Basic Approaches for the Design of Active Sites on the Traditional Ziegler Catalysts

Abstract

In this paper, three basic approaches for the design of active sites on the traditional Ziegler catalysts are discussed for the future breakthrough of this type of catalysts. Firestly, the Variation of isospecific active sites formed on a MgCl₂-supported TiCl₄ catalyst in the absence or presence of external electron donor was specified by the stopped-flow method based on the isotacticity distribution of the polypropene. Besides the depression of the formation of some aspecific active sites, the effect of addition of external electron donor is to transfer some of the aspecific titanium species into isospecific active site. Secondly, hydrogen dissociation sites were found to be derived from the over-reduced Ti species due to deactivation during propene polymerization. Finally, the enantioselectivity and diastereoselectivity of the active sites for copolymerization of propene and 1, 5- hexadiene were studied. It was made clear that the steric hindrance in the vicinity of active sites increases with the isospecificity of the active sites.