Aluminoxane-based Activator Chemistry

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Plastics are versatile materials used in an enormous array of products. Polyolefins are one class of plastics made from polymerizing olefin monomers (simple molecules containing a C=C double bond) to form a long chain hydrocarbon (with a backbone of C-C single bonds). They are made in huge quantity worldwide with the help of catalysts. Catalysts speed chemical reactions without themselves being affected, and in the preparation of polyolefins, catalysts containing transition metals are used. However, the catalyst requires activation before it is able to assist the desired transformation, and the key industrial approach to this activation step is to use a large excess of a highly reactive compound called methylaluminoxane (MAO). The excess used is so high (1000-10,000 equivalents) that MAO represents a significant proportion of the cost of the catalytic system. The excess used is probably due to the fact that the activating component(s) of MAO are present only as a small fraction of the whole, but the complexity of MAO is such that it has resisted unambiguous characterization for over 25 years.