Dynamical Transition and Crystallization of Polymers

The results of simultaneous time-resolved measurements of dielectric relaxation and x-ray scattering during isothermal crystallization from the glassy state of poly(ethylene terephthalate) are reported. We find a dynamical transition in the early stage of crystallization. The $\alpha$-relaxation process, associated with glass transitions, is transformed into another relaxation process, the ${\alpha }^{\prime }$ process, via a coexistence state before an observable change in x-ray scattering patterns due to the formation of crystalline structures appears. Analysis of x-ray scattering patterns reveals that this dynamical transition is related to a change in the thermal fluctuations of the electron density, i.e., to isothermal compressibility.