A REINVESTIGATION OF THE HYPERSONIC PROPERTIES AND THE SPECIFIC-HEAT CAPACITY OF PMMA AROUND THE QUASI-STATIC GLASS-TRANSITION .2. HIGH-PERFORMANCE CALORIC INVESTIGATIONS

To continue dynamic Cp measurements in the range of smallest temperature rates and non-linear thermal relaxation investigations into the linear range, simultaneous Cp and thermal relaxation measurements were carried out in an adiabatic vacuum calorimeter, using the pulse heating method. The rate-dependent Cp behaviour, known from dynamic measurements, does not continue at small temperature rates. This is confirmed by the relaxation process which is observed. The results suggest an extended interpretation of the glass transition in atactic polymethylmethacrylate (PMMA).