Crystalline, mobile amorphous and rigid amorphous fractions in isotactic polystyrene

Abstract

The method recently proposed in order to monitor simultaneously the development of crystalline, mobile amorphous and rigid amorphous fractions during cooling from the melt in semicrystalline polymers is here applied to isotactic polystyrene. The procedure, which allows the determination of the temperature evolution of the three nanophases, is the development of a previous enthalpy-based method founded on a two-phase description of semicrystalline polymers, with only one crystalline phase and one amorphous phase accounted for. The three-phase method that is here utilized proves to be able to correct the erroneous trend predicted by the two-phase method in the temperature region close to T g. For isotactic polystyrene it was found that the rigid amorphous fraction starts to vitrify during the final stages of the non-isothermal crystallization process, with the full establishment of the rigid amorphous structure completed during the subsequent cooling to room temperature. The reported results confirm the existence of a link between vitrification of the rigid amorphous phase and secondary crystallization, and prove that in isotactic polystyrene only the rearrangements of the amorphous regions localized in proximity of the growing secondary lamellae are subjected to geometrical restrictions, with consequent formation of rigid amorphous phase.