Synthesis and characterization of soluble polypyrrole

Soluble polypyrrole(PPy) was synthesized chemically by using ammonium persulfate and dodecylbenzene sulfonic acid as an oxidant and a dopant, respectively. It was found that the soluble PPy powder as well as the cast film contained a high concentration of free radicals detected by an electron paramagnetic resonance spectrometer. The polymer solution was cast into a film with a very fine reflective surface. A thin film with the light transmittance of 80% showed the surface resistivity of 25 kΩ/square displaying an increase in the resistivity only by 20 kΩ/square compared to the resistivity of a thick film. DC conductivity of the PPy film fitted nicely the quasi-one-dimensional variable range hopping model. The bulk electrical conductivity of the cast film increased by one order during initial heating to 200°C in air and changed little during isothermal heating at 200°C for 120 minutes. The conductivity kept a half of the initial increase after cooling from 200°C to room temperature. The surface resistivity of the film, however, was found to increase dramatically on heating at 200°C in air. Since the surface resistivity showed no change on heating in nitrogen atmosphere at 200°C, oxidation during heating caused the decrease in the conductivity of the polymer.