(nBuCp)(2)ZrCl2 was grafted on a series of modified silica and evaluated in ethylene/1-hexene copolymerization and their performance was compared with the homogenous system and with that resulting from its immobilization on bare silica. Silica was modified by polymethylhydrosiloxane (PMHS), Me3SiCl, Ph3SiOH, SnCl4, isodrin and aldrin. (nBuCp)(2)ZrCl2 grafted on PMHS-modified silica afforded the catalyst with the highest activity. Comonomer incorporation, melting point and polydispersity was shown to be dependent on the catalyst nature. Bimodality was observed in the case of ethylene homopolymerization employing PMHS-silica-based catalysts. (C) 2003 Elsevier B.V. All rights reserved.