Poly(ethylene-g-styrene) and poly(ethylene-g-methyl methacrylate) graft copolymers were prepared by atom transfer radical polymerization (ATRP). Commercially available poly(ethylene-co-glycidyl methacrylate) was converted into ATRP macroinitiators by reaction with chloroacetic acid and 2-bromoisobutyric acid, respectively, and the pendant-functionalized polyolefins were used to initiate the ATRP of styrene and methyl methacrylate. In both cases, incorporation of the vinyl monomer into the graft copolymer increased with extent of the reaction. The controlled growth of the side chains was proved in the case of poly(ethylene-g-styrene) by the linear increase of molecular weight with conversion and low polydispersity (M-u/M-n < 1.4) of the cleaved polystyrene grafts. Both macroinitiators and graft copolymers were characterized by H-1 NMR and differential scanning calorimetry.