Ziegler-Natta catalysts discovery

One of the landmark discoveries in catalytic chemistry was the Ziegler-Natta catalyst. The award of the Nobel prize in chemistry in 1963 to Ziegler and... 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

Since the discovery of steric control and the development of Ziegler-Natta catalysts, there has been considerable research on the mechanism of steric control. An attempt to review all of the pertinent literature on this topic would be a gigantic job, completely out of the scope of this paper. In the reviews by Kennedy and Langer (1), Roha (2), Bawn and Led with (3) and Bier (4) much of the past information has already been summarized and discussed, including some of the roles played by ionic factors. 

Homogeneous alkylaluminium (alkylaluminoxane)-free olefin polymerisation catalysts are commonly referred to as catalysts containing group 4 metallocene cationic species. These catalysts resemble the structure and properties of the respective metallocene-based Ziegler-Natta catalysts but, by definition, are not included among the latter catalysts. The development of alkylaluminium-free metallocene-based olefin polymerisation catalysts is connected with discoveries... 

Since the discovery of Ziegler-Natta catalysts, polyolefin industries have been developed mainly by using titanium-based catalysts. However, after the appearance of metallocene catalysts, much emphasis has been placed on those based on zirconium owing to the superiority of their performance over titano-cene catalysts. 

Ever since their original discoveries, Ziegler Natta catalysts and Phillips catalysts have been used for both the homopolymerisation and the copolymerisation of olefins. Moreover, Ziegler-Natta catalysts also allowed the copolymerisation of olefins with vinylaromatic monomers, conjugated dienes and cycloolefins. Other coordination catalysts such as group 8 metal compounds, especially cationic Pd(II) complexes, enabled the alternating copolymerisation of olefins and carbon monoxide [2,29,30,37,43,46,241,448 450],... 

Commercial polystyrene, one of the most representative general-purpose resins, is an amorphous atactic polymer with no melting point (softening temperature ca 100 °C, glass transition temperature ca 70-100 °C). Since the discovery of Ziegler-Natta catalysts, many efforts to produce stereoregular polystyrenes have been made. 

However, no method of polymerisation known before 1954 allowed one to obtain polymers with a high regularity of structure from the most common conjugated dienes. A true breakthrough in the development of conjugated diene rubbers took place after the discovery of stereospecific polymerisation with transition metal-based coordination catalysts. From the late 1950s, a rapid development of industrial production of solution types of polybutadiene by means of polymerisation with Ziegler-Natta catalysts was observed. 

Cince the discovery of Ziegler-Natta catalysts, the efforts of many sci- entists have been directed toward elucidating the mechanism of stereospecific polymerization. As a result of extensive investigations during the last decade a theory of stereospecific polymerization has been proposed. Some authors (2, 11,16) suggest that 7r-complexes participate in polymerization. However, since not all results can be explained using the proposed hypotheses, further investigations seem worthwhile. 

The remarkable stability of the 1,1-dichlorocyclopropane system has been recognized ever since the discovery of the carbenes has enabled them to be prepared easily (6). The structure is, however, destroyed by Lewis acids (27). Therefore, polymerizations were first carried out using cationic catalysts and then Ziegler-Natta catalysts which give better results. A first group of monomers consists of 2,2-dimethyl-, 2,2,3-tri-... 

The discovery of active magnesium chloride as the ideal support for the fixation of titanium tetrachloride and its derivatives opened a new era in the field of Ziegler-Natta catalysis, both from the industrial and the scientific viewpoint. During the last 15 years MgCl2-supported catalysts brought about revolutionary industrial developments, as compared to those of the traditional Ziegler-Natta catalysts. 

Ziegler-Natta catalysts made it possible to obtain linear polyethylene and isotactic polypropylene under mild reaction conditions however, they are not active enough to avoid the need for polymer deashing. Consequently, many efforts were undertaken in order to overcome this drawback and different directions were followed. One of these was aimed at improving the activity of TiCl3, and led to the discovery of crystalline forms of TiClg which are more active and stereospecific than those... 

Chemists were unable to synthesize rubber with useful mechanical properties until the discovery of Ziegler-Natta catalysts in 1953. 

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