Water-Soluble Self-Doped 3-Substituted Polypyrroles

The preparation of sodium salts of 3-alkylsulfonate pyrroles with various lengths of the alkyl chain (propyl-, butyl-, and hexylsulfonate) and their electrochemical polymerization to poly (3-alkylsulfonate pyrroles) are described. The low oxidation potential of the monomers allows a direct oxidative electrochemical polymerization, without additional conduction salts. The experimental conditions provide, for the first time, solid evidence of the existence of self-doped conducting polypyrroles. The polymers are characterized by spectroscopy (FTIR, UV-vis-NIR, ESR, H-1, NMR in D2O solution), X-ray diffraction, cyclic voltammetry, and elemental analyses. The covalently attached sulfonate groups act as counterions for the charged backbone. The charge carriers are mainly spinless bipolarons. The conductivities are in the range 0.5-10(-3) S/cm, the lower value referring to the hexyl chain. Indications are given for deviations from planarity of the main chain. The substituted polypyrroles are water soluble in the self-doped state. TO NMR spectra of the aqueous solutions of self-doped polymers are discussed.