Ziegler-Natta polymerization catalysis

Key words Olefin polymerization, Ziegler-Natta catalysis... 

Solution and emulsion polymerization Ziegler-Natta catalysis Mostly cis configuration... 

Under the reaction conditions employed, the oligomerization is living the aluminium is removed from the chain in a separate process step [2]. Further research on the Aufbau reaction led to the discovery of transition metal catalyzed olefin polymerization (Ziegler-Natta catalysis) [3]. 

Alkene polymerization Ziegler-Natta catalysis and metallocene catalysts... 

Stable transition-metal complexes may act as homogenous catalysts in alkene polymerization. The mechanism of so-called Ziegler-Natta catalysis involves a cationic metallocene (typically zirconocene) alkyl complex. An alkene coordinates to the complex and then inserts into the metal alkyl bond. This leads to a new metallocei e in which the polymer is extended by two carbons, i.e. 

Several articles on these topics have appeared in earlier volumes. For the convenience of readers they are listed here. In addition, articles on Ziegler-Natta catalysis and on organolithium compounds in diene polymerization are planned for the next volume of this serial publication. 

Figure 14.6 Ziegler-Natta catalysis in the polymerization of propylene.

The versatility of Ziegler-Natta catalysis is shown in the polymerization of butadiene. Polybutadiene may have either a 1,2 or 1,4 configuration. The 1,4 polymer has a double bond as part of the main chain and this can be atactic, isotactic, or syndiotactic. Thus many different polybutadienes can be made and all of them have been made with the aid of Ziegler-Natta catalysts. 

J. Boor, Jr., Ziegler-Natta Catalysis and Polymerization, Academic Press, New York, 1979. 

One of the great discoveries of organomctallic chemistry was the catalyzed polymerization of alkenes at atmospheric pressure and ambient temperature. Vast quantities of polyethylene and polypropylene (over 15 million tons annually) are made by Ziegler-Natta catalysis. Ziegler and Natta received the Nobel prize in chemistry in 1963, and the importance of their work w stimulating interest in organometallic chemistry should not be underestimated. 

Coose P, Ziegler-Natta Catalysis I Mechanism of Polymerization of a-Olefins with Ziegler-Natta Catalyst, J Catal, 3, 80 (1964)... 

The copolymerization theory presented in Chapter is of limited applicability to processes involving heterogeneous Ziegler-Natta catalysis. The simple copolymer model assumes the existence of only one active site for propagation, whereas the supported catalysts described above have reaction sites that vary in activity and stereoregulating ability. In addition, the catalytic properties of the active sites may vary with polymerization time. The simple copolymer model can be used with caution, however, by employing average or overall reactivity ratios to compare different catalysts and monomers. 

In conclusion, the theories based on the plurality of the catalytic active species appear more convincing than those based only on physical phenomena in explaining MWD. Together with some general principles, only a better knowlegde of number and types of polymerization centres and of the relevant kinetic constants could lead to a more effective MWD control. This should represent one of the future trends of research and development in Ziegler-Natta catalysis. 

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