Polyaniline derivatives, self-doped

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Different self-doped polyanilines have been prepared using aniline derivatives eontaining earboxylate or sulfonate groups, or the aeid funetionalities were ineor-porated during a post-modifieation step using the appropriate ehemieal or eleetro-ehemieal reaetions [158,197,254,303],... 

Figure 1.18 Various self-doped polyaniline derivatives.

Polyaniline is the conducting polymer most commonly used as an electrocatalyst and immobilizer for biomolecules [258-260]. However, for biosensor applications, a nearly neutral pH environment is required, since most biocatalysts (enzymes) operate only in neutral or slightly acidic or alkaline solutions. Therefore, it has been difficult or impossible to couple enzyme catalyzed electron transfer processes involving solution species with electron transport or electrochemical redox reactions of mostly polyaniline and its derivatives. Polyaniline is conducting and electroactive only in its protonated (proton doped) form i.e., at low pH valnes. At pH values above 3 or 4, polyaniline is insulating and electrochemically inactive. Self-doped polyaniline exhibits redox activity and electronic conductivity over an extended pH range, which greatly expands its applicability toward biosensors [209, 210, 261]. Therefore, the use of self-doped polyaniline and its derivatives could, in principle. 

H. Varela, R. M. Torres , D. A. Buttry, Mixed cation and anion transport during redox cycling of a self-doped polyaniline derivative in nonaqueous media, Journal of the Electrochemical Society 2000, 147, 4217. 

H. Mizobuchi, T. Kawai, K. Yoshino, Ferromagnetic behavior of self-doping type polyaniline derivatives depending on oxidation state, Solid State Communications 1995, 96, 925. 

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