Synthesis Of Polyethylene With Various Morphologies Using Cp2ZrCl2 Supported On Pure and Al-containing MCM-41.

João M. Campos 1Maria R. Ribeiro 1João P. Lourenço 2Auguste Fernandes 1

1. Instituto Superior Técnico, Departamento de Engenharia Química e Biológica (IST-DEQB), Av. Rovisco Pais, Lisboa 1049-001, Portugal
2. Universidade do Algarve (FCT-UALG), Campus de Gambelas, Faro 8005-139, Portugal

Abstract

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.

SEM analysis showed different polyethylene morphologies depending greatly on the catalyst support and the experimental conditions used. Polyethylene nanofibers were clearly observed for the polymers synthesised with low activity catalytic systems. The DSC thermograms for the polymers synthesised with heterogeneous and homogeneous catalysts were compared.

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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium B, by João M. Campos
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-15 17:33
Revised:   2009-06-07 00:44
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