Compensation effect observed in thermally stimulated depolarization currents analysis of polymers

Thermally stimulated depolarization currents (TSDC) and differential scanni ng calorimetry (DSC) are performed on thermoplastic polyesters and dimethac rylate resins over temperature ranges covering the alpha and beta relaxatio n regions. The noncooperative beta relaxation is characterized by a continu ous variation of activation energies as a function of temperature and follo ws the activated states equation with a zero activation entropy. The cooper ative alpha relaxation shows a prominent maximum of the activation energies at the glass transition temperature. Compensation behavior is often observ ed by TSDC for many polymers in the glass transition temperature range. We show that this behavior is not systematic and that it appears for the alpha relaxation if the increase of the apparent activation enthalpy is strong a nd if the width of the glass transition is weak. (C) 1999 John Wiley & Sons , Inc.