PHYSICAL AGING AND TACTICITY EFFECTS ON THE A RELAXATION MODE OF AMORPHOUS POLYMERS BY THERMALLY STIMULATED TECHNIQUES

Samples of amorphous poly (ethylene terephthalate) (PET) vitrified und er different cooling rates and a series of samples of poly (methyl met hacrylate) (PMMA) of various tacticities have been characterized by di fferential scanning calorimetry (DSC), thermally stimulated current (T SC) and thermally stimulated creep (TSCr). The alpha relaxation and re tardation modes, associated with the glass transition, have been analy zed. The dielectric relaxation mode observed in PET has relaxation tim es following a compensation law with compensation parameters independe nt of physical aging. Contrarily, the maximum value of the activation enthalpy increases upon aging. The anelastic retardation mode observed in PMMA is also constituted of retardation times following a compensa tion law. In that case, the T-c - T-g lag varies according to the chai n conformation. It is also interesting to note that the maximum of the activation enthalpy increases with the level of local interactions. T his evolution is due to the increasing of the domain sizes in which mo lecular mobility takes place. (C) 1998 Elsevier Science B.V. All right s reserved.