Mobilities of charge carriers in poly(o-methylaniline) and poly(o-methoxyaniline)

Mobilities of charge carriers in poly(o-methylaniline) (PMA) and poly(o-methoxyaniline) (PMOA) films are electrochemically determined over a range of oxidation stages of the polymer films. In the low oxidation region, mobilities of both the polymers are comparable to that of polyaniline (PANI). In the high oxidation region, however, mobility values systematically decrease in the order of PANI > PMA > PMOA, showing that the bulky groups present at the ortho position play a more important role in the high oxidation region. The low mobilities of charge carriers in the high oxidation region explain why PMA and PMOA are less conducting than PANI.     

Characterization of ultrathin electroactive films synthesized via the self-limiting electropolymerization of o-methoxyaniline

The electropolymerization of o-methoxyaniline under self-limiting deposition conditions yields ultrathin (<20 nm) coatings of an insoluble, low-molecular-weight polymer on planar indium-tin-oxide electrode substrates. The self-limiting nature of the electropolymerization is achieved by using citrate-buffered aqueous electrolytes (pH 4.7) in which the developing polymer that deposits at the electrified interface is neither conductive nor permeable to monomer. Although non-conductive as electrodeposited, the resulting poly(o-methoxyaniline) coating becomes electroactive when transferred to acidic aqueous electrolytes. The morphology and chemical structure of the poly(o-methoxyaniline) coatings are characterized by surface-sensitive methods including atomic force microscopy, specular-reflectance infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemistry. Fundamental understanding of the structure/property relationships derived from these investigations on planar substrates will ultimately be applied to three-dimensional electrode nanoarchitectures that incorporate such electroactive coatings for enhanced charge-storage functionality.     

Photosensitive poly(benzoxazole) based on precursor from diphenyl isophthalate and bis(o-aminophenol)

A new synthetic method for the preparation of poly(benzoxazole) (PBO) precursor, poly(o-hydroxyamide) (7) from bis(o-aminophenol) (5) and diphenyl isophthalate (6) has been developed. Polymer 7 was prepared by the polycondensation of 5 and 6 in 1-methyl-2-pyrrolidinone (NMP) at 185-205 °C. Model reactions were carried out in detail to elucidate appropriate conditions for the formation of 2-hydroxybenzanilide (3) from o-aminophenol (1) and phenyl benzoate (2). The photosensitive (PBO) precursor based on polymer 7 containing a 22% of benzoxazole unit and 30 wt% 1-{1,1-bis[4-(2-diazo-1-(2H)naphthalenone-5-sulfonyloxy)phenyl]ethyl}-4-{1-[4-(2-diazo-1(2H)naphthalenone-5-sulfonyloxy)phenyl]methylethyl}benzene (S-DNQ) showed a sensitivity of 110 mJ cm⁻² and a contrast of 5.0 when it was exposed to 436 nm light followed by developing with a 2.38 wt% aqueous tetramethylammonium hydroxide solution at room temperature. A fine positive image featuring 8 μm line and space patterns was observed on the film of the photoresist exposed to 200 mJ cm⁻² of UV-light at 436 nm by the contact mode.     

Electrochemical and in situ TM-AFM studies of the polymerization conditions on poly(o-methoxyaniline) film morphology

The in situ atomic force microscopy and the electrochemical studies on electropolymerization of the o-methoxyaniline in the 0.0-0.8 V versus NHE range of the electrode potential are described. It is proved that in the 0.0-0.3 V versus NHE a redox process takes place, resulting in the formation of poly(o-methoxyaniline) in its reduced form, leucoemeraldine. The different morphologies are exhibited by poly(o-methoxyaniline) under different polymerization conditions. The microscopic results show that with the increase of the monomer concentration in the bulk of electrolyte solution the globular morphology, related to the coil like molecular structure, is replaced by the fibrilar one, related to the opened-up, more conductive extended coil structure. It is shown that oxidation of a leucoemeraldine state of polymer to its emeraldine state results in the change of the morphology from the chain like structure to the massive fibrilar like structure. The reduction of oxidized polymer results in its irreversible fragmentation.     

Potentiodynamic deposition of poly (o-anisidine-co-metanilic acid) on mild steel and its application as corrosion inhibitor

For the first time, poly (o-anisidine-co-metanilic acid) (PASM) was deposited on mild steel substrate by electrochemical polymerization of o-anisidine and metanilic acid monomers in aqueous solution of 0.1 M H₂SO₄. The electrochemical polymerization of o-anisidine takes place in the presence of metanilic acid monomer and uniform, strongly adherent coating was obtained on the substrate. The electroactivity of copolymer was studied by cyclic voltammetry and AC impedance techniques. There is an increasing anodic current due to oxidation of metanilic acid monomer at the surface of the electrode when the applied potential is cycled from −0.2 V to 0.8 V. These deposits were characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis and TG/DTA techniques. The effect of various concentrations of PASM copolymer solution in acid rain corrosive media has been studied through potentiodynamic polarization, AC impedance and I-E curve methods. The soluble form of polymeric solution provided better anti-corrosive behavior in artificial acid rain solution.     

Corrosion protective poly(o-ethoxyaniline) coatings on copper

Poly(o-ethoxyaniline) (POEA) coatings were synthesized on copper (Cu) by electrochemical polymerization of o-ethoxyaniline in aqueous salicylate solution by using cyclic voltammetry. These coatings were characterized by cyclic voltammetry, UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The performance of POEA as protective coating against corrosion of Cu in aqueous 3% NaCl was assessed by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization and EIS studies demonstrate that the POEA coating has ability to protect the Cu against corrosion. The corrosion potential was about 0.330 V versus SCE more positive in aqueous 3% NaCl for the POEA coated Cu than that of uncoated Cu and reduces the corrosion rate of Cu almost by a factor of 140.     

In situ UV-vis spectroelectrochemistry of poly(o-phenylenediamine-co-m-toluidine)

Results of in situ UV-vis spectroelectrochemical studies of the electropolymerization of o-phenylenediamine (OPD), m-toluidine (MT) and the copolymerization of OPD with MT are reported. Electropolymerization was performed in aqueous acidic medium at a constant potential of E_SCE = 1.0 V at an indium doped tin oxide (ITO) coated glass electrode. The course of homopolymerization was followed for MT and OPD solutions with various monomer concentrations. The spectral characteristics of the mixed solutions were studied at a constant concentration of MT and various concentrations of OPD in the comonomer feed. An absorption band at λ = 497 nm was assigned to the head-to-tail mixed dimer/oligomer resulting from the cross reaction between OPD and MT cation radicals. UV-vis spectra recorded during copolymerization show dependence of the growth of the band at λ = 497 nm on OPD concentration in the feed. At lower OPD feed concentration it appears as the major band in the corresponding spectra. The UV-vis spectra recorded for the copolymer films suggest the incorporation of both monomer units in the copolymer. The FT-IR spectra of the copolymers show the presence of phenazine type structures in the copolymer backbone.     

Poly(o-ethylaniline) coatings for stainless steel protection

The poly(o-ethylaniline) coatings were electrochemically synthesized on 304-stainless steel by using cyclic voltammetry from an aqueous salicylate medium. Cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize these coatings, which indicates that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethyaniline on 304-stainless steel. The performance of poly(o-ethylaniline) as protective coating against corrosion of 304-stainless steel in aqueous 3% NaCl was evaluated by the open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The results of the potentiodynamic polarization and cyclic potentiodynamic polarization demonstrate that the poly(o-ethylaniline) coating provides excellent protection to both localized and general corrosion of 304-stainless steel. The corrosion potential was about 0.190 V more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated steel than that of bare steel and reduces the corrosion rate of steel almost by a factor of 20.     

Spectroelectrochemistry of two-layered composites of polyaniline and poly(o-aminophenol)

Electropolymerization of aniline on poly(o-aminophenol)(POAP)-coated gold and indium-doped tin oxide (ITO)-coated glass electrodes yields polyaniline(PANI)/POAP two-layer composite films, exhibiting reversible redox functions in aqueous acidic solution. The PANI deposition on the POAP-coated electrodes was monitored by cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. CV results show that PANI/POAP composite films exhibit better stability as compared to PANI films during potential cycling in aqueous acidic solutions. Characteristic UV-vis and Raman features of the composite films have been identified and their dependencies on the electrode potential are discussed. They were significantly different from the corresponding spectral characteristics of PANI and POAP films alone.     

Poly(N-methylpyrrole) electrodeposited on copper: Corrosion protection properties

Electrochemical synthesis of poly(N-methylpyrrole) films on copper electrodes from an aqueous oxalic acid has been achieved. A potential higher than 2 V (SCE) was needed to generate the polymer, for this reason, the polymer was in the overoxidized state. The inhibiting corrosion properties of this coating on copper were investigated for the first time in aqueous 0.1 M sodium chloride solution using potentiodynamic polarization, Tafel analyses, open-circuit potential and electrochemical impedance spectroscopy. Corrosion protection properties comparable to those of polypyrrole (PPy) films were observed for these films. A physical barrier effect is the most likely protection mechanism.     

Ethanol electrooxidation on platinum particles dispersed on poly(neutral red) film

The conductive polymer poly(neutral red) polymerized on a graphite electrode (PNR/graphite) as a support material was used for catalytic oxidation of ethanol in acidic solution and investigated by electrochemical methods. Pt particles loaded on the surface of PNR/graphite electrode exhibited higher electrocatalytic activity for ethanol oxidation in comparison with Pt particles supported directly on graphite. With the equivalent loading mass of Pt catalyst, the special activity (S _A ) at peak a of the Pt/PNR/graphite electrode polymerized for 10 cycles in 5 × 10⁻⁴ M NR + 0.5 M H₂SO₄ solution is 3,478 A C⁻¹ and about 2.20 times higher than that of the Pt/graphite electrode (1,582 A C⁻¹). The results show that the electrochemical performance of Pt catalyst for ethanol oxidation is improved by the addition of PNR     

Corrosion protection aspects of electrochemically synthesized poly(o-anisidine-co-o-toluidine) coatings on copper

The poly(o-anisidine-co-o-toluidine) coatings were synthesized on copper substrates by electrochemical copolymerization of o-anisidine with o-toluidine using sodium salicylate as supporting electrolyte. These coatings were characterized by cyclic voltammetry, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM). The formation of the copolymer with the mixture of monomers in the aqueous sodium salicylate solution was ascertained by a critical comparison of the results obtained with the polymerization of the individual monomers, o-anisidine and o-toluidine, respectively. The corrosion protection aspects of poly(o-anisidine-co-o-toluidine) coatings to copper was investigated in aqueous 3% NaCl solution by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization measurements and EIS studies showed that the poly(o-anisidine-co-o-toluidine) coatings provided the effective corrosion protection to copper than that of respective homopolymers. The corrosion rate is observed to depend on the feed ratio of o-toluidine used for the synthesis of the copolymer coatings.     

Comparative studies of solid-state synthesized poly(<Emphasis Type="Italic">o</Emphasis>-methoxyaniline) doped with organic sulfonic acids

Poly(o-methoxyaniline) (POMA) salts doped with organic sulphonic acids (methanesulphonic acid, p-toluenesulphonic acid and dodecylbenzenesulphonic acid) were firstly synthesized by using solid-state polymerization method. The polymers were characterized by Fourier transform Infrared (FTIR) spectra, ultraviolet visible (UV–vis) spectrometry, X-ray diffraction (XRD), Cyclic Voltammetry (CV), and conductivity measurements. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were done to study the morphologies of POMA salts. The results showed that the POMA doped with methanesulphonic acid displayed higher doping level and conductivity. On the contrary, POMA doped with dodecylbenzenesulphonic acid was lower at doping level and conductivity. In accordance with these results, the electrochemical activity was also found to be lower in dodecylbenzenesulphonic acid doped POMA. The results also revealed that the particles of POMA salts have the average size of less than 100 nm.     

Electrooxidation of methanol on Pt microparticles dispersed on SnO2 thin films

In this work, we have prepared electrodes through the electrodeposition of platinum micro particles on SnO₂ thin films in order to verify the application of this system as a catalyst for the electrooxidation of methanol. The oxide films were prepared through the method of polymeric precursor decomposition and calcinated at 550 °C. The employed oxides have proved to be a good matrix for the dispersion of platinum particles since they present high roughness. The maximum electrooxidation current was attained for a platinum content of approximately 600 μg cm⁻². The chronoamperometric results showed that the current values obtained for the electrooxidation of methanol were up to 10 times higher than the current values obtained with platinized platinum under the same conditions. The possible mechanisms that lead to this enhancement were discussed.     

A correlation of electrochemical and spectroelectrochemical properties of poly(o-toluidine)

A comparative discussion of the electrochemical and spectroelectrochemical properties of poly(o-toluidine) POT, a methyl substituted derivative of polyaniline, PANI, is presented. POT exists in various oxidation states and shows an insulator to conductor transition when doped by electrooxidation. The transformation of the polymer film from its non-conducting leucoemeraldine to its conducting emeraldine state and further on to its again non-conducting pernigraniline form was observed with different techniques including cyclic voltammetry, in situ conductivity measurements and in situ UV-vis and Raman spectroelectrochemical methods. Results reveal that POT shows a good correlation between its electrochemical and spectroelectrochemical properties in its different oxidation states.     

Inhibition of steel corrosion by electrosynthesized poly(o-anisidine)-dodecylbenzenesulfonate coatings

Poly(o-anisidine)-dodecylbenzenesulfonate (POA-DBSA) coatings were synthesized on stainless steel from aqueous solution containing o-anisidine and dodecylbenzene sulfonic acid by using cyclic voltammetry. These coatings were characterized by Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Corrosion tests of these coatings were carried out in aqueous 3% NaCl solution by using open circuit potential (OCP) measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The results reveal that POA-DBSA acts as a corrosion protective coating on steel and reduces the corrosion rate (CR) of steel almost by a factor of 14.5.     

Electrochemical preparation and kinetic study of poly(o-tolidine) in aqueous medium

Poly(o-tolidine), PoT, film was prepared by electrochemical oxidation of the monomer, oT, in 0.1 M HCl + 0.1 M KClO₄. The presence of KClO₄ in the formation medium was found to be essential for the electropolymerization process to proceed. Increasing the upper potential limit up to +1.5 V, instead of +1.0 V, leads to appearance of a new anodic peak at +1.36 V and enhancement of the polymer formation of PoT without changing the film structure. The electrochemical behavior of the formed polymer films was investigated in 1.0 M HClO₄. The kinetic parameters were calculated from the values of the charge consumed during the electropolymerization process. The rate of the polymerization reaction was found to depend on the concentration of the monomer rather than the electrolyte. The polymerization rate is first order with respect to the monomer concentration and zero order with respect to the electrolyte. The electrolyte plays no active role in the kinetics of the electropolymerization process and its role is most likely limited to polymer doping.     

Synthesis and characterization of electrically conducting poly-o-methoxyaniline Zr(1V) molybdate Cd(II) selective composite cation-exchanger

In this study a composite cation-exchanger poly-o-methoxyaniline Zr(1V) molybdate was prepared and the ion-exchange properties like ion-exchange capacity for different metal ions, elution behavior, pH titration and a temperature dependent study of ion-exchange capacity were explored. The physical properties of the material were also determined using TGA-DTA, FTIR, X-ray and SEM studies. The results of physical properties were found progressive in terms of their specific properties. Electrical conductivity of this composite determined by four-in-line probe method was found to be in semi-conducting range i.e. 10^− 4-10^− 2 S cm^− 1. The adsorption efficiency towards heavy metal ions was determined by distribution studies and material was found highly selective for cadmium a heavy toxic metal ion indicating the utility for the removal from waste stream.     

Electrochemical copolymerization of m-toluidine and o-phenylenediamine

Electroactive copolymers of m-toluidine (MT) and o-phenylenediamine (OPD) were prepared electrochemically in aqueous sulfuric acid by potential cycling and characterized with cyclic voltametry, in situ conductivity measurements and FT-IR spectroscopy. The voltammograms of the copolymers exhibit different behavior for different concentrations of OPD in the comonomer feed. At optimum conditions the resulting poly(OPD-co-MT) shows an extended useful potential range of the redox activity as compared to the corresponding homopolymers. The effect of scan rate and pH on the electrochemical activity was studied. The copolymer was electrochemically active even at pH 8.0. The stability of the copolymer film was also tested. The copolymer has a potential region of maximum conductivity different from that of PMT and POPD. The conductivity of the copolymer is between the conductivity of the homopolymers. The vibrational bands at 3122/3450 and 2922/875 cm⁻¹ in the FT-IR spectra of the copolymer indicate the presence of both OPD and MT units, respectively, in the copolymer backbone.     

Electrosynthesis and characterization of a poly(paraphenylene) deriving from p-fluoroanisole

The electrochemical oxidation of p-fluoroanisole (p-FA) in the solvent acetonitrile leads to oligomers and polymers of poly(paraphenylene) type. The electropolymerization process involves coupling reactions of the cation radicals intermediates. The obtained polymers are separated according to their chain length by selective precipitation in cyclohexane and ether. The corresponding structures are characterized by NMR, MS, FTIR, UV and XR diffraction. A preliminary physical study shows that the polymers are photoluminescent with a maximum emission in the near infrared.