Evaluation of silica-supported zirconocenes in ethylene/1-hexene copolymerization

A series of zirconocenes differing in the coordination sphere, namely (R)ZrCl2 (R = (MeCp)(2), (i-BuCp)(2), (n-BuCp)(2), rac-Et(Ind)(2) and rac-Et(IndH(4))(2)) were immobilized on silica Grace 948 pretreated at 723 K under vacuum. The highest metal loading, determined by Rutherford's backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy, was achieved with rac-Et(Ind)(2)ZrCl2. The steric effect played by the ligands on the cyclopentadienyl ring was seen to influence on the grafted content: less Zr was immobilized on silica using n-Bu as ligand, as compared to the zirconocene that uses Me as ligand. Nevertheless, this catalyst was the most active both in homogeneous and supported copolymerizations. Copolymers were characterized with respect to their molecular weights, polydispersity (M-w/M-n), crystallinity, comonomer incorporation and melting temperature. (C) 2002 Elsevier Science B.V. All rights reserved.