Heat flows on the heating process after aging of glassy poly(methyl methacrylate) measured by temperature modulated differential scanning calorimeter

Reversing and non-reversing heat flows on the heating process after isothermal aging of glassy atactic poly(methyl methacrylate) was measured by temperature modulated differential scanning calorimeter. The reversing and non-reversing heat flows of the non-aged sample were subtracted from those of the aged sample to investigate only the isothermal aging effects. The difference between the aged and non-aged sample was most significant in the sample aged at 100 °C in both the reversing and non-reversing heat flows. Starting temperature of the difference in the non-reversing heat flow became higher with the aging temperature. On the other hand that of the reversing heat flow was around 70 °C irrespective of the aging temperature. Based on these results it is suggested that recovery of the molecular mobility at the glass transition occurs by two steps.