Polypyrrole oxidized

Dall Acqua et al.45 reported the development of conductive fibres made by cellulose-based fibres embedded with polypyrrole. Several efforts with cotton, viscose, cupro and lyonell have followed. The conductivity is directly related to the amount of polypyrrole, oxidant ratio and fibre structure with significant differences between viscose and lyonell. Polymerisation occurs uniformly inside the fibre bulk, by producing a coherent composite polypyrrole/cellulose. The mechanical and physical properties of cellulose fibres were not significantly modified as they are the best available45. 

Otero, T.E, H. Grande, and J. Rodriguez. 1996. Conformational relaxation during polypyrrole oxidation From experiment to theory. Electrochim Acta 41 1863-1869. 

Otero, T. F. Atias-Pardilla, J. Chermak, E. Reactive polymer films Polypyrrole oxidation kinetics in aqueous solution. Synth. Met. 2010, 425-431. 

Similarly to previous cases, polypyrrole oxidation in methanol proceeds at relatively negative potentials and leads to the formation of multimethoxylation products. 

Otero, T. F, Grande, H., and Rodriguez, J., Conformational relaxation during polypyrrole oxidation from experiment to theory, Electwchim. Acta, 41, 1863-1869 (1996). 

Cyclic voltammetry can be used to estimate the charge transfer rate and also evaluate how this rate depends on parameters such as morphology and the chemical structure. The cyclic voltammetric examination of electroactive polymers is usually done in monomer-free solutions containing only the solvent and supporting electrolyte. In order to avoid the complication of mixed electrolytic equilibria, the supporting electrolyte and the solvent are usually the same as employed for the polymerization. Figure 3 shows the cyclic voltammogram (CV) of a polypyrrole film prepared in acetonitrile/tetra-w-butyl ammonium fluoborate medium. The anodic peak corresponds to polypyrrole oxidation, while the cathodic one corresponds to the reduction of this species. 

Bonifas, A. P. and McCieety, R. L. 2012 Solid state spectroelectrochemistry of redox reactions in polypyrrole/oxide molecular heterojunctions. Anal. Chem. 84 2459-2465. 

Cyclic voltammetry was chosen for polymer deposition as a one-step process. Figure 15.2a presents a typical voltammogram obtained for polypyrrole electrodeposition in the presence of p-TSA as the dopant. In the first cycle, the strong passivation of A1 is present and expressed by the peak at +1.5 V vs SCE. After the first cycle, the surface is passivated, partially by the polymer deposition and partially by the formation of the corresponding oxide which dramatically decreases the current intensity in the next cycles. Polypyrrole oxidation takes place at potentials close to 0 V vs SCE followed by a reduction at lower potentials. The peak appearing at -0.75 V vs SCE only within the first two cycles is attributed to an anion exchange reaction. 

Polypyrroles. Highly stable, flexible films of polypyrrole ate obtained by electrolytic oxidation of the appropriate pyrrole monomers (46). The films are not affected by air and can be heated to 250°C with Htde effect. It is beheved that the pyrrole units remain intact and that linking is by the a-carbons. Copolymerization of pyrrole with /V-methy1pyrro1e yields compositions of varying electrical conductivity, depending on the monomer ratio. Conductivities as high as 10 /(n-m) have been reported (47) (see Electrically conductive polymers). 

Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

Conducting Polymers Electronically conducting polymers (such as polypyrrole, polythiophene, and polyaniline) have attracted considerable attention due to their ability to switch reversibly between the positively charged conductive state and a neutral, essentially insulating, form and to incorporate and expel anionic species (from and to the surrounding solution), upon oxidation or reduction ... 

Describe clearly why the oxidation of polypyrrole film results in the uptake of an anion from the surrounding solution. 

Komori and Nonaka132,133 electrochemically oxidized methyl, isopropyl, n-butyl, isobutyl, r-butyl and cyclohexyl phenyl sulfides (108) and cyclohexyl p-tolyl sulfide (109) to their sulfoxides using a variety of polyamino acid-coated electrodes to obtain the range of e.e. values shown in parentheses. The highest enantiomeric purities were obtained using an electrode doubly coated with polypyrrole and poly(L-valine), an electrode which also proved the most durable of those prepared. 

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (— )camphoric anhydride or (S)-phenylalanine methyl ester299. Much better results were obtained with the poly(L-valine) coated platinum electrodes300. For example, t-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

The flow of an anodic current oxidizes the conducting polymer and the film swells. At the polypyrrole/tape interface, electrochemically stimulated conformational changes in the polymer promote an expansion that... 

Figure 19. (1) Oxidized polypyrrole (PPy) film electrogenented on a steel electrode. (2) A tape was fastened to the dry polypyrrole film (A). B is doublesided tape and C is a protective sheet of paper. (3) The bilayer device with a protective film is removed from the electrode. (4) The protective sheet is peeled off and the bilayer is ready to work. (Reprinted from Handbook of Organic Conductive Molecules ami Polymers, H.S. Nalwa, ed.,Vol. 4,1997, Figs. 10.13, 10.15a, 10.18, 10.36. Reproduced with permission of John Wiley Sons, Ltd., Chichester. UK.)...

Figure 29. (a) Evolution of the absorption spectra of an electro-chromic polypyrrole as a function of the oxidation potential obtained during voltammetry between -900 and 400 mV from a 2.5 M LiCI04 aqueous solution. The voltammetry was performed at a scan rate of 20 mV s 1. (From Ref. 161). (b) Evolution of the absorption spectra of an electrochromic polypyrrole as a function of the reduction potential obtained during voltammetry between 400 and -900 mV from a 2.5 M LiCI04 aqueous solution. The voltammetry was performed at a scan rate of 20 mV s 1. (From Ref. 161). 

At dusk the window becomes lighter. When the polypyrrole film is completely reduced and the oxide is fully oxidized and darkening continues, the current of the photocell decreases at it and the electric light in the room is switched on. The intensity of the electric current sent to the lamp is increased in such a way that the luminosity in the room remains constant at all times. In cars or for other applications, the device can work automatically or by hand, darkening all the windows when the car is parked on a sunny day. 

Figure 37. Lateral section of a polymeric film during the nucleation and growth of the conducting zones after a potential step. (Reprinted from T. F. Otero, H.-J. Grande, and J. Rodriguez, A new model for electrochemical oxidation of polypyrrole under conformational relaxation control. /. Electroanal. Chem. 394, 211, 1995, Figs. 2-5. Copyright 1995. Reprinted with permission from Elsevier Science.)...

Figure 38. Evolution of the proposed surface aspect of a polypyrrole film during an oxidation reaction initiated from high cathodic potentials (E < -800 mV vs. SCE). The chronoamperometric response is shown at the bottom. Experimental confirmation can be seen in the pictures in Ref. 177. (Reprinted from T. F. Otero and E. Angulo, Oxidation-reduction of polypyrrole films. Kinetics, structural model, and applications. Solid State Ionics 63-64, 803, 1993, Figs. 1-3. Copyright 1993. Reprinted with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055, KV Amsterdam, The Netherlands.)...

Figure 55. Separation of the overall oxidation curve into its two components a relaxation part [according to Eq. [30]] responsible for the initial shape of the curve, and a diffusion part [Eq. [39]], which controls the final shape of the chronocoulogram. (Reprinted from T. F. Otero and H.-J. Grande, Reversible 2D to 3D electrode transition in polypyrrole films. Colloid Surf. A. 134, 85, 1998, Figs. 4-9. Copyright 1998. Reproduced with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 Amsterdam, The Netherlands.)...

Electrochemically synthesized and then oxidized and reduced conducting polymers, such as polypyrrole, polythiophene, and polyaniline, which are amorphous, are nonstoichiometric compounds ... 

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