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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), poly(ethyl methacrylate), and poly(2, 2, 2-trifluoroethyl methacrylate) by creep and stress relaxation (SR) experiments. Dielectric analysis (DEA) and dynamic mechanical analysis (DMA) are used to measure and compare the structural relaxations associated with side group motion and with the glass transition, T g , region. An analysis of shift factor data for creep and SR experiments reveals two modes of molecular motion in the glass-rubber relaxation region, but the modes are less discernible than those reported previously for a series of styrene polymers. The high temperature side exhibits WLF behavior while the low temperature side exhibits Arrhenius behavior. The extent of definition of the two modes of deformation is related to the effect of cooperative a dynamics on the β relaxation process. Some discussion is presented concerning the magnitude of the activation energy for both processes and the sharpness of the transition between the two modes.