Oxidative Polymerization and Doping

Although known for decades, the particular reactivity of 3,4-ethylenedioxy-thiophene (EDOT) with chemical oxidants was found not earlier than 1988. First investigations about the electrochemical oxidation followed soon within the same year. The story of the PEDOT invention is disclosed in more detail in Chapter 4. The chemical and technical facts with emphasis on chemical methods will be summarized here. 

Generally speaking, EDOT is not too stable against oxidation, and it may be completely decomposed by very strong oxidants. So, for example, mixtures of EDOT and nitration agents like concentrated nitric acid quickly exhibit a dark blue color, which after a short time disappears. No defined nitration products can be isolated from these reaction mixtures.  

S)mthesized in boiling acetonitrile (bp 82°C), the PEDOT tetrachloroferrate exhibits a conductivity 3000-fold to polypyrrole x FeCl4, prepared under the same conditions 15 S/cm versus 5 x 10 S/cm, measured with pressed pellets. Surprisingly, the conductivity of PEDOT-tetrachloroferrate can be further enhanced by an extended reaction of EDOT and FeClg in boiling benzonitrile 

Several ofher mefal ions have been used rvith different success to oxidize EDOT. Manganese in higher oxidation states, especially manganese dioxide, is commercially used in a special application. PEDOT can be deposited on Mn02 layers to be further used as conductive base for galvanostatic copper plating.5 This will be discussed in detail in Chapters 8 and 10. 

Cerium(IV) was checked in the form of its sulfate Ce(S04)2 and, because of its better solubility, also with ammonium cerium nitrate (NH4)2Ce(N03)s in aqueous solution. Despite the high reactivity of cerium(lV) resulting in a very rapid reaction, the PEDOT from oxidation by Ce(lV) had a disappointing low conductivity of not more than 0.075 S/cm.  

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