50%(2)1 out of 2 people found this document helpful
This preview shows page 1 - 4 out of 16 pages.
CHEM 5384 Polymer Characterization II Lab 5: Cp2ZrHCl Catalyzed Ring Opening Polymerization of -Caprolactone Mengfang Li 02/26/2013
Introduction: Currently, living radical polymerization has become one the most efficient synthetic methods in polymer industry. Apart from the common coordination polymerizations, there is increased interest in the radical polymerization using early transition metal complexes [1-3]. In this report, the paramagnetic Cp2Zr(H)(Cl) complex, is used as a mild electron transfer agent and can be used to catalyzes variety of radical polymerization. Polyesters are one of the most important classes of polymers. The common method to synthesize polyester is by ring-opening polymerization of cyclic esters. However, this type of reaction is usually produces polymer with low molecular weights. The limitation of molecular weight could lead to low modulus, tensile strength and viscosity. A new way of ROP of caprolactone(CL) has been invented by Dr. Alexandru Asandei in the presence of catalytic amount of Group 4 transition metal hydride[1-3]. This Group 4 transition metal hydride reacts with an equivalent of caprolactone to form a metal alkoxide, which functions as the catalyst for living polymerization. As shown in Scheme 1, the polymerization of caprolactone by Cp2ZrHCl to form (3) which isomerize to form (5) and initiate the polymerization[1-3]. Figure 1. Cp2ZrHCl catalyzed ROP of CL initiated by benzaldehydeFigure 2. Sn(II)(Ethyl Hexanoate)2catalyzed ROP of CL initiated by benzyl alcohol
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.