Heterogeneous ethylene polymerization

Heterogeneous Ethylene Polymerization Induced by Radiation Influence of the Catalyst Amount... 

Cp = C5(CH3)5 L = CH3Li, ether, THE or Al(CH3)3), polymerize ethylene at rates comparable to Zr(benzyl)4/AI2O3. Thus they are less active by two orders of magnitude than the zirconium-alumin-oxane systems reported recently by Kaminsky and Sinn, (22) but muchi more active than most other reported homogeneous and heterogeneous ethylene polymerization catalysts. (23, 24)... 

American and English investigators in studies121,122) proposed a model of heterogeneous ethylene polymerization on Ziegler-Natta catalysts, which takes into account the dependence of chain termination rate constants on the chain length. 

Heterogeneous Catalytic Polymerization. The preparation of polymers of ethylene oxide with molecular weights greater than 100,000 was first reported in 1933. The polymer was produced by placing ethylene oxide in contact with an alkaline-earth oxide for extended periods (61). In the 1950s, the low yield and low polymerization rates of the eady work were improved upon by the use of alkaline-earth carbonates as the catalysts (62). 

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). 

Bohm, L. L, Franke, R., Thum, G., The microreactors as a model for the description of the ethylene polymerization with heterogeneous catalysts, in Kaminsky, W., Sinn, H. (Eds.), Transition metals and organometallics as catalysts for olefln polymerization, pp. 391-403, Springer-Verlag, Berlin (1988). 

Although chromium-based ethylene polymerization catalysts have already been developed commercially, these processes are based on a heterogeneous catalyst... 

In 1951 Robert Banks and Paul Hogan of Phillips Petroleum discovered that ethylene could be polymerized under rather mild conditions of temperature and pressure to afford high molecular weight polyethylene using chromium trioxide as the catalyst. This invention laid the foundation for both the Phillips and Union Carbide processes for ethylene polymerization (both use heterogeneous chromium catalysts). 

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 Ziegler-Natta polymerization of ethylene and propylene is among the most significant industrial processes. Current processes use heterogeneous catalysts formed from Ti(IH)Cl3 or MgCl2-supported Ti(IV)Cl4 and some otganoaluminum compounds. The widely accepted Cossee mechanism of ethylene polymerization is illustrated in Scheme 62. 

As already mentioned, until about the beginning of 1990 only heterogeneous catalysts have been used for the polymerization of ethylene and propylene. For ethylene polymerization the catalysts used are essentially of three types. These are the Phillips catalyst, the Union Carbide catalyst, and the Ziegler catalyst. 

Ind-amido titanium complexes with o -alkenyl functions in position 2 of the indenyl ring have been synthesized and characterized. After activation with MAO, these complexes were used as homogeneous and heterogeneous catalysts for the homopolymerization of ethylene and propylene and the co-polymerization of ethylene and 1,7-octadiene.406 A series of alkyl-, u -alkenyl-, and u -phenylalkyl-substituted Cp- and Ind-amido dichloro titanium complexes have been synthesized and characterized. The cj-phenylalkyl-substituted complexes react with LiBu to give metallacycles via a CH activation reaction on the ortho-position of the phenyl group (Scheme 305).741 742 After activation with MAO, these complexes catalyze ethylene polymerizations. The substituents on the aromatic system influence the polymerization activity of the catalysts and the properties of the polyethylene. The u -alkenyl-substituted catalysts show self-immobilization in ethylene polymerization. 

Cp[C5H4Si(Me2)CH=CH2]TiCl2 and Me2Si[OCH2CH2CH2SiMe2CH2CH2SiMe2-C5H4-TiCpCl2]2 (Scheme 453) and have been used as heterogeneous catalysts on clay minerals for ethylene polymerization.1069... 

The complex Cp2TiCl(C=CSiMe3) supported on clay minerals has been used as heterogeneous catalyst for ethylene polymerization.1069 The heterogenization of homogeneous bis-Cp catalysts for olefin polymerization in order to support these sytems for industrial applications has been studied.1499... 

Ziegler-Natta catalysts can polymerize a variety of structurally different monomers. Examples of stereoregular homopolymers (Table IV), elastomeric or crystalline copolymers, as well as block copolymers may be found in the patent and open literature (, 49-51). Ethylene polymerizes easily with many soluble and heterogeneous Ziegler catalysts. Some ethylene-active catalysts, for example, Cp2TiCl2 + aluminum alkyl (52). are not active for a-olefin polymerizations. However, all known Ziegler catalysts that polymerize propylene are also active in ethylene polymerization. 

A heterogeneous [VCr] catalyst prepared from [VCrCp3(CO)3] on Si02 was used as an ethylene polymerization catalyst... 

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