Silica–polyimide hybrid composites were prepared via a sol–gel process and thermal imidization. Two different types of soluble precursors, poly(amic acid) (PAA) and poly(amic diethyl ester) (ES), chemically convertible to poly(p‐phenylene biphenyltetracarboximide), were used as organic polymer matrix component, and tetraethoxysilane (TEOS), convertible to silica, as the inorganic component. The structure of composites prepared as thin films was investigated by means of small‐angle X‐ray scattering, scanning electron microscopy and atomic force microscopy. Nanometre‐scale composites were successfully obtained for ≤30wt% TEOS‐loaded mixtures with ES and PAA. It was considered from the microstructural investigation that the composite films based on ES were not significantly affected by the inorganic particles generated, maintaining the structure of the homopolyimide, while those based on PAA did not preserve the structure due to the nanoparticles grown in situ during the sol–gel process. © 1997 SCI.

The heat resistance of the multiphase friction materials made with straight phenolic resin (ST), boronphosphorous (B-P)-modified phenolic resin (BP), or polyimide (PI) was investigated using a Krauss-type friction tester. Thermal analysis of the cured resins was also carried out to examine the chemical and mechanical properties of the resin and their effects on the wear rate and the coefficient of friction. The results showed that the fade and wear of the friction materials were closely related to the thermal decomposition of the binder resin and durability of the contact plateaus, which were produced by the compaction of wear debris around hard ingredients on the rubbing surface. The friction material containing the B-P modified resin was more resistant to wear and fade than the other binder resins. On the other hand, the friction material with polyimide showed good fade resistance but exhibited excessive wear despite its good thermal resistance.