Impression recovery of amorphous polymers

The impression made by a loaded cylindrical flat-end punch on a polymer surface was observed to disappear with time at the same temperature after the load was removed. The depth-time relation appeared to obey second order kinetics. The temperature dependence of the rate constant shows two consecutive processes with activation energies, 906 kJ/mole (between 143 and 147°C) and 91 kJ/mole (between 150 and 160°C) for PC (Tg is at about 146°C) and 440 kJ/mole (between 104 and 110°C) and 95 kJ/mole (between 115 and 140°C) for PMMA (Tg is at about 112°C). These activation energies are probably associated with the motion and annihilation of conformational or structural defects of opposite signs. This kind of shape memory phenomena may be general for all amorphous polymers.