Novel and well-defined amphiphilic dendrimer-star copolymer poly(epsilon-caprolactone)-block-(poly(2-(2-methoxyethoxy) ethylmethacrylate-co-oligo(ethylene glycol) methacrylate))(2) with Y-shaped arms were synthesized by the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The investigation of thermal properties and the analysis of crystalline morphology indicate that the high-branched structure of dendrimer-star copolymers with Y-shaped arms and the presence of amorphous P(MEO(2)MA-co-OEGMA) segments together led to the complete destruction of crystallinity of the PCL segments in the dendrimer-star copolymer. In addition, the hydrophilicity-hydrophobicity transition of the dendrimer-star copolymer film can be achieved by altering the external temperatures. The amphiphilic copolymers can self-assemble into spherical nanomicelles in water. Because the lower critical solution temperature of the copolymers can be adjusted by varying the ratio of MEO(2)MA and OEGMA, the tunable thermosensitive properties can be observed by transmittance, dynamic laser light scattering, and transmission electron microscopy (TEM). The release rate of model drug chlorambucil from the micelles can be effectively controlled by changing the external temperatures, which indicates that these unique high-branched amphiphilic copolymers have the potential applications in biomedical field. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4071-4080, 2011