Stereospecific polymerization discovery

Discovery of Linear (High-Density) Polyethylene Use of Comonomers Linear Low-Density Polyethylene Stereospecific Polymerization Discovery of Polypropylene Manufacturing Processes High-Pressure LDPE Low-Pressure, Linear HOPE LLDPE... 

Also in the 1980s, the discovery of homogeneous stereospecific catalysts for the polymerization of 1-alkenes has opened up new prospects for research on stereospecific polymerization and stereoregular polyolefins. Ewen and coworkers79 achieved this discovery on the basis of earlier research on metallocenes in combination with alkyl-Al-oxanes by Sinn and Kaminsky.10... 

He was a Professor of Industrial Chemistry, School of Engineering, Polytechnic Institute of Milan, Milan, Italy since 1937. He became involved with applied research, which led to the production of synthetic rubber in Italy, at the Institute in 1938. He was also interested in the synthesis of petrochemicals such as butadiene and, later, oxo alcohols. At the same time he made important contributions to the understanding of the kinetics of some catalytic processes in both the heterogeneous (methanol synthesis) and homogeneous (oxosynthesis) phase. In 1950, as a result of his interest in petrochemistry, he initiated the research on the use of simple olefins for the synthesis of high polymers. This work led to the discovery, in 1954, of stereospecific polymerization. In this type of polymerization nonsymmetric monomers (e.g., propylene, 1-butene, etc.) produce linear high polymers with a stereoregular structure. 

Interest in optically active polymers arose from analogy with macromolecules of biological origin. In addition, there was the hope to obtain new information to clarify the stereochemical features of synthetic polymers this, in fact, did come about. Attempts to direct the course of polymerization using chiral reagents had been made already prior to the discovery of stereospecific polymerization. It was only after the 1950s, however, that the problem of polymer chirality was tackled in a rational way. The topic has been reviewed by several authors (251-257). In this section I shall try to illustrate three distinct aspects the prediction of chirality in macromolecular systems, the problems regarding the synthesis of optically active polymers, and polymer behavior in solution. 

After the Natta s discovery of highly stereospecific polymerization processes, the interest in the preparation and properties of optically active polymers has greatly increased. In fact, the use of asymmetric catalysts or monomers to obtain optically active polymers may supply interesting informations on the mechanism of steric control in stereo-specific polymerization furthermore optical activity is an useful tool to study the polymer stereoregularity and the chain conformations of polymers in the molten state or in solution. 

The research in the field of optically active addition homopolymers, which have been considered in this review, was remarkably stimulated by the discoveries of Natta and co-workers on the stereospecific polymerization, and has advanced considerably in the last ten years. 

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 discovery of. stereospecific polymerization methods, which led to the production of practically pure cis-1,4 polyisoprene (natural rubber contains 85 per cent of this isomer), raises the problem of the economic production of isoprene monomer (bPi.013 = 340c, df =0.681 >). 

IV to VIII metals and base metal alkyls of Group II or III metals (Penczek and Premia, 2012 Boor, 1979 Ciardelli, 1992). It arose from the spectacular discovery of Ziegler et al. (1955) that mixtures of titanium tetrachloride and aluminum alkyls polymerize ethylene at low pressures and temperatures and from the equally spectacular discovery by Natta (1955) that the Ziegler catalysts can stereospecifically polymerize monoolefins to produce tactic, crystalline polymers. As can be imagined, these systems can involve many combinations of catalyst components, not all of which are catalytically active or stereospecific. However, we shall be concerned here only with polymerizations involving the commercial elastomers, principally polyisoprene, polybutadiene (Duck and Locke, 1977 Zohuri et al., 2012 Teyssie et al., 1988), and the ethylene-propylene copolymers (Schobel et al., 2012 Ver Strate, 1986 Davis et al., 1996 Noordermeer, 2003 Baldwin and Strate, 1972). 

The discovery, by Ziegler, et. si., (1, 2) of stereospecific polymerization, transformed isoprene into a monomer of great commercial importance. The continuing increase in world demand for synthe.tic poLy-isoprene has catalyzed the search for less costly isoprene processes. 

Syndiotactic polystyrene (sPS) is a relatively new material discovery in semicrystalline pol5nners with a high melting point and rapid crystallization rate, which makes it possible to injection mold the material. The stereospecific polymerization was made possible by the combination of a transition metal catalyst with weakly coordinating cocatalysts, such as methylaluminoxane. The excellent balance of mechanical, electrical, solvent resistance, and dimensional stability properties combined with a relatively low price (based on styrene monomer) have made this material a competitor to existing engineering plastics. The products also have excellent heat performance and are finding application in antomotive (under the hood), electrical, and electronic connector systems. 

Another very important discovery, in 1955, was that of olefin polymerization catalyzed by soluble titanium and aluminum compounds by Ziegler and Natta. These authors were awarded the Nobel Prize for chemistry in 1963. The stereospecific polymerization of propylene, which was also discovered by Ziegler and Natta, was... 

Organometallic compounds known as Ziegler catalysts were produced industrially at rates measuring thousands of tonnes annually. Stereospecific polymerization of propylene, butylene and styrene was done by Natta in March 1954. Natta s discovery broke nature s monopoly of building macromolecules of regular structure using enzymes. 

The discovery of rare earth coordination catalysts in stereospecific polymerization not only contributes to the development of Ziegler-Natta catalysts and stereospecific polymerization from the usual d-orbital transition elements to... 

A large part of the stereospecific behavior of polymerization catalysts presented in this review can be rationalized in the framework of a stereoselectivity mechanism involving a chiral orientation of the growing chain. The discovery... 

The all cis polymerization of isoprene when carried out in hydrocarbon solvents with Li counter ions provides the most spectacular case of stereospecificity. It was reported by Stavely and his colleagues(13) in 1956, and their discovery greatly... 

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