Dielectric Properties of Free Radical Initiators-Investigation of Thermal Decomposition Products

Studies into the phenomena that explain the dielectric properties of azo initiators (AMBN and V70) at high temperatures are reported in this paper. Previous studies have successfully related the variation in dielectric properties of these species below 110 degrees C to either phase changes or the thermal production of free radicals. In the latter case the marked increase in their response was attributed to the free radicals having more prominent dipoles than their initiator precursors. This study reports the results of experiments designed to explain their observed dielectric characteristics within the temperature range of 110-150 degrees C. At these elevated temperatures, the decomposition half-life of the initiators studied should be of the order of few seconds. However, in both this and the previous reports, the dielectric response is found to remain at a significant level for several hours. The two prime explanations for the unexpected duration of the increased dielectric properties are (i) the presence of microwave induced protected radicals or (ii) the dielectric properties of the initiator decomposition products. The observations made in this study were subsequently used to define that the latter of these is the key to the observed phenomenon.