11 - Intrinsically Conducting Polymers

Abstract

Conducting polymers have been synthesized before by mixing polymers with metal or graphite powders. But in the case of a new class of materials, the conductivity was an intrinsic property. Therefore, the name intrinsically conducting polymers (ICPs) was recommended. Conducting properties can be achieved by reduction of the neutral state. An example is the poly(dibutoxyphenylenevinylene). A platinum electrode coated with polymer in acetonitrile showed the transition between neutral and oxidized state at +1V versus a platinum quasi-reference electrode and the transition between neutral and reduced state at –1.8V. The reduced state has received much less attention than the oxidized state. The oxidation process is reversible as it is possible to switch between the oxidized and neutral states. Otherwise, oxidation and reduction of conducting polymers are very complex processes. Therefore, the reversibility is limited and depends on the timescale. In a periodic oxidation–reduction cycle, only quasi-stable oxidized and reduced polymers can be expected. During synthesis or in the process of oxidation the chain of the conjugated polymer is positively charged. The charging can reach a degree of up to 25–30%. Anions are intercalated into the polymer structure to compensate the positive charges of the polymer chain. Conducting polymers can be synthesized by following conventional polymer synthesis routes. One can transfer the Ziegler-Natta synthesis of polyethylene to polyacetylene. The Ziegler–Natta catalyst is solved in large excess in an inert solvent with acetylene streaming over the surface. A black film of polyacetylene is formed on the liquid surface.