Fast scanning calorimetry study of the structural relaxation in a random propylene-co-1-octene copolymer

The structural relaxation (or physical aging) has been analyzed by means of fast scanning calorimetry for a random propylene-co-1-octene copolymer, in a wide range of annealing temperatures and times. For annealing temperatures well below Tg only the structural relaxation is observed, and both the rate of enthalpy recovery and the peak temperatures related to the relaxation show a remarkable reduction with decreasing annealing temperatures. When the glass transition temperature is approached, although the structural relaxation is observed first, mesophase ordering is obtained at higher annealing times. The analysis of this mesophase ordering suggests homogeneous nucleation, and, in agreement with prior research in this field, the main feature is that the ordering in the glassy state requires prior completion of the enthalpy relaxation.