Methylaluminoxane: NMR analysis, cryoscopic measurements and cocatalytic ability in ethylene polymerization

Methylaluminoxane (MAO) solutions containing known amounts of AlMe3 and solutions of different MAO samples were characterized by several methods: a) low temperature C-13 NMR analysis; b) determination of the molecular weight of the MAO samples by cryoscopy in benzene; c) titration of AlMe3 using P-31 NMR analysis of the AlMe3 . PPh3 complex (PPh3 = triphenylphosphine) formed after addition of defined amounts of PPh3 to the MAO solutions. The results confirm the disproportionation reaction caused by AlMe3 addition. The MAO molecular weights are shown to decrease after the AlMe3 addition according to a linear relationship. The cocatalytic ability of these characterized MAOs was tested in ethylene polymerization catalyzed by rac-Et(ind)(2)ZrCl2 (ind = indenyl) and the influence of the AlMe3 content, the "type" and the "aging" of MAO is correlated to the cocatalytic performance.