Poly-MMA initiators were used in the bulk polymerization of S to obtain poly (MMA-b-S) block copolymers. Poly-MMA initiators containing undecomposed peroygen groups were used for the graft copolymerization of polybutadiene (PBd) and natural rubber (RSS-3) to obtain crosslinked poly (MMA-g-PBd) and poly(MMA-g-RSS-3) graft copolymers. Swelling ratio values (q(v)) of the graft copolymers in CHCl3 were calculated. The characterizations of the polymers were achieved by Fourier-transform infrared spectroscopy (FTIR), H-1-nuclear magnetic resonance (H-1 NMR), gel-permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and the fractional precipitation (gamma) techniques. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1364-1373, 2010