Isothermal aging effects on PMR-15 resin

Specimens of PMR-15 polyimide neat resin were aged in air at temperatures of 288, 316, and 343°C. Weight losses and dimensional changes were monitored during the course of the exposure time. Physical changes were also observed by optical and electron microscopy. As a result of this study, it was found that polyimide polymer degradation occurred within a thin surface layer that developed and grew during thermal aging. The cores of the polymer specimens were protected from oxidative degradation, and they were relatively unchanged by the thermal treatment. Surface cracking was observed at 343°C and was probably due to an interaction between voids and stresses that developed in the surface layer.