RELATION BETWEEN PEEK SEMICRYSTALLINE MORPHOLOGY AND ITS SUBGLASS RELAXATIONS AND GLASS-TRANSITION

The PEEK glass transition (alpha-relaxation) is studied as a function of polymer semicrystalline morphology, characterized by small-angle X-ray scattering. An inverse relationship is observed between glass transition temperature and amorphous interlayer thickness. This is interpreted in terms of configurational entropy differences in the amorphous regions of semicrystalline samples, as compared to a bulk amorphous sample. The existence of so-called rigid amorphous fractions is shown to result partly from these entropy differences. The PEEK subglass transitions have also been studied. The highly-localized wagging of the polar bridges corresponding to the gamma-relaxation is insensitive to ageing history and details of the semicrystalline morphology. The combination of the gamma-wagging with phenyl flips results in the appearance of the beta-relaxation. The energy barriers controlling the onset of beta-motions are intermolecular in nature. Thus, perturbations of the environment of the relaxing moiety (water content, ageing history, details of the semicrystalline morphology) affect the beta-relaxation.