Bipolaron saturation in polypyrrole

Saturation of bipolaron, the species responsible for conduction in polypyrr ole (PPy), has been studied using positron annihilation lifetime (PAL) spec troscopy, conductivity, and electron spin resonance (ESR) measurement. It i s observed that when strong oxidizing agents are used, the defects are pred ominantly bipolarons as is evident from the PAL spectroscopic studies coupl ed with ESR measurements and its saturation occurs right at the onset of ox idation. However, in the case of a mild oxidizing agent, the dominant defec ts are bipolarons only at higher oxidizing strengths [greater than or equal to 1.0(N)] and no saturation is attained even at the highest strength stud ied. Conductivity data corroborate the findings. [S0163-1829(99)11031-2].