Poly-3,4-ethylenedioxythiophene

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Structural formula
Structural formula of PEDOT
General
Surname Poly-3,4-ethylenedioxythiophene
other names

Abbreviation : PEDOT

CAS number 155090-83-8 (PEDOT: PSS)
Monomers / partial structures 3,4-ethylenedioxythiophene ,
Type of polymer

Polythiophene

properties
Physical state

firmly

density

1.011 g / cm 3 (PEDOT: PSS, solid)

Melting point

300 ° C (decomposition) (PEDOT: PSS)

safety instructions
GHS labeling of hazardous substances
no classification available
H and P phrases H: see above
P: see above
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Poly-3,4-ethylenedioxythiophene ( PEDOT , sometimes PEDT or PDT ) is an electrically conductive thiophene- based polymer . It consists of 2,5-linked 3,4-ethylenedioxythiophene units (EDOT). The polymer has a fully conjugated π system of double bonds . The automatically occurring " doping " during the polymerization to PEDOT by a dopant enables conductivity . In the oxidized, conductive state, the positive charges of the holes in the conjugated chain are compensated by anions. So PEDOT is a hole conductor.

There are a number of different PEDOT variants and display options, with PEDOT: PSS and PEDOT: Tos being addressed here as examples due to their significant differences.

synthesis

A distinction must be made between PEDOT: PSS and other PEDOT variants (such as PEDOT: Tos, PEDOT: Cl etc.), as these differ significantly in their representation and processing steps. PEDOT: PSS is a ready-to-use aqueous suspension, whereby PEDOT: Tos or PEDOT: Cl can only be formed as an insoluble film on a substrate. If an oxidizing agent is added to EDOT in solution, it precipitates out as a blue solid, which after separation and drying can be pressed into electrically conductive PEDOT pellets.

Synthesis of PEDOT: PSS

PEDOT: PSS is represented by the oxidation of EDOT by catalytic amounts of iron (III) sulfate in water. The reoxidation of iron is given by sodium persulfate . In addition, the polyelectrolyte sodium polystyrene sulfonate is added, which, in addition to doping the PEDOT, also ensures its water solubility. After a deep blue dispersion has formed, the reaction mixture is purified with the aid of anion and cation exchange resins. The aqueous PEDOT: PSS dispersion achieves electrical conductivities of approx. 0.1 - 2 S / cm . High-boiling solvents such as DMSO or ethylene glycol increase the conductivity massively to up to 500 S / cm. The increase in conductivity is due to the separation of PEDOT and PSS during film formation. PSS in itself is an isolator.

Synthesis of PEDOT: Tos and derivatives

PEDOT: Tos is produced by the oxidative polymerisation of EDOT with the help of iron (III) tosylate. Non-polar solvents such as butanol , ethanol or acetonitrile are primarily used as the reaction medium. The mixture of EDOT, iron (III) tosylate and solvent is applied to a substrate with the help of appropriate methods such as spin coating , knife coating or ink jetting . Oxidative polymerization then takes place in the heat (70–100 ° C). The by-products of the polymerization are removed from the film by washing with ethanol, acetone or water. An insoluble blue film remains, which usually has an electrical conductivity between 300 and 1400 S / cm. Polymer additives, especially polyethylene glycols, lead to such high electrical conductivity. The counterion of the iron (III) salt determines the doping anion; tosylate is usually chosen because it leads to very high conductivities.

In the chemical preparation it precipitates as an insoluble, blue precipitate. A suitable oxidizing agent is iron (III) chloride (FeCl 3 ). Water, methanol , ethanol , acetonitrile and other polar solvents can be used for the synthesis. During the electrochemical polymerization of PEDOT, it is deposited as a blue, electrically conductive layer on the anode . In order to link n thiophene units, ideally 2 · n −2 electrons are withdrawn. The PEDOT is also oxidized during the polymerization because of its lower oxidation potential compared to the EDOT. The degree of oxidation is usually between 0.25 and 0.4. As a result, every third to fourth monomer unit in the polymer chain carries a positive charge. To compensate for the charge, anions of the conductive salt are therefore incorporated during polymer formation. The counterion used largely determines the arrangement of the resulting PEDOTs to one another and thus also the polymer properties.

Reaction mechanism

In the first reaction step, EDOT is oxidized to the radical cation , which is an essential intermediate in oxidative polymerization. Two radical cations recombine to form the dimeric dication . It is possible that two protons are split off simultaneously during this dimerization. Since the oxidation potential of the dimer that is now formed is below that of the monomer, it is preferentially oxidized to the radical cation. In the end, equivalent polymerization steps result in PEDOT, which is not obtained as a neutral PEDOT, but is quickly doped by excess oxidizing agent.

PolyPEDOT.svg

application

PEDOT is used in electrical engineering for the production of polymer-aluminum and polymer-tantalum electrolytic capacitors , in sensor technology, solar cell technology and microbiology . On an industrial scale, PEDOT is used as an electrode material in capacitors.

Electrochromy

PEDOT is used as an electrochromic material in thin layers . In the oxidized state, the polymer is light sky blue and almost transparent. In the reduced state the absorption is increased especially in the wavelength range between 550 and 650 nm and PEDOT becomes dark blue.

PEDOT in thermoelectrics

Since 2008 there has been an increased interest in PEDOT in thermoelectrics as an organic alternative material to inorganic bismuth telluride . Efficiencies that come close to those of conventional thermoelectrics have already been achieved. However, these top values ​​could only be achieved under optimal laboratory conditions, which has so far prevented PEDOT from being used economically.

Web links

Individual evidence

  1. ^ Entry on poly-3,4-ethylenedioxythiophene at ChemicalBook , accessed on October 10, 2012.
  2. ↑ Hyun Ju, Mihyun Kim, Jooheon Kim: Thermoelectric behavior of poly (3,4-ethylenedioxythiophene) / graphene composites depending on benzenesulfonate derivatives doped in polymer chains . In: Journal of Materials Science: Materials in Electronics . tape 26 , no. 4 , January 25, 2015, p. 2544-2554 , doi : 10.1007 / s10854-015-2721-0 .
  3. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  4. ^ W. Lövenich, R. Hill: Polymer coatings containing conductive polymers . Google Patents, February 2011.
  5. ↑ Tsung-Che Tsai, Hsiu-Cheng Chang, Chun-Hua Chen, Wha-Tzong Whang: Widely variable Seebeck coefficient and enhanced thermoelectric power of PEDOT: PSS films by blending thermal decomposable ammonium formats . In: Organic Electronics . tape 12 , no. December 12 , 2011, p. 2159–2164 , doi : 10.1016 / j.orgel.2011.09.004 .
  6. ↑ Olga Bubnova, Zia Ullah Khan, Abdellah Malti, Slawomir Braun, Mats Fahlman, Magnus Berggren, Xavier Crispin: Optimization of the thermoelectric figure of merit in conducting polymer poly (3,4-ethylenedioxythiophene) . In: Nature Materials . tape 10 , no. 6 , June 2011, p. 429-433 , doi : 10.1038 / nmat3012 .
  7. ↑ Elise M. Stewart, Manrico Fabretto, Mischa Mueller, Paul J. Molino, Hans J. Griesser, Robert D. Short, Gordon G. Wallace: Cell attachment and proliferation on high conductivity PEDOT-glycol composites produced by vapor phase polymerization . In: Biomaterials Science . tape 1 , no. 4 , March 5, 2013, p. 368-378 , doi : 10.1039 / C2BM00143H .
  8. ^ S. Machida, S. Miyata, A. Techagumpuch: Chemical synthesis of highly electrically conductive polypyrrole . In: Synthetic Metals . tape 31 , no. 3 , 1989, pp. 311-318 , doi : 10.1016 / 0379-6779 (89) 90798-4 .
  9. ^ Jürgen Heinze: Electronically conducting polymers . In: Eberhard Steckhan (Ed.): Electrochemistry IV. Topics in Current Chemistry. 152 . Springer, Berlin / Heidelberg 1990, ISBN 3-540-51461-9 , pp. 1-47 , doi : 10.1007 / BFb0034363 .
  10. ↑ Stephen V. Lowen, John D. Van Dyke: Mechanistic studies of the electrochemical polymerization of pyrrole: Deuterium isotope effects and radical trapping studies . In: Journal of Polymer Science Part A: Polymer Chemistry . tape 28 , no. 3 , 1990, p. 451-464 , doi : 10.1002 / pola.1990.080280301 .
  11. ↑ St. Kirchmeyer, D. Gaiser, HC Starck GmbH & Co KG: Electronic components: extremely flat and flexible
  12. ↑ Andreas Elschner, Stephan Kirchmeyer, Wilfried Lovenich, Udo Merker, Knud Reuter: PEDOT: Principles and Applications of an Intrinsically Conductive Polymer . CRC Press, 2010, ISBN 978-1-4200-6912-9 .
  13. ↑ Anna Maier: Functional coordination polymer films made from polyiminoarylenes with terpyridine ... disserta Verlag, 2011, ISBN 3-942109-48-4 , p. 10 ( limited preview in Google Book search).
  14. ↑ Prospero J. Taroni, Itziar Hoces, Natalie Stingelin, Martin Heeney, Emiliano Bilotti: Thermoelectric Materials: A Brief Historical Survey from metal junctions and Inorganic Semiconductors to Organic polymer . In: Israel Journal of Chemistry . tape 54 , no. 5-6 , June 1, 2014, pp. 534-552 , doi : 10.1002 / ijch.201400037 .
  15. ↑ Olga Bubnova, Zia Ullah, Abdellah Malti, Slawomir Braun, Mats Fahlman, Magnus Berggren, Xavier Crispin: Optimization of the thermoelectric figure of merit in conducting polymer poly (3,4-ethylenedioxythiophene) . In: Nature Materials . tape 10 , no. 6 , June 2011, p. 429-433 , doi : 10.1038 / nmat3012 .
  16. ↑ Teahoon Park, Chihyun Park, Byeonggwan Kim, Haejin Shin, Eunkyoung Kim: Flexible PEDOT electrodes with large thermoelectric power factors to generate electricity by the touch of fingertips . In: Energy & Environmental Science . tape 6 , no. 3 , February 20, 2013, p. 788-792 , doi : 10.1039 / C3EE23729J .
  17. ↑ G.-H. Kim, L. Shao, K. Zhang, KP Pipe: Engineered doping of organic semiconductors for enhanced thermoelectric efficiency . In: Nature Materials . tape 12 , no. 8 , August 2013, p. 719-723 , doi : 10.1038 / nmat3635 .