Calorimetric Study of Dynamical Heterogeneity in Blends of Polyisoprene and Poly(vinylethylene)

The specific heat capacities C p of blends consisting of cis -polyisoprene (PI) and poly(vinylethylene) (PVE) were measured in the temperature range from 80 to 320 K by using an adiabatic calorimeter. The configurational heat capacities C conf of blends around the glass transition temperature T g have been determined by subtracting the vibrational heat capacities estimated with the Einstein and Debye theories. The C conf vs temperature T curves of the blends exhibit double sigmoidal increase at two glass transition temperatures T g1 and T g2 and can be resolved into two empirical sigmoidal curves. For each sigmoidal curve with the index j = 1 or 2, we have also determined the magnitude of the jump Δ C j and the broadness parameter B j of the sigmoidal curves. The dielectric relaxation spectrum for the primary process of PI/PVE blends is known to be bimodal due to dynamical heterogeneity. The relationship between the bimodal dielectric segmental relaxation and the double glass transition processes has been analyzed.