Sa. Chen et Gw. Hwang, STRUCTURE CHARACTERIZATION OF SELF-ACID-DOPED SULFONIC-ACID RING-SUBSTITUTED POLYANILINE IN ITS AQUEOUS-SOLUTIONS AND AS SOLID FILM, Macromolecules, 29(11), 1996, pp. 3950-3955
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).