Coordination 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.{{cite book|title=Coordination Polymerization A Memorial to Karl Ziegler|editor=James C.W. Chien|isbn=978-0-12-172450-4|publisher=Academic Press|year=1975}}

In some applications heterogeneous Ziegler–Natta polymerization has been superseded by homogeneous catalysts such as the Kaminsky catalyst discovered in the 1970s.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.{{cite journal|doi=10.1021/cr900079r|pmid=19807133|title=Coordination−Insertion Copolymerization of Fundamental Polar Monomers|year=2009|last1=Nakamura|first1=Akifumi|last2=Ito|first2=Shingo|last3=Nozaki|first3=Kyoko|journal=Chemical Reviews|volume=109|issue=11|pages=5215–44}} Examples of monomers that can be incorporated are methyl vinyl ketones,{{cite journal|doi=10.1021/ja953247i|title=Copolymerization of Ethylene and Propylene with Functionalized Vinyl Monomers by Palladium(II) Catalysts|year=1996|last1=Johnson|first1=Lynda K.|last2=Mecking|first2=Stefan|last3=Brookhart|first3=Maurice|journal=Journal of the American Chemical Society|volume=118|pages=267–268}} methyl acrylate,{{cite journal|doi=10.1039/b111252j|pmid=12119702|title=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. |year=2002|last1=Drent|first1=Eite|last2=Van Dijk|first2=Rudmer|last3=Van Ginkel|first3=Roel|last4=Van Oort|first4=Bart|last5=Pugh|first5=Robert. I.|journal=Chemical Communications|pages=744–745|issue=7}} and acrylonitrile.{{cite journal|doi=10.1021/ja0725504|pmid=17595086|title=Formation of Linear Copolymers of Ethylene and Acrylonitrile Catalyzed by Phosphine Sulfonate Palladium Complexes|year=2007|last1=Kochi|first1=Takuya|last2=Noda|first2=Shusuke|last3=Yoshimura|first3=Kenji|last4=Nozaki|first4=Kyoko|journal=Journal of the American Chemical Society|volume=129|issue=29|pages=8948–9}}

File:metallocenes3.png

Kaminsky catalysts are based on metallocenes of group 4 metals (Ti, Zr, Hf) activated with methylaluminoxane (MAO).{{cite journal|title=Highly Active Metallocene Catalysts For Olefin Polymerization|author=Walter Kaminsky|year=1998|journal=Journal of the Chemical Society, Dalton Transactions|issue=9|pages=1413–1418|doi=10.1039/A800056E}}{{cite journal|author1=Klosin, J.|author2=Fontaine, P. P.|author3=Figueroa, R. |title=Development of Group Iv Molecular Catalysts for High Temperature Ethylene-Α-Olefin Copolymerization Reactions|journal=Accounts of Chemical Research|year=2015|volume=48|issue=7|pages=2004–2016|doi=10.1021/acs.accounts.5b00065|pmid=26151395|doi-access=free}}

Polymerizations catalysed by metallocenes occur via the Cossee–Arlman mechanism. The active site is usually anionic but cationic coordination polymerization also exists.

File:ZNonSingleSite.png

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.{{cite journal|title=Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts|author=Eugene Y.-X. Chen|journal=Chem. Rev.|year=2009|volume=109|issue=11|pages=5157–5214|doi=10.1021/cr9000258|pmid=19739636 }}

The annual production of polybutadiene is 2.1 million tons (2000). The process employs a neodymium-based homogeneous catalyst.{{cite journal | last1 = Friebe | first1 = Lars | last2 = Nuyken | first2 = Oskar | last3 = Obrecht | first3 = Werner | year = 2006 | title = Neodymium-Based Ziegler/Natta Catalysts and their Application in Diene Polymerization | journal = Advances in Polymer Science | volume = 204 | pages = 1–154 | doi = 10.1007/12_094 | isbn = 978-3-540-34809-2 }}

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 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.{{cite journal| last1 =Aitken | first1 =C.| last2 =Harrod| first2 =J. F.| last3 =Gill | first3 =U. S.| title =Structural studies of oligosilanes produced by catalytic dehydrogenative coupling of primary organosilanes | journal = Can. J. Chem.| volume =65| year =1987| issue =8| pages =1804–1809 | doi =10.1139/v87-303 }}{{cite journal|title=The Coordination Polymerization of Silanes to Polysilanes by a "σ-bond Metathesis" Mechanism. Implications for Linear Chain Growth|author=Tilley, T. Don|journal=Accounts of Chemical Research|year=1993|volume=26|pages=22–9|doi=10.1021/ar00025a004}}

Lactides also polymerize in the presence of Lewis acidic catalysts to give polylactide:{{cite book | isbn = 978-0-470-29366-9 | title = Poly(lactic acid): Synthesis, Structures, Properties, Processing, and Applications | author1 = R. Auras | author2 = L.-T. Lim | author3= S. E. M. Selke |author4= H. Tsuji | publisher = Wiley | year = 2010 }}{{cite journal|title=Controlled Ring-Opening Polymerization of Lactide and Glycolide|author1=Odile Dechy-Cabaret |author2=Blanca Martin-Vaca |author3=Didier Bourissou | journal=Chem. Rev.|year=2004|volume=104|issue=12|pages=6147–6176|doi=10.1021/cr040002s|pmid=15584698}}

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• Cossee–Arlman mechanism
• Ziegler–Natta catalyst
• Polymerization
• Coordination bond

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Category:Polymerization reactions