In recent years, several reports have shown that polymerisation catalysts supported on mesoporous silicas are able to produce polyolefins with unusual morphological properties. Nevertheless, the method of catalyst preparation, the chemical composition of the support and the experimental conditions used, were not always clearly correlated with the catalyst activity and polymer morphology.

In this work, polyethylene was synthesised using zirconocene supported on pure siliceous MCM-41 and Al-containing MCM-41 variants. The mesoporous supports were characterized by powder X-ray diffraction and nitrogen adsorption. The heterogeneous catalytic systems were prepared using controlled Cp₂ZrCl₂ loads below the maximum of adsorption limit for each mesoporous support. The metallocene was present in the polymerisation reactor in known amounts. This procedure allowed a quick and direct comparison of the performances of the various catalytic systems in selected experimental conditions. It was observed that the Si/Al ratio affects the zirconocene load and the corresponding catalytic activity. Small Al amounts greatly improve the polymerisation activity of the catalytic system, but high Al levels become detrimental. On the other hand, modification of supports, by prior impregnation with MAO modifies the surface properties, leading to a change on polymerisation activity.

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