PHYSICOCHEMICAL PROPERTIES AND INTRINSIC STRUCTURES OF CHEMICALLY SYNTHESIZED POLYPYRROLE AND ITS COMPLEXES

Abstract

Oxidative polymerization of pyrrole has been carried out with halogens, ferric salts and organic electron acceptors (2,3-dichloro-5,6-dicyano-p-benzoquinone,halobenzoquinone) as oxidant and dopants in both aqueous media and organic solvents. Conductivities of the polypyrrole complexes formed range from good (40 S/cm) to poor (9x10-6 S/cm). Kinetic studies show that trimer and hexameric dications are probably the two main species formed at the initial stage of the polymerization of pyrrole with iodine. Deprotonation by a base, reprotonation by acids, reduction by phenylhydrazine and anion exchange with protonic acids are carried out in some of the complexes. X-ray Photoelectron Spectroscopy (XPS) data show that the pyrrolylium nitrogen can exist in three chemical states: imine, amine and positively charged states. Proton modifications of nitrogens in polypyrrole give rise to a number of intrinsic redox states analogous to those observed in polyaniline. The nitrogens associated with the corresponding oxidation states in both polymers exhibit similar behaviour towards protonation/deprotonation, oxidation/ reduction or charge transfer interactions with electron acceptors. Dopants such as chloride and bromide have also been found to exist in three chemical states: ionic, intermediary and covalent. Anion exchange reaction was found to proceed via the counterion associated with the pyrrolylium nitrogen. XPS data reveal that the organic electron acceptor such as the halobenzoquinone could undergo probably two modes of complexation with the pyrrolylium nitrogens. The thermal stability of the complexes are dopant dependant. Imine structure is invariably formed via a deprotonation process during thermal decomposition in all the complexes studied.