Post-metallocene catalyst

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A post-metallocene catalyst is a kind of catalyst for the polymerization of olefins, i.e., the industrial production of some of the most common plastics. "Post-metallocene" refers to a class of homogeneous catalysts that are not metallocenes. This area has attracted much attention because the market for polyethylene, polypropylene, and related copolymers is large. There is a corresponding intense market for new processes as indicated by the fact that, in the US alone, 50,000 patents were issued between 1991-2007 on polyethylene and polypropylene. [1]

Contents

Many methods exist to polymerize alkenes, including the traditional routes using Philips catalyst and traditional heterogeneous Ziegler-Natta catalysts, which still are used to produce the bulk of polyethylene.

Catalysts based on early transition metals

Homogeneous metallocene catalysts, e.g., derived from or related to zirconocene dichloride introduced a level of microstructural control that was unavailable with heterogeneous systems. [2] Metallocene catalysts are homogeneous single-site systems, implying that a uniform catalyst is present in the solution. In contrast, commercially important Ziegler-Natta heterogeneous catalysts contain a distribution of catalytic sites. The catalytic properties of single-site catalysts can be controlled by modification of the ligand. Initially ligand modifications focused on various cyclopentadienyl derivatives, but great diversity was uncovered through high throughput screening. These post-metallocene catalysts employ a range of chelating ligands, often including pyridine and amido (R2N−). These ligands are available in great diversity with respect to their steric and electronic properties. Such postmetallocene catalysts enabled the introduction of Chain shuttling polymerization. [1]

Catalysts based on late transition metals

The copolymerization of ethylene with polar monomers has been heavily studied. The high oxophilicity of the early metals precluded their use in this application. [3]

Efforts to copolymerize polar comonomers led to catalysts based upon nickel and palladium, inspired by the success of the Shell Higher Olefin Process. Typical post-metallocene catalysts feature bulky, neutral, alpha-diimine ligands. [3] DuPont commercialized the Versipol olefin polymerization system. [5] Eastman commercialized the related Gavilan technology. [6] These complexes catalyze the homopolymerize ethylene to a variety of structures that range from high density polyethylene through hydrocarbon plastomers and elastomers by a mechanism referred to as “chain-walking”. By modifying the bulk of the alpha-diimine, the product distribution of these systems can be 'tuned' to consist of hydrocarbon oils (alpha-olefins), similar to those produced by more tradition nickel(II) oligo/polymerization catalysts. As opposed to metallocenes, they can also randomly copolymerize ethylene with polar comonomers such as methyl acrylate.

A second class of catalysts feature mono-anionic bidentate ligands related to salen ligands. [7] and DuPont. [8] [9]

The concept of bulky bis-imine ligands was extended to iron complexes [3] Representative catalysts feature diiminopyridine ligands. These catalysts are highly active but do not promote chain walking. The give very linear high-density polyethylene when bulky and when the steric bulk is removed, they are very active for ethylene oligomerization to linear alpha-olefins. [3]

A salicylimine catalyst system based on zirconium exhibits high activity for ethylene polymerization. [10] The catalysts can also produce some novel polypropylene structures. [11] Despite intensive efforts, few catalysts have been successfully commercialized for the copolymerization of polar monomers.

Related Research Articles

A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:

Polyethylene Most common thermoplastic polymer

Polyethylene or polythene is the most common plastic in use today. It is a polymer, primarily used for packaging. As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.

In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar. Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups.

Kaminsky catalyst Ethylene polymerization catalyst

A Kaminsky catalyst is a catalytic system for alkene polymerization. Kaminsky catalysts are based on metallocenes of group 4 transition metals activated with methylaluminoxane (MAO). These and other innovations have inspired development of new classes of catalysts that in turn led to commercialization of novel engineering polyolefins.

In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid-gas, respectively. The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is established technology that continues to evolve. An illustrative major application is the production of acetic acid. Enzymes are examples of homogeneous catalysts.

Polyketones are a family of high-performance thermoplastic polymers. The polar ketone groups in the polymer backbone of these materials gives rise to a strong attraction between polymer chains, which increases the material's melting point (255 °C for copolymer, 220 °C for terpolymer. Trade names include Poketone, Carilon, Karilon, Akrotek, and Schulaketon. Such materials also tend to resist solvents and have good mechanical properties. Unlike many other engineering plastics, aliphatic polyketones such as Shell Chemicals' Carilon are relatively easy to synthesize and can be derived from inexpensive monomers. Carilon is made with a palladium catalyst from ethylene and carbon monoxide. A small fraction of the ethylene is generally replaced with propylene to reduce the melting point somewhat. Shell Chemical commercially launched Carilon thermoplastic polymer in the U.S. in 1996, but discontinued it in 2000. SRI International offers Carilon thermoplastic polymers. Hyosung announced that they would launch production in 2015.

Linear low-density polyethylene

Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching and impurity. The linearity of LLDPE results is almost same as LDPE because LDPE is recycled to make LLDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.

Coordination polymerisation is a form of polymerization that is catalyzed by transition metal salts and complexes.

A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More specialized polyolefins include polyisobutylene and polymethylpentene. They are all colorless or white oils or solids. Many copolymers are known, such as polybutene, which derives from a mixture of different butene isomers. The name of each polyolefin indicates the olefin from which it is prepared; for example, polyethylene is derived from ethylene, and polymethylpentene is derived from 4-methyl-1-pentene. Polyolefins are not olefins themselves because the double bond of each olefin monomer is opened in order to form the polymer. Monomers having more than one double bond such as butadiene and isoprene yield polymers that contain double bonds (polybutadiene and polyisoprene) and are usually not considered polyolefins. Polyolefins are the foundations of many chemical industries.

Constrained geometry complex

In organometallic chemistry, a "constrained geometry complex" (CGC) is a kind of catalyst used for the production of polyolefins such as polyethylene and polypropylene. The catalyst was one of the first major departures from metallocene-based catalysts and ushered in much innovation in the development of new plastics.

Steven Ittel

Steven Dale Ittel is an American chemist specializing in organometallic chemistry and homogeneous catalysis.

In 1957, the research organization of the Chemicals Department of E. I. du Pont de Nemours and Company was renamed Central Research Department, beginning the history of the premier scientific organization within DuPont and one of the foremost industrial laboratories devoted to basic science. Located primarily at the DuPont Experimental Station and Chestnut Run, in Wilmington, Delaware, it has expanded to include laboratories in Geneva, Switzerland, Seoul, South Korea, Shanghai, China, and India(Hyderabad). In January, 2016 a major layoff marked the end of the organization.

Maurice Brookhart

Maurice S. Brookhart is an American chemist, and professor of chemistry at the University of Houston since 2015.

John E. Bercaw American chemist (born 1944)

John E. Bercaw is an American chemist and Centennial Professor of Chemistry, Emeritus at the California Institute of Technology.

Concurrent tandem catalysis

Concurrent tandem catalysis (CTC) is a technique in chemistry where multiple catalysts produce a product otherwise not accessible by a single catalyst. It is usually practiced as homogeneous catalysis. Scheme 1 illustrates this process. Molecule A enters this catalytic system to produce the comonomer, B, which along with A enters the next catalytic process to produce the final product, P. This one-pot approach can decrease product loss from isolation or purification of intermediates. Reactions with relatively unstable products can be generated as intermediates because they are only transient species and are immediately used in a consecutive reaction.

In polymer chemistry, chain walking (CW) or chain running or chain migration is a mechanism that operates during some alkene polymerization reactions. CW can be also considered as a specific case of intermolecular chain transfer. This reaction gives rise to branched and hyperbranched/dendritic hydrocarbon polymers. This process is also characterized by accurate control of polymer architecture and topology. The extent of CW, displayed in the number of branches formed and positions of branches on the polymers are controlled by the choice of a catalyst. The potential applications of polymers formed by this reaction are diverse, from drug delivery to phase transfer agents, nanomaterials, and catalysis.

Brookharts acid Chemical compound

Brookhart's acid is the salt of the diethyl ether oxonium ion and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAr′4). It is a colorless solid, used as a strong acid. The compound was first reported by Volpe, Grant, and Brookhart in 1992.

Diiminopyridines are a class of diimine ligands. They featuring a pyridine nucleus with imine sidearms appended to the 2,6–positions. The three nitrogen centres bind metals in a tridentate fashion, forming pincer complexes. Diiminopyridines are notable as non-innocent ligand that can assume more than one oxidation state. Complexes of DIPs participate in a range of chemical reactions, including ethylene polymerization, hydrosilylation, and hydrogenation.

Diimines are organic compounds containing two imine (RCH=NR') groups. Common derivatives are 1,2-diketones and 1,3-diimines. These compounds are used as ligands and as precursors to heterocycles. Diimines are prepared by condensation reactions where a dialdehyde or diketone is treated with amine and water is eliminated. Similar methods are used to prepare Schiff bases and oximes.

Functionalized polyolefins are olefin polymers with polar and nonpolar functionalities attached onto the polymer backbone. There has been an increased interest in functionalizing polyolefins due to their increased usage in everyday life. Polyolefins are virtually ubiquitous in everyday life, from consumer food packaging to biomedical applications; therefore, efforts must be made to study catalytic pathways towards the attachment of various functional groups onto polyolefins in order to affect the material's physical properties.

References

  1. 1 2 Chum, P. S.; Swogger, K. W., "Olefin Polymer Technologies-History and Recent Progress at the Dow Chemical Company", Progress in Polymer Science 2008, volume 33, 797-819. doi : 10.1016/j.progpolymsci.2008.05.003
  2. ↑ Brintzinger, H. H.; Fischer, D.; Muelhaupt, R.; Rieger, B.; Waymouth, R. M., "Stereospecific Olefin Polymerization with Chiral Metallocene Catalysts", Angew. Chem. Int. Ed. Engl. 1995, 34, 1143-1170. doi : 10.1002/anie.199511431
  3. 1 2 3 4 Domski, G. J., Rose, J. M., Coates, G. W., Bolig, A. D., Brookhart, M., "Living alkene polymerization: New methods for the precision synthesis of polyolefins", Prog. Polymer Sci. 2007, volume 32, p.30. doi : 10.1016/j.progpolymsci.2006.11.001
  4. ↑ Janeta, Mateusz; Heidlas, Julius X.; Daugulis, Olafs; Brookhart, Maurice (2021). "2,4,6-Triphenylpyridinium: A Bulky, Highly Electron-Withdrawing Substituent That Enhances Properties of Nickel(II) Ethylene Polymerization Catalysts". Angewandte Chemie International Edition. 60 (9): 4566–4569. doi:10.1002/anie.202013854. ISSN   1521-3773. OSTI   1755772. PMID   33230900. S2CID   227159941.
  5. ↑ US 5,866,663 "Process of Polymerizing Olefins," Samuel David Arthur, Alison Margaret Anne Bennett, Maurice S. Brookhart, Edward Bryan Coughlin, Jerald Feldman, Steven Dale Ittel, Lynda Kaye Johnson, Christopher Moore Killian; Kristina Ann Kreutzer, Elizabeth Forrester McCord, Stephan James McLain, Anju Parthasarathy, Lin Wang, Zhen-Yu Yang; February 2, 1999. WO 9623010 A2 960801.
  6. ↑ MacKenzie, P. B.; Moody, L. S.; Killian, C. M.; Ponasik, J. A.; McDevitt, J. P. WO Patent Application 9840374, Sept. 17, 1998 to Eastman, priority date Feb 24, 1998.
  7. ↑ C. Wang, S. Friedrich, T. R. Younkin, R. T. Li, R. H. Grubbs, D. A. Bansleben, M. W. Day, Organometallics , 17, 3149 (1998).
  8. ↑ US 6,174,975, “Polymerization of Olefins,” Lynda Kaye Johnson; Alison Margaret Anne Bennett, Lin Wang, Anju Parthasarathy, Elisabeth Hauptman, Robert D. Simpson, Jerald Feldman, Edward Bryan Coughlin, and Steven Dale Ittel. January 16, 2001.
  9. ↑ Janeta, Mateusz; Heidlas, Julius X.; Daugulis, Olafs; Brookhart, Maurice (2021). "2,4,6-Triphenylpyridinium: A Bulky, Highly Electron-Withdrawing Substituent That Enhances Properties of Nickel(II) Ethylene Polymerization Catalysts". Angewandte Chemie International Edition. 60 (9): 4566–4569. doi:10.1002/anie.202013854. ISSN   1521-3773. OSTI   1755772. PMID   33230900. S2CID   227159941.
  10. ↑ S. Matsui, Y. Tohi, M. Mitani, J. Saito, H. Makio, H. Tanaka, M. Nitabaru, T. Nakano, T, Fujita, Chem. Lett., 1065 (1999).
  11. ↑ Steven D. Ittel and Lynda K. Johnson and Maurice Brookhart, Late-Metal Catalysts for Ethylene Homo- and Copolymerization, Chem. Rev. 2000, 100, 1169-1203.
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