Poly(lactide) (PLA), poly(epsilon-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) homopolymers of high molecular weight were prepared using potassium-based catalyst. Polymerizations were carried out in toluene at room temperature. The chemical structure of the polymers was investigated by H-1 and C-13 NMR. The physical properties investigated by GPC and DSC for the polymers obtained are similar to those prepared using tin octanoate based catalyst. Using a sequential polymerization procedure, PLA-b-PCL, PLA-b-PTMC, and PCL-b-PTMC diblock copolymers were synthesized and characterized in terms of their composition and physical properties. The formation of diblock copolymers was confirmed by NMR and DSC measurements. In vitro cytotoxicity tests have been carried out using MTS assay and the results show the biocompatibility of these polymers in the presence of the fibroblast cells. (C) 2008 Wiley Periodicals, Inc.