Thermally stimulated current studies of poly(aryl ether ketone ketone) and polycarbonate

Thermally stimulated current depolarization (TSC) and conventional a.c. dielectric techniques were used to study relaxation in the regions of localized(β relaxation) and cooperative(α or glass transition) motions. The two techniques together cover the frequency range from approximately 10^-3 to 10⁵ Hz. There are difficulties in interpretation of solid state relaxation dynamics because of the complexity of the systems which leads to broad distributions at all temperatures and very high apparent activation energies(E_a) in the glass transition region. Amorphous poly(aryl ether ketone ketone) PEKK begins to cold-crystallize at temperatures a few degrees above T_g. TSC was found to be useful in studying the glass transition in the amorphous state because the low equivalent frequency shifts T_g away from the crystallization region. Comparison with crystalline PEKK indicated that crystallites had a large effect on amorphous relaxations.^3,4 Polycarbonate(PC) was studied in the purely amorphous state because thermal crystallization is negligible. Thermal peak cleaning of TSC spectra of PEKK and PC indicate that most of the relaxation region can be characterized by a continuous variation of activation energies. Other general features of the dependence of E_a on temperature are found, which help explain the magnitude of the activation energies obtained from other relaxation methods.