Catalyst for ethylene polymerization

Yttrium is also finding application in laser systems and as a catalyst for ethylene polymerization. 

EinaHy, in 1976, Kaminsky and Sinn in Germany discovered a new family of catalysts for ethylene polymerization. These catalysts (ie, Kaminsky catalysts) contain two components a metallocene complex, usually a zkconocene, and an organoaluminum compound, methylaluminoxane (8,9). These catalysts and thek various later modifications enable the synthesis of ethylene copolymers with a high degree of branching uniformity. Formally classified as MDPE, LLDPE, or VLDPE, the resins thus produced have a number of properties that set them apart from common PE resins in terms of performance... 

In several papers (51, 84, 96, 104) the decrease of the polymerization rate with time was assumed to be caused by the decrease of C as a result of diffusional restrictions due to the formation of a polymer film on the catalyst surface. However, as a matter of experience in work with heterogeneous catalysts for ethylene polymerization, it is known that even for polymerization with no solvent, the formation of a solid polymer is possible at high rates (thousands of grams of polymer per gram of catalyst per hour) that are constant until large yields are reached (tens of kilograms of polymer per gram of catalyst). 

CHfrSiCH , and -CH2OCH3. Tetrakis-component catalyst for ethylene polymerization after activation by exposure to light. 

Nickel(II) complexes of ligands 38 (R=H,Me R =H,Me,Et,Tr,CH30 R =H, CH3O R =H, F, CH3O) are highly active catalysts for ethylene polymerization [86,159], whereas palladium(II) complexes possess catalytic properties in the copolymerization of CO and alkenes [160] (Scheme 36). 

Synthesis of active Ni(II) a-diimine catalysts for ethylene polymerization study on substituent and cocatalyst effects... 

The Phillips catalyst has attracted a great deal of academic and industrial research over the last 50 years. Despite continuous efforts, however, the structure of active sites on the Phillips-type polymerization systems remains controversial and the same questions have been asked since their discovery. In the 1950s, Hogan and Banks [2] claimed that the Phillips catalyst is one of the most studied and yet controversial systems . In 1985 McDaniel, in a review entitled Chromium catalysts for ethylene polymerization [4], stated we seem to be debating the same questions posed over 30 years ago, being no nearer to a common view . Nowadays, it is interesting to underline that, despite the efforts of two decades of continuous research, no unifying picture has yet been achieved. 

Discovery of Highly Active Molecular Catalysts for Ethylene Polymerization... 

A large number of transition metal complexes whose cationic complexes are 10- to 16-electron species (including those with the ligands summarized in Fig. 7) were investigated to determine their potential as ethylene polymerization catalysts with methyaluminoxane (MAO) activation at 25 °C under atmospheric pressure. As a result, we discovered a number of high-activity catalysts for ethylene polymerization that contain electronically flexible ligands [11]. 

At 24 °C and 15-60 bar ethylene, [Rh(Me)(0H)(H20)Cn] catalyzed the slow polymerization of ethylene [4], Propylene, methyl acrylate and methyl methacrylate did not react. After 90 days under 60 bar CH2=CH2 (the pressure was held constant throughout) the product was low molecular weight polyethylene with Mw =5100 and a polydispersity index of 1.6. This is certainly not a practical catalyst for ethylene polymerization (TOP 1 in a day), nevertheless the formation and further reactions of the various intermediates can be followed conveniently which may provide ideas for further catalyst design. For example, during such investigations it was established, that only the monohydroxo-monoaqua complex was a catalyst for this reaction, both [Rh(Me)3Cn] and [Rh(Me)(H20)2Cn] were found completely ineffective. The lack of catalytic activity of [Rh(Me)3Cn] is understandable since there is no free coordination site for ethylene. Such a coordination site can be provided by water dissociation from [Rh(Me)(OH)(H20)Cn] and [Rh(Me)(H20)2Cn] and the rate of this exchange is probably the lowest step of the overall reaction.The hydroxy ligand facilitates the dissociation of H2O and this leads to a slow catalysis of ethene polymerization. 

Figure 14.6 A heterobimetallic Ti-Mg silsesquioxane, a homogeneous catalyst for ethylene polymerization after AlEtj activation, a possible model for the heterogeneous catalyst TiCl4/MgCl2/Si02 (one of the proposed surface structures) and a patented route to precatalyst, active after activation with MAO.

The initiation of polymerizations by metal-containing catalysts broadens the synthetic possibilities significantly. In many cases it is the only useful method to polymerize certain kinds of monomers or to polymerize them in a stereospecific way. Examples for metal-containing catalysts are chromium oxide-containing catalysts (Phillips-Catalysts) for ethylene polymerization, metal organic coordination catalysts (Ziegler-Natta catalysts) for the polymerization of ethylene, a-olefins and dienes (see Sect. 3.3.1), palladium catalysts and the metallocene catalysts (see Sect. 3.3.2) that initiate not only the polymerization of (cyclo)olefins and dienes but also of some polar monomers. 

Title Catalyst for Ethylene Polymerization, Preparation Thereof, and Method for Controlling the Polymerization Kinetic Behavior of Said Catalyst... 

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