Polymerization of olefins

When the alkylation step was recognized as essential, various alkyl-titanium compounds were employed as modified Ziegler-Natta catalysts. It is reasonably postulated that ethylene coordinates to the titanium at positions cis to the R ligand. This cis ligand orientation effect on the metal ion is essential to polymerization. 

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Tiianium(III) chloride, TiClj. Violet or brown solid (TiCU plus H3 at 700°C TiCU plus AIR3 (brown form)). Forms violet 6 hydrate. Used as a reducing agent. The fibrous brown form is an active agent in the Ziegler-Natta siereoregular polymerization of olefines. 

Ziegler-Natta polymerization Stereospecific polymerization of olefines using a Ziegler catalyst. See titanium(IIl) chloride. 

Titanium Trichloride. Titanium trichloride [7705-07-9] exists in four different soHd polymorphs that have been much studied because of the importance of TiCl as a catalyst for the stereospecific polymerization of olefins (120,124). The a-, y-, and 5-forms are all violet and have close-packed layers of chlorines. The titaniums occupy the octahedral interstices between the layers. The three forms differ in the arrangement of the titaniums among the available octahedral sites. In a-TiCl, the chlorine sheets are hexagonaHy close-packed in y-TiCl, they are cubic close-packed. The brown P-form does not have a layer stmcture but, instead, consists of linear strands of titaniums, where each titanium is coordinated by three chlorines that act as a bridge to the next Ti The stmctural parameters are as follows ... 

The exopolyhedral metaHacarborane complex Ti(C2B2QH22)4, which is prepared by the reaction of TiCl and 1-Li-1,2-C2B2QH22, has also been reported to be an active heterogeneous catalyst for the polymerization of olefins when supported on alumina and in the presence of (C2H3)2A1C1 co-catalyst (230). 

Polymerization of olefins such as styrene is promoted by acid or base or sodium catalysts, and polyethylene is made with homogeneous peroxides. Condensation polymerization is catalyzed by acid-type catalysts such as metal oxides and sulfonic acids. Addition polymerization is used mainly for olefins, diolefins, and some carbonyl compounds. For these processes, initiators are coordination compounds such as Ziegler-type catalysts, of which halides of transition metals Ti, V, Mo, and W are important examples. 

Volume 25 Catalytic Polymerization of Olefins. Proceedingsofthe International Symposium... 

Strong protonic acids can affect the polymerization of olefins (Chapter 3). Lewis acids, such as AICI3 or BF3, can also initiate polymerization. In this case, a trace amount of a proton donor (cocatalyst), such as water or methanol, is normally required. For example, water combined with BF3 forms a complex that provides the protons for the polymerization reaction. 

Catalysts developed in the titanium-aluminum alkyl family are highly reactive and stereoselective. Very small amounts of the catalyst are needed to achieve polymerization (one gram catalyst/300,000 grams polymer). Consequently, the catalyst entrained in the polymer is very small, and the catalyst removal step is eliminated in many new processes. Amoco has introduced a new gas-phase process called absolute gas-phase in which polymerization of olefins (ethylene, propylene) occurs in the total absence of inert solvents such as liquefied propylene in the reactor. Titanium residues resulting from the catalyst are less than 1 ppm, and aluminum residues are less than those from previous catalysts used in this application. 

Mejzlik, J., Lesna, M. and Kratochvila, J. Determination of the Number of Active Centers in Ziegler-Natta Polymerizations of Olefins. Vol. 81, pp. 83 — 120. 

Kennedy, J. P. and Gillham, J. K. Cationic Polymerization of Olefins with Alkylaluminium Initators. Vol. 10, pp. 1-33. 

A. Polymerization of Olefins in the Presence of Individual Organometallic Compounds. 184... 

The splitting of catalyst macrograins during the polymerization of olefins is a well-known fact (93, 113). Thus, the increase of the polymerization rate during the initial period can also result from an increase in Sett (93). 

In essence the active centers for catalytic polymerization of olefins are organometallic complexes of transition metals. For this reason a search for individual organometallic compounds that would possess catalytic activity in olefin polymerization is of great interest. The first attempts to use organometallic compounds of transition metals as catalysts for olefin polymerization were made long ago [e.g. CH3TiCl3 as a catalyst for polymerization of ethylene 116). However, only in recent years as a result of the application of relatively stable organometallic compounds of transition... 

The study of catalytic polymerization of olefins performed up to the present time is certain to hold a particular influence over the progress of the concepts of the coordination mechanism of heterogeneous catalysis. With such an approach the elementary acts of catalytic reaction are considered to proceed in the coordination sphere of one ion of the transition element and, to a first approximation, the collective features of solids are not taken into account. It is not surprising that polymerization by Ziegler-Natta catalysts is often considered together with the processes of homogeneous catalysis. 

V. I. Komarewsky and J. R. Coley Polymerization of Olefins from Cracked Gases... 

The behavior of kinetic systems with even a few interacting species can become very complex. L. Ber nek treats a few key principles and accompanies them with experimental observations in Kinetics of Coupled Heterogeneous Catalytic Reactions. In One-Component Catalysts for Polymerization of Olefins, Yu. Yermakov and V. Zakharov review results... 

Kennedy, J. P. Cationic polymerization of olefins A critical inventory. New York Wiley-Interscience PubL 1975... 

Kennedy JP (1975) Cationic Polymerization of Olefines A Critical Inventury. Wiley, New York... 

Much of the recent interest in insertion reactions undeniably stems from the emphasis placed on development of homogeneous catalysis as a rational discipline. One or more insertion is involved in such catalytic processes as the hydroformylation (31) or the polymerization of olefins 26, 75) and isocyanides 244). In addition, many insertion reactions have been successfully employed in organic and organometallic synthesis. The research in this general area has helped systematize a large body of previously unrelated facts and opened new areas of chemistry for investigation. Heck 114) and Lappert and Prokai 161) provide a comprehensive compilation and a systematic discussion of a wide variety of insertion reactions in two relatively recent (1965 and 1967) reviews. 

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