HYDROTHERMAL DEGRADATION AND THERMAL REGENERATION OF AN AMINOSILANE INTERFACE USED TO COUPLE POLYIMIDE TO ALUMINA

We have studied the adhesion-promoting layer of a composite interface consisting of alumina, 3-aminopropyltriethoxysilane (APS), and polyimi de (PI) reactants. The aminosilane appears to exist as a submonolayer and is N-15 isotope-enriched, which renders it 'visible' to solid-stat e N-15-NMR detection. The interactions of the APS nitrogen with four d ifferent 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 hydr othermal stress, and (4) after a post-temperature and humidity (T&H) b ake. Conclusions about the chemical reactivity of the APS am drawn fro m interpretation of the N-15-NMR spectra. These experiments offer dire ct evidence of chemical reactions in an area where little direct evide nce is available. The surface-bonded APS is shown to have different re activities 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 f ormation of PI/APS aryl/alkyl imide bonds. Hydrothermal stress shows d egradation 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.