A DFT study on the role of alkoxysilanes in the polymerization of isoprene over Ziegler-Natta catalyst

Abstract

Ziegler-Natta catalysts are widely used in the production of polyolefin with the advantages of low cost and high efficiency. The external electron donors are usually used during the polymerization to obtain the polyolefins with higher isotacticity. Four alkoxysilanes external electron donors were investigated by Density Functional Theory (DFT) calculations. Local Electron Attachment Energy (LEAE) calculations showed that alkoxysilanes tend to adsorb at the Mg1 site and the Mg4 site of the MgCl2(110) surface (The first and fourth Mg atoms from right to left on the MgCl2(110) surface, respectively), and that differences in substituents have a large effect on the stability of alkoxysilanes adsorption. In addition, it was found that the adsorption of alkoxysilanes at the Mg1 site affects the active center in two ways, decreasing the electron cloud density of the active center Ti and increasing the steric hindrance of the active center Ti. Comparing the four alkoxysilanes, it is found that DIPMS can maximize the regional selectivity of catalysts, while DCPDMS can maximize the stereoselectivity of catalysts.