Stereoregular polymerization olefins

Many studies, the first of which began shortly after the discovery of stereoregular polymerization of olefins, demonstrated that macromolecules could adopt stable helical conformations not only in the solid state but also in solution. These efforts have led to the realization that certain helical polymers reach a level of chiral recognition adequate for commercial development as an important aspect of chromatography. Researchers from the leading laboratory in this field, Okamoto, Yashima, and Yamamoto, have written Chapter 3 painting a detailed picture of the current status and future possibilities in this... 

In the early 1950s Karl Ziegler in Germany and Giulio Natta in Italy found catalysts that polymerized olefins and dienes with stereoregularity and with mild polymerization conditions. For this revolutionary discovery they both won the Nobel Prize. Let us take the example of propylene, which we... 

Figure 9 Non-metallocene complexes for stereoregular o-olefin polymerization.

Previously, we synthesized and studied various Group 4 complexes with different ligations as alternatives to the cyclopentadienyl ligand. Here we present an overview of the synthesis, structure, and catalytic properties in the polymerization of a-olefins of several zirconium octahedral complexes. We show how the stereoregular polymerization of a-olefins using these octahedral zirconium complexes can be modulated by pressure. These results raise conceptual questions regarding the general applicability of ds-octahedral C2-sym-metry complexes to the stereospecific polymerization of a-olefins. 

Before the 1970s, Ziegler-Natta catalysts for a-olefin production were normally prepared from certain compounds of transition metals of Groups IV-VI of the periodic table (Ti, V, Cr, etc.) in combination with an organoraetallic alkyl or aryl (Table I). Practically all subhalides of transition metals have been claimed as catalysts in stereoregular polymerization. Only those elements with a first work function <4 eV and a first ionization potential <7 V yield sufficiently active halides, that is, titanium, vanadium, chromium, and zirconium (7, Only titanium chlorides have gained widespread acceptance in crystalline polyolefin production. 

An evaluation of the electronic, steric, and stereochemical factors involved in the kinetics and thermodynamics of this kind of process may be most helpful in elucidating the course of the Ziegler carbometallation process [Eq. (5)], central to the industrial production of long-chain alcohols and olefins from ethylene and to the stereoregular polymerization of a-olefms (18, 21). 

Many attempts have been made to explain the stereoregular polymerization of a-olefins. An excellent discussion of the various hypotheses advanced prior to 1962 has been published by Bawn and Ledwith (1962). No effort will be made here to review different mechanistic schemes which in this writer s opinion are superseded by the theory advanced by Cossee (1964) and Arlman (1964). 

Stereoregular a-olefin polymerization by early transition metal Ziegler-type compounds was first reported in 1955 by Natta et al. Since then, major industrial and academic research efforts have focused mainly on the development of highly efficient, stereoselective catalyst systems for propylene polymerization. Concurrently, the polymerization of higher a-olefins was also investigated, with the hope of revealing new opportunities in the field of polymeric materials. 

Multicomponent Polymer Systems Polymerization - Depolymerization Equilibria Copolymers of - Olefins Medical Applications of Plastics Scanning Electron Microscopy Kinetics and Mechanism of Stereoregular Polymerization Glass Transition Phenomena in Plastics and Coatings Properties of Polymers in Interfaces... 

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