Iodo functionalized polyethylene (PE-I), prepared by the addition of iodine after catalyzed polyethylene chain growth on magnesium, is demonstrated to be an efficient macroinitiator for thermally induced, controlled free radical polymerization using dimanganese decacarbonyl (Mn-2(CO)(10)). The free radical polymerization of methyl methacrylate is initiated by thermal homolysis of (Mn-2(CO)(10)) at 80 degrees C, forming reactive manganese pentacarbonyl radical species [center dot Mn(CO)(5)] capable of activating the C-I bond of PE-I. The metal catalyzed radical generation and degenerative iodine processes yielded polyethylene-b-poly(methyl methacrylate) (PE-b-PMMA) block copolymers with relatively low dispersities. The end group functionality of the block copolymer is confirmed by the successful thermal polymerization of styrene by using PE-b-PMMA as a macro initiator in the described process. This work conclusively provides a new approach for combining polyethylene with vinyl polymers via manganese chemistry in a simple and efficient pathway of importance in synthetic polymer chemistry and other related applications.