A new high-molecular-weight three-arm poly(e-caprolactone) (PCL) polymer was synthesized in bulk (in the absence of any solvent) by using aluminum tri-sec butoxide as a tri-functional initiator. The ring-opening polymerization of epsilon-caprolactone occurs via a coordination-insertion mechanism that links three growing polyester chains to the Al central atom via metal alkoxide bonds. The global kinetics of the bulk polymerization was determined, and a kinetic model based on monomer-polymer equilibrium was developed to predict the fractional extent of monomer conversion. Monomer conversions in excess of 95% to form high-molecular-weight PCL were achieved. (C)2004 society of Plastics Engineers.