Poly(3,4-ethylenedioxythiophene)

Abbreviation: PEDOT

Conductive polymer

Can only exist with the counter ions

1.011 g/cm3 ( PEDOT: PSS, fixed)

100 ° C ( PEDOT: PSS)

Poly -3 ,4- ethylenedioxythiophene ( PEDOT, and PEDT ) is a polymeric chemical compound that consists of 2,5- linked units ethylenedioxythiophene ( EDOT ). It belongs to the class of conductive polymers. The extended over the entire molecular system of conjugated double bonds in combination with a "doping" with a negatively charged counterion permits the conductivity. In the oxidized conductive state, the charges of the defect electrons in the conjugated chains are compensated by intercalated anions.

Depending on the application PEDOT is prepared with different counter ions. An important is the negatively charged polymer PSS ( polystyrene sulfonate ), the conjugated polymer is then as PEDOT: PSS respectively. PEDOT: iodide is an anion exchanger.

Synthesis

PEDOT is prepared by oxidative polymerization of EDOT. In the chemical preparation, it precipitates as insoluble black precipitate. A suitable oxidizing agent is iron (III ) chloride ( FeCl3). Water, methanol, ethanol, acetonitrile and other polar solvents may be used for the synthesis. In the electrochemical polymerization of PEDOT it precipitates as a black, electrically conductive layer onto the anode. In order to concatenate n pyrrole, 2 · n-2 electrons are withdrawn ideally. The PEDOT is also oxidized because of its lower oxidation potential compared to EDOT during polymerization. The degree of oxidation is generally 0.25 to 0.4. Consequently, bears any third or fourth monomer unit in the polymer chain has a positive charge. For charge compensation therefore the supporting electrolyte are incorporated during the formation of polymer anions. The counterion used largely determines the polymer properties.

Reaction mechanism

EDOT is oxidized in the first reaction step to the radical cation, which is a key intermediate in the oxidative polymerization. Two radical cations couple to the dimeric dication. May simultaneously two hydrogen ions are removed already during this dimerization. Since the oxidation potential of the dimer formed is now below that of the monomer, it is immediately oxidized to the radical cation. However, the polymerization is continued only if the oxidation potential remains sufficiently high to oxidize further EDOT to the radical cation.

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. Special processes can even immobilize enzymes on the Polypyrroloberfläche.

Electrochromism

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