chemistry

Methylaluminoxane

Methylaluminoxane is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Methylaluminoxane rather than just read about it. In short: Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH3)O)n. It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization.

Key takeaways

Methylaluminoxane belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Methylaluminoxane to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Methylaluminoxane from memory before moving on to harder problems.

Reference excerpt

Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH3)O)n. It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization.

Preparation and structure

MAO is prepared by the incomplete hydrolysis of trimethylaluminium, as indicated by this idealized equation:

n Al(CH3)3 + n H2O → (Al(CH3)O)n + 2n CH4 After many years of study, single crystals of an active MAO were analyzed by X-ray crystallography. The molecule adopts a ruffled sheet of tetrahedral Al centers linked by triply bridging oxides.

Uses MAO is well known as catalyst activator for olefin polymerizations by homogeneous catalysis. In traditional Ziegler–Natta catalysis, supported titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconocene dichloride. In the mid-1970s Kaminsky discovered that metallocene dichlorides can be activated by MAO (see Kaminsky catalyst). 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. MAO also functions as scavenger for protic impurities.

Previous studies Diverse mechanisms have been proposed for the formation of MAO and many structures as well.

Chen, E. Y.-X.; Marks, T. J. (2000). "Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure-Activity Relationships". Chem. Rev. 100 (4): 1391–1434. doi:10.1021/cr980462j. PMID 11749269. Lacramioara Negureanu; Randall W. Hall; Leslie G. Butler & Larry A. Simeral (2006). "Methyaluminoxane (MAO) Polymerization Mechanism and Kinetic Model from Ab Initio Molecular Dynamics and Electronic Structure Calculations". J. Am. Chem. Soc. 128 (51): 16816–16826. Bibcode:2006JAChS.12816816N. doi:10.1021/ja064545q. PMID 17177432. Harlan, C. Jeff; Mason, Mark R.; Barron, Andrew R. (1994). "Tert-Butylaluminum Hydroxides and Oxides: Structural Relationship between Alkylalumoxanes and Alumina Gels". Organometallics. 13 (8): 2957–2969. doi:10.1021/om00020a011. Mason, Mark R.; Smith, Janna M.; Bott, Simon G.; Barron, Andrew R. (1993). "Hydrolysis of tri-tert-Butylaluminum: The First Structural Characterization of Alkylalumoxanes [(R2Al)2O]n and (RAlO)n". Journal of the American Chemical Society. 115 (12): 4971–4984. Bibcode:1993JAChS.115.4971M. doi:10.1021/ja00065a005. Ziegler, T.; Zurek, E. (2004). "Theoretical studies of the structure and function of MAO (methylaluminoxane)". Progress in Polymer Science. 29 (2): 107–198. doi:10.1016/j.progpolymsci.2003.10.003.

Illustrations

Worked examples

Example 1 — a first encounter with Methylaluminoxane

Start with the simplest possible case. Write down what Methylaluminoxane claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Methylaluminoxane before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Methylaluminoxane ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Methylaluminoxane

In research: Methylaluminoxane appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Methylaluminoxane in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Methylaluminoxane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium compounds, Catalysts, Methyl compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Methylaluminoxane outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Methylaluminoxane in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Methylaluminoxane means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Methylaluminoxane out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Methylaluminoxane in simple terms?

Why does Methylaluminoxane matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Methylaluminoxane?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Methylaluminoxane.