thumb|200px|Structure of a poly(1,1{{prime}}-ferrocene-silane).
'''Polyferrocenes''' are polymers containing ferrocene units. Ferrocene-derived polymers have been studied for their optical and electrical properties. Despite nearly a half-century of research, polyferrocenes still have no commercial applications.
==Construction== [[File:Biferrocene.svg|thumb|left|122 px|Biferrocene is the smallest unit of polyferrocene.]] The simplest notional polyferrocene is poly(1,1{{prime}}{{nbh}}ferrocenylene), corresponding to a series of bis(fulvalene)diiron molecules, but with the fulvalene moieties offset to link the molecules. It is extraordinarily difficult to manufacture pure, as even small oligomers rapidly precipitate from solution into an inhomogenous mass.<ref>{{cite journal|doi=10.1002/adfm.202006391|journal=Advanced Functional Materials|title=On-surface synthesis of polyferrocenylene and its single-chain conformational and electrical transport properties|first1=Vijai M.|last1=Santhini|first2=Oleksandr|last2=Stetsovych|first3=Martin|last3=Ondráček|first4=Jesus I.|last4=Mendieta Moreno|first5=Pingo|last5=Mutombo|first6=Bruno|last6=de la Torre|first7=Martin|last7=Švec|first8=Jiří|last8=Klívar|first9=Irena G.|last9=Stará|first10=Héctor|last10=Vázquez|first11=Ivo|last11=Starý|first12=Pavel|last12=Jelínek|p=2006391|year=2020}}</ref> Nevertheless, yields of up to ~80% are possible, and the product is a p-type semiconductor.<ref>{{Cite journal|journal=Chemical Reviews|year=1999|volume=99|title=Organometallic polymers with transition metals in the main chain|first=Paul|last=Nguyen|first2=Paloma|last2=Gómez-Elipe|first3=Ian|last3=Manners|orig-date=7 Dec 1998|doi=10.1021/cr960113u|publisher=American Chemical Society|p=1517}}</ref>
Many spacer-substituted polyferrocenes are accessed relatively easily. Ring-opening polymerization usually leads to polymers containing ferrocene in the backbone: for example, poly(1,1'-ferrocene-silane).<ref name="Manners2"> R. Resendes, A. Berenbaum, G. Stojevic, F. Jäkle, A. Bartole, F. Zamanian, I. Manners: ''Application of ring-opened poly(ferrocene)s as protective charge dissipation coatings for dielectrics''. In: ''Advanced Materials'', 12(5), (2000), pp. 327-330, {{doi|10.1002/(SICI)1521-4095(200003)12:5<327::AID-ADMA327>3.0.CO;2-L}}.</ref> Oxidizing the resulting polymers can convert up to half the sandwiches to ferrocinium ions, as electrostatic repulsion prevents the oxidation of adjacent metallocenes.<ref>{{cite journal|p=15|doi=10.1002/ejic.201600983|journal=European Journal of Inorganic Chemistry|title=Why is ferrocene so exceptional?|first=Didier|last=Astruc|publisher=Wiley}}</ref>
Ferrocene can also be attached as pendant unit (ferrocenylated polymers, as it were).<ref name="DOI10.1039/c6cs00196c">Rudolf Pietschnig: ''Polymers with pendant ferrocenes.'' In: ''Chemical Society Reviews.'' 45, 2016, p. 5216, {{doi|10.1039/c6cs00196c}}.</ref>
== Potential applications == === Conductive materials === Polyvinylferrocene gives electroactive films that have been investigated as glucose sensors,<ref>{{cite journal|title= Ferrocene-mediated enzyme electrode for amperometric determination of glucose|author1=Cass, Anthony E. G. |author2=Davis, Graham |author3=Francis, Graeme D. |author4=Hill, H. Allen O. |author5=Aston, William J. |author6=Higgins, I. John |author7=Plotkin, Elliot V. |author8=Scott, Lesley D. L. |author9=Turner, Anthony P. F. |journal=Analytical Chemistry|year=1984|volume=56|issue=4 |pages=667–671|doi=10.1021/ac00268a018|pmid=6721151}}</ref> and spacecraft anti-charging coatings.<ref name="Manners2"/>
=== High refractive index === Polyferroccenes have attracted interest as high-refractive-index polymers, for anti-reflective coatings or light-emitting diodes.<ref name="DOI10.1088/1464-4258/4/6/356">Ian Manners: ''Polyferrocenylsilanes: metallopolymers for electronic and photonic applications.'' In: ''Journal of Optics A: Pure and Applied Optics.'' 4, 2002, p. S221, {{doi|10.1088/1464-4258/4/6/356}}.</ref> Poly(1,1'-ferrocene-silane)e, poly(1,1'-ferrocene-phosphane) and polyferrocenes with phenyl side chains are polymers with unusually high refractive index, with values in the refractive index of up to 1.74. These polyferrocenes show good film-forming ability.<ref name="DOI10.1002/anie.200604420">Vasilios Bellas, Matthias Rehahn: ''Polyferrocenylsilane-Based Polymer Systems.'' In: ''Angewandte Chemie International Edition.'' 46, 2007, p. 5082, {{doi|10.1002/anie.200604420}}.</ref>
=== Plasma resistance === Poly(ferrocene-dimethylsilane)s (PFS) are promising as barrier materials in plasma-assisted reactive ion etching. Due to the presence of iron and silicon in the main chain, the polymer proved to be relatively stable compared to purely organic polymers. During the etching, a thin iron and silicon-containing oxide layer was formed on the surface of the poly(ferrocene-dimethylsilane).<ref name="DOI10.1021/cm001052q">Rob G. H. Lammertink, Mark A. Hempenius, Vanessa Z.-H. Chan, Edwin L. Thomas, G. Julius Vancso: ''Poly(ferrocenyldimethylsilanes) for Reactive Ion Etch Barrier Applications.'' In: ''Chemistry of Materials.'' 13, 2001, p. 429, {{doi|10.1021/cm001052q}}.</ref>
== Further reading == * {{cite journal | author = Ian Manners | year = 1996 | title = Polymers and the Periodic Table: Recent Developments in Inorganic Polymer Science. | journal = Angewandte Chemie International Edition in English | volume = 35 | issue = 15 | pages = 1602–1621 | doi = 10.1002/anie.199616021 }} * Jürgen Falbe, Manfred Regitz (eds.): ''Römpp-Lexikon Chemie'' (in German), 9th edition, vol. 5, PI-S, 1999, {{ISBN|3-13-735010-7}}, pp. 3449-3455.
==References== {{Reflist}}
==External links== *{{Commonscat-inline|Polyferrocene}}
Category:Ferrocenes Category:Iron compounds Category:Polymers