Study of the influence of physical aging on macroradical decay in poly(methyl methacrylate)

The macroradical decay in poly(methyl methacrylate) samples with different thermal histories was investigated in the temperature interval 20–100 °C using ESR spectroscopy and the second order kinetic model. The rate constants exhibit two different regimes with the transitions atTtr=68±1°C which are independent of thermal treatment. ForT Ttr the rate constants as well as the corresponding activation parameters are sensitive to history because of different physical microstructures. The compensation law, i.e., the linear relation between lnko, eff andEeff, was analyzed in terms of the so-called compensation quantitieskc andTc and a proximity betweenTc=Ttr andTo=53±3 °C — Vogel temperature for α-segmental dynamics was found. A comparison of kinetic and dynamic data suggests that the decay of terminal macroradicals in the low-temperature region is controlled by secondary relaxations and that the α-mobility contributes to a more rapid decay at higher temperatures belowTg.