Kinetics of polymerization of epsilon-caprolactone (CL) initiated with tin(II) octoate (Sn(Oct)(2)) in THF as a solvent at 80 degrees C was studied. The results strongly indicate that polymerization initiated with Sn(Oct)(2) proceeds on the tin(II)-alkoxide bond and are not compatible with a mechanism in which propagation was proposed to proceed by a nucleophilic attack of the ...-OH ended macromolecules on the monomer-Sn(Oct)(2) complex.