Physical characterization of electrochemically and chemically synthesized polypyrroles

The results of temperature-dependent de conductivity, EPR magnetic suscepti bility, and X-ray photoelectron spectroscopy (XPS) experiments are compared for electrochemically and chemically synthesized polypyrrole (PPy) samples . For chemically synthesized PPy samples soluble in organic solvent with la rge size dopants such as dodecylbenzenesulfonic acid (DBSA) or naphthalenes ulfonic acid (NSA), de conductivity (sigma(dc)) is less than or equal to 0. 1 S/cm at room temperature, and its temperature dependence [sigma(dc)(T)] s hows strong localization behavior, while sigma(dc)(T) of the electrochemica lly synthesized PPy samples doped with hexafluorophosphate (PF6) is in the critical or the metallic regime. The density of states of chemically prepar ed PPy-DBSA samples is less than one-fourth that of electrochemically synth esized PPy-PF6 samples. The g values and temperature dependence of the line width obtained from EPR experiments show that the paramagnetic signals in both electrochemically and chemically synthesized PPy samples are mainly du e to the polarons in pi-conjugated polymer chains. We observe the existence of one dopant per three pyrrole rings in PPy-DBSA and PPy-PF6 samples. Fro m the XPS experiments, one-fifth of the pyrrole rings of chemically prepare d PPy-DBSA are incorporated into interchain links or side chains, while for electrochemically prepared PPy-PF6, one-third of the pyrrole units are in side chains or crosslinks. We analyze that the side chains or cross-links o f chemically synthesized PPy samples are relatively reduced, and subsequent ly the interchain interaction weakens. For chemically synthesized PPy sampl es, the synthesis method using large size dopants is one of the important r oles for the reduction of side chains or cross-links and for the increase o f solubility. The weakness of the interchain interaction and the reduction of side chains or interchain links for PPy systems play an important role f or charge transport.