Kinetic investigation of the active sites precursors on MgCl2-supported Ziegler catalyst through interaction with a Lewis base

Abstract

The initial polymerization stage of propene with a MgC1 2 -supported Ziegler catalyst after the pre-treatment with a Lewis base was examined as a study of the stereospecificity of the active sites precursors. A drastic depressing effect on the catalyst activity occurs, accompanied by an increase in stereospecificity, by the direct interaction of cyclohexylmethyldimethoxysilane (CMDMS) with the catalyst before the polymerization. The kinetic study of the polymerization indicated that the active sites concentration ([C * ]) decreases drastically by the catalyst pre-treatment with CMDMS. On the other hand, the increase of propagation rate constant (k p ) is relatively small and corresponds to the moderate increase of the mmmm pentad fraction. This is an indication that the interaction of the Lewis base with the active sites precursors prevents formation of the active sites and that inhibition occurs preferentially at the aspecific precursor.