ABSTRACT.: Thermoplastic blends have been created by in situ growth of polypyrrole in an insulating PVC matrix. This type of synthesis gives a level of conductivity of the order of 10−5 to 1 S/cm for concentrations of less than 15% (in weight). A study of the synthetic conditions shows that the reaction parameters (solvent, nature of oxidizing agent) control the eventual properties of the blend (structure, conductivity level). The microwave characterization of these materials has allowed us to establish a direct link between the method of processing and the radioelectric properties.