Redox centres poly

Nafion was rendered electroactive by cation exchange of a redox centre. Other polymers such as poly-4-vinylpyridine (PVP) may be protonated or quaternized to provide the possibility of introducing a redox anion such as [IrCl6]3- or [Fe(CN)6]3-.50 51 Alternatively, the pendant pyridyl groups on the neutral polymer may function as ligands and species such as [Ru(bipy)J2+ may be polymer bound. 

Poly-4-vinylpyridine is a versatile polymer since in the non-protonated form it may function as a polymeric nitrogen-donor ligand. Thus, redox centres may be anchored by coordination to pendant 4-pyridyl groups on the polymer chains. 

Vinylferrocene (22) may be polymerized (Section 57.3.2.2.i) to give a polymer in which the iron(II/III) redox centres are pendant from a carbon backbone. Copolymers have also been formed with styrene61 and acrylonitrile.62 Another approach using a different polymer is illustrated by the covalent binding of poly(methacryl chloride) to Sn02 electrodes followed by attachment of pendant ferrocene centres by reaction of hydroxymethylferrocene.63... 

Gorton and coworkers have been particularly active in this field and produced an excellent review of the methods and approaches used for the successful chemical modification of electrodes for NADH oxidation [33]. They concentrated mainly on the adsorption onto electrode surfaces of mediators which are known to oxidise NADH in solution. The resulting systems were based on phenazines [34], phenoxazines [35, 36] and pheno-thiazines [32]. To date, this approach has produced some of the most successful electrodes for NADH oxidation. However, attempts to use similar mediators attached to poly(siloxane) films at electrode surfaces have proved less successful. Kinetic analysis of the results indicates that this is because of the slow charge transfer between the redox centres within the film so that the catalytic oxidation of NADH is restricted to a thin layer nearest the electrode surface [37, 38]. This illustrates the importance of a charge transfer between mediator groups in polymer modified electrodes. 

Earlandite structure, 849 Electrical conductivity metal complexes, 133 tetracyanoplatinates anion-deficient salts, 136 Electrical properties metal complexes, 133-154 Electrocatalysis, 28 Electrochemical cells, 1 Electrochemistry, 1-33 hydrogen or oxygen production from water coordination complex catalysts, 532 mineral processing, 831 reduction, 831 Electrodeposi (ion of metals, 1-15 mineral processing difficulty, 831 Electrodes clay modified, 23 ferrocene modified, 20 nation coated, 15 polymers on, 16 polyvinylferrocene coated, 19 poly(4-vinylpyridine) coated, 17 redox centres, 17 Prussian blue modified, 21 surface modified, 15-31 Electrolysis... 

Poly(8-quinolinol) electrode coatings, 19 Polysaccharides metal complexes geochemistry, 868 Polyselenides metal complexes geochemistry, 854 Polytyramines electrode modification, 23 Polyvinylferrocene electrode coatings, 19 attachment, 19 Poly(N-vinylimidazole) metal complexes color photography, 109 Poly(4-vinylpyridine) electrode coatings, 17 redox centres, 17 electrodes, 16 Porins... 

As the degradation of polyaniline occurs via an imine intermediate [281,284], Kim et al. [285] prepared self-doped polymer by alkylsulphonate substitution in the polymer backbone, Besides self-doping for a facile redox process, the perceived advantage of this bulky substituent includes the protection of nitrogen centres from nucleophiles responsible for irreversible degradation of polyaniline. Poly(aniline N-butylsulphonate) retained its reversible electrochromic response up to 150 000 cycles when scanned between its oxidized and reduced states (between 0.2 and 0.5 V) then started diminishing slowly. The excellent redox cyclability of poly(aniline N-butylsulphonate) over unsubstituted polyaniline was also confirmed by chronoabsorptom-etry by Kim et al. [285],... 

Reactivity modes of the poly(pyrazolyl)borate alkylidyne complexes follow a number of recognised routes for transition metal complexes containing metal-carbon triple bonds, including ligand substitution or redox reactions at the transition metal centre, insertion of a molecule into the metal-carbon triple bond, and electrophilic or nucleophilic attack at the alkylidyne carbon, C. Cationic alkylidyne complexes generally react with nucleophiles at the alkylidyne carbon, whereas neutral alkylidyne complexes can react at either the metal centre or the alkylidyne carbon. Substantive work has been devoted to neutral and cationic alkylidyne complexes bearing heteroatom substituents. Differences between the chemistry of the various Tp complexes have previously been rationalised largely on the basis of steric effects. 

A second type of electroactive polymer film is the redox polymer which contains localized sites that may be oxidized and reduced. Charge is not distributed along the polymer chain but is localized at specific, pendant redox sites. An example of this type of polymer is poly(vinylferrocene) (PVF) which is shown in Figure 2.1 in both the reduced and oxidized forms. Poly(vinylferrocene) undergoes a reversible redox reaction when used with an appropriate electrolyte (such as LiC104 in acetonitrile) and has been used as a model redox polymer system [17-19]. The oxidation process occurs by removal of electrons and the simultaneous insertion of anions from the electrolyte. The Fe centre in the pendant ferrocene group undergoes oxidation. 

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