Influence of impurities on the TSDC signal obtained for unsaturated polyester resins

The origins of the peaks observed in thermally stimulated depolarized current (TSDC) spectra obtained with unsaturated polyester resins (UPRs) with different amounts of promoter were investigated. It was possible to observe both the classical noncooperative β relaxation peak and the α peak (the dielectric manifestation of the glass transition). This peak is overlapped with a third one, called ρ, of very great magnitude, located a few degrees above the α peak. With the help of X-ray fluorescence spectroscopy investigations, we have shown that the promoter of the UPR contains many impurities. Using systems with different amounts of promoter, we have shown that the origin of the ρ peak can be directly linked to the presence of these impurities