| Identifiers | |
|---|---|
3D model (JSmol) | |
| ChemSpider | |
| EC Number |
|
| |
| |
| Properties | |
| (Al(CH3)xOy)n | |
| Appearance | White solid |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Pyrophoric |
| GHS labelling: | |
 | |
| Warning | |
| H228,H250,H252 | |
| P210,P222,P235+P410,P240,P241,P280,P302+P334,P370+P378,P407,P413,P420,P422 | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Methylaluminoxane, commonly calledMAO, is a mixture oforganoaluminium compounds with the approximate formula (Al(CH3)O)n. It is usually encountered as a solution in (aromatic)solvents, commonlytoluene but alsoxylene,cumene, ormesitylene,[1] Used in large excess, it activates precatalysts for alkene polymerization.[2][3][4]
MAO is prepared by the incompletehydrolysis oftrimethylaluminium, as indicated by this idealized equation:[5]
After many years of study, single crystals of an active MAO were analyzed byX-ray crystallography. The molecule adopts a ruffled sheet of tetrahedral Al centers linked by triply bridging oxides.[4]
MAO is well known ascatalyst activator forolefinpolymerizations byhomogeneous catalysis. In traditionalZiegler–Natta catalysis, supportedtitanium trichloride is activated by treatment withtrimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such aszirconocene dichloride. In the mid-1970sKaminsky discovered that metallocene dichlorides can be activated by MAO (seeKaminsky catalyst).[6] The effect was discovered when a small amount of water was found to enhance the activity in the Ziegler–Natta system.
MAO serves multiple functions in the activation process. First it alkylates the metal-chloride pre-catalyst species giving Ti/Zr-methyl intermediates. Second, it abstracts a ligand from the methylated precatalysts, forming an electrophilic, coordinatively unsaturated catalysts that can undergo ethylene insertion. This activated catalyst is anion pair between a cationic catalyst and an weakly basic MAO-derived anion.[7] MAO also functions asscavenger for protic impurities.
Diverse mechanisms have been proposed for the formation of MAO and many structures as well.
