Styrene underwent the ATRP process using an asymmetric difunctional initiator, 2-hydroxylethyl 2'-bromobutyrate in combination with CuBr and 2,2'-bipyridine (bpy). Polystyrene with hydroxyl and bromine groups at each end of the polymer (HO-PSt-Br) was obtained, and used as a chain-transfer agent in the cationic ring-opening polymerization of 1,3-dioxepane with triflic acid as initiator. The structures of the polymerization products were analyzed by H-1 NMR and GPC analyses, indicating the formation of block copolymer. The molecular weight distribution of the block copolymer was relatively narrow and the molecular weight of the polyDOP block was high.