Figure 3. Mechanism of Cp2ZrClH catalyzed CL living ring opening polymerization Experimental Procedure: Materials.The following reagent were used as received: bis (cyclopentadienyl) zirconium chloride hydride (Schwartz’s Reagent, Cp2ZrHCl, 95%, Strem Chemicals). Sn(II)(Ethyl Hexanoate)2, Toluene (99.9%), Benzyl Alcohol (98%, Aldrich) and Caprolactone (CL, 99%, Acros) was dried over CaH2 and distilled at 110 C in vacuum. Tetrahydrofuran (THF, 99.9%, Fisher), Benzaldehyde (99%, Aldrich) Characterization.1H-NMR (500MHz) spectra were recorded on a Bruker DRX-500 at 25 C in CDCl3. GPC analyses were performed at 34 C on a Waters 150-C plus gel permeation chromatograph equipped with a Waters 410 differential refractometer, a Waters 2487 dual wavelength absorbance UV-Vis detector set at 254 nm. Tetrahydrofuran (THF) (Fisher; 99.9%) was used as eluent at a flow rate of ml/min. Number-average(Mn) and weight-average molecular weights (Mw) were determined from calibration plots with polystyrene standards.