Supported Metallocene Catalysts

Metallocene catalysts supported on SiC>2 are practically free of chlorine. This could be an advantage from an ecological standpoint when the chemical or thermal recycling of polymeric products reaches a large scale [211]. 

Acid-Treated Clays as Metallocene Catalyst Supports... 

Nakano, H., Takahashi, T., Uchino, H., Tayano, T., and Sugano, T. 2006. Polymerization behavior with metallocene catalyst supported by clay mineral activator. In Progress in Olefin Polymerization Catalysts and Polyolefin Materials, T. Shiono, K. Nomura, and M. Terano (eds.), pp. 19-24, vol. 161. Amsterdam, the Netherlands Elsevier... 

Moreno, J. Van Grieken, R. Carrero, A. Paredes, B., Ethylene Polymerization by Metallocene Catalysts Supported over Materials with Bimodal Pore Size Distributions. Macromol. Symp. 2011, 302,198-207. 

Marques et al. [76] also showed that when SiMe2(2-Me-Ind)2ZrCl2 was supported on Cloisite 15A, the propylene activity was remarkably decreased. This behavior is in agreement with what has been reported for metallocene catalysts supported on other carriers, such as Si02 and MgCh. 

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

Eluidized-bed reactors are highly versatile and can accommodate many types of polymerization catalysts. Most of the catalysts used for LLDPE production are heterogeneous Ziegler catalysts, in both supported and unsupported forms. The gas-phase process can also accommodate supported metallocene catalysts that produce compositionaHy uniform LLDPE resins (49—51). 

The goal of precise synthesis of supported mononuclear and polynuclear metal complexes can be traced to the early work of Yermakov [1], Ballard [2], and others. Their work stimulated the hvely field referred to as surface organometalhc chemistry [3-6]. The success and importance of precise synthesis of supported molecular catalysts are illustrated by the apphcation of supported metallocene catalysts for industrial alkene polymerization [7j. 

Figure 34 A polymer-supported metallocene catalyst (51) with a weakly coordinating anion, [B(C6F5)4] , produced from lightly cross-linked, chloromethylated polystyrene beads for olefin polymerization. (Adapted from ref. 75.)...

UNIPOL [Union Carbide Polymerization] A process for polymerizing ethylene to polyethylene, and propylene to polypropylene. It is a low-pressure, gas-phase, fluidized-bed process, in contrast to the Ziegler-Natta process, which is conducted in the liquid phase. The catalyst powder is continuously added to the bed and the granular product is continuously withdrawn. A co-monomer such as 1-butene is normally used. The polyethylene process was developed by F. J. Karol and his colleagues at Union Carbide Corporation the polypropylene process was developed jointly with the Shell Chemical Company. The development of the ethylene process started in the mid 1960s, the propylene process was first commercialized in 1983. It is currently used under license by 75 producers in 26 countries, in a total of 96 reactors with a combined capacity of over 12 million tonnes/y. It is now available through Univation, the joint licensing subsidiary of Union Carbide and Exxon Chemical. A supported metallocene catalyst is used today. 

The cyclopentadienyl group is another interesting ligand for immobilization. Its titanium complexes can be transformed by reduction with butyl lithium into highly active alkene hydrogenation catalysts having a TOF of about 7000 h 1 at 60 °C [85]. Similar metallocene catalysts have also been extensively studied on polymer supports, as shown in the following section. 

Silica-supported catalysts, 23 54-55 Silica-supported metallocene catalysts, 76 88... 

The three-dimensional electron tomographical construction of silica-supported metallocene catalysts using conventional TEM (Steinmetz et al 2000), and a novel method for the automated acquisition of tilt series for electron tomography of nanoparticles using STEM have been reported (Zeisse et al 2000). The HAADE-STEM is shown to be capable of determining the compositions of individual nanoparticle catalysts of a few atoms supported on porous substrates (Vaughan et al 1999). 

Covalently attaching molecular catalysts to supports is a method that can minimize catalyst leaching. In 1998, a PS-supported titanocene was prepared by Barrett and de Miguel, which displayed 41 g-PE mmol-Ti h of activity. Soga and co-workers reported a series of poly(siloxane)-supported metallocene catalysts. These supported catalysts combined with MAO were found to have high activity for the (co)polymerization of ethylene, propylene, and ethylene/l-octene, though the reaction products typically displayed broad molecular weight distributions. ... 

A unique immobilization strategy was developed by Alt, who synthesized metallocenes with alkene functionalities and employed these functionalized metallocene catalysts for polymerization. During the polymerization process, the metallocene catalysts are consumed as a co-monomer, leading to the generation of polymer-supported metallocene catalysts. 

The ansa-sandwich complexes, sometimes called constrained-geometry catalysts, exhibit a good ability to incorporate co-monomers. The catalysts (a) to (g) are soluble in solvents such as toluene. In the catalyst (h) the metallocene is supported on silica. Such solid-supported catalysts can be suspended in hydrocarbons for metering into the polymerization reactor [4],... 

Polypropylenes, and metallocene catalysts amorphous PP, 4, 1052 flexible and elastomeric isotactic PP, 4, 1064 isotactic PP, 4, 1056 syndiotactic PP, 4, 1070 Polypyrroles, with ferrocene groups, 12, 305 Polypyrrole supports, for diphosphine borane complex,... 

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