Activation-energy spectra for retraction of hot-stretched polystyrene and shear creep in polymethyl methacrylate

The data of Andrews for the retraction kinetics of hot-stretched polystyrene and the data of Thompson for shear creep in polymethyl methacrylate in the glassy state have been analyzed to obtain activation-energy spectra characterizing the kinetic processes. For the retraction data, singly peaked spectra covering the range between 15 and 35 kcal/mole were found. These were virtually independent of widely varying sample history, and the range of activation energies was somewhat higher than that found for volume relaxation in unoriented samples of the same polymer. The energy spectrum for the creep data is similar in shape to the retardation-time spectrum derived by Thompson, and covers the range 6-43 kcal/ mole. This range includes the three energy values previously calculated from the temperature dependence of the shift factor, log₁₀a_T. Changes in structure with temperature are easily inferred from the temperature dependence of the shift factor used to derive the energy spectrum.