Effects of Various Preparation and Polymerization Procedures on the Isospecific Nature of TiCl3-Based Polypropylene Catalysts

Abstract

As one of a series approaches in using two-component and three-component donor-free Ziegler–Natta catalysts, in this preliminary work, the effects of various preparation and polymerization conditions including catalyst preparation by wet- or dry- grinding, the type of cocatalyst, with or without pretreatment of catalyst by cocatalyst before polymerization, Al/Ti molar ratio and polymerization temperature, etc., on the isospecific nature of active sites of the TiCl3 catalyst were studied through a systematic characterization of the PPs by a combination of GPC, 13C-NMR with TREF method. It was demonstrated that the types of Al-alkyl cocatalysts play the most dominant role in determination of isospecificity of activate sites and its distribution. A plausible mechanism (Scheme 1) regarding the formation of isospecific active sites with different stability in terms of Ti–Al bimetallic complexing depending on the type of cocatalyst had been proposed. Except the catalyst grinding method, other factors eg., pretreatment, temperature, and Al/Ti molar ratio, etc. did not show obvious effects on the isospecific nature of active sites.