Ziegler–Natta catalysis
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:
Ziegler–Natta catalysts are used to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond):
The 1963 Nobel Prize in Chemistry in 1963 was awarded to German Karl Ziegler, for his discovery of first titanium-based catalysts, and Italian Giulio Natta, for using them to prepare stereoregular polymers from propylene. Ziegler–Natta catalysts have been used in the commercial manufacture of various polyolefins since 1956. As of 2010, the total volume of plastics, elastomers, and rubbers produced from alkenes with these and related (especially Phillips) catalysts worldwide exceeds 100 million tonnes. Together, these polymers represent the largest-volume commodity plastics as well as the largest-volume commodity chemicals in the world.
In the early 1950s workers at Phillips Petroleum discovered that chromium catalysts are highly effective for the low-temperature polymerization of ethylene, which launched major industrial technologies culminating in the Phillips catalyst. A few years later, Ziegler discovered that a combination of TiCl4 and Al(C2H5)2Cl gave comparable activities for the production of polyethylene. Natta used crystalline α-TiCl3 in combination with Al(C2H5)3 to produce first isotactic polypropylene. Usually Ziegler catalysts refer to titanium-based systems for conversions of ethylene and Ziegler–Natta catalysts refer to systems for conversions of propylene. In the 1970s, magnesium chloride was discovered to greatly enhance the activity of the titanium-based catalysts. These catalysts were so active that the residual titanium was no longer removed from the product. They enabled to the commercialization of linear low-density polyethylene (LLDPE) resins and allowed the development of noncrystalline copolymers.
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