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

Thermally stimulated current depolarization (TSC), dielectric, and differential scanning calorimetry (DSC) techniques were used to study crystallization and molecular relaxations in poly(aryl ether ketone ketone) (PEKK). The alpha relaxation, associated with the glass transition (T sub g = 155 deg C), was studied with TSC before and after crystallization, showing that crystallinity substantially hinders amorphous relaxations, consistent with DSC analysis of the glass transition. Thermal peak cleaning was used to deconvolute the global TSC spectra, giving apparent activation energies E sub a over the range --120 to +240 deg C. Comparison of analysis schemes to obtain activation energies either by numerical integration or by fit of the raw TSC spectra in current space is discussed. The mean values of E sub a from thermally cleaned TSC spectra were in agreement with those determined from classical Arrhenius plots of the dielectric alpha and beta relaxation data of 1n f vs. 1/T sub max , where T sub max is the peak temperature. TSC has the advantage that values of E sub a can be determined at any temperature, regardless of whether a specific transition is present. In the sub-T sub g region from --120 to 130 deg C, the activation energy increased gradually with temperature and the values of E sub a were found to agree quantitatively with those predicted by using Eyring's activated states equation with a zero activation entropy. The activation energies of both amorphous and semicrystalline PEKK were found to be identical over the range covered. At higher temperatures, the measured values of E sub a depart from the zero activation entropy line and exhibit a sharp maximum at T sub g , indicating a high degree of cooperativity in the relaxations. Graphs. 28 ref.--AA