Polypyrrole water-soluble forms

Electrically conducting polymer particles such as polypyrrole and polyaniline could also be prepared by dispersion polymerization in aqueous ethanol (31). The oxidation polymerization of pyrrole and aniline has been carried out at the electrode surfaces so far and formed a thin film of conducting polymer. On the other hand, polypyrrole precipitates as particles when an oxidizing reagent is added to a pyrrole dissolved ethanol solution, which contains a water-soluble stabilizer. In this way electrically conducting polymer particles are obtained and, in order to add more function to them, incorporation of functional groups, such as aldehyde to the surface, and silicone treatment were invented (32). 

Fig. 3.10. Some of the more commonly encountered organic conductor materials (a) polypyrrole, (b) polyaniline, and (c) poly(3,4-ethylenedioxythiophene) (PEDOT). When combined with water soluble organic acids (e.g. sulfonic acids like benzosul-fonic acid) many of these polymers can form doped complexes which are highly conductive and can be dispersed into suspension. Substituted versions of these polymers which are self-doped have also been developed.

Soluble conducting polymers can be solvent cast to form coatings. The addition of appropriate substituents to the polymer backbone or to the dopant ion can impart the necessary solubility to the polymer. For example, alkyl or alkoxy groups appended to the polymer backbone yield polypyrroles [117,118], polythiophenes [118], polyanilines [119,120], and poly(p-phenylenevinylenes) [97] that are soluble in common organic solvents. Alternatively, the attachment of ionizable functionalities (such as alkyl sulfonates or carboxylates) to the polymer backbone can impart water solubility to the polymer, and this approach has been used to form water-soluble polypyrroles [121], polythiophenes [122], and polyanilines [123]. These latter polymers are often referred to as self-doped polymers as the anionic dopant is covalently attached to the polymer backbone [9]. For use as a corrosion control coating, these water-soluble polymers must be cross-linked [124] or otherwise rendered insoluble. 

Since pyrrole and its derivatives form very stable conducting surfaces, Za-gal, Bedioui, and coworkers used ultramicro-carbon-fiber electrode modified with polypyrrole-dopped cobalt-tetrasulfonated phthalocyanine for the electrocatalytic oxidation of 2-ME The resulting electrode was stable and showed a detection limit of 8 10 M. Pyrolle substituted phthalocyanines have been used for the analysis of cysteine. Electrocatalytic behavior of MPc complexes has also been examined under homogeneous conditions. Water soluble OMo (OH)TSPc catalyzed the oxidation of cysteine under homogeneous conditions. ... 

A new class of water soluble polypyrrole has been prepared by selfdoping of the polymer. These self-doped polypyrroles can be prepared electrochemically or chemically, using various dopant anions covalently bound to the polymer backbone. The self-doped sulfonated polypyrrole is most commonly synthesized electrochemically in nonaqueous media. Electrochemical synthesis in aqueous media and chemical synthesis are not typically used, presumably due to issues with overoxidation. The postpolymerization modification of polypyrrole, in a manner similar to that used to form sulfonated polyaniline is rare [41]. The various synthetic approaches and properties of the polymer are discussed in the following sections. 

A characteristic feature of the parent polypyrroles, polythiophenes and polyanilines is their insolubility in water and common organic solvents (although the EB form of polyaniline is soluble in NMP, DMSO and several other solvents). This intractability and consequent difficulties in processing have until recently limited their exploitation. However, the introduction of substituents onto the aromatic rings of the polymers, the use of surfactant-like dopant anions and the generation of colloidal dispersions have markedly enhanced the processability of ICPs (see Section 8 below). 

Highly ordered conductive polypyrroles have been obtained by polymerization of self-assembling electroactive monomers, such as potassium 3-(3-alkylpyrrol-1-yl) propane sulfonates [206,207]. Monomers with appropriate alkyl side-chain lengths (octyl to tetradecyl) form micelles in an aqueous solution, and polymerize giving lamellar, semicrystalline thin films, with a head-to-head bilayer type packing. Some of those polymers are soluble in water (Scheme 10.13). 

---