Formation of Isolated Titanium(III) Ions as Active Sites of Supported Titanium–Magnesium Catalysts for Polymerization of Olefins

Abstract

Electron spin resonance (ESR) studies reveal a high yield of isolated Ti3+ compounds (30–70% of the total titanium content) that form in superactive supported titanium–magnesium catalysts (TMCs) of composition TiCl4/MgCl2 with a low titanium content (≤0.1 wt%) after their interaction with different aluminum trialkyls (AlR3). These catalysts strongly differ from conventional TMCs with titanium contents of 1–3 wt%, which produce a set of isolated or associated Ti(II) and Ti(III) species after the interaction with the AlR3. A correlation is found between the content of the isolated Ti(III) ions and the activity in ethylene polymerization. According to temperature rising elution fractionation (TREF) data, the catalysts with a low titanium content (isolated Ti(III) ions) mainly produce polypropylene with a very high atactic‐fraction content. Organic products formed on the interaction of AlEt3 and AlMe3 with TMC are identified. The data obtained allow a scheme of Ti3+ and Ti2+ compounds formed in these catalysts to be proposed. image