STUDY OF THE INFLUENCE OF PHYSICAL AGING ON MACRORADICAL DECAY IN POLY(METHYL METHACRYLATE)

The macroradical decay in poly(methyl methacrylate) samples with diffe rent thermal histories was investigated in the temperature interval 20 -100 degrees C using ESR spectroscopy and the second order kinetic mod el. The rate constants exhibit two different regimes with the transiti ons at T-tr = 68 +/- 1 degrees C which are independent of thermal trea tment. For T < T-tr and T > T-tr the rate constants as well as the cor responding activation parameters are sensitive to history because of d ifferent physical microstructures. The compensation law, i.e., the lin ear relation between ln k(0,eff) and E(eff), was analyzed in terms of the so-called compensation quantities k(c) and T-c and a proximity bet ween T-c = T-tr and T-0 = 53 +/- 3 degrees C - Vogel temperature for a lpha-segmental dynamics was found. A comparison of kinetic and dynamic data suggests that the decay of terminal macroradicals in the low-tem perature region is controlled by secondary relaxations and that the al pha-mobility contributes to a more rapid decay at higher temperatures below T-g.