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Ziegler-Natta (ZN) Catalysts

The Ziegler-Natta catalysts of today originated in 1953 when Karl Ziegler of the Max Planck Institute, Germany, found that nickel in combination with triethylaluminum (TEAL) dimerized olefins. This prompted a survey of the effect of other transition metals. It was discovered that Group IV metals, especially titanium, were effective polymerization catalysts for ethylene. Following Ziegler’s successful preparation of linear polyethylene in 1953, Giulio Natta prepared an isolated isotactic (crystalline) polypropylene at the Milan Polytechnic Institute. This was immediately recognized for its practical importance. Ziegler and Natta shared the Nobel Prize in Chemistry in 1963.

A Ziegler-Natta catalyst is composed of at least two parts: a transition metal component and a main group metal alkyl compound. The transition metal component is usually either titanium or vanadium. The main group metal alkyl compound is usually an aluminum alkyl. In common practice, the titanium component is called "the catalyst’ and the aluminum alkyl is called "the co-catalyst". However, it is really the combination of the two which form the active catalyst.

In some instances, especially for catalyzing the polymerization of propylene, a third component is used. This component is used to control stereoregularity and can either be incorporated into the catalyst during its synthesis (internal donor) or can be added to the polymerization reactor with the catalyst during the polymerization (external donor). Aromatic esters can be used as internal donors. Aromatic esters, alkoxysilanes and hindered amines can be used as external donors.

Ziegler and Natta’s work to demonstrate that the stereoregular polymerization of polypropylene could be achieved opened the scientific floodgates. An explosion of new chemistry, processes, and new products engulfed the world, virtually overnight. While in 1950, no one had ever seen crystalline PP, there were by 1960 several commercial producers, delivering some 50,000 tons of PP into several rapidly expanding applications. Today, Ziegler-Natta catalysts are used worldwide to produce the following classes of polymers from alpha olefins:

  • High density polyethylene (HDPE)
  • Linear low density polyethylene (LLDPE)
  • Ultra-high molecular weight polyethylene (UHMWPE)
  • Polypropylene (PP) homopolymer, random copolymer and high impact copolymers
  • Thermoplastic polyolefins (TPO’s)
  • Ethylene propylene diene monomer polymers (EPDM)
  • Polybutene (PB)
AkzoNobel has a long history in metal alkyl co-catalysts, starting with large-scale production of aluminum alkyls in 1959, using technology licensed by Karl Ziegler. Today, we're one of the world's top producers of metal alkyls, including aluminum, magnesium, boron and zinc alkyls.

Contact us for more information.