MAO is the major commercial activator for metallocene/single-site polyolefin catalyst activation. However, the MAO active site and activation mechanism remain unclear several decades after the MAO discovery.1 Both free and coordinated TMA are experimentally detectable in MAO solution.1, 3 This contribution provides evidence of coordinated TMA in MAO serving as the precursor of the active species AlMe2+, which does not exist in non-ionic MAO until it meets electron donors such as THF or the leaving groups on metallocenes, e.g., halide, alkoxide, or alkyle.2 The coordinated TMA can now be quantified through the irreversible reaction of MAO with a so-called “coordinated TMA remover”, such as KF, which can quantitatively precipitate MAO as an ionic compound forming a 2nd liquid phase (clathrate) in the MAO solution (Reaction I). Both THF extractable AlMe2+ concentration and the activation efficiency decrease as the KF quantitatively replaces coordinated TMA. The AlMe2+ promoted activation mechanism can also be replicated through an non-MAO strong Lewis acid with a free TMA, e.g., B(C6F5)3/AlMe3 or Ph3C+B(C6F5)4-/AlMe3. Similar to MAO, these systems are unable to form AlMe2+ without the present of e-donors but capable of providing AlMe2+ for non-alkylated metallocene activation following the path of MAO activation similar to Reaction II.2c) More examples of coordinated TMA removal and regeneration will be presented and the plausible active MAO structures will be discussed.

Deactivation and reactivation of methylaluminoxane (MAO) and the derived metallocene catalysts. New insight into MAO active site structure and activation mechanism

253rd National Meeting (2017)

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