Biodegradable, amphiphilic, diblock poly(epsilon-caprolactone)-block-poly(ethylene glycol) (PCL-b-PEG), triblock poly(epsilon-caprolactone)-block-poly(ethylene glycobblock-poly(P-caprolactone) (PCL-b-PEG-b-PCL), and star shaped copolymers were synthesized by ring opening polymerization of P.-caprolactone in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) or star poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by H-1 and C-13 NMR. The formation of block copolymers was confirmed by C-13 NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. For the same PCL chain length, the materials obtained in the case of linear copolymers are viscous whereas in the case of star copolymer solid materials are obtained with low T, and T. temperatures. (C) 2007 Wiley Periodicals, Inc.