We have studied the adhesion-promoting layer of a composite interface consisting of alumina, 3-aminopropyltriethoxysilane (APS), and polyimide (PI) reactants. The aminosilane appears to exist as a submonolayer and is N-15 isotope-enriched, which renders it ＇visible＇ to solid-state N-15-NMR detection. The interactions of the APS nitrogen with four different PI reactants including two amic acids, an amic ester, and an isoimide are investigated: (1) at mom temperature, (2) during thermal curing up to temperatures of 300-400-degrees-C, (3) after typical hydrothermal stress, and (4) after a post-temperature and humidity (T&H) bake. Conclusions about the chemical reactivity of the APS am drawn from interpretation of the N-15-NMR spectra. These experiments offer direct evidence of chemical reactions in an area where little direct evidence is available. The surface-bonded APS is shown to have different reactivities toward different kinds of PI reactant at low temperatures, with the isoimide being the most reactive. At higher temperatures, the reactivities am observed to be similar. Thermal treatment shows the formation of PI/APS aryl/alkyl imide bonds. Hydrothermal stress shows degradation of the PI/APS imide bonds via a two-step mechanism. However, a post-T&H bake at an elevated temperature appears to substantially heal the T&H degradation.