Stopped-flow study of the interaction of MgCl2-supported Ziegler catalyst with (Me)nSi(OEt)4-n: a tool for understanding the active sites precursors and the correlation to stereospecificity

Abstract

The active sites precursors on a MgCl2-supported Ziegler catalyst and the correlation to catalyst stereospecificity were investigated in the initial stage of propene polymerization in terms of the interaction of a variety of ethoxysilanes with the structure (Me)nSi(OEt)4-n. The kinetic study using the stopped-flow technique indicated that the interaction of the catalyst with a variety of ethoxysilanes prevents formation of active sites, and the degree of inhibition depends upon the number of ethoxy groups. It is considered that the values of propagation rate constant on the isospecific active sites are essentially the same regardless of the structure of the ethoxysilane, but the ratio of the isospecific active sites to the total number of active sites depends on the number of ethoxy groups. The same tendency in the variation of the activity, the stereospecificity, and the kinetic parameters depending on the number of ethoxy groups attached to a silane atom was observed regardless of whether the ethoxysilanes were treated with the catalyst or with triethylaluminium before polymerization.