The Heterogeneous Ziegler-Natta (ZN) catalytic process was discovered in the 1950s and is still a fundamental part of the manufacture of many plastics - e.g. polyethylene (polythene) and polypropylene. Earning the creators the 1963 Nobel Prize for Chemistry.
The process is part of a group of reactions called Coordination Polymerizations, and typically uses titanium tetrachloride (TiCl4) and an organoaluminium co-catalyst based on trialkylaluminium complexes. Sometimes magnesium chloride (MgCl2) is also used.
Because of its commercial significance, the nature of the active catalytic centre(s) has been of intense research, but has not yet been clarified.
Despite of the relevance of ZN catalysts for the large-scale production of polyolefins, a clear mechanistic understanding of these catalysts is still incomplete due to the elusive nature of the active site structures. Over the last two decades, researchers have used density functional theory (DFT) methods to clarify the polymerization mechanisms and to identify the nature of the active sites, unraveling the influence of supports, cocatalysts, and the effect of internal and external donors on the polymerization processes.
Source: Progress in Polymer Science, Volume 84, Pages 89-114
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