Book excerpt: Conjugated polymers suoh as polyaoetylene (CH)x polyphenylene (C6H4)x' poly thiophene (C4H2S)x' etc., which are insulators in their pristine state, can be brought to the metallic state after "doping" with ohemioal speoies whioh oan be either eleotron donors or I aoceptors. . This doping prooess involves a oharge transfer between the dopant moleoule and the polymer ohain whioh are then supposed to be spatially olose to each other. It follows that the meohanism of doping must be oonsidered as an aotual interoalation process, which will greatly affeot the struotural oharacteristios of the starting material, as well as its morphology, as has been observed during the 2 intercalation of graphite and layered compounds . In parallel with these modifioations, the band struoture of the system changes yielding a new set of eleotronio properties. It is evident therefore that the struotural and eleotronio properties are intimately related, and must be studied simultaneously in the same system to give reliable information. A great number of studies have been devoted to the structural and electronic properties of conjugated polymers after a chemical or 2 electrochemical doping process . Most of these concern the properties of the system for a given dopant concentration. With this approach a universal pioture of the polymer/dopant system is very diffioult to obtain, as a comparison between different experiments is very hazardous. On the other hand, only a small number of measurements have been performed during the continuous electroohemioal doping of various polymers.