SILICA-SUPPORTED METALLOCENES - STEREOCHEMICAL COMPARISON BETWEEN HOMOGENEOUS AND HETEROGENEOUS CATALYSIS

Propylene was polymerized in the presence of the isospecific Et(Ind)(2 )ZrCl2 (Et: ethylene, Ind: indenyl) and the aspecific (Ind)(2)ZrCl2 co mplexes in solution and anchored to SiO2 and SiO2/MAO (MAO: methylalum inoxane) supports. From the stereochemical analysis of the polypropene samples obtained it can be deduced that i) the same active species is formed when a metallocene is in solution and when it is anchored to t he SiO2/MAO support and ii) a completely different active species is f ormed when the metallocene is anchored to the silica. The fact that bo th systems Et(Ind)(2)ZrCl2-SiO2 and (Ind)(2)ZrCl2-SiO2 produce the sam e prevailingly isospecific polymer suggests that only isospecific cent ers are formed in this case, independently of the metallocene stereoch emical structure.