SILICA-SUPPORTED ZIRCONOCENE CATALYSTS - PREPARATION, CHARACTERIZATION AND ACTIVITY IN ETHYLENE POLYMERIZATION

Supported catalysts for ethylene polymerization have been prepared by interaction of Cp2ZrX2 (Cp = eta(5)-C5H5, X = Cl or CH3) with silica c hemically modified by (CH3)(3)SiCl(TMCS) or trialkylaluminium compound s AlR3 (R = C2H5 (TEA) and (C4H9)-C-1 (TIBA)). The interactions betwee n the modificators and the silica surface have been examined by H-1 so lid-state MAS NMR spectroscopy, DRIFTS and chemical analysis. The Cp2Z r(CH3)(2)/SiO2-TMCS catalyst showed a fairly high activity in ethylene polymerization (30-300 kg PE(mol Zr . h . bar)(-1)) even in the absen ce of any cocatalysts specially added. The addition of the cocatalyst (MAO or TIBA) led to a further increase in the activity of the support ed catalysts. Polyethylene obtained with the Cp2Zr(CH3)(2)/SiO2-TMCS c atalyst without any cocatalyst consisted of uniform polymer particles of a spherical shape replicating that of the silica particles, whereas the shapeless aggregates of finely dispersed polymer particles simila r to those usually obtained with homogeneous systems were produced wit h the same supported catalyst in the presence of the MAO cocatalyst. ( C) 1998 Elsevier Science B.V.