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

Methylaluminoxane (MAO) solutions containing known amounts of AlMe 3 and solutions of different MAO samples were characterized by several methods: (a) low temperature 13 C NMR analysis; (b) determination of the molecular weight of the MAO samples by cryoscopy in benzene; (c) titration of AlMe 3 using 31 P NMR analysis of the AlMe 3 · PPh 3 complex (PPh 3 = triphenylphosphine) formed after addition of defined amounts of PPh 3 to the MAO solutions. The results confirm the disproportionation reaction caused by AlMe 3 addition. The MAO molecular weights are shown to decrease after the AlMe 3 addition according to a linear relationship. The cocatalytic ability of these characterized MAOs was tested in ethylene polymerization catalyzed by rac ‐Et(ind) 2 ZrCl 2 (ind = indenyl) and the influence of the AlMe 3 content, the “type” and the “aging” of MAO is correlated to the cocatalytic performance.