Methylaluminoxane

Methylaluminoxane or MAO is a term introduced by Walter Kaminsky and Hansjörg Sinn cocatalyst for highly active Ziegler -Natta catalysts ( Kaminsky catalysts) metallocene-based.

Production

MAO (3 x 18 H 2 O, for example, Al2 (SO4 ) ), or prepared by the partial hydrolysis of trimethylaluminum with hydrated salts by controlled addition of ice.

A defined structure for MAO can not be specified, it is much more a mixture of linear, cyclic and polycyclic complex units. These oligomers have an average molecular weight of about 1000 g · mol -1.

Properties

MAO is also pyrophoric and reacts violently with any substance that contributes acidic protons. Use of MAO found in solution of aromatic hydrocarbons due to good solubility. It is usually sold as a solution in toluene, as well as xylene, cumene or mesitylene provide good solvent represents the solubility of MAO is highly dependent on the content of trimethylaluminum which is up to five percent by weight of the solution is usually contained as the precursor in portions. A MAO toluene solution is clear to opaque and reacts with air to form dense smoke.

The structure of MAO is little known, making it probably a variety of oligomers in solution.

Application

MAO is used as cocatalyst for olefin polymerization using metallocene complexes. It is believed that the MAO metallocene converted by di- methylation followed by abstraction of a Methylanions in a squatting active Metallocenmethyl cationic species.

The Ziegler- Natta process, methylaluminoxane has three functions:

• It alkylates the transition metal
• It acts as a Lewis acid and creates a vacant coordination site by elimination of a halide or alkyl anion
• It acts as a cleaning agent, by reacting with impurities (H2O, CO2)