Creep and stress relaxation in methacrylate polymers: Two mechanisms of relaxation behavior across the glass transition region

This study explores the long-term behavior of poly(methyl methacrylate), po ly(ethyl methacrylate), and poly(2, 2, 2-trifluoroethyl methacrylate) by cr eep and stress relaxation (SR) experiments. Dielectric analysis (DEA) and d ynamic mechanical analysis (DMA) are used to measure and compare the struct ural relaxations associated with side group motion and with the glass trans ition, Tg, region. An analysis of shift factor data for creep and SR experi ments reveals two modes of molecular motion in the glass-rubber relaxation region, but the modes are less discernible than those reported previously f or a series of styrene polymers. The high temperature side exhibits WLF beh avior while the low temperature side exhibits Arrhenius behavior. The exten t of definition of the two modes of deformation is related to the effect of cooperative oc dynamics on the P relaxation process. Some discussion is pr esented concerning the magnitude of the activation energy for both processe s and the sharpness of the transition between the two modes.