Simultaneous Electropolymerization and Degradation Processes

Degradation processes can be caused by the discharge of residual water in acetonitrile solutions of thiophene.47-48 The presence of increasing amounts of residual water in this media promotes a faster degradation-passivation of the growing film when it is generated at constant potential. A subsequent faster drop of the flowing current is observed (Fig. 9). 

These facts are different demonstrations of the same event degradation reactions occur simultaneously with electropolymerization.49-59 These reactions had also been called overoxidation in the literature. The concept is well established in polymer science and consists of those reactions between the pristine polymer and the ambient that promote a deterioration of the original polymeric properties. The electrochemical consequence of a strong degradation is a passivation of the film through a decrease in the electrical conductivity that allows a lower current flow at the same potential than the pristine and nondegraded polymer film did. Passivation is also a well-established concept in the electrochemistry of oxide films or electropainting. 

Since one of the main chemical and technological problems of conducting polymers is their low stability for long-term applications, and since storage capacity is a quantification of the basic property of these 

Polythiophene electrogeneration on a rotating disc electrode. The water content influence on polymerization and on the polymeric properties. J. Electroanal Chem., 310, 219, 1991, Fig. 9. Copyright 1991. Reprinted with permission of Elsevier Science.) 

The final conclusion from the different kinetic studies that simultaneously followed productivity, consumed current, storage capacity of the obtained films, and the current efficiency in generating electroactive polymer in the final film is that any electropolymerization of conducting polymers occurs together a partial degradation of the electroactive polymer. The final film is a mixed material. From the kinetic studies we know the variables that increase or deplete the degradation reaction in relation to the polymerization reaction. 

---