On the effect of adding a Lewis acid as a modifier of metallocene-based polymerization catalysts

BELELLI, P.G.; FERREIRA, M.L.; DAMIANI, D.E.

STUDIES IN SURFACE SCIENCE AND CATALYSIS

Elsevier Inc.

Año: 2000 vol. 130 p. 3855 - 3860

0167-2991

The effect of a Lewis acid (AlCl3) on the activity and selectivity of EtInd2ZrCl2/MAO catalyst either soluble or supported was investigated for propene polymerization. For the soluble catalyst the modifier was externally added while for the supported one, AlCl3 was either incorporated onto the surface SiO2 acting as metallocene carrier or added with additional MAO to the metallocene supported onto a MAO-modified SiO2. An optimum modifier to Zr ratio was found for soluble catalysts. At this optimum the catalyst activity increased while the polymer characteristics remain almost unchanged. For the supported catalyst the presence of the modifier is detrimental for the activity and the average molecular weight of the polymer remains unchanged. Results are explained in terms of the influence of the modifier on the active site formation by altering the nature of the co-catalyst. Molecular orbital calculations on catalysts models support these ideas.