Low‐temperature 1H and 13C NMR investigation of trimethylaluminium contained in methylaluminoxane cocatalyst for metallocene‐based catalysts in olefin polymerization

Toluene‐d8 solutions of methylaluminoxane (MAO) after the addition of different amounts of trimethylaluminium (TMA) have been studied by means of 1H and 13C NMR at a temperature as low as −78°C to freeze out some of the fluxional equilibria of the molecule. A comparison of the half height width of the NMR signal W1/2 and of the mole ratio of the methyl signals before and after addition of known amounts of TMA allowed us to reach the following conclusions about the TMA contained in MAO solutions: (a) TMA is mainly bound to MAO; (b) TMA participates in disproportionation reactions.