Constrained geometry catalyst systems

As mentioned in Section 10.3.2, there has been recent interest in the use of the Dow constrained geometry catalyst system to produce linear low-density polyethylenes with enhanced properties based, particularly, on ethylene and oct-l-ene. 

The Z-tail-to-tail dimers can also be obtained with high selectivity from aryl-substituted alkynes using the trisamide Ln N(SiMe3)2 3 (Ln = Y, La, Sm) [206] or the constrained-geometry catalyst system 40 [203]. The latter system is more... 

A review of the most cited U.S. patents in the polyolefins field as of August 2006, gives an indication of the most important patents in this fast-developing field. The two patents by Lai et al. (U.S. 5,272,236 and 5,278,272) are the two most cited patents in the field of polyolefins (553 and 445 citations, respectively) and these two patents survived opposition worldwide. The third most cited patent (389 citations) in the polyolefins area is by Stevens and Neithamer of The Dow Chemical Company, describing constrained geometry catalyst systems for producing homogeneous polyethylene. The fourth and fifth most cited U.S. patents in this field are ExxonMobil Chemical s U.S. 

Although ethylene/1-olefin copolymers were well documented in the late 1950s with the discovery of the chromium-based Phillips catalyst and the titanimn-based Ziegler catalyst, it was the discovery of metallocene-based single-site catalysts and the constrained geometry catalyst system that significantly increased the various types of new ethylene-based copolymers that are available for commercial applications. These new catalysts created new products, applications and markets for the polyethylene industry. 

In U.S. Patent 6,579,961 issued to Q. Wang and coworkers on June 17, 2003, Nova Chemicals International reported using a different catalyst system to prepare ethylene/styrene copolymers over a broad compositional range of styrene. With this catalyst system. Nova scientists report that styrene is inserted into the growing polymer chain in a unique manner in which the sequence distribution along the polymer backbone is different than similar copolymers prepared with the Dow constrained geometry catalyst system. 

However, since the 1990s, Dow scientists discovered a single-site designated as a constrained geometry catalyst system which has been used to significantly expand the product mix available from the Dow solution process. Dow presently produces copolymers based on 1 -butene, 1 -hexene and 1-octene over a wide density and Melt Index range. Note the reader is referred to Chapter 4 of this book, which discusses the Dow catalyst in more detail. 

Y.-X. Chen, P.-F. Fu, C. L. Stem, T. J. Marks, A novel phenolate constrained geometry catalyst system. 

Constrained-geometry catalysts for C2H4 polymerization 88 that are counterparts of well-known ansa-metallocene systems have been prepared and shown to be active, in combination with MAO, toward polymerization of ethylene the product is almost entirely polyethylene, with ca. 1% of 1-octene obtained. The titanium complex was found to be four times as active as the zirconium species.1... 

This chapter covers the elementary steps which are relevant to the polymerization of olefins with group 4 catalysts, and special emphasis is dedicated to systems with a substituted biscyclopentadienyl-based ligand, or with a monocyclopentadienylamido-based ligand (the so-called constrained geometry catalysts, CGC) of Figure 1, since these are the most investigated (the mono-Cp systems to a less extent) and the ones of possible industrial relevance. 

Over the last two decades, organometallic complexes have been at the heart of many of the key advances in metal-mediated alkene polymerization technology, with many examples now reaching the early stages of commercialization. While early transition metal complexes (e.g., metallocenes, constrained-geometry catalysts) have led the way, the advent of late transition metal catalysts has presented a rich library of highly active systems that can be employed... 

Perhaps the most striking example of how ion pairing can impact catalysis is found in the mono-cyclopentadienyl (MCP) or constrained geometry catalyst family, 15, discovered by Bercaw and coworkers see Figure 1 for the molecular structure." This system possesses a particularly open active site. In the Exxon extrapolation of the Bercaw Sc catalyst to Ti. Canich reported" the production of crystalline poly-a-olefins for several of the substituted Cp systems. That is. poly-a-olefins with enriched isotacticity were produced. In the Dow extrapolation of the Bercaw Sc catalyst to Ti, syndiotactic polymer was produced." Subsequent efforts have reported slightly enhanced syndiotacticity " and counteranion-dependent isotacticity." The most obvious difference between the Dow and Exxon reports is the solvent. Aside from differences in the Cp ring substitution, Dow utilized Isopar E as solvent whereas Exxon employed toluene. 

Many new developments on the so-called constrained geometry catalyst (CGC) (Fig. 3.3) system have been reported in the patent literature and were reviewed [18]. 

Miilhaupt and coworkers studied homo- and copolymerizations of 1,5-HD with ethylene and styrene using the MAO-activated constrained geometry catalyst 8. This catalyst system afforded very high 1,5-HD incorporation (reaching 52 mol%) with randomly distributed cis- and transcyclopentane rings in the homo- and copolymer backbones. The ratio of vinyl side chains to cyclic rings was controlled by the 1,5-HD concentration, where low concentrations of 1,5-HD promoted cyclopolymerization. 

Group 4 system contested by Dow and Exxon. Open structure leads to very good comonomer incorporation. And high-molecular-weight capability. Constrained Geometry Catalyst. ... 

World offices within days of each other, resulting in interferences and court actions over catalyst, activator, and polymer, which were finally settled after more than a decade. Dow proceeded with commercialization of the system dubbing them constrained geometry catalysts (CGC) because of the bridge between the cyclopentadienyl and amide ligands. 

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