Polyolefins iron catalysts

Iron catalysts [20-24] have been used to make polyethylene-clay nanocomposites where the polyethylene had very broad molecular weight distribution (MWD). Ziegler-Natta [25, 26], organo-chromium (Phillips) [27], and bis(imino)pyridine iron and cobalt catalysts [28] have also been used to make polyolefin-late transition metal catalysts [29, 30], capable of producing highly branched polyethylene from only ethylene and of promoting the copolymerization of ethylene with polar comonomers, have also been apphed to make polyolefin-clay nanocomposites. 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

The use of two or more different catalysts in the same reactor, sometimes known as in situ reactor blending or tandem catalysis, has been widely employed industrially as means of controlling the properties of a polyolefin (e.g. molecular weight and the molecular weight distribution). Recent years have seen a variety of reports emerge on the use of bis(imino)pyridine iron/cobalt systems as one component of the process [169, 170, 171, 172, 173, 174, 175, 176, 177,178, 179],... 

Hitachi Cable Ltd. (35) has claimed that dehydrogenation catalysts, exemplified by chromium oxide—zinc oxide, iron oxide, zinc oxide, and aluminum oxide—manganese oxide inhibit drip and reduce flammability of a polyolefin mainly flame retarded with ATH or magnesium hydroxide. Proprietary grades of ATH and Mg(OH)2 are on the market which contain small amounts of other metal oxides to increase char, possibly by this mechanism. 

Boutevin et al. [177-180] treated different types of wastes of polyolefins (more often low density polyethylene) with a mixture air/ozone. They focused their studies on the quantification of the formed oxygenated species based on colorimetric titration using stable radicals such as diphenylpicryl-hydrazyl. They investigated the influence of mineral compounds (iron oxide, for example) used as catalysts for oxidative reactions. The ozonized polymers have been used as binders for composites materials containing mineral materials (sand, stones, etc.). 

The majority of polyolefins is produced with titanium (Zeigler catalysts) and zirconium (metallocene catalysts) or by a fiee radical process Oow-density polyethylene (LDPE)). Recently, late transition metals (LTMs), in particular nickel and palladium [10, 11], and iron and cobalt, are seeing a renewed interest as olefin polymerization catalysts [12, 13]. 

The discovery of a highly active family of catalysts based on iron, a metal that had no previous track record in this field, has highlighted the possibilities of further new catalyst discoveries. The search for new catalysts be restricted to metals that have a history of giving polymerization-active centers was no longer needed. The LTMs especially are likely to provide fertile ground for future development, and the greater functional group tolerance of the LTMs also offers the attractive prospect of polar co-monomer incorporation. A relatively small amount of functionality can dramatically transform the adhesion and wettability properties of polyolefins more heavily functionalized products offer the prospect of materials with totally new properties and performance parameters. It is clear that, for olefin polymerization catalysis, the process of catalyst discovery and development is far from over. 

Late transition metal catalysts that are highly active and produce high molecular weight polyolefins were recently reported [198,199]. For example, nickel and palladium-diimine catalysts 67 produce highly branched polyethylene that is totally different from those produced by conventional or homogeneous Ziegler-Natta catalysts [200]. On the other hand, iron and cobalt 2,6-pyridine bis(imine) complexes 68 give linear polyethylene [201,202]. These catalysts are used with co-catalysts such as MAO, and the active species are cationic. Neu-... 

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