Effect of anisotropic deformation on the differential scanning calorimetry response of polymer glasses

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 at T_g − 30°C and T_g − 40°C, that is, closer to T_g than in the previous work. Unlike in the well below T_g deformation 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.