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 di fferent amounts of ethyl propionate (EP) as internal donor were prepar ed and tested in the propene polymerization in order to evaluate their activity and stereospecificity. These catalysts were obtained by trea ting chemically activated MgCl2 supports bearing variable ethyl propio nate contents with TiCl4. The supports and the derived catalysts so pr epared were characterized by elemental analysis, XRD and FT-IR techniq ues. The polymerization tests were carried out at 70 degrees C and 7.5 atm using dimethoxydiphenylsilane as external donor and hydrogen as c hain transfer reagent. A correlation between the procatalyst structure and composition and their activity as well as stereoselectivity was o btained. On processing the obtained results it was possible to evaluat e the trend of both the activity and the stereoselectivity on the simu ltaneous changes of the Ti/Mg, Ti/EP and EP/Mg molar ratios. Actually, these catalysts show the best performance with a composition correspo nding to the following molar ratios: Ti/Mg approximate to 0.03, Ti/EP approximate to 0.14 and EP/Mg approximate to 0.27. Finally, these stud ies confirm again that the active supports and the procatalysts are es sentially based on a Cl-Mg-Cl chain structure model.