STRUCTURE CHARACTERIZATION OF SELF-ACID-DOPED SULFONIC-ACID RING-SUBSTITUTED POLYANILINE IN ITS AQUEOUS-SOLUTIONS AND AS SOLID FILM

Self-doped sulfonic acid ring-substituted polyaniline (SPAN) reported so far is only slightly soluble in water. This work reports the synthe sis route of SPAN in water with a solid content at least 50% by weight , which is stable (without precipitation) for more than 1 year and can be cast into freestanding films. The protons on the bound sulfonic ac id groups can dope the imine nitrogens both in its aqueous form and as a solid film as evidenced by the presence of polaron absorption bands in its UV-vis spectra and of free spins from the ESR measurement. Tit ration analysis and spectroscopic data of the polymer in aqueous solut ion and as solid film, respectively, show that, surprisingly, the frac tions of -SO3H groups that protonate (dope) the imine nitrogens to giv e semiquinone radical cations are equal in both cases, about 0.60 (equ ivalent to the doping level, 0.30). However, the free spins in the aqu eous solution are more localized than those in the solid film. The the rmostability of SPAN is also investigated. The conductivity of SPAN fi lm (at 25 degrees C, 0.01 S/cm) increases with temperature from -10(0. 002 S/cm) to 190 degrees C (0.09 S/cm) and decreases with temperature from 190 to 225 degrees C (0.06 S/cm) due to thermal undoping accompan ying a loss of some polarons as confirmed by the UV-vis, LR, and TGA a nalyses. After the heating scan, the conductivity at room temperature drops by a factor of 10(3).