Reversible redox behaviour of two electroactive polymethacrylates

Summary The radical melt polymerization of 2-[4-(6-methacryloyloxyhexa-1,6-diyloxy)phenylazo]-anthraquinone is described yielding the homopolymer p _m with the number average molecular weight (M _n ) of M _n =74kg/mol determined by gel permeation chromatography (GPC) using polystyrene (PS) calibration. The redox properties of a thin film of p _m were investigated by cyclic voltammetry. Two reversible redox waves were found at all applied sweep rates indicating two reversible electron (E) transfer processes of the anthraquinone units according the EE-mechanism. A thin film of the randomlike copolymethacrylate cp _r with the molar mass of M _n =73kg/mol was investigated, too. The sidegroups of cp _r are substituted by 77mol% with benzyl, by 22mol% with phenylazoanthraquinone and by 1mol% with COOH groups. The redox properties of cp _r depend on the timescale of the cyclovoltammetric experiment. At high sweep rates two reversible redox waves are observable corresponding to the EE-mechanism. At low sweep rates an additional reversible redox wave appears, which is essentially smaller than the other two. The third wave is explained to be a result of hydrogen bonding between the COOH groups and anthraquinone mono- and dianions. The most anthraquinone units are reduced according the EE-mechanism without hydrogen bonding due to statistical reasons. The reversible redox properties of p _m and cp _r are closely connected to their molar masses (M _n ≈75kg/mol), because both polymers have been previously obtained by radical solution polymerization yielding low molecular products with molar masses of M _n ≈10kg/mol. The low molecular polymers have shown an irreversible redox behaviour. Therefore, it could be demonstrated that the molar mass of an electroactive polymer significantly affects its redox properties. Received: 13 November 1998/Revised version: 30 March 1999/Accepted: 20 April 1999     

Covalent functionalization of single-walled carbon nanotubes by aniline electrochemical polymerization

Electrochemical polymerization of aniline in an HCl solution on a single-walled carbon nanotubes (SWNTs) film has been studied by Raman and FTIR spectroscopy. It is shown that this method leads to a covalent functionalization of SWNTs with polyaniline (PANI). A careful study in Raman scattering shows that the increase in the intensity of the band at 178 cm⁻¹ associated with radial breathing modes of SWNTs bundles suggests an additional nanotubes roping with PANI as a binding agent. A post chemical treatment with the NH₄OH solution of polymer-functionalized SWNTs involves an internal redox reaction between PANI and carbon nanotubes. As a result, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one.     

Transport of Iron and Cobalt Complex Ions through Liquid Membrane Mediated by Methyltrioctylammonium Ion with the Aid of Redox Reaction

Abstract

A new type of carrier-mediated metal transport through liquid membrane is presented. The system involves redox reactions rather than acid-base reactions which have often been utilized in metal transport systems. Iron ion was selectively transported and concentrated through the membrane via a chloride complex by use of a lipophilic quaternary ammonium ion, methyltrioctylammonium (MTOA, Q⁺), as a carrier. The two aqueous solutions of different redox potentials were separated by a polymer-supported liquid membrane in which MTOA · chloride (Q⁺·CI^?) was dissolved as the carrier. Iron(III) ion in hydrochloric acid media formed a FeCl₄ ^? type complex which was readily extracted to the organic membrane phase as an ion-pair complex Q⁺·FeCl₄ ^?. On contact with a reducing agent on the other side of the membrane, iron(III) was reduced to iron(II) and liberated into aqueous solution; the chloride complexes of iron(II) are too hydrophilic to stay in the membrane phase. On the other hand, cobalt ion was transported via nitrilotriacetic acid (NTA) complex by MTOA carrier in a similar manner to the iron transport. The nature of the transport reactions was studied under various operational conditions (redox agents, carrier and ligand concentration, pH, coexisting metals, etc.). The extension of these transport reactions to a water-in-oil-in-water type emulsion system as well as to a photoassisted transport system was studied.     

OSCILLATORY EXTRACTION OF URANIUM

ABSTRACT

The kinetics of U and Ce extraction by tri-n-butyl-phosphate ( TBP) and the redox potential behavior in the aqueous phase have been investigated in an oscillatory extraction system. The extraction has been followed continuously by UV-visible spectroscopy, potentiometry, and radioactive counting methods. Data collected showed the changes of Ce⁴⁺ and U0²⁺ concentrations in organic and aqueous phases with time. Uranium actively responded to the redox potential fluctuations. The uranium distribution coefficient changed repeatedly and was out-of-phase with Ce( IV) fluctuations.     

Characterisation of polypyrrole electrosynthesised on aluminium

Cyclic voltammetry has been used to investigate the role of the anions and the solution pH on the redox properties of polypyrrole electrosynthesised onto aluminium in alkaline solutions. The polymer film was characterised by SEM and IR spectroscopy. Moreover, the influence of the cathodic potential on the redox process was analysed for films formed in acid and alkaline solutions. The electrochemical response was compared with that obtained on vitreous carbon electrode. The differences in the shape and evolution of the voltammograms during cycling have been explained by a different participation of the ions. The best redox activity of the polymer is obtained in NO₃⁻ due to the fact that this anion could limit the anodic dissolution of Al. The other anions analysed cannot be incorporated into the polymer matrix. As a consequence, the transport of OH⁻ occurs, which provokes a significative Al dissolution. It is expected that the Al³⁺ ions generated during the electrodissolution are incorporated into the polymer in order to equilibrate the charge of the film.     

A GLR Control Chart for Monitoring the Process Mean with Sequential Sampling

Abstract

Variable sampling rate (VSR) control charts have been used where the sampling rate changes as a function of the data from the process. In this article we investigate a generalized likelihood ratio (GLR) control chart based on sequential sampling (the SS GLR chart). The objective of process monitoring is assumed to be the effective detection of a wide range of two-sided shifts in the process mean. The performance of the SS GLR chart is evaluated and compared with other control charts. The SS GLR chart has much better performance than that of the fixed sampling rate GLR chart. It is also shown that the overall performance of the SS GLR chart is better than that of the variable sampling interval (VSI) GLR chart and the VSR CUSUM chart. The SS GLR chart has the additional advantage that it requires fewer parameters to be specified than other VSR charts. The optimal parameter choices are given in the article, and regression equations are provided to find the limits for the SS GLR chart.     

A chemically regenerative redox fuel cell. II

Our previous paper [1] has described an unconventional chemically regenerative redox fuel cell, including a modest amount of performance data, and has pointed out a number of problem areas. This paper describes additional work and some attempts that have been made to improve the cell performance in several of the problem areas described in the first paper. Two different redox fuel cell systems employing the V²⁺/V³⁺ and Mo³⁺Mo⁴⁺ redox couples as the anolyte, and a new NO ₃ ^–/NO catalyst system for VO²⁺ oxidation were explored and described. The reduction of Na₂MoO₄ to Mo⁴⁺ and Mo³⁺ by H₂ in concentrated H₂SO₄ solution was studied in small scale laboratory experiments and discussed. The performance of a redox cell in which H₂ was obtained from the Pd-catalysed decomposition of formic acid, HCOOH, is described and the results of experiments with different membranes are reported. The results of experiments using WC as a hydrogenation catalyst at a temperature of 70–90° C with mixed molybdo-tungsto-silicic acids are reported and discussed.     

Mechanism of Low Profile Behavior in Unsaturated Polyester Systems

Abstract

The mechanism of low profile, low shrink behavior in single- and two-phase unsaturated polyester systems has been investigated. The curing process of several compositions has been followed by optical microscopy at various heating rates, fracture surfaces of cured samples have been observed using scanning electron microscopy and some of their physical properties have been measured. A mechanism is proposed, based on data obtained in this work and additional published data, which consists of shrinkage reduction in the continuous phase by thermal expansion of styrene and other constituents and in the dispersed phase by void formation.     

Studies of the Effect of Comonomers on the Microstructure of Polyacrylonitrile in Radical Polymerization Using NMR Spectroscopy

Abstract

The free radical polymerization method has been employed to synthesize homopolymers of acrylonitrile (AN), its copolymers with methylacrylate (MA) and terpolymers containing itaconic acid (IA) in homogeneous solution (aqueous solution of sodium thiocyanate and dimethylsulfoxide media) and aqueous redox slurry system. ¹³C NMR was used to characterize these polymers in terms of steric configurations in order to study the effect of co and ter monomers on microstructure of polyarylonitrile both at low and high conversions. The study showed no significant change in microstructure of polyacrylonitrile on the introduction of MA and IA. Different techniques of polymerization for ACN-MA-IA had no effect on the microstructure of terpolymer. ¹H NMR and IR techniques were used to determine the composition of copolymers and a good agreement was observed between the results from the two techniques. The presence of unsaturated carboxylic acid monomer (IA) was confirmed by ¹H NMR.     

High Pressure Synthesis and Characterization of Acrylonitrile Based Copolymers in Aqueous Free Radical Polymerization Using NMR Spectroscopy

Abstract

The influence of reaction pressure on rate of polymerization and intrinsic viscosity in acrylonitrile (AN), methyl acrylate (MA) and itaconic acid (IA) ternary suspension polymerization system has been studied using free radical forming potassium persulphate and sodium metabisulphite water soluble redox initiator pair. The resulting polymers synthesized at various reaction pressures were characterized for tacticity and composition by NMR and other spectroscopic (FT-IR. ESCA) techniques. These polymers were also subjected to differential scanning calorimetric (DSC) analysis and significant change in heat of cyclization were observed with the change in reaction pressure.     

Electrochemical behavior of o-chloranil in aqueous solution at an activated glassy carbon electrode

A study has been conducted on the effect of specific adsorption of o-chloranil, OCA, at an activated glassy carbon electrode, AGCE, surface on its electrochemical behavior in an aqueous solution. The voltammetric responses of OCA at an AGCE show an anodic prepeak and a cathodic postpeak other than the diffusion main couple in weak acidic and neutral pHs. The anodic prepeak and the cathodic postpeak are ascribed to specific adsorption of OCA. The pK_a value of the adsorbed redox couple of OCA at an AGCE is at least by 4 and 2 pK_a units higher than those of the free redox couple in solution at bare and activated glassy carbon electrodes, respectively. The slop of (I_p)_ads/(I_p)_diff ratio versus ν^1/2 for the cathodic and anodic peaks indicates a stronger adsorption of OCA at AGCE in comparison with OCAH₂. The effects of OCA concentration on its adsorption behavior and applied potential on anodic adsorption of OCA at AGCE have been studied and the surface coverage of OCA (Γ_OCA) has been calculated.     

New Pt(II)(dithiolate) Compounds Possessing an Energetically Accessible Diphosphine-Based LUMO: Syntheses,Redox Properties,and Solid-State Structures of PtCl<Subscript>2</Subscript>(pbpcd), Pt(tdt)(pbpcd), and Pt(tdt)(bpcd)

Abstract  

The new ligand 2-(pyren-1-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (pbpcd) has been synthesized from the Knoevenagel condensation using 1-pyrenecarboxaldehyde with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Displacement of the cod ligand in PtCl₂(cod) by pbpcd furnishes PtCl₂(pbpcd) (2) in near quantitative yield. Treatment of 2 with the dipotassium salt of toluene-3,4-dithiol (K₂tdt) affords the dithiolate compound Pt(tdt)(pbpcd) (3) as a 1:1 mixture of diastereomers. An alternative synthesis of 3 from Pt(tdt)(bpcd) (5) and 1-pyrenecarboxaldehyde also affords 3 in 23% yield. The pbpcd ligand and all new diphosphine-substituted compounds have been isolated and fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures of 2·CH₂Cl₂, 3·toluene, and 5·CH₂Cl₂ established by X-ray diffraction analyses. The solid-state structure of each product exhibits a square-planar architecture at the metal center. The redox properties of the pbpcd ligand and the tdt-substituted compound 3 have been explored by cyclic and differential-pulse voltammetry, and these data are discussed with respect to extended Hückel MO calculations and the nature of the HOMO and LUMO levels in each compound.     

Absorptive NOX-Reduction

Abstract

Absorptive reduction of NO-from off-gas has been investigated. With regard to negligibly low solubility of nitrogen monoxide in aqueous solutions, technical application of any absorption process has to be based on absorption with chemical reaction at the interphase. The present investigations have been based on the redox reaction

Combining this thermodynamic principle of NO-reduction with a redox-absorption process should enable separation processes comparable with SCR-denoxing. Several processes with promising redox conditions have been investigated. The program has considered the reactivity, the nature of products and mass transfer problems. The results confirm, that NO itself does not participate any kind of reactive absorption process. Nitrogen monoxide has to be preferably oxidized in a first step to form NO₂ and has to be absorbed in a second step. Depending on the ratio of NO/NO₂ (or NO/NO₂O₄) the products may differ. Gaseous N₂ has definitely been observed only, when absorbing NO₂/N₂O₄.     

Influence of anion and pH on the electrochemical behaviour of polypyrrole synthesised in alkaline media

The electrochemical behaviour of conducting polypyrrole films electrosynthesised on vitreous carbon electrodes in alkaline solutions has been investigated by means of cyclic voltammetry and open circuit potentiometric measurements. The shape and evolution of the voltammograms during cycling depend strongly on the kind of anion and solution pH used. From these results, anion and cation participation in the redox process of the polymer has been analysed. The transport of anions like NO₃⁻ or Cl⁻ is dominant, while the transport of OH⁻ is the most important contribution when the polymer is cycled in the presence of anions that cannot be incorporated into the polymer matrix. The incorporation of Na⁺ also takes place and its contribution is more significant as deposition charge increases. The characteristics of the films are compared with those obtained in acid media. The polymerisation efficiency is similar in both cases. Films electrodeposited in alkaline solution can be doped and undoped in acid solution without loosing its redox behaviour.     

Cation Separations Using A Proton-Ionizable Macrocycle in a Dual Module Hollow Fiber Membrane System

Abstract

Separation of metal cations in aqueous solution using a proton-ionizable macrocycle in a dual module hollow fiber membrane system is described. The advantages of this system, such as easy access to all phases, rapid transport rates, and the potential for continuous operation are maintained with the proton-ionizable macrocycles which allow for proton driven transport. Transport is diffusion limited in the organic phase boundary layer near and on the fibers. Hence, the selectivity of the extraction system is maintained. Selective transport of Ag⁺ over all other cations tested from neutral source phases and of K⁺ over other alkali metal cations from basic source phases using a triazole-18-crown-6 carrier has been demonstrated. Selective K⁺ transport from less basic source phases has been demonstrated using the more acidic thiopyridone-18-crown-6 ligand. However, the large aqueous partition of this ligand makes it difficult to maintain it in the organic phase. Design of the separation systems requires a knowledge of extraction equilibrium constants and partition coefficients. These data have been measured in order to understand these membrane systems.     

Bathocuproine-Mediated Copper Transport through Liquid Membrane Driven by Redox Potential

Abstract

A new type of carrier-mediated copper transport system driven by redox potential was studied. The two aqueous solutions of different redox potentials were separated by a polymer-supported organic liquid membrane in which Bathocuproine (L) was dissolved as a “carrier”. Copper(II) was reduced in the reducing phase to form [Cu¹L₂]⁺·X^? type complex at the membrane interface and extracted. The copper complex diffused to the other side of the membrane and decomposed to form the copper(II) species in the oxidizing phase, leaving the carrier in the membrane phase. The nature of the system under various operational conditions (pH, redox agents, pairing anions X^?, coexisting metals, etc.) was studied and compared with the metal transport system which can take place without the intervention of redox reaction. An extension of these transport reactions to water-in-oil-in-water type emulsion system was studied.     

Redox (pro-oxidant/antioxidant) balance in the spray drying of orange peel extracts

ABSTRACT

Phenolic compounds have been reported to show both antioxidant and pro-oxidant properties. The effects of spray drying conditions on the balance between antioxidant and pro-oxidant properties of orange peel extract have been evaluated in this work. The inlet drying temperatures (ranging between 100 and 175°C) gave no significant effect on the redox recoveries. On the other hand, the main air flow rate (between 28 and 38?m³/h) and feed pump rate (between 4 and 7?mL/min) significantly affected the pro-/antioxidant recovery ratio. The ratios of pro-/antioxidant recovery were found to be between 1.00 and 1.13, and the pro-oxidant and antioxidant recoveries in this study were found to be between 87–96 and 83–93%, respectively.     

The Relation of Collector Redox Potential to Flotation Efficiency: Monothiocarbonates

Abstract

The redox potentials of monothiocarbonates and xanthates have been determined and a correlation established with their collector properties for the flotation of galena. Flotation efficiency increases with the ease of oxidation of the collector. The role in flotation of the oxidation products, the disulfides, is discussed.     

A Sharp Drying Front Model

Abstract

The drying of materials is often described by nonlinear diffusion equations. Up to now the only way to solve these equations is by numerical simulations. Recently an analytic solution has been proposed for the drying problem. Based on this solution a sharp drying front model is presented. Measured moisture profiles during drying and the drying curve of gypsum are compared with approximate models.     

Microemulsion polymerization in the water,aerosol-OT,tetrahydrofurfuryl methacrylate system

Summary Part of the phase diagram at low (<10%) oil content and 25°C has been mapped in the water, Aerosol-OT (AOT), tetrahydrofurfuryl methacrylate (THFM) ternary system. Sodium persulfate/sodium metabisulfite was used as a redox initiator to induce polymerization in this microemulsion system at 7.8% (w/w) THFM and 4.4% AOT. Conversions in excess of 90% were obtained. The parent microemulsion droplets have diameters on the order of 5 nm. The resulting latexes have average particle diameters of 37–39 nm. The latex particles are cross-linked as a result of radical induced opening of the tetrahydrofurfuryl ring, and exhibit nearly the same density (1.216 g/cm³) and glass transition temperature (67°C) as material (1.222 g/cm³; 62°C) produced by solution polymerization. This three-component microemulsion, and the corresponding latexes, have been imaged directly by cryo-electron microscopy. The first reports of three-component polymerized (oil in water) microemulsions, stabilized by cationic surfactants, were made by Murtagh, Ferrick, and Thomas [ACS Polymer Preprints 1987, 28, 441] and more recently by Perez-Luna, Puig, Castano, Rodriguez, Murthy, and Kaler [Langmuir 1990, 6, 1040]. this report appears to be the first such polymerization in a three-component system stabilized with an anionic surfactant. These latexes are cross-linked beads, and are the first such examples to be prepared by microemulsion polymerization.