Poly overoxidation

Reactions with other nucleophiles follow a similar mechanism. For the reaction of Cl with poly(3-methylthiophene) in acetonitrile, the reaction stops at structure 5 (Scheme 2).128 A fully conjugated, Cl-substi-tuted product 6 can subsequently be obtained by electrochemical or chemical dehydrogenation.128 With Br and alcohols, the overoxidation... 

Figure 3.81 Typical cyclic voltammograms of a poly pyrrole film on Pt in Nrsatu rated 1 M NaClOj. The voltammograms were collected immediately after holding the film at -0.6 V vs, SCE for 5 min and after cycling for 5 min. The scan rate was 100 mV s "1 and the film thickness 84 nm. Reprinted from Electrochimica Acta, 36, P.A, Christensen and A. Hamnett, In situ Spectroscopic Investigations of the Growth, Electrochemical Cycling and Overoxidation of Polypyrrole in Aqueous Solution , pp. 1263-1286(1991), with kind permission from Pergamon Press Ltd., Headington Hill Hall, Oxford OX3 0BW, UK.

An eco-friendly oxidation of alcohols under an oxygen atmosphere using catalytic amounts of [bis(acetoxy)iodo]benzene-TEMPO-KN02 has been reported. The use of a catalytic amount of poly[4-(bis(acetoxy)iodo)]styrene allowed the successful recycling of this catalytic component. The protocol can be used to promote the oxidation of different kinds of alcohols in the presence of other functional groups and also in the oxidation of primary benzylic alcohols in the presence of secondary and aliphatic ones. Primary alcohols can be oxidized to the corresponding aldehydes without any noticeable overoxidation to the carboxylic acids.269... 

Shi et al. [70] were the first to demonstrate the use of an air and moisture stable ionic liquid, [C4mim][PF,s], for the electrochemical synthesis of poly(thiophene), grown onto a platinum working electrode by potentiodynamic, constant potential or constant current techniques. The use of growth potentials between 1.7 and 1.9 V (vs. Ag/AgCl) reportedly gave smooth, blue-green electroactive films, whereas potentials above 2 V resulted in film destruction by overoxidation. 

Poly(vinylpyridinium dichromate) can be prepared in a similar way to PVPCC. To be effective it must be used in the presence of water and in the most noiq>olar solvent possible. It gives moderate to good yields, but long reaction times may be required for the reaction to proceed to completion. Even with die long reaction times, very little overoxidation is observed. Up to five oxidation-regeneration cycles may be completed without significant loss of activity. 

Fig. 25. Potential domains for reversible cycling (left) and for irreversible overoxidation (right) in the case of polypyrrole (PPy) and of poly thiophene (PThio).

The next group of materials comprises conducting polymers (ICP). Systems with identical polymers have often been reported for polyacetylene. It is known that this ICP forms insertion compounds of the A and D types (see Section 6.4, and No. 5 in Table 12). Cells of this Idnd were successfully cycled [277, 281-283]. However, the current efficiency was only 35% heavy losses were observed due to an overoxidation of the PA [284]. In other cases as for polypyrrole (PPy), the formation of D-PPy was anticipated but did not occur [557, 558]. Entry (6) in Table 12 represents some kind of ideal model. A PPy/PPy cell with alkyl or aryl sulfates or sulfonates rather than perchlorates is claimed in [559]. Similar results were obtained with symmetric polyaniline (PANI) cells [560, 561]. Symmetric PPy and RANI cells yield about 60% current efficiency, much more than with PA. An undoped PPy/A-doped PPy combination yields an anion-concentration cell [562, 563], in analogy to graphite [47], (cf. No. 7). The same principle can be applied with the PPy/PT combination [562, 563] (cf. No. 8). Kaneto et al. [564] have reported in an early paper the combination of two pol54hiophene (PT) thin layers (< 1 pm), but the chargeability was relatively poor (Fig. 40, and No. 9 in Table 12). A pronounced improvement was due to Gottesfeld et al. [342, 343, 562, 563], who employed poly[3-(4-fluoro-phenyl)thiophene], P-3-FPT, in combination with a stable salt electrolyte (but in acetonitrile cf. Fig. 40 and No. 10 in Table 12). In all practical cases, however, Es.th was below 100 Wh/kg. 

Therefore, if using constant-current or constant-potential polymerization, the product obtained will be a mixture of poly thiophene and overoxidized polythiophene. 

Because poly thiophene itself is prone to overoxidation during polymerization, most practical work has been carried out using alkylated thiophenes, which have higher overoxidation potentials. Synthesis of functionalized thiophenes (such as alkylated monomers) is much easier to achieve than that of its pyrrole counterpart. The decreased activity of the sulfur group compared to that of the -NH group means that the laborious steps involved in protecting the heteroatom during synthesis are not required for thiophene. 

As stated earlier, the presence of alkyl functional groups on the monomer118 can be used to advantage in preventing overoxidation of the polythiophenes during synthesis. Conductivities as high as 7500 S cm-1 have been obtained for poly(methylthiophene).119... 

Insulating films can be formed either by using monomers such as phenol [182, 183] or 1,2-diaminobenzene which yield non-conducting polymers or by overoxidation of conducting polymer films as described above. Insulating polymers, such as poly(phenol), form as thin (0.1 iim range) pinhole-free films at the surface. This allows very thin uniform films to be deposited. Films of... 

Immobilization of the DNA onto polymer modified surface can be realized by electrodeposition, which is a well-known method [25]. Application of positive potential in this process can enhance the DNA immobilization as well as the stability of immobilized DNA. Diaz-Gonzalez etal. [26] studied the DNA immobilization onto a polylysine-modified electrode at different potentials. The best results were obtained using a potential of-1-0.5 V for 120 seconds. DNA was also electrodeposited onto a poly(p-aminobenzensulfonic acid)-modified glassy carbon electrode (GCE) at -fl.5 V for 30 minutes [27] or onto overoxidized Ppy-modified electrode at -1-1.8 V for 30 minutes [28]. 

Recent applications of nonconducting polymers, such as PPD and overoxidized poly(pyrrole), as permselective and biocompatible membranes hold great promise for the future of biosensors used for in vivo monitoring. Also the suitability of polymeric films (e.g., Eastman AQ 55) for organic-phase biosensors has led to a new opportunity for amperometric detection of analytes in real nonaqueous matrices. Since enzymes are stable in nonaqueous media, many analytes can be detected amperometrically with organic-phase biosensors. 

Asturias et al noted that overoxidized poly aniline will gradually degrade toward the emeraldine structure (in 80% acetic acid solution) due to the hydrolysis of -C=N- double bonds). We find, however, that fully oxidized poly aniline is stable in concentrated sulfuric acid (97%). 

Poly(2,5-dim ethoxy aniline] Creatinine amidohydrolase Overoxidized PPy Creatine amidinohydrolase... 

Poly(3 -(2-aminopyrimidyl -2,2 5, 2 -terthiophene)), reduced graphene oxide = MeOH, graphene oxide Overoxidized polypyrrole Poly(2,6-pyridine-dicarboxylic acid]... 

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