Synthesis of Titanium–Magnesium Catalysts for Propylene Polymerization: Substitution of Ketones by Dibutyl Phthalate

Abstract

Titanium-magnesium catalysts (TMCs) of propylene polymerization have been synthesized in the presence of ketones as internal donors. The molar ratio of titanium chloride to ketone in TMCs was found to depend on the structure of ketone. The composition and catalytic properties of the synthesized TMCs in propylene polymerization were significantly different from those of TMCs prepared without ketone. The TMCs were synthesized by replacing ketones with a stereoregulating donor dibutyl phthalate (DBP, DBP/Mg = 0.05 mol/mol). It was shown that ketones were substituted by phthalate; the crystallite size of MgCl2 (~6.5 nm in the 110 direction) did not change. The data on the molar ratio Ti/donor = 2 for different donors (ketone, phthalate) and the same MgCl2 crystallites are consistent with the predominance of 104 lateral cuts. The catalytic properties of the substituted catalysts are almost independent of the type of ketone used and are close to those of the standard TMC obtained with phthalate alone (DBP/Mg = 0.2 mol/mol) during the formation of MgCl2. Therefore, ketones, like esters, are involved in the formation of magnesium chloride. Their subsequent substitution by phthalate allows synthesis of TMCs with high activity and stereospecificity.