Oligomerization of an aminosilane coupling agent and its effects on the adhesion of thin polyimide films to silica

This work studies the effects of self-oligomerization of the aminosilane coupling agent 3-aminopropyltriethoxysilanc-also called γ-aminopropyltriethoxysilane, 3-APS, γ-APS, APS or A1100 (Union Carbide)-on the adhesion of thin polyimide films to a native-oxide silica surface under no stress, i.e. T(0) conditions, and after standard 85°C/81% T& H (temperature and humidity) stress. Techniques have been developed using both silicon and hydrogen NMR to control and monitor the degree of oligomerization in aqueous solutions at low concentrations (0.1 vol %). The results of these studies suggest that: (1) Highly self-oligomerized 0.1 vol% APS solutions promote adhesion as do those with very low amounts of self-oligomerization; (2) T& H conditions cause an overall decrease in adhesion. However, this loss is not well-correlated with the degree of oligomerization and the likely perturbations of the silicon-oxygen environment at the surface; (3) If the current ideas of APS/mineral surface interactions are to be supported, then the highly-oligomerized APS molecules must first revert to more reactive states such as monomers. Perhaps the surface itself catalyzes such a reversion. The newly formed APS silanols are then free to form surface bonds and eventually a two-dimensional surface network. Alternatively, the formation of Si-O covalent surface bonds may not even be required for APS-promoted adhesion. Finally, studies of aqueous APS concentrations and their effects on adhesion under T& H stress suggest that aqueous APS solutions with concentrations above 0.01 vol % produce effective coupling at T(500) T& H conditions. Concentrations below this level produce lower adhesion that degrades quickly under T& H stress.