Solvent effects on the characteristics of soluble polypyrrole

Chemically synthesized polypyrrole (PPy) with electrical conductivity of 1.0 S/cm doped with dodecylbenzene sulfonate anion was dissolved in organic polar solvents but showed reduced conductivity of 10^-2 S/cm when cast into a film. The PPy was also soluble in weakly polar solvents when dodecylbenzene sulfonic acid (DBSA) was mixed with the solvents and showed no change in the conductivity when cast into films. The electronic absorption spectra of the polymer solutions in the mixed solvent of DBSA/chloroform revealed the absorption maximum in the NIR while the solutions in the polar solvent showed the maximum at 410 nm. The solutions were spin-cast into films with a mirror-like surface regardless of the solvents used, which indicates that the solutions were homogeneous. A dynamic light scattering study confirmed that the molecular size of PPy dissolved in the polar solvents was too small to carry out the experiment. However, the dynamic light scattering of PPy dissolved in the mixed solvents showed that the scattering entities were grown with a narrow size distribution. The hydrodynamic radius of scattering entities in chloroform was 27 nm with the DBSA/polymer weight ratio of 2 and grew to 40 nm with an increase of the DBSA/polymer weight ratio to 50.