Sintese, propriedades e aplicações do poli-pirrol dopado com anions anfifilicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

Research on intrinsically conducting polymers has grown in the last years due their potential technological applications. They can be reversively driven to their conductive or insulator states by a redox process. This involves the introduction or ions into the material in order to maintain the charge eletroneutrality and, generally, occurs during polymer synthesis. In the case of poly(pyrrole), PPy, the doping ions are inserted or expelled from the film during the ciclying between the oxidized and reduced states and depends on the nature of the doping anion used in the synthesis. In this work we studied the redox properties of PPy galvanostatically synthesized by oxidation of pyrrole in an aqueous solution containing dodecylbenzenesulfonate anion. A study of the morphology of the polymer by Scanning Electron Microscopy and X-Ray Scattering showed that the surface topography of film depends on the synthesis conditions and its thickness. These changes are due to different kinetics of film growth. The X-Ray difratograms revealed that the amphiphilic anion has a higher degree of order than that of the polymer chain. The study of the redox properties in aqueous solutions revealed that the synthesis conditions affect these properties, probably due to the morphological changes. The cyclic voltammograms indicate that ion difusion and electron transfer have an important effect on the kinetics of the redox reactions. The nature of the electrolyte and the thickness of the film influences the ion difusion into the polymer matrix. Cation difusion is the driving force of the redox process. In this case, the high molecular weight and affinity of the doping anion immobilize it in the polymeric matrix when the pyrrolic chain is reduced. In order to hold the charge electroneutrality the cation of the electrolyte is inserted into polymer. When the pyrrolic matrix is oxidized the cation is expelled from the material. Electrogravimetric studies showed that when the polymer is overoxidized the anion of the electrolyte also participates in the process. This redox process bahavior allows the application of PPyDBS as ionic exchangers depending on its doping leveI. Another important characteristic of the redox process is that two cathodic peaks can be seen which are assigned to the ordered arrangement of the doping anion. This arrangement influences the relaxation processes of the polymeric chain, as can be observed in the transmitance variation measurements as a function of potential. The film of PPyDBS maintains its electrochromic behavior whe switched for 3000 cycles. The color changes from yellow (reduced form) to brown (oxidized). These properties were aIso influenced by the electrolyte. The study of the redox properties in an organic solvent showed that the ion diffusion occurs only in a superficial layer. This causes polymer degradation and decreases its cyclability. The capacity and specific energy values are similar to those of a Pb/sulfuric acid battery. The results obtained show that PPy doped with amphiphilic anions is a good candidate for electrode in rechargeable batteries. The data obtained in this work shows that PPyDBS can be used in several technological applications. It is easiIy prepared in aqueous solution and uses low cost raw materiaIs. The film has good adherence to a metallic substratum and eIectrochemical stability. The properties of the film can be modified by the doping level of the polymeric chain.

ASSUNTO(S)

polimeros e polimerização quimica organica - sintese

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