K.I. Chane-Ching

Electrosynthesis of adherent polyaniline films on iron and mild steel in aqueous oxalic acid medium

Abstract Polyaniline (PANi) films can be electrosynthesized by oxidation of aniline on iron and mild steel in a one-step process from an aqueous oxalic acid medium which passivates substrates. Homogeneous and strongly adherent films of controlled thickness can be deposited either in the potentiodynamic or galvanostatic modes. These films are characterized by IR, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC) and matrix-assisted UV-laser desorption ionization (MALDI) techniques, and have a structure similar to that of PANi deposited on platinum. Iron samples coated with PANi exhibit much better protection against corrosion in an acidic solution (0.4 M NaCl + 0.1 MHCl) than the polypyrrole-coated ones. Attempts to grow PANi films on zinc or zinc—nickel alloy in oxalic acid were unsuccessful because the formation of insulating layers prevents electropolymerization.

Electrodeposition of protective polyaniline films on mild steel

Abstract The electrodeposition of protective polyaniline (PANi) films on mild steel from aqueous oxalic acid is reported. The electropolymerization of aniline occurs on a surface passivated by the precipitation of an Fe(II)-oxalate layer and leads to strongly adherent films with a controlled thickness and with the same structure as the idealized emeraldine base. When they are dipped in an acidic solution (0.4 M NaCl + 0.1 M HCl) the PANi-coated iron samples exhibit very good protection against corrosion and are much more effective than polypyrrole coated ones.

Synthesis of 2,5-di(2-thienyl)-1H-pyrrole N-linked with conjugated bridges

Abstract The Knorr–Paal reaction of 1,4-di(2-thienyl)-1,4-butanedione with anilines to yield N-substituted-2,5-di-(2-thienyl)-1H-pyrroles (SNS derivatives) was tested by using different acid catalysts in toluene and acetic acid. Di-SNS derivatives were also synthesized in toluene at reflux in the presence of propionic acid, these mild conditions giving acceptable yields in a one-step procedure.

Polythienobenzothiophenes, a new family of electroactive polymers: electrosynthesis, spectral characterization and modelling

New conducting polymers, including poly[thieno[3,2-b][1]benzothiophene] (poly-TBT) and poly [6-methoxythieno[3,2-b][1]benzothiophene] (poly-MeOTBT) were electrosynthesized by anodic oxidation of the corresponding monomers in 0.1 M LiClO4 acetonitrile solution. Poly-TBT and poly-MeOTBT electroactive films were formed on platinum electrodes and characterized spectroscopically. FT-IR studies show that both polymers present couplings occurring on the thiophene moiety and the phenyl ring, with a step-like structure. MALDI-TOF mass spectrometry indicates that poly-TBT and poly-MeOTBT films are mainly constituted of short-chain oligomers. The results of molecular orbital (MO) calculations performed on the basis of a radical-cation electropolymerization mechanism are in good agreement with our spectral data.

Anodic oxidation of dipyrrolyls linked with flexible or rigid spacers: study of the electropolymerization mode

Dipyrrolyl monomers with more or less flexible and bulky spacers have been synthesized. The electrochemical behaviour of these monomers and their corresponding polymers has been investigated. Convergent results, obtained by cyclic voltammetry of the monomers and the polymers, ESCA analysis and mass measurements, demonstrate that from an early stage of polymerization, the monomers are oxidized at both pyrrolyl units, leading to different polymer structures, depending on the spacers used.

Anodic oxidation of dipyrrolyls linked with conjugated spacers: study of electronic interactions between the polypyrrole chain and the spacers

In order to promote interchain electronic connections in conducting polymers, three dipyrrolyl monomers have been synthesized, with conjugated spacers mimicking chains of the oligo-phenylene, oligo-phenol and oligo-aniline type. The electrochemical behaviour of these molecules as well as the characteristics of the resulting polymers have been investigated, with the help of molecular modelling (AM1-SM2). Convergent results, obtained by cyclic voltammetry, quartz crystal microbalance and ESCA, demonstrate that both pyrrolyl moieties are involved in the polymerization process, leading therefore, to ladder-like structure polymers. FTIR studies show strong interactions between the polymer backbone and the conjugated bridges.

Macroscopic modulation of the π-electron density of pendant groups grafted on conductive polymers

Abstract The influence of the redox switching reaction of a conductive polymer upon the π electron density of grafted pendant groups has been studied. Poly( N -phenylpyrrole) and poly( N -benzylpyrrole) have been compared by means of IR spectroscopy and molecular modelling. In the case of poly( N -phenylpyrrole), the evolution of the infrared vibrational bands expresses a reversible modulation of the π electron density of the benzene nucleus when the polymer is switched from its reduced to its oxidized form. There is no such effect when the aromatic moieties are separated from the polymer backbone by a CH 2 group. Moreover, molecular modelling suggests that oxidation of poly( N -phenylpyrrole) makes it possible to break the conjugation between the benzene nuclei and the polypyrrole backbone.

Electrochemical and pH control of the complexation/decomplexation of 4-amino-N,N-diphenylamine with β-cyclodextrin

The behavior of the inclusion complex based on 4-amino-N,N-diphenylamine (ADPA) and cyclodextrin was studied by several techniques at different pH values and in different oxidation states. The results indicate that the reversible inclusion of the guest compound depends on its protonation state, and that its oxidation and reduction occur outside the cyclodextrin cavity. Moreover, the product of the guest bielectronic oxidation reaction is protonated and is free mainly, but in the presence of cyclodextrin and at neutral pH, it fits back into the cavity. This work shows that it is possible to control, by the pH and/or the applied potential, the complexation of ADPA or its oxidation product in a cyclodextrin cavity and gives information for synthesizing encapsulated conductive polymers based on a PANI like structure.

Bithiophene electropolymerization in aqueous media: a specific effect of SDS and β-cyclodextrin

The electrochemical polymerization of bithiophene was performed in water in the presence of either sodium dodecyl sulfate (SDS) or hydroxypropyl-β-cyclodextrin (HPβCD), mainly under potentiostatic conditions. The polymerization process was followed by electrochemical quartz crystal microbalance in order to determine the yield as a function of the current and the potential. Comparable results are obtained in both media (SDS and HPβCD). The polymerization process appears to be critically dependent on the potential and seems to be rate-limited by slow bithiophene diffusion through an interface consisting of accumulated CD or SDS on the electrode surface.

Polymer chain encapsulation followed by a quartz microbalance during electropolymerization of bithiophene-β-cyclodextrin host–guest compounds in aqueous solution

Abstract Hydroxypropyl-β-cyclodextrins (HPβCD) which form 1:1 host–guest inclusion compounds with bithiophene (BT) are used for the anodic electropolymerization of bithiophene in aqueous solution. Partial encapsulation of the polymer chains by cyclodextrins is suspected from the quartz balance response during polymer reduction by cyclic voltammetry or double-step chronoamperometry. In this case, relatively thin films containing more than one HPβCD molecule for ten BT monomers are formed on platinum electrodes. On the other hand, HPβCD insertion or adsorption in the oxidized form of the polymer, obtained under galvanostatic or potentiostatic conditions, was found to be dependent on experimental conditions (long polymerization time). These results tend to confirm that polymerization occurs outside the CD cavity and that cyclodextrin insertion may occur by chain encapsulation after the polymer formation.