The radical polymerization of styrene was performed at 130 degrees C for 72 h using 4-methoxy-2,2,6,6-tetramethylpipcridine-1-oxyl (MTEMPO) and paly(dimethylsiloxane) (PDMS) containing azo moiety (PDMS-AZ) as a macroinitiator. It was found that the block copolymer of DMS with styrene was quantitatively obtained when the ratio of MTEMPO to the azo moiety in PDMS-AZ was 0.6. The structure was expected to be of the A-B type, rather than A-B-A, when the low initiator efficiency and the molecular weight of the PSt segments isolated were taken into account. The polymerization proceeded in accordance with a Living mechanism,because the conversion of styrene linearly increased over time, and the molecular weight of the copolymer produced was directly proportional to the conversion. Furthermore, the polymerization of p-methoxystyrene was also found to proceed where the PDMS-block-polystyrene was used as an initiator, to give the triblock copolymer quantitatively.