Single metallocene catalysts

The LCB structure of polyolefins obtainable with a single metallocene catalyst can be altered in several ways. For instance, two or more metallocenes can be used to control, simultaneously, the MWD and LCB of polyolefins [48,49]. If an even more drastic micro-structural change is required, one that would make the LCB structure of polyolefins made with coordination catalysts resemble that of LDPE, dienes can be copolymerized with ethylene and a-olefins [50]. The cited references provide some additional information on this subject. 

Catalyst, metallocene Also called single site, Me and m. Metallocene catalysts achieve creativity and exceptional control in polymerization and product design permitting penetration of new markets and expand on of present markets. 

What differences would be observed between linear low density polyethylenes manufactured with a Ziegler-Natta catalyst versus a single site catalyst, such as a metallocene ... 

Exxpol [Exxon polymerization] A gas-phase process for making polyethylene from ethylene. The process uses single-site catalysis (SSC), based on a zirconium metallocene catalyst. Developed by Exxon Chemical Company in 1990 with plans to be commercialized in 1994. 

Future challenges for polymerization model catalysts are to study the structure of polymers below their melting point in what is called the nascent morphology. Such work can be undertaken on silica-supported chromium catalysts as discussed above, or on so-called single-site catalysts, such as metallocenes, applied on flat silica supports. 

The advent of homogeneous olefin polymerization based on metallocenes has also ushered in a new era in olefin polymerization. In fact, the recent commercialization of numerous poly(olefins) prepared using metallocene strategies is testament to the importance of this field from both an academic and an industrial viewpoint. One of the main intellectual driving forces is the realization that as a specific example of single site catalysts, these systems are also amenable to... 

Swogger, K. W., An Outlook for Metallocene and Single Site Catalyst Technology into the 2U Century, SPE ANTEC Tech. Papers, 44, 1790 (1998)... 

The mixture of metallocene and co-catalyst is soluble. Its active center, which is chiral, induces with a very low rate of defects only one type of monomer linkage ( single site catalysts )- That is why high activities (some 1,000 kg polymer/g... 

Site-controlled syndioselectivity of C/-symmetric metallocenes is unprecedented and represents a major achievement of the rational molecular design of single-site catalysts. Recent highly syndioselective metallocenes are listed in Figure The flat fluorenyl ligand has been further spatially extended by substituents at the 2,6- and/or 3,7-... 

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