Coordination polymerization

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Coordination polymerisation is a form of polymerization that is catalyzed by transition metal salts and complexes. [1] [2]

Contents

Types of coordination polymerization of alkenes

Heterogeneous Ziegler–Natta polymerization

Coordination polymerization started in the 1950s with heterogeneous Ziegler–Natta catalysts based on titanium tetrachloride and organoaluminium co-catalysts. The mixing of TiCl4 with trialkylaluminium complexes produces Ti(III)-containing solids that catalyze the polymerization of ethene and propene. The nature of the catalytic center has been of intense interest but remains uncertain. Many additives and variations have been reported for the original recipes. [3]

Homogeneous Ziegler–Natta polymerization

In some applications heterogeneous Ziegler–Natta polymerization has been superseded by homogeneous catalysts such as the Kaminsky catalyst discovered in the 1970s. The 1990s brought forward a new range of post-metallocene catalysts. Typical monomers are nonpolar ethene and propene. The development of coordination polymerization that enables copolymerization with polar monomers is more recent. [4] Examples of monomers that can be incorporated are methyl vinyl ketones, [5] methyl acrylate, [6] and acrylonitrile. [7]

Illustrative metallocene-based coordination catalysts Metallocenes3.png
Illustrative metallocene-based coordination catalysts

Kaminsky catalysts are based on metallocenes of group 4 metals (Ti, Zr, Hf) activated with methylaluminoxane (MAO). [8] [9] Polymerizations catalysed by metallocenes occur via the Cossee–Arlman mechanism. The active site is usually anionic but cationic coordination polymerization also exists.

Simplified mechanism for Zr-catalyzed ethene polymerization ZNonSingleSite.png
Simplified mechanism for Zr-catalyzed ethene polymerization

Specialty monomers

Many alkenes do not polymerize in the presence of Ziegler–Natta or Kaminsky catalysts. This problem applies to polar olefins such as vinyl chloride, vinyl ethers, and acrylate esters. [10]

Butadiene polymerization

The annual production of polybutadiene is 2.1 million tons (2000). The process employs a neodymium-based homogeneous catalyst. [11]

Principles

Coordination polymerization has a great impact on the physical properties of vinyl polymers such as polyethylene and polypropylene compared to the same polymers prepared by other techniques such as free-radical polymerization. The polymers tend to be linear and not branched and have much higher molar mass. Coordination type polymers are also stereoregular and can be isotactic or syndiotactic instead of just atactic. This tacticity introduces crystallinity in otherwise amorphous polymers. From these differences in polymerization type the distinction originates between low-density polyethylene (LDPE), high-density polyethylene (HDPE) or even ultra-high-molecular-weight polyethylene (UHMWPE).

Coordination polymerization of other substrates

Coordination polymerization can also be applied to non-alkene substrates. Dehydrogenative coupling of silanes, dihydro- and trihydrosilanes, to polysilanes has been investigated, although the technology has not been commercialized. The process entails coordination and often oxidative addition of Si-H centers to metal complexes. [12] [13]

Lactides also polymerize in the presence of Lewis acidic catalysts to give polylactide: [14] [15]

Polylactide synthesis v.1.png

See also

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:

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<span class="mw-page-title-main">Polyethylene</span> Most common thermoplastic polymer

Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, etc.). As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.

<span class="mw-page-title-main">Polypropylene</span> Thermoplastic polymer

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<span class="mw-page-title-main">Kaminsky catalyst</span> 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.

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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 an established technology that continues to evolve. An illustrative major application is the production of acetic acid. Enzymes are examples of homogeneous catalysts.

Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH3)O)n. It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization.

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.

<span class="mw-page-title-main">Linear low-density polyethylene</span>

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In polymer chemistry, vinyl polymers are a group of polymers derived from substituted vinyl monomers. Their backbone is an extended alkane chain [−CH2−CHR−]. In popular usage, "vinyl" refers only to polyvinyl chloride (PVC).

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<span class="mw-page-title-main">Constrained geometry complex</span>

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The Cossee–Arlman mechanism in polymer chemistry is the main pathway for the formation of C–C bonds in the polymerization of alkenes. The mechanism features an intermediate coordination complex that contains both the growing polymer chain and the monomer (alkene). These ligands combine within the coordination sphere of the metal to form a polymer chain that is elongated by two carbons.

<span class="mw-page-title-main">Organozirconium chemistry</span>

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References

  1. ↑ Polymer science and technology (2000) Robert Oboigbaotor Ebewele
  2. ↑ Kent and Riegel's handbook of industrial chemistry and biotechnology, Volume 1 2007 Emil Raymond Riegel, James Albert Kent
  3. ↑ James C.W. Chien, ed. (1975). Coordination Polymerization A Memorial to Karl Ziegler. Academic Press. ISBN   978-0-12-172450-4.
  4. ↑ Nakamura, Akifumi; Ito, Shingo; Nozaki, Kyoko (2009). "Coordination−Insertion Copolymerization of Fundamental Polar Monomers". Chemical Reviews. 109 (11): 5215–44. doi:10.1021/cr900079r. PMID   19807133.
  5. ↑ Johnson, Lynda K.; Mecking, Stefan; Brookhart, Maurice (1996). "Copolymerization of Ethylene and Propylene with Functionalized Vinyl Monomers by Palladium(II) Catalysts". Journal of the American Chemical Society. 118: 267–268. doi:10.1021/ja953247i.
  6. ↑ Drent, Eite; Van Dijk, Rudmer; Van Ginkel, Roel; Van Oort, Bart; Pugh, Robert. I. (2002). "Palladium catalysed copolymerisation of ethene with alkylacrylates: polar comonomer built into the linear polymer chainElectronic supplementary information (ESI) available: NMR data for entries 1, 9, 10, 12 and size exclusion chromatographic data for entries 1, 3, 8, 12". Chemical Communications (7): 744–745. doi:10.1039/b111252j. PMID   12119702.
  7. ↑ Kochi, Takuya; Noda, Shusuke; Yoshimura, Kenji; Nozaki, Kyoko (2007). "Formation of Linear Copolymers of Ethylene and Acrylonitrile Catalyzed by Phosphine Sulfonate Palladium Complexes". Journal of the American Chemical Society. 129 (29): 8948–9. doi:10.1021/ja0725504. PMID   17595086.
  8. ↑ Walter Kaminsky (1998). "Highly Active Metallocene Catalysts For Olefin Polymerization". Journal of the Chemical Society, Dalton Transactions (9): 1413–1418. doi:10.1039/A800056E.
  9. ↑ Klosin, J.; Fontaine, P. P.; Figueroa, R. (2015). "Development of Group Iv Molecular Catalysts for High Temperature Ethylene-Α-Olefin Copolymerization Reactions". Accounts of Chemical Research. 48 (7): 2004–2016. doi: 10.1021/acs.accounts.5b00065 . PMID   26151395.
  10. ↑ Eugene Y.-X. Chen (2009). "Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts". Chem. Rev. 109 (11): 5157–5214. doi:10.1021/cr9000258. PMID   19739636.
  11. ↑ Friebe, Lars; Nuyken, Oskar; Obrecht, Werner (2006). "Neodymium-Based Ziegler/Natta Catalysts and their Application in Diene Polymerization". Advances in Polymer Science. 204: 1–154. doi:10.1007/12_094. ISBN   978-3-540-34809-2.
  12. ↑ Aitken, C.; Harrod, J. F.; Gill, U. S. (1987). "Structural studies of oligosilanes produced by catalytic dehydrogenative coupling of primary organosilanes". Can. J. Chem. 65 (8): 1804–1809. doi:10.1139/v87-303.
  13. ↑ Tilley, T. Don (1993). "The Coordination Polymerization of Silanes to Polysilanes by a "σ-bond Metathesis" Mechanism. Implications for Linear Chain Growth". Accounts of Chemical Research. 26: 22–9. doi:10.1021/ar00025a004.
  14. ↑ R. Auras; L.-T. Lim; S. E. M. Selke; H. Tsuji (2010). Poly(lactic acid): Synthesis, Structures, Properties, Processing, and Applications. Wiley. ISBN   978-0-470-29366-9.
  15. ↑ Odile Dechy-Cabaret; Blanca Martin-Vaca; Didier Bourissou (2004). "Controlled Ring-Opening Polymerization of Lactide and Glycolide". Chem. Rev. 104 (12): 6147–6176. doi:10.1021/cr040002s. PMID   15584698.
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