Additive Effects of Lewis Bases on Propene Polymerization over MgCl2-Supported TiCl4 Catalysts Combined with Cp2TiMe2

Abstract

Propene polymerization was conducted with TiCl4/(Lewis base)/MgCl2-Cp2TiMe2 catalysts in the presence of ethyl benzoate (EB) and/or 2,2-diisobutyl-1,3-dimethoxypropane (DBDMP). The addition of small amounts of these Lewis bases to MgCl2 before supporting TiCl4 decreased the amount of Ti in the catalyst and improved catalyst isospecificity. The results suggested that the Lewis base is selectively coordinated on the MgCl2 surface where aspecific sites had been formed. The addition of the Lewis bases during the polymerization increased polymerization rate followed by rapid deactivation. Deactivation was second order on the polymerization rate and the deactivation rate constant depended on both structure and amount of the Lewis base. GPC analysis of the produced polymers indicated that the addition of the Lewis bases increased the molecular weight of isotactic polypropene (IPP). Polydispersity depended on the Lewis base: it became narrower by EB and broader by DBDMP. The 13C NMR spectra of IPPs revealed that EB improved the microtacticity of IPP more effectively than DBDMP. ESR spectra of the catalysts indicated that the amount of isolated Ti3+ species increased in the presence of EB.