Poly(dithiotriethylene adipate): Melting behavior, crystallization kinetics and morphology

The melting behavior and the crystallization kinetics of poly(dithiotriethylene adipate) (PSSTEA) were investigated by differential scanning calorimetry and hot-stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (Tc) and ascribed to melting and recrystallization processes. Linear and nonlinear theoretical treatments were applied to estimate the equilibrium melting temperature for PSSTEA, using the corrected values of the melting temperature; the nonlinear estimation yielded a higher value by about 15 °C. Isothermal crystallization kinetics were analyzed according to the Avrami's theory. Values of the Avrami's exponent n close to 3 were obtained, independently of Tc, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, space-filling spherulites were observed by optical microscopy at all Tc's. The rate of crystallization became lower as Tc increased, as usual at low undercooling, the crystallization process being controlled by nucleation.