High yield MgCl2-supported catalysts for propene polymerization: effects of ethyl propionate as internal donor on the activity and stereospecificity

A series of MgCl2-supported Ziegler-Natta type catalysts containing different amounts of ethyl propionate (EP) as internal donor were prepared and tested in the propene polymerization in order to evaluate their activity and stereospecificity. These catalysts were obtained by treating chemically activated MgCl2 supports bearing variable ethyl propionate contents with TiCl4. The supports and the derived catalysts so prepared were characterized by elemental analysis, XRD and FT-IR techniques. The polymerization tests were carried out at 70°C and 7.5 atm using dimethoxydiphenylsilane as external donor and hydrogen as chain transfer reagent. A correlation between the procatalyst structure and composition and their activity as well as stereoselectivity was obtained. On processing the obtained results it was possible to evaluate the trend of both the activity and the stereoselectivity on the simultaneous changes of the Ti/Mg, Ti/EP and EP/Mg molar ratios. Actually, these catalysts show the best performance with a composition corresponding to the following molar ratios: Ti/Mg ≈ 0.03, Ti/EP ≈ 0.14 and EP/Mg ≈ 0.27. Finally, these studies confirm again that the active supports and the procatalysts are essentially based on a Cl-Mg-Cl chain structure model.