Olefin polymerisation is a key to the production of the most widely used polymers in the world such as polypropylene and polyethylene. The use of metallocene based catalyst technology has presented a revolution in the enormous polyolefin industry - but not without drawbacks.
The metallocene/methylaluminoxane (MAO) catalyst system allows properties of the polymer to be tailored in many ways. These custom properties include greater stiffness and impact strength, greater stretch and puncture resistance and improved sealability. Other properties that can be tailored for individual applications include temperature resistance, hardness, impact strength and transparency.
Unfortunately, in order to achieve these results, a large amount of expensive MAO may be required. This in turn may make the final polymer material not financially viable for the proposed application. The process also requires soluble metallocene catalysts to be removed, recovered and purified. Various methods have been examined to circumvent these negative outcomes and in several cases, it is claimed that additional MAO is not necessary during polymerization if it is initially deposited on the surface of silica.
In this paper by João Henrique Zimnoch Dos Santos, Paula Palmeira Grecco, Fernanda Chiarello Stedile and Boris Chornik from Instituto de Química and Universidad de Chile, they demonstrate that it is possible to overcome the problem of low activity of grafted zirconocene catalysts by the previous chemical modification of the silica surface with SnCl4. They also found that silica-supported systems generally produced polymers with higher molecular weight
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