Kinetic study of bis(imino)pyridine cobalt complex supported on silica: effect of temperature on the number of active sites, propagation rate constant and MWD of polyethylene produced
In the present work we obtain the data on the effect of polymerization temperature in the range of 35-70 deg. C on the number of active sites and MWD of polymer produced at ethylene polymerization with supported catalyst LCoCl2/SiO2+Al(i-Bu)3. We observed the unusual effect of increasing of polyethylene molecular weight at the polymerization temperature increasing. It is shown by deconvolution of MWD curves that this effect is due to a decrease of the portion of the polymer fractions with low molecular weight and the increase of the portion of the high molecular weight fractions in the polymer. It is found by a method of polymerization inhibiting by radioactive carbon monoxide that the number of active centers is only weakly dependent from temperature, which significantly differs from previously studied catalyst LFeCl2/SiO2+Al(i-Bu)3. The data on the effect of temperature on the propagation rate constant was obtained. From these data the values of effective activation energy and activation energy of propagation reaction were calculated.