Multiple melting behavior of poly(thiodiethylene terephthalate): Further investigations by means of X-ray and thermal techniques.

The complex multiple melting behavior of poly(thiodiethylene terephthalate) (PSDET) was investigated by means of differential scanning calorimetry, X-ray diffraction and hot-stage optical microscopy. The phenomenon was ascribed to the existence of two different crystal structures (a and b), each of them being able to melt and recrystallize under the experimental conditions adopted. Linear and nonlinear treatments were applied in order to estimate the equilibrium melting temperature for a PSDET, by using the corrected values of Tm. The nonlinear estimation led to a higher value by about 25 8C. Isothermal crystallization kinetics of each crystalline form were analyzed according to Avrami’s treatment. In both cases, values of Avrami’s exponent, n, close to 3 were obtained, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. The rate of crystallization of each crystalline structure was found to become lower as the crystallization temperature is increased, as usual at low undercooling, where the crystallization process is controlled by nucleation.