Methylaluminoxane

Source: Wikipedia, the free encyclopedia.
Methylaluminoxane
Identifiers
3D model (
JSmol
)
ChemSpider
EC Number
  • 485-360-0
  • InChI=1S/CH3.Al.O/h1H3;;
    Key: CPOFMOWDMVWCLF-UHFFFAOYSA-N
  • C[Al]=O
Properties
(Al(CH3)xOy)n
Appearance White solid
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Pyrophoric
GHS labelling:
GHS02: Flammable
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 their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Methylaluminoxane, commonly called MAO, is a mixture of

aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene,[2] Used in large excess, it activates precatalysts for alkene polymerization.[3][4]

Preparation and structure

MAO is prepared by the incomplete hydrolysis of trimethylaluminium, as indicated by this idealized equation[5]

n Al(CH3)3 + n H2O → (Al(CH3)O)n + 2n CH4

Diverse mechanisms have been proposed for the formation of MAO.[6] Well defined analogues of MAO can be generated with tert-butyl substituents.[7][8]

Aluminoxane with OH groups (R = tert-Bu).

Uses

MAO is well known as

titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconacene dichloride. In the mid-1970s Kaminsky discovered that metallocene dichlorides can be activated by MAO (see Kaminsky catalyst).[9]
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 an

ion pair between a cationic catalyst and an weakly basic MAO-derived anion. [10] MAO also functions as scavenger
for protic impurities.

See also

References

  1. PMID 11749269
    .
  2. ^ "MAO Datasheet" (PDF). Albemarle. Archived from the original (PDF) on 2004-04-11.
  3. doi:10.1016/S0926-860X(01)00829-8
    .
  4. doi:10.1039/A800056E
    .
  5. ^ Process for the preparation of aluminoxanes – Patent EP0623624
  6. PMID 17177432
    .
  7. doi:10.1021/om00020a011
    .
  8. doi:10.1021/ja00065a005
    .
  9. doi:10.1002/anie.197606301
    .
  10. doi:10.1002/anie.198003901
    .

Further reading

  1. Ziegler, T.; Zurek, E. (2004). "Theoretical studies of the structure and function of MAO (methylaluminoxane)".
    doi:10.1016/j.progpolymsci.2003.10.003
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Methylaluminoxane&oldid=1173122765"