The relation between relaxed enthalpy and volume during physical aging of amorphous polymers and selenium

This paper reports physical aging results for PMMA, PMMA/PEO blends, PS, PC, PVC and PET (semicrystalline). Also included in this study is amorphous selenium. Temperature down-jumps from equilibrium above Tg to a temperature below Tg were carried out. Relaxed enthalpy, Δh and volume contraction, Δv, were measured. From the aging records, the constant ratio Δh/Δv = Ka was evaluated. For the polymeric samples Ka values of about 2 GPa were observed, thus similar to the inverse value of the isothermal compressibility close to Tg. Similarly for Se the Ka value obtained from Δh and Δv was in fair agreement with its isothermal compressibility.