Propylene polymerization catalysts

There are other methods of preparation that iavolve estabhshing an active phase on a support phase, such as ion exchange, chemical reactions, vapor deposition, and diffusion coating (26). For example, of the two primary types of propylene polymerization catalysts containing titanium supported on a magnesium haUde, one is manufactured usiag wet-chemical methods (27) and the other is manufactured by ball milling the components (28). 

The syndiotactic polymer configuration is not obtained in pure form from polymerizations carried out above 20°C and, thus has not been a serious concern to most propylene polymerization catalyst designers. Eor most commercial appHcations of polypropylene, a resin with 96+% isotacticity is desired. Carbon-13 nmr can be used to estimate the isotactic fraction in a polypropylene sample. Another common analytical method is to dissolve the sample in boiling xylene and measure the amount of isotactic polymer that precipitates on cooling. 

Additional high-activity propylene polymerization catalysts, (II), are described by Nifant evi et al. (3). 

Fig. 12. The ratio between the activity of propylene polymerization catalysts and their specific surface. The specific surface of the samples was calculated from the average sizes of primary crystallites, determined by using X-ray techniques, on the assumption that the crystallites have the form of hexagonal prisms (001 axis). Polymerization at 70°C, cocatalyst AlEtjCl, monomer concentration 1 M. From Yermakov et at. (13).

The active site model of a modern propylene polymerization catalyst, 3, shown in Figure 2 demonstrates the molecular complexity of the question at hand. A large and elaborate ligand, labeled... 

The pooled library of salicylaldimine-titanium products was combined with MAO and 150 ml toluene in a pressure vessel, and screened at 20 °G under 2.7 atm of propylene for 6h. Although 90% of the polymers produced were determined to be atactic through extraction experiments with diethylether, the remaining 10% of the polymers produced were found to contain insoluble syndiotactic polypropylene. Small subsets of the complex libraries were then resynthesized and screened in order to ascertain the particular metal-ligand combination responsible for the stereocontrol. The authors concluded the study by identifying and isolating a new syndiospecific propylene polymerization catalyst 2. 

A most significant example, which was also provided by the Symyx team, deployed the same methodology to uncover an entirely new family of isospecific propylene polymerization catalysts. The Symyx team, in collaboration with Dow Chemical, discovered and developed a new catalyst class, and a new commercial solution process for the production of isotactic polypropylene-based elastomers and plastomers. " ... 

GoodaU, B. L. The History and Current State of the Art of Propylene Polymerization Catalysts. /. Chem. Educ. 1986, 63,191. 

The cover background photograph shows a reactor in the laboratory of Professor Stephen A. Miller, containing syndiotac-tic polypropylene prepared by graduate student Levi). Irwin. The Miller-Bercaw metallocene catalyst employed (catalyst s-90 in Chapter 2) is one of the most syndioselective propylene polymerization catalysts currently known. Unlike isotactic polypropylene, which can also be prepared with Ziegler-Natta initiators, syndiotactic polypropylene is only obtained in appreciable quantities using single-site catalysts. 

Infrared Characterization of Supported Propylene Polymerization Catalysts-A Link to Catalyst Performance... 

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