Metallocene catalysis polyethylenes

During the 1990s there was enormous activity in the development of a further type of polyethylene based on metallocene catalysis methods. One patent search... 

For films. Table 4.1 proposes an arbitrary classification of the polyethylene subfamilies (where m indicates metallocene catalysis). 

Polypropylene (PP) and polyethylene (PE) fibres float in water, they are not soluble in cold concentrated sulphuric acid but soluble in boiling perchloroethylene. They are also easily recognizable and distinguishable by their melting points PE 124-138 °C (occasionally up to 155 °C) (low density PE 105-129 °C), PP = 160-175 °C (if based on metallocene catalysis 15-20° C lower). 

Bonduel D, Bredeau S, Alexandre M, Monteverde F, Dubois P (2007) Supported metallocene catalysis as an efficient tool for the preparation of polyethylene/carbon nanotube nanocomposites effect of the catalytic system on the coating morphology. J Mater Chem... 

Garcia-Franco and Mead [142] proposed the use of the parameters of Eq. 5.65 to describe the behavior of polyethylenes prepared by means of anionic polymerization, gas-phase metallocene catalysis, and Ziegler-Natta catalysis. They reported that Eqs. 5.67 gave a good fit of their data and suggested that it is valid for all linear, flexible polymers with monomodal molecular weight distributions except in the terminal zone. They found that except in the terminal zone it provides a representation of the data that is similar to that given by the double-reptation model. They... 

Ethene HOPE, high-density polyethylene Ziegler-Natta, metallocene catalysis Piping, containers, plastic bags... 

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

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. 

These developments and non-metallocene single site catalysts in general represent the next wave of innovation in polyolefin catalysis which should permit production of polyethylenes with unique properties at lower cost. They will complement, and perhaps even supplant, many of the metallocene single site catalysts commercialized in the 1990s. 

The period following the Second World War saw the emergenee, with an accelerated speed, of new polymerization methods in 1953-1954, polymerization catalysis by coordination was developed by K. Ziegler and G. Natta (Nobel Prize, 1963), which led to for high-density polyethylene (PEHD) and polypropylene (PP). Anionic polymerization and the concept of living polymerization proposed by M. Szwarc in 1956 led to the design of blocks copolymers and the first macromolecular architectures. We then saw the emergence of catalysis by metallocene in 1980 by W. Kaminski. Radical polymerization controlled by M. Sawamoto and K. Matyjaszewski in 1994 combined the benefits of radical and ionic polymerization without the drawbacks of the former. 

The sheer size and value of the polyethylene industry ensure that there is continued research, progress, and development in catalysis, for their potential commercial impact. Although this whole subject is not within the scope of this chapter, we mention a couple of aspects of the progress, which offer the potential to impact this industry. In 1995, DuPont introduced work, carried out with them at the University of North Carolina—via the largest patent applicafion ever in the USA. They disclosed what are described as post-metallocene catalysts. These are transition and late transition metal complexes with di-imine ligands, which form part of the DuPont Versipol technology. Such catalysts create highly branched to exceptionally linear ethylene homopolymers and linear alpha-olefins. Late transition metals offer not only the potential for the incorporation of polar comonomers, which until now has only been possible in LDPE reactors, but also their controlled sequence distribution, compared to the random composition of free radical LDPE copolymers. Such copolymers account for over 1 million tons per annum [20]. Versipol has so far only been cross-licensed and used commercially by DuPont Dow Elastomers (a former joint venture, now dissolved) in an EPDM plant. 

In addition to long-chain branching binary metallocene systems are also used to constiurt bimodal MWDs for polyolefins that have betta processability than narrow distribution materi-als. The Iowa molecular weight chains reduce melt viscosities and thus make the materials easia to be processed. Another development is the tandem catalysis for LLDPEs. The current industrial practice involves two steps. Ethylene monomas are first oligomerized into a-olefms such as butene, hexene, and oaene. The a-olefins are incorporated into polyethylene chains... 

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