Olefin Polymerisation
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Following Ziegler's ground-breaking discovery of metal catalysed olefin polymerisation in the early 1950's, metal catalysts have been used to produce polyolefin products on a massive world-wide scale (presently approaching 100 million tonnes p.a.). Until the mid-to-late 1990's, only a narrow range of metals, Ti, V and Cr, had been shown to give industrially relevant activities for polyolefin production. |
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Other relatively cheap and non-toxic metals, such as iron, had no track record of being capable of polymerising olefins. The independent discovery by ourselves and Brookhart/Bennett of iron complexes capable of affording industrially significant activities provided an important step-change in the design of new generation catalyst systems and signposted the way forward for the discovery of other new systems based on the late transition metals. The iron centres are supported by bis(imino)pyridine ligands with bulky substituents and give highly linear polyethylene with good molecular weight control. Closely related cobalt derivatives are amongst the most highly active catalysts for the Group 9 metals. It was also shown that iron catalysts bearing smaller imino substituents are highly efficient and selective for the production of linear alpha-olefins. |
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In mechanistic studies, an unusual 'chain transfer to metal' process was identified as being a key aspect of the iron-based catalyst system, differentiating it from many other highly active olefin polymerisation catalysts. This observation provided the foundation for the discovery of a highly efficient chain transfer process involving dialkylzinc, effectively an iron-catalysed Aufbaureaktion on zinc, which can be used to produce industrially significant Poisson distributions of alpha-olefins. |
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A variety of other catalyst systems have been discovered by the Group. These range from chelating diamides of zirconium to the first examples of copper-based catalysts for ethylene polymerisation. The Group has also been at the forefront of developing high throughput screening (HTS) methodology to assist polymerisation catalyst discovery. For example, the highlighted chromium complex bearing a [N,N,O] chelate ligand is exceptionally active for ethylene oligomerisation and was the first reported example of an entirely new class of catalyst discovered with the aid of HTS techniques. |
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