Poly epsilon-caprolactone-polystyrene blockcopolymers (PCL-b-PSt) were synthesized using a modified titanium catalyst as the dual initiator. Alcoholysis of Ti(OPr)(4) by 4-hydroxy 2,2,6,6 tetramethyl piperidinyl-loxyl (HO-TEMPO) gave a bifunctional initiator Ti(OTEMPO)(4). Poly epsilon-caprolactone prepolymer end-capped with the nitroxide group was first prepared by ring opening polymerization of epsilon-caprolactone with this initiator at high conversion. The nitroxide-end-capped structure and molar mass (M-n) of the polymers were demonstrated by typical UV absorption band. This analytical technique indicates a near-quantitative nitroxide functionality and a M-n in good agreement with size exclusion chromatography (SEC) ones. This polyester prepolymer was used to further initiate the radical polymerization with styrene and reach the block copolymers (PCL-b-PSt). All the prepolymers and block copolymers were characterized by SEC and NMR spectroscopy. Additionally, the preparation of star polymers bearing two kinds of arms (PCL and PSt) was envisaged and a preliminary result was given. (c) 2007 Wiley Periodicals, Inc.