Successive melting and crystallization of poly(3-hexylthiophene) in the melt-memory domain versus isotropic melt domain

We studied the influence of self-nuclei of poly(3-hexylthiophene), present at different temperatures in the melt-memory domain, and thermal polymer degradation during repeated cycles of melting and recrystallization. During a rapid crystallization by cooling from an isotropic melt to low crystallization temperatures, we observed two populations of crystals characterized by melting temperatures differing by ca. 6 °C. Intriguingly, the population with the higher melting temperature disappeared upon “static annealing” at temperatures well below the melting point, which was accompanied by an increase in the amount of the component with the lower melting temperature. “Dynamic annealing”, however, favored the increase of the fraction of crystals with a higher melting temperature. As this population was not present when the polymer was crystallized more slowly at higher crystallization temperatures, we tentatively attribute this component to transient unstable but thicker structures formed during rapid crystallization.