Structure-dynamics relationships of the alpha-relaxation in flexible copolyesters during crystallization as revealed by real-time methods

The evolution of the ol-relaxation during an isothermal crystallization pro cess of a series of flexible copolyesters of hydroxybutyrate (HB) and hydro xyvalerate (HV) has been followed in real-time by wide-angle X-ray scatteri ng and dielectric complex permittivity measurements. The change of the diel ectric parameters with crystallization time can be phenomenologically descr ibed in terms of the Havriliak-Negami equation. The dielectric strength fol lows a sigmoidal-shaped pattern similar to that shown by the crystallinity. A reduction of the overall mobility with crystallization time of the polym eric chains in the amorphous phase has been observed. This slowing down eff ect depends on the HV molar content. The influence of the chain flexibility on the crystalline-induced restriction has been discussed in the light of similar studies carried out with more rigid polymers. Dielectric experiment s suggest that the progressive immobilization of polymer segments as crysta llization proceeds cannot be exclusively associated with the amount of crys talline material. Differences in microstructure, depending on the HV molar content, seem to be responsible for the observed behavior. The progressive broadening and symmetrization of the ol-relaxation with increasing crystall ization time has been explained as due to a restriction of the large-scale motions of the polymeric chains, as the material is being filled in with cr ystals. (C) 1999 John Wiley & Sons, Inc.