Metallocenes polymerization catalysts

Examples of catalytic reactions and processes relevant to hydrocarbon chemistry are numerous. The technologies of the oil refinery with extremely low (<0.1) E factors are excellent examples demonstrating the possibilities that can be achieved by the development of selective catalytic methods, particularly by the use of various solid acids (see detailed discussions in Chapter 2). Further examples of commercially highly successful processes are the oxidation catalyst TS-1 developed by Enichem researchers160 161 (see Sections 9.1.1, 9.2.1, and 9.4.1), the homogeneous aqueous-phase Rh-catalyzed hydroformylation (see Sections 7.1.3 and 7.4.1), and single-site metallocene polymerization catalysts, which allow the preparation of tailored polymers with new properties (see Sections 13.3.2).162-164... 

In the 1990s, metallocene polymerization catalysts began to be used commercially. Metallocene chemistry was developed in the early 1950s independently by Geoffrey Wilkinson at Harvard and Ernest Otto Fischer at the Technische Hochshule in Munich. They would share the 1973 Nobel Prize in Chemistry... 

Grubbs, R. H. Coates, G W. a-Agostic interactions and olefin insertion in metallocene polymerization catalysts. Acc. Chem. Res. 1996, 29, 85-93. 

Since these early discoveries, an enormous amount of effort has been put forth to understand and improve upon stereoselective catalyst systems. Because of the excellent research that has been accomplished over the past 20-1- years, the ability to influence the mechanistic details of each step of the polymerization process from insertion to chain release now exists. This chapter will focus on how the tuning of metallocene polymerization catalyst structures can be carried out to influence stereoregularity in the resulting polymer. 

Bercaw, J. E. Herzog, T. A. Stereospecific metallocene polymerization catalysts for olefins. U.S. Patent 5,708,101 A (California Institute of Technology), August 12, 1999. 

Ewen, J. A. Metallocene polymerization catalysts Fast, present and fnture. In Metallocene-Based Polyolefins—Preparation, Properties and Technology Scheirs, J., Kaminsky, W., Eds. John Wiley and Sons Chichester, 2000 Vol. 1, pp 3-31. 

Unlike molecules containing electron-rich heteroatoms, boron compounds do not poison Ziegler-Natta or metallocene polymerization catalysts. Borane-containing olefin comonomers are therefore well suited to produce olefin copolymers while retaining good catalyst activity. The resulting polymers are suitable for subsequent conversion into a variety of functional groups. In principle, two approaches are possible (1) hydroboration of the terminal double bond (formed by typical chain transfer processes) of a preformed polyolefin, and (2) direct copolymerization of propylene or a 1-alkene with an alkenyl borane (Scheme 11.4). 

Chien recently reviewed supported metallocene polymerization catalysts. Here, we will indicate more recent efforts and trends. Many of the support systems are polymers being derived from silicon dioxide. Thus it is appropriate to consider this topic within this chapter. 

The advantages and disadvantages of supported metallocene polymerization catalysts versus the analogous homogeneous catalysts are well known. ... 

First metallocene polymerization catalysts (Natta, Breslow)... 

Unlike the conversion of ethylene to linear polyethylene (PE), propylene polymerization to polypropylene (PP) introduces stereochemical complexity because we can obtain 12.8,12.9 or a random atactic product. Surprisingly, selective formation of syndiotactic propylene (12.9) is seen for many metallocene polymerization catalysts. To see why, we need to know that (f [Cp2ZrR]+ is pyramidal (12.12 in Fig. 

Last but not least, Tl-based MOFs were tried in the Zieglff-Natta polymerization of ethylene and propylene, though these systems were infaior to the well-known single-site metallocene polymerization catalysts with their trCTiendous turnover frequencies and space-time yields [107]. 

---