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  1. Abstract

    Large anisotropic deformation affects the physical state of a polymer glass, where the changes in the state of material are revealed by performing a differential scanning calorimetry (DSC) experiment. Previously, the deformation was applied to polymers well below their glass transition temperatures, and it was found that uniaxial compressive loading–unloading resulted in a broad exothermic peak on the DSC trace. Here we report on the effect on the subsequent DSC response of a deformation experiment performed in uniaxial extension on a ductile 50:50 co‐polymer poly(BMA‐co‐MMA) (PBMA/MMA). The deformation of up to 80% strain was applied atTg − 30°C andTg − 40°C, that is, closer toTgthan in the previous work. Unlike in the well belowTgdeformation case, the DSC trace contains an endothermic peak followed by an exothermic peak. The magnitude of the endothermic peak as well as the asymptotic glassy heat capacity increase with the amount of mechanical work performed during the deformation cycle.

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  2. Abstract

    The effects of annealing a glassy polymer at temperatures well belowTgon the dynamic linear viscoelastic properties were investigated. The polymer was an epoxy thermoset with aTgof 182°C. Specimens were annealed from 2 h to up to 600 h at temperatures from −100°C (Tg−282°C) up toTg. At annealing temperatures just belowTg, there was no effect of annealing, and annealing at −100°C (Tg−282°C) showed no difference between 2 and 6 h annealing, although annealing effects might be seen at longer times. At temperatures between −50°C (Tg−232°C) and 170°C (Tg−12°C) the storage isotherms increased with annealing while the loss isotherms decreased. In addition, the heat capacity as measured via DSC after annealing at 50°C (Tg−132°C) and 100°C (Tg−82°C) exhibited endothermic peaks approximately 40°C above the annealing temperature. This study clearly shows that a material deep in the glassy state is not frozen, but undergoes continuing evolution. The nature of deep glass aging is different than physical aging in theTgregion, where deep in the glass the relaxation spectrum changes magnitude and shape but does not shift along the log frequency axis in contrast to physical aging in theTgregion.

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