Study of poly(methyl methacrylate) relaxations by thermally stimulated depolarization currents and the thermal step method

A combined study of beta' and alpha relaxations in poly(methyl methacrylate ) (PMMA) by thermally stimulated depolarization currents and thermal step m ethods has been made. The use of null width polarization windows to form th e electrets allows us to isolate the beta' peak. The charge distribution pr ofiles allow us to assign a polar orientational mechanism for the Pl relaxa tion and in the case of the alpha peak a background polar mechanism over wh ich a temperature-dependent injection and a conduction processes are overla pped. The charge distribution profiles observed by the thermal step method indicate that the increase of the conductivity observed in this material at temperatures just below the glass transition is mainly due to the positive carriers. (C) 1999 Elsevier Science Ltd. All rights reserved.