Impression recovery of PMMA

Impression recovery in which the deformation temperature is the same as recovery temperature is studied for the first time. PMMA is deformed by impression above the glass transition temperature to a depth of less than 0.3 mm and recovered at the same temperature. Almost complete recovery of dimension is observed every time. The dimensional changes obey second order kinetics and the temperature dependence of the rate constant shows two consecutive processes with activation energies 440 kJ/mole (between 104 and 113 °C) and 95 kJ/mole (between 113 and 140 °C). Two pairs of defects of opposite signs are believed to be involved in the dimensional recovery processes.