Supported Ziegler-Natta Catalysts

Czaja, K. and Bialek, M., Vanadium-based Ziegler-Natta Catalyst Supported on MgCl2(THF)2 for Ethylene Polymerisation , Macromol. Rapid Commun., 17, 253-260 (1996). 

The keys of these technologies have been the development of "Ziegler-Natta" catalyst support systems and the control of the polymer growth mechanism. 

Hybrid MgCf-Clays as Ziegler-Natta Catalyst Supports... 

Ramazani et al. explored the use of acid-treated bentonite, prepared by refluxing the clay in hot H2SO4 for 2h, as a Ziegler-Natta catalyst support. The modified clay was dried at 200°C, then treated with AIR3 (R = Et, Bu) to create a supported aluminoxane... 

Schematic representation of in situ polymerization of PE (a) directly and exclusively from the Ziegler-Natta catalyst supported on the palygorskite surface ("macromolecular comb" structure) or (b) also from a second dispersed catalyst.

A typical Ziegler-Natta catalyst might be made from TiCl or TiCl and Al(C2H )3. Vanadium and cobalt chlorides are also used, as is A1(C2H3)2C1. When these substances are mixed in an inert solvent, a crystalline soHd is obtained. Early catalysts consisted of the finely divided soHd alone, but in modern catalysts, it is often supported on Si02 or MgCl2. 

Supported oxide catalysts were discovered at the same time (8-5) as the two-component Ziegler-Natta catalysts (6, 7) in the early 1950 s. The publications on other types of one-component catalysts [supported organo-metallic compounds of transition elements (8, 9, 9a) and titanium dichloride (10) ] appeared quite recently. 

Evaluation and Analysis of a Multisite Kinetic Model for Polymerization Initiated with Supported Ziegler—Natta Catalysts... 

In the following review we will focus on two classes of systems dispersed metal particles on oxide supports as used for a large variety of catalytic reactions and a model Ziegler-Natta catalyst for low pressure olefin polymerization. The discussion of the first system will focus on the characterization of the environment of deposited metal atoms. To this end, we will discuss the prospects of metal carbonyls, which may be formed during the reaction of metal deposits with a CO gas phase, as probes for mapping the environment of deposited metal atoms [15-19]. 

The world market for polypropylene is currently over 30 x 106 tons, and more than 80% of the global polymer is obtained with heterogeneous Ziegler-Natta catalysts. Over the years, these catalysts have evolved from simple TiCl3 crystals into the current systems based on MgCl2 as a support for TiCLt. 

New and improved polymerization catalysts are continuously being developed to produce polymer with higher rates and with improved properties. Early Ziegler Natta catalysts were supported on porous alumina or sihca catalyst supports. These catalysts had low activity, and large amounts of catalysts had to be used that had to be separated from the molten polymer because otherwise the catalyst would color the polymer. With high-activity catalysts, the catalyst can be left in the polymer, thus saving considerable cost in separation. 

The Ziegler-Natta catalysts are prepared by the reduction of TiIV compounds, e.g., TiCl4 or esters of titanic acid, by organoaluminum compounds. A higher catalyst activity and thus an improved polymer color is achieved by the use of MgCh as support component. 

Ziegler-Natta catalysts are not active at all in polymerization of disubstituted acetylenes.415 Mo- and W-based systems (for alkynes with small substituents) and Nb- and Ta-based catalysts (for alkynes with bulky groups), in turn, are very effective catalysts used to convert disubstituted acetylenes into polymers with very high molecular weight.414 415 A polymerization mechanism similar to that of metathesis polymerization of cycloalkenes are supported by most experimental observations.414 423 424... 

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