Dynamics of alpha-relaxation and structure formation during crystallization process of polymers: Dielectric relaxation and small-angle X-ray scattering on PET

We made time-resolved simultaneous measurements of dielectric relaxation and small-angle X-ray scattering (SAXS) on poly (ethylene terephthalate) (PET) in order to investigate the relationship between the alpha-relaxation and the structure formation during the crystallization process. We found that the alpha-relaxation changes to the alpha'-relaxation via a coexistent state of the two relaxations. The change in dynamics of alpha-relaxation occurs before the formation of higher-ordered structure observed by SAXS. The results suggest the existence of a precursor phenomenon in polymer crystallization, which is related to the dynamics in the amorphous phase.