The dielectric spectra of two aliphatic polyesters, poly(propylene succinate) and poly(propylene adipate), are reported. For these two model aliphatic polyesters the a and P relaxations appear simultaneously and well resolved in the experimental frequency window. During isothermal crystallization, this fact allows one to use the 0 relaxation to characterize the crystalline structural development while the a relaxation provides information about the evolution of the amorphous phase dynamics. In this way structural development and dynamics evolution can be characterized by a single experiment during the crystallization process. Additionally, the unambiguous determination, in the amorphous polymers, of the relaxation times for the a and 0 relaxations further support a close relationship between local and segmental dynamics in polyesters as proposed by the coupling model. (c) 2007 Elsevier Ltd. All rights reserved.