Activation of Metallocenes for Olefin Polymerisation as Monitored by IR Spectroscopy

The binary mixtures of Cp2ZrMe2, Cp2ZrCl2, DMAC, TMA, and MAO have been studied by in situ IR spectroscopy in order to clarify the activation mechanism of metallocenes with MAO. In the mixture of MAO and Cp2ZrMe2, a new unidentified stable complex is observed with an IR band at 822 cm. It is rapidly formed at low Al/Zr ratio and may be a precursor to the active catalyst. A new mechanism is proposed for the activation of metallocenes with MAO, that may explain the need for a large MAO excess. The new feature of the mechanism is formation of a MAO cage dimer, that hides the protruding charged methide from the electrophilic cation.