Thermal stability of the silica‐aminopropylsilane‐polyimide interface

Thermal degradation of the silica–aminopropylsilane–amic acid/imide interface was studied by modifying a high‐surface‐area, neutral silica gel with a number of substituted aminopropylsilanes (APS). These substrates were reacted further with phthalic anhydride or aromatic amic acid monomers and the thermal decomposition of the adsorbed/reacted materials was monitored by thermogravimetric analysis (TGA) and infrared (IR) spectroscopy. The 3‐aminopropyltriethoxysilane/poly[N,N′‐(p,p′‐oxydiphenylene)pyromellitimide] interface was also evaluated by this method. Comparison clearly distinguishes the thermal decomposition of surface‐bound APS from surface‐bound alkylphthalimides, the adhesion product of alkylamines and aromatic amic acids. Alkylamine imidization with the elimination of aromatic amine (analogous to polymer scission) and the decomposition of the surface‐bound imide are shown in the amic acid TGA profiles. This imidization and the accompanying aniline elimination begin at about 130°C, under nitrogen, to form the surface alkyl imide which slowly decomposes at 400°C. TGA analysis indicates that the surface‐bound imide undergoes minimal degradation under nitrogen at 370 ± 10°C; temperatures above this threshold range produce changes in the APS–imide interface.