Polypyrrole degradation

Reactions (5) and (6) offer an explanation for the appearance of a carbonyl band at 1720 cm" and of a new band at 775 cm in infrared (IR) spectroscopy of polypyrrole degradation products, ascribed to substitution products in the pyr-rolic rings. 

In a less nucleophilic medium, such as acetonitrile, overoxidation is impeded and proceeds at more positive potentials (1.9 V approximately), although it leads to the same products as in neutral aqueous media [114]. From the data of Novak et al. [124,125], polypyrrole degradation in propylene carbonate proceeds through a mechanism different from that in acetonitrile or water, with destruction of the polyconjugated structure and formation of new degradation products. However, the rate of overoxidation increases strongly with water contamination ... 

Polypyrrole degradation (pyrolysis at 600°C or anodic over-oxidation) gave benzene, indole, carbazole, etc. fragments. 

Several other groups have since published studies involving the stability of polypyrrole and polypyrrole-coated textiles. A plot produced from data obtained at Milliken Research Corporation that displays the resistance as a function of time at several different temperatures for an anthraquinone-2-sulfonic acid doped polypyrrole-coated textile is shown in Fig. 35.8. Similar results were obtained by Truong and coworkers [82,831 and Thieblemont and coworkers [ 16,841. Contrary to the earlier reports, these studies concluded that the kinetic of polypyrrole degradation are not first-order but follow a diffusion-controlled curve similar to a Frickian sorption plot. 

There are large numbers of naturally occurring representatives, especially of pyrrole that include the important polypyrroles (porphyrins and corrins), and the nitropyrrole antibiotics such as pyr-rolomycins and pyrroxamycin. Derivatives of furan have been used as fungicides and A-vinylpyr-rolidone is an important monomer for the production of blood plasma extenders and for cosmetic applications. On account of the similarity in the pathways for the aerobic degradation of monocyclic furan, thiophene, and pyrrole, all of them are considered here. Anaerobic degradation of furans is discussed in Part 2 of this chapter. 

In considering the potential applications of electroactive polymers, the question always arises as to their stability. The deterioration of a physical property such as conductivity can be easily measured, but the chemical processes underlying it are not as easy to be revealed. In order to understand them, XPS has been used to follow the structural changes which occur in the polymer chain and the counter-ions of the doped polymer. The following sections present some XPS findings on the degradation of electroactive polymers, such as polyacetylene, polypyrrole, polythiophene and polyaniline, in the undoped and doped states. 

DETECTION OF V-TYPE NERVE AGENT DEGRADATION PRODUCTS USING A POLYPYRROLE / PYRROLOQUINOLINE QUINONE-MODIFIED ELECTRODE... 

Oxide, flouride, and polymeric films, as well as certain others, are used as protective coatings for HTSC materials (for example, see [505]). The electrodeposition of conducting polymers such as polypyrrole [433,491, 493, 506], polythiophene and its derivatives [493, 507], and polyaniline [478] is the most effective process. Anodic electropolymerization in acetonitrile solutions proceeds without any degradation of the HTSC substrate and ensures continuous and uniform coatings. Apparently, this method is promising not only for the fabrication of compositions with special properties based on HTSC [50, 28,295] as mentioned above, but also for the creation of junctions with special characteristics [507]. 

Biswas and Roy [118,119] studied the degradation and stability of chemically prepared polypyrrole substituted by phthalic anhydride (PPY-PhAn) and pyromellitic dianhydride (PPY-PMDA) by using a thermal analyser and IR spectroscopy. They found that the chemical modification enhanced the thermal stability of the modified polypyrrole as compared with... 

The stabilities of polypyrrole-coated conductive fabrics were highly dependent on the doping counterion as well as the polymerization conditions. The rate of degradation showed a diffusion controlled kinetics at high temperatures. The room temperature half-life for the most stable conductive fabric was estimated to be about five years [129]. 

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