Solid-state relaxations in poly(ethylene oxide). I. Study using the differential scanning calorimetry method

Differential scanning calorimetry (DSC) studies show that poly(ethylene oxide) (PEO) exhibits three transition regions below its melting point. The effects of annealing on the intensity and temperature of these transitions enable us to locate T < T_g (T_γ) T_g, and T_α at about 130–140. 190–240, and 263–313°K, respectively. Our results argue for a small transition T_g (L) at 190–200°K with a second T_g (U) above 233°K, the temperature of which increases on annealing. The shape of DSC derivative curves reveals that T < T_g and T_α are complex and suggests the possibility of two steps in these processes. In addition, a splitting of T_α is observed every time a multiple melting endotherm appears as a result of annealing. Up to three separate melting endotherms can be observed. One of them is related to the normal primary crystallization process. Its peak temperature increases linearly with the annealing temperature, yielding an extrapolated value for the equilibrium melting temperature T of 347°K as found before.