Polypyrroles, properties fundamentals

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

Polypyrrole is one of a series of heterocyclic polymers which has attracted much attention due to its characteristic electric and electronic properties. However, there are some problems relating to the physical and material properties associated with its structure. The fundamental structural formulae shown in Fig. 16.5 have been generally proposed for the structures of dedoped and doped polypyrroles, where the aromatic form corresponds to the dedoped state and the quinoid form corresponds to the doped state [9-11]. However, the actual structure appears to be more complicated. At present the exact structure is not known because the polymer is amorphous and insoluble. Consequently, various structures have been proposed for polypyrrole [10]. 

Once the coexistence of different processes during electropolymerization is detected, the final composition and properties of the electrogenerated polypyrroles can be related to the chosen parameters of synthesis. The reverse reasoning is always true and fundamental from a technological point of view on defining a property, specific conditions of synthesis can be selected in order to optimize it. As the electrochemical polymerization of pyrrole involves many experimental variables, adequate control of the polymer synthesis will require analysis of the effects of the individual parameters (electrode, solvent, electrolyte, pH of the solution, temperature, and potential of synthesis) and their interdependence. 

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