The synthesis of syndiotactic polypropene was achieved by using new C-S-symmetric ansa-metallocene catalysts of the type [Ph-2'C(Cp)(2.7-(tert)Bu(2)Flu)]ZrCl2 (Ph-2' = Ph-2, (4-MePh)(2), 3,4'-Me2Ph2, (4-OCH3Ph)(2)). Applying these catalysts, the influence of the substitution pattern of the bridge on the polymerization performance can be studied and highly syndiotactic polypropene (rrrr > 99%) with high molar masses (M-eta > 10(6) g/mol) and high melting temperatures (up to 153 degreesC) was obtained. Propene was polymerized at different temperatures under four sets of conditions: in toluene solution, bulk, toluene slurry, and gas phase with NaCl as stirred bed material. Methylaluminoxane (MAO) and methylaluminoxane supported on silicagel (MAO/SiO2) were used as cocatalyst. respectively. In order to estimate the influence of the process on the single site properties of the catalysts, comparisons were made between polymer proper-ties, i.e. microstructure, melting temperature, molar mass, and polymer morphology, thus allowing the effect of the support on the catalyst to be observed. (C) 2004 Elsevier Ltd. All rights reserved.