On the Oxidative Degradation of Nadic Endcapped Polyimides: I. Effect of Thermocycling on Weight Loss and Crack Formation

Abstract

The effects of thermocycle frequency, aging temperature and post-cure conditions on weight loss, microhardness and crack formation of PMR-15 neat resins were investigated. Crack formation was monitored by metallography. The molecular level changes, occurring under the same conditions, were monitored by microscopic FT-IR in reflectance mode on the same samples. FT-IR analysis was carried out in zones 100 μm in diameter, allowing examination of different regions of the aged samples. It was found that weight loss, crack formation and microhardness were highly dependent on aging time and temperature, but not thermocycling frequency. Molecular level changes were also highly correlated to time and temperature of aging. Both the physical effects of aging and the chemical effects were isolated to a thin surface layer. No changes whatsoever to the interiors of the samples were evident by FT-IR, microhardness or microscopy.