SEPARATION OF COMPONENTS OF DIFFERENT MOLECULAR MOBILITY BY CALORIMETRY, DYNAMIC-MECHANICAL AND DIELECTRIC-SPECTROSCOPY

The relaxation strength at the glass transition for semi-crystalline p olymers observed by different experimental methods shows significant d eviations from a simple two-phase model. Introduction of a rigid amorp hous fraction, which is non-crystalline but does not participate in th e glass transition, allows a description of the relaxation behavior of such systems. The question arises when does this amorphous material v itrify. Our measurements on PET identify no separate glass transition and no devitrification over a broad temperature range. Measurements on a low molecular weight compound which partly crystallizes supports th e idea that vitrification of the rigid amorphous material occurs durin g formation of crystallites. The reason for vitrification is the immob ilization of co-operative motions due to the fixation of parts of the molecules in the crystallites. Local movements (beta-relaxation) are o nly slightly influenced by the crystallites and occur in the whole non -crystalline fraction.