24 June 1996 00:00 [Source: ICB]
A new system of homogeneous catalysts developed by DSM is said to offer the advantages of metallocenes while using a lower-valency metal system.
DSM has developed an homogeneous catalyst system called Lovacat for high temperature solution polymerisation, using a lower-valency metal system than metallocene catalysts.
The catalysts are said to offer the advantages of metallocenes, such as narrow molecular weight distribution and the ability to produce a tailor-made polymer. They also offer high selectivity at elevated temperatures because of their efficiency and result in lower energy consumption.
Pilot plant trials have been carried out for EPDM production. The first commercial application will be on a new plant at Addis, Louisiana (ECN 24 June p22).
One base patent has been awarded and further patent applications have been made in the US and European countries.
After screening some metallocenes, DSM decided to develop homogeneous catalysts for the production of ethylene/alpha-olefin copolymers in high temperature solution processes.
DSM says it is difficult to find catalysts which are active at high temperatures, particularly when making polyolefins with high molecular weight. It becomes even harder when lowering the density of the polymer by increasing the alpha-olefins content. A third requirement for catalyst systems is that the molecular weight and composition distributions should stay narrow.
DSM describes the basis of the Lovacat catalysts as 'a chelating monoanionic ligand having at least one neutral electron donating group connected to the anionic moiety, in combination with a transition metal of groups 4-6 in a reduced oxidation state.'
These complexes can be used with cocatalysts such as methyl aluminoxane (MAO), borates and aluminium alklys and can be monomeric, dimeric or even a higher aggregation state, depending on the choice of ligands and metals.
Experiments performed by DSM include Ti(III) based catalysts which have substituted cyclopentadienyls as the anionic moiety. They have shown that Ti in a reduced oxidation state is the active site in the polymerisations and the molecular weight capability of these catalysts is extremely good.
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