The lower phase has, after washing with toluene, a composition of 1 diethyl ether
molecule for 8 aluminum atoms, 12 methyl groups, and 6 oxygen atoms. If the lower
phase is washed by diethyl ether the composition changes to 1 toluene molecule, 3–4
diethyl ether molecules for 16 aluminum atoms, 24 methyl groups, and 12 oxygen
atoms. Cryoscopic measurements in tetrahydrofuran results in a molecular mass of
250–300. Therefore, MAO consists mainly of units of the basic structure
[Al 4 O 3 Me 6 ], a hexa-methyl-tetra-aluminoxane, which contains four aluminum,
three oxygen atoms and six methyl groups. The ratio CH 3 /Al ¼ 1.5 for MAO was
confirmed by the studies of Eilertsen, Rytter, and Ystenes [39].
As the aluminum atoms in the unit structures of MAO are coordinatively unsaturated, the units join together to form clusters and cages. These have molecular
weights from 1,200 to 1,600 (as measured by cryoscopy in benzene) and are soluble
in hydrocarbons, especially in aromatic solvents. A probably association of two and a
cage structure of four [Al 4 O 3 Me 6 ] units are shown in Figs. 3 and 4.
The association is destroyed when the complexes are treated with diethyl ether.
In the case of MAO, an ideal cluster structure of [Al 4 O 3 Me 6 ] 4 could not be isolated
although such a cluster with tertiary-butyl groups instead of methyl groups was
isolated and characterized by Barron [40, 41]. It was also possible to synthesize
similar aluminoxane with ethyl groups. This ethylaluminoxane has a molecular
Fig. 3 MAO association of
two linear unit structures:
big balls aluminium;
small balls oxygen and
methyl groups
Fig. 4 MAO cage formed by
four linear unit structures
Methylaluminoxane: Key Component for New Polymerization Catalysts
7
molecule for 8 aluminum atoms, 12 methyl groups, and 6 oxygen atoms. If the lower
phase is washed by diethyl ether the composition changes to 1 toluene molecule, 3–4
diethyl ether molecules for 16 aluminum atoms, 24 methyl groups, and 12 oxygen
atoms. Cryoscopic measurements in tetrahydrofuran results in a molecular mass of
250–300. Therefore, MAO consists mainly of units of the basic structure
[Al 4 O 3 Me 6 ], a hexa-methyl-tetra-aluminoxane, which contains four aluminum,
three oxygen atoms and six methyl groups. The ratio CH 3 /Al ¼ 1.5 for MAO was
confirmed by the studies of Eilertsen, Rytter, and Ystenes [39].
As the aluminum atoms in the unit structures of MAO are coordinatively unsaturated, the units join together to form clusters and cages. These have molecular
weights from 1,200 to 1,600 (as measured by cryoscopy in benzene) and are soluble
in hydrocarbons, especially in aromatic solvents. A probably association of two and a
cage structure of four [Al 4 O 3 Me 6 ] units are shown in Figs. 3 and 4.
The association is destroyed when the complexes are treated with diethyl ether.
In the case of MAO, an ideal cluster structure of [Al 4 O 3 Me 6 ] 4 could not be isolated
although such a cluster with tertiary-butyl groups instead of methyl groups was
isolated and characterized by Barron [40, 41]. It was also possible to synthesize
similar aluminoxane with ethyl groups. This ethylaluminoxane has a molecular
Fig. 3 MAO association of
two linear unit structures:
big balls aluminium;
small balls oxygen and
methyl groups
Fig. 4 MAO cage formed by
four linear unit structures
Methylaluminoxane: Key Component for New Polymerization Catalysts
7