Chemical and Electrochemical Syntheses of Conducting Polymers

Polymers can be prepared using chemical and/or electrochemical methods of polymerization (see Chap. 2), although most redox polymers have been synthesized by chemical polymerization. Electrochemically active groups are either incorporated into the polymer structure inside the chain or included as a pendant group (prefunctionalized polymers), added to the polymer phase during polymerization, or fixed into the polymer network in an additional step after the coating procedure (post-coating functionalization) in the case of polymer film electrodes. The latter approach is typical of ion-exchange polymers. Several other synthetic approaches exist; in fact, virtually the whole arsenal of synthetic polymer chemistry methods has been exploited. Polyacetylene—now commonly known as the prototype conducting polymer—was prepared from acetylene using a Ziegler–Natta catalyst [1–7]. Despite its historical role and theoretical importance, polyacetylene has not been commercialized because it is easily oxidized by the oxygen in air and is also sensitive to humidity. From the point of view of applications, the electrochemical polymerization of cheap, simple aromatic (mostly amines) benzoid (e.g., aniline, o-phenylenediamine) or nonbenzoid (e.g., 1,8-diaminonaphthalene, 1aminoanthracene, 1-pyreneamine) and heterocyclic compounds (e.g., pyrroles, thiophenes, indoles, azines) is of the utmost interest. The reaction is usually an oxidative polymerization, although reductive polymerization is also possible [8, 9]. Chemical oxidation can also be applied (e.g., the oxidation of pyrrole or aniline by Fe(ClO4)3 or peroxydisulfate in acid media leads to the respective conducting polymers), but electrochemical polymerization is preferable, especially if the polymeric product is intended for use as a polymer film electrode, thin-layer sensor, in microtechnology, etc., because potential control is a prerequisite for the production of good-quality material and the formation of the polymer film at the desired spot in order to serve as an anode during synthesis. A chemical route is recommended if large amounts of polymer are needed. The polymers are obtained in an oxidized, high conductivity state containing counterions incorporated from the solution used in the preparation procedure. However, it is easy to change the oxidation state of the polymer electrochemically, e.g., by potential cycling between the oxidized, conducting state and the