Effect of internal donors on the performance of Ti-Mg catalysts in propylene polymerization: Donor introduction during or after MgCl2 formation

Abstract Propylene polymerization catalysts with different internal donors (ID) are synthesized by two methods: (1) a standard method with ID introduction during formation of MgCl 2 by reacting Mg(OEt) 2 with TiCl 4 , and (2) the introduction of ID on MgCl 2 already formed in the presence of butyl acetate (the substitution method). 1,3-diether, dibutyl phthalate (DBP) and pentane-2,4-diol-dibenzoate (PDDB) are used as ID. Catalysts prepared with the same ID by both methods slightly differ in their composition, activity and stereospecificity (the content of xylene soluble polypropylene (PP) fraction). But the catalyst active sites produce PP, whose properties (melt flow index, MFI, and molecular-weight distribution as M w /M n ) depend on ID in the same manner for both methods of catalyst synthesis. Hence, the effect of ID on the catalyst active sites is not related with the effect of ID on the formation of MgCl 2 crystallites with different cuts.