Isotactic polypropylene, discovery

Propylene polymerization processes have undergone a number of revolutionary changes since the first processes for the production of crystalline polypropylene (PP) were commercialized in 1957 by Montecatini in Italy and Hercules in the United States. These first processes were based on Natta s discovery in 1954 that a Ziegler catalyst could be used to produce highly isotactic polypropylene. The stereoregular, crystalline polymers produced by this technology had sufficiently attractive economic and property performance that they became significant commercial thermoplastics in a remarkably short period. 

The discovery of the Ni effect led to the invention of polyethylene production catalysed by TiCI4 combined with Et3Al, the so-called the Ziegler catalyst, in 1953. Soon after, the process for isotactic polypropylene was invented by Natta using a slightly modified catalyst prepared from TiCl3 and Et3Al, which is called the Natta catalyst (eq. 1.7) [7],... 

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... 

A further breakthrough was the synthesis of enantiomeric sterorigid ansa-metallocenes by Brintzinger and co-workers [33] and the discovery by Ewen [34] that such racemic metallocene/methylalumoxane systems generate isotactic polypropylene. It was further found that the metallocene structure determines the polymer structure [35-37]. Again, with these compounds polyolefins such as syndiotactic polypropylene become available on a large scale [38]. Indeed, metallocene/methylalumoxane catalysts offer new prospects for olefin oligomers and polymers [39 2],... 

The following article discusses the history of Natta s discovery of stereoregular polymers P. Corradini, The Discovery of Isotactic Polypropylene and Its Impact on Pure and Applied Science, J. Polym. Sci., Part A, Polym. Chem., 2004, 42, 391. 

Staudinger predicted a correlation between the physical properties of a polymer and its main-chain stereochemistry as early as 1929. Flowever it was not imtil 1947 that Schildknecht reported the first stereoregular synthetic polymer. - Amidst considerable controversy, he attributed the crystalline properties of a polyfisobutyl vinyl ether) to an ordered stereochemistry, or tacticity, of the polymer backbone. In 1954, research in the field of stereoregular polymers gained a tremendous amormt of momentum when Natta discovered the synthesis of a crystalline isotactic polypropylene using a heterogeneous or-ganometallic catalyst. Since these initial discoveries, the synthesis of polymers of defined stereochemistry... 

Since the discovery of Ziegler-Natta catalyst, isotactic polypropylene has been widely used as a commodity material due to its low cost and excellent physical properties. As the modulus of the resin is closely related to isotacticity, an understanding in polymerization mechanism is important in the chemistry of propylene polymerization as well as in the industry. 

Discovery of isotactic polypropylene (PP) in 1954 started a search for methods to improve its low-temperature impact strength [1, 2]. These activities commenced in the late 1950s by blending PP with poly-ethylenes (PE) or elastomers, then by copolymerizing it with ethylene into ethylene-propylene rubber (EPR) and ethylene-propylene-diene (EPDM). 

The significance of these developments was two-fold. On the one hand, these discoveries first established that it was possible to produce isotactic polypropylene with homogeneous catalysts, thus opening the possibility for the development of a new generation of stereospecific olefin polymerization catalysts. 

Discovery of low pressure polyethylene and isotactic polypropylene 60 years ago started a material revolution that has improved the quality of life for nearly all people on earth. Today, these polyolefin materials account for more than 50% of all synthetic materials produced, ranging from commodities to various engineering level materials. The common denominator for all high-end polyolefin materials is the use of the most advanced catalyst and process technologies for manufacturing. 

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