epsilon-caprolactone/ZnCl2 complex formation: Characterization and wing-opening polymerization mechanism

epsilon-Caprolactone (epsilon-CL) has been mixed with ZnCl2 at different mo l ratios. The resulting complex was characterized through H-1 and C-13 NMR spectroscopy in bulk and in solutions, differential scanning calorimetry (D SC, wide-angle X-ray diffraction (WAXD), and optical microscopy. Ring-openi ng polymerization of epsilon-caprolactone [M] using ZnCl2 as an initiator [ I] at different monomer/initiator ratios has been successfully performed in xylene. The molecular weight of poly(epsilon-caprolactone) (PCL) as measur ed by gel permeation chromatografy (GPC) was found to depend linearly on th e [M]/[I] ratio. Theoretical calculations were carried out to understand th e geometry of the complex and the operating ring-opening mechanism. Both ex perimental and computational results and the presence of methylene-chloride end group, confirmed by NMR, are in agreement with a coordination-insertio n mechanism for the ring-opening polymerization proposed in this article. ( C) 2000 John Wiley & Sons, Inc.