WATER-SOLUBLE SELF-ACID-DOPED CONDUCTING POLYANILINE - STRUCTURE AND PROPERTIES

The water-soluble self-acid-doped conducting polyaniline poly(aniline-co-N-propanesulfonic acid aniline) (PAPSAH) with an oxidation level of about 0.5 in aqueous solution and as a solid film has been characterized. Elemental analysis and spectroscopic data show that almost each amine nitrogen (approximatly 50% of the total nitrogen) in the polymer is linked with a -(CH2)(3)SO3H group, in which the proton is capable of doping the quinoid unit of the polymer. Titration analysis and spectroscopic data of the polymer in aqueous solution and as a solid film, respectively, show that suprisingly the fractions of -(CH2)(3)SO3H groups that protonate (dope) the imine nitrogens to give semiquinone radical cations are equal in both cases, about 0.66 (equivalent to the doping level, 0.33). However, the free spins in the aqueous solution are more localized than those in the solid film. The fractions of proton, about 34%, that do not participate in the doping have no effect on the conductivity of the film. As the doping level is reduced by increasing the degree of neutralization, the conductivity drops by a factor of 10(4) at the doping level of zero. The conductivity, UV-vis spectroscopy, and X-ray diffraction pattern of the polymer, in comparison with those of HCl-doped polyaniline, exhibit that the decreases of polaron delocalization and structural order result from the steric hindrance imparted by the substituent alkanesulfonic acid. The conductivity of PAPSAH film (at 25 degrees C, 10(-2) S/cm) increases with temperature from -50 degrees C (10(-8) S/cm) to +110 degrees C (10(-1) S/cm) due to thermal activation, and decreases with temperature from 110 to 170 degrees C (10(-5) S/cm) due to thermal undoping accompanied by the loss of some polarons. After the heating scan, the conductivity at room temperature drops by a factor of 10(3). Cyclic voltammetry of the polymer coated on a platinum electrode in aqueous acid solutions shows two redox reactions between -0.2 and +0.8 V vs SCE. The two oxidation potentials are dependent on pH in the range -0.05 to +2.09. During the redox process; the PAPSAH film exhibits reversible color changes from pale yellow to green to blue as in the case of polyaniline.