Anchoring of Metallocene Catalysts to Supports

In only a few polymerization processes are metallocene catalysts used in a soluble form. Supported metallocene catalysts are preferred for the production of polyethylene or isotactic polypropylene on an industrial scale, especially in the slurry and gas-phase processes. To use them in existing technological processes (drop-in technology) as replacements for the conventional Ziegler-Natta catalysts, the metallocenes have to be anchored to an insoluble powder support, including silica, alumina, and magnesium dichloride (208-217). Various methods of anchoring catalysts to supports are possible (Fig. 25)  

Initial absorption of MAO on the support with subsequent addition to metallocenes in a second step this is the procedure most commonly used. The washed catalysts are used in combination with additional MAO or other aluminum alkyls in polymerization (208-210). 

A mixture of the metallocene and MAO is adsorbed on the support. In this case, the prereaction time plays an important role (213). 

Absorption and immobilization of the metallocene on the support surface first then, after addition of MAO, this catalytic is used in the polymerization process (213, 214). 

The metallocene can be bonded directly to the support by a spacer and an anchor group, resulting in effective immobilization (211). 

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