mu-Gels which consist of poly(organosilicon) networks can be employed as efficient support materials for ethylene polymerization catalyst precursors. Alkylaluminum cocatalysts can be fixed on the mu-gel surfaces using the PHT ("partially hydrolyzed trimethylaluminum") method. The influence of different aluminum/water ratios on the ethylene polymerization properties of these heterogeneous systems is investigated. Dinuclear silicon bridged zirconium complexes are used as catalyst precursors yielding polyethylenes with broad or bimodal molecular weight distributions. (C) 2008 Wiley Periodicals, Inc.