Aluminoxane
Encyclopedia
Aluminoxanes refer to compounds that are obtained by the partial hydrolysis of trialkylaluminium compounds. Aluminoxanes serve as activators for catalytic olefin polymerisation, such as the Ziegler-Natta catalyst
. They also serve a function as scavenger
for impurities (e.g. water
) in reactions that are sensitive to these impurities.
Examples of aluminoxanes include:
The hydrolysis
of trialkylaluminium compounds is a highly exothermic
process, and the starting trialkylaluminium compounds are often pyrophoric (i.e. burns on contact with air).
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...
. They also serve a function as scavenger
Scavenger (chemistry)
A scavenger in chemistry is a chemical substance added to a mixture in order to remove or inactivate impurities or unwanted reaction products. Their use is wide-ranged:...
for impurities (e.g. water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
) in reactions that are sensitive to these impurities.
Examples of aluminoxanes include:
- Triisobutylaluminoxane (TiBAO), formed by the hydrolysis of triisobutylaluminiumTriisobutylaluminiumTriisobutylaluminium is an organoaluminium compound with the formula Al3. This a colorless pyrophoric liquid is mainly used to make linear primary alcohols and α-olefins.-Structure:...
- MethylaluminoxaneMethylaluminoxaneMethylaluminoxane, commonly called MAO, is a white solid with the general formula n.-Physical properties:MAO is pyrophoric, and is violently reactive with any chemical bearing an acidic proton. However, MAO is generally used as a solution in an hydrocarbon due to its relatively high solubility in...
(MAO), formed by the hydrolysis of trimethylaluminiumTrimethylaluminiumTrimethylaluminium is the chemical compound with the formula Al26, abbreviated as Al2Me6, 2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound...
The hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of trialkylaluminium compounds is a highly exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
process, and the starting trialkylaluminium compounds are often pyrophoric (i.e. burns on contact with air).