Reactive Organotransition Metal Complexes Used In

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Reactive Organotransition Metal Complexes Used in Catalysis for Olefin Polymerization Reactions I. Introduction Since the discovery of the polymerization of ethylene with TiCl4-AlR3 by Ziegler combined with Natta's discovery of the stereoselective polymerization of propene nearly forty years ago, -olefin polymerization has become a giant industry. In 1995, the world production of polyolefins was estimated to be 53.6 million tons, and is expected to grow by 50% by 2005.1 The conventional heterogeneous catalysts on which this industry is based have made great improvements in selectivity and efficiency since their development. Traditional heterogeneous Ziegler-Natta catalyst polymerize olefins on dislocations and edges of TiCl3 crystals resulting in many different types of active sites. As a result, the polymer products from these systems have a typically broad molecular weight distribution (MWD) and incorporate comonomer unevenly throughout the polymer chains. The accepted mechanism for polymerization of -olefins by conventional Ziegler-Natta catalysts is depicted in Scheme 1.

The broad MWD is generally associated with a wide range of polymer products, and the variety of active sites in heterogeneous catalysts leads to an uneven degree of comonomer incorporation.1 Homogeneous metallocene catalysts are able to overcome these disadvantages. The "single-sited" character of these catalysts exhibit high, commercial level of activity and allow for a wide scope of olefins to be polymerized with uniform polymer properties. Such properties include narrow MWD and uniform comonomer incorporation. These charatcteristics result in polymer products with superior mechanical properties. The purpose of this paper is to compare the performance of multi-sited, heterogeneous catalysts and multi-sited, homogeneous type catalyst systems. The Scheme 1 focus will be on the use of metallocene catalyst systems in olefin polymerization as well as to provide insight to their advantageous properties.

The first Group IV metallocene complexes were developed around the same time (1953 by Wilkinson, et...