The inverse star block copolymer, (poly(epsilon-caprolactone)-b-polystyrene)(2)-core-(poly(r.-caprolactone )-b-polystyrene)(2), [(PCL-PS)(2)-core-(PCL-PS)(2)] has been successfully prepared by combination of atom transfer radical polymerization (ATRP), ring opening polymerization (ROP), and "Click Chemistry." The synthesis includes the following five steps: (1) synthesis of a heterofunctional initiator with two ATRP initiating groups and two hydroxyl groups; (2) formation of (Br-PS)(2)-core-(OH)(2) via ATRP of styrene; (3) preparation of the (PCL-PS)2-core-(OH)2 through "click" reaction of the alpha-propargyl, omega-acetyl terminated PCL with (N-3-PS)(2)-core-(OH)(2) Which was prepared by transformation of the terminal bromine groups in (Br-PS)2-core-(OH)2 into azide groups; (4) the ROP of CL using (PCL-PS)(2)-core-(OH)(2) as macroinitiator to form (PCL-PS)(2)-core-(PCL-OH)(2); and (5) preparation of the (PCL-PS)(2)-core-(PCL-PS)(2) through the ATRP of styrene using (PCL-PS)(2)-core-(PCL-Br)(2) as macroinitiator which was prepared by reaction of the terminal hydroxyl groups at the end of the PCL chains with 2-bromoisobutyryl bromide. The characterization data support structures of the inverse star block copolymer and the intermediates. The differential scanning calorimeter results and polarized optical microscope observation showed that the intricate structure of the inverse star block copolymer greatly restricted the movement of the PS segments and PCL segments, resulted in the increase of the glass transition temperature of PS segments and the decrease of crystallization ability of PCL segments. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 77577772,2008