Catalyst, highly active system

For experimental convenience, previous studies on the catalysts derived from the compounds (I) have concentrated on propylene as a substrate at subambient temperatures. These conditions were selected to obtain managable activities from this extremely highly active system. 

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... 

One-shot processes require sufficiently powerful catalysts to catalyze both the gas evolution and chain extension reaction (Figure 1.29). Use of varying combinations of an organometallic tin catalyst (such as dibutyltin dilaurate and stannous octoate) with a tertiary amine (such as alkyl morpholines and triethylamine), makes it possible to obtain highly active systems in which foaming and cross-Knking reactions could be properly balanced. 

Very recently, Hou and coworkers have reported that rare earth half-metallocene complexes (Figure 14.16, 85-88) activated with [Ph3C] [B(C6F5)4] afford highly active systems for syndio-specific styrene polymerization, producing sPS with high syndiotacticities rrrr > 99%) and rather narrow polydispersities (Mw/Mn = 1.29-1.55). The activity of scandium complex 85 is comparable with that for the most active titanium catalysts (1.36 x 10 g sPS/(mol Sc-h)). The neutral allyl lanthanide complexes 89-92 (Figure 14.16) in the absence of a cocatalyst are also active for the syndiospecific polymerization of styrene (rrrr > 99%), but with lower activities that are in the order... 

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

In the 1970s, Solvay iatroduced an advanced TiCl catalyst with high activity and stereoregulahty (6). When this catalyst was utilized ia Hquid monomer processes, the level of atactic polymer was sufftciendy low so that its removal from the product was not required. Catalyst residues were also reduced so that simplified systems for post-reactor treatment were acceptable. Sumitomo has developed a Hquid monomer process, used by Exxon (United States), ia which polymer slurry is washed ia a countercurrent column with fresh monomer and alcohol to provide highly purified polymer (128). 

The catalysts used in incinerator systems for gaseous organic compound control are usually precious or base metals or metal salts. The catalysts can be supported on inert materials such as alumina (AI2O3) or ceramics. For the destruction of organic compound mixtures, a highly active but nonselective catalyst is required. ... 

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