Commercial polyolefin production

Metallocene catalysis is an alternative to the traditional Ziegler-Natta vanadium-based catalysis for commercial polyolefin production, e.g. the use of metallocene-catalyzed ethylene alpha-olefin copolymers as viscosity index modifiers for lubricating oil compositions [23]. The catalyst is an activated metallocene transition metal, usually Ti, Zr or Hf, attached to one or two cyclopentadienyl rings and typically activated by methylaluminoxane. Metallocene catalysis achieves more stereo-regularity and also enables incorporation of higher alpha-olefins and/or other monomers into the polymer backbone. In addition, the low catalyst concentration does not require a cleanup step to remove ash. 

Knowledge of the coordination polymerisation of olefins would not be complete without consideration of the types of process used in industry for polyolefin manufacture. Problems encountered in production influence developments in the area of catalysis in olefin polymerisation, an improvement in a catalyst being defined as leading to a reduction in the cost of making the polymer or giving better product properties. Therefore, the principal types of polyolefin production involving coordination catalysts of various types are dealt with briefly. Since modern polyolefin production processes offer a versatile range of polymers, the main commercially available olefin polymerisation products and their typical uses are also considered. 

The commercial applications of the organometallic species are typically in the area of catalysis (see Chapters 33 and 34) and preparation of precursors for chemical vapor deposition [201]. An example of the synthetic usefulness of Grignard reagents is demonstrated in the preparation of the new breed of metallocene catalyst that are used for polyolefin production (Scheme 7) [106,202,203]. 

The development of commercially useful polymers in the early 20th century ushered in an era where mass-produced, organo-polymeric materials have become a ubiquitous part of daily life. " Sixty years after the Nobel prize-winning discovery by Ziegler and Natta, " the scale of worldwide polyolefin production is massive. The current estimated aimual global production of polyolefins is over 150 million metric tons. However, the inherent chemical inertness of these substances causes them to persist in the environment centuries after they have been discarded. The detrimental environmental impact of a man-made waste problem of this scale has generated an interest in commercially viable, biodegradable alternatives. ... 

Commercial polyolefins often contain additives such as colorants, flame retardants, antioxidants, light stabilizers, nucleating agents, antistatic agents, lubricants (microcrystalline waxes, hydrocarbon waxes, stearic acid, and metal stearates), and so on. These additives aid the processing and fabrication of products from polyolefins. Detailed treatments about specific polyolefins, polymerization systems/ mechanism/processes, structures, properties, processing, and applications may be found in References 2-9. 

Polyolefins are a multibillion dollar a year industry with worldwide production in excess of 160 billion pounds and polyethylene alone in excess of 100 billion pounds. Despite this size and the commodity nature of the business, polyolefins are the fastest-growing segment of the polymer industry. Although it has been almost half a century since polyethylene s commercialization. polyolefins remain highly technology-driven. " ... 

What are some important factors to consider when choosing commercially available light stabilizers, and what are some examples of how they have been used in specific situations to aeate resilient, weatherable polyolefin products ... 

Two of the most interesting aspects of the catalysts used in this work are their ability to copolymerize ethylene and a-olefins with polar monomers and their inertness toward impurities, allowing for a relatively straightforward production of these types of polymers in SCCO2. Although the activity of these catalysts is still rather low for commercial use, it may be expected that this will improve significantly in the near future. This would enable the development of clean polyolefin production based on C02-technology, for which future applications may be expected in the production of EPDM and other elastomers. 

Union Carbide, now part of Dow Chemical, was the first company to commercialize the technology for polyolefin production using fluidized-bed gas-phase reactors. Since polymerization occurs in the gas phase, separation of the unreacted monomer from the polymer product is achieved simply by flashing off the monomer. Any low molecular weight polymer formed remains in the polymer particles and no further separation is necessary. The process only requires a fluidized-bed gas-phase reactor, a product discharge system to get... 

Most commercial polyolefins are produced by coordination polymerization catalysts. When compared to free radical processes used to make low-density polyethylene (LDPE), these catalysts work in comparatively gentle conditions, such as lower pressures and temperatures, while providing greater flexibility in controlling the polyolefin molecular structure. An understanding of the polymerization mechanism with coordination catalysts is essential for designing proper systems for the production of polyolefin-clay nanocomposites and wUl be covered in the next section. 

The only commercial hydroxylamine product used in polyolefins and other selected polymers is a product of a process based on the oxidation of bis-tallow amine [14325-92-2],... 

Other thermoplastic elastomer combinations, in which the elastomer phase may or may not be cross-linked, include blends of polypropylene with nitrile (26), butyl (28), and natural (29) rubbers, blends of PVC with nitrile rubber and plasticizers (30-32), and blends ofhalogenated polyolefins with ethylene interpolymers (30). Commercially important products (33,34) based on blends of polystyrene with S-B-S and oil and also on blends of polypropylene with S-EB-S and oil are described later in this article. They are also considered as thermoplastic elastomer combinations. The oils nsed in these prodncts are nsnally hydrocarbons but blends with silicone oils have also been described (35). Collectively, all thermoplastic elastomers of this type (both bends and dynamic vnlcanizates) are referred to herein as hard polymer/elastomer combinations. 

Polypropylene is the second most important commercial polyolefin. Isotactic PP has the lowest density (0.90-0.91 g/mL) of the major plastics. It has a high crystalline melting point of 165°C. The first commercial production of polypropylene was in the 1950s following the discovery of Z-N catalysts. 

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