Abstract: A self-supporting film of a curable fluorine-containing aromatic polyimide precursor resin is applied to and cured at elevated temperature and pressure on one or more outer surfaces of a reinforced substrate. The substrate is (1) a prepreg lay-up of (a) reinforced plies of a curable aromatic polyimide precursor or (b) fibers impregnated with a cured polyimide powder, or (2) a composite previously formed by curing a lay-up of a reinforced plies of a curable aromatic polyimide precursor. The resultant cured coating improves the erosion resistance of the composites so formed. Use of such films avoids the difficulties experienced when using conventional spray coating procedures.

Abstract: Thermoplastic polyimides of benzophenone tetracarboxylic acid or an ester or anhydride thereof and a 2,2-bis[4-(amino-phenoxy)phenyl]hexafluoropropane are excellent adhesives for bonding polyimide films to various substrates including polyimide film, metals, etc. The film and substrate need not be abraded before application of the polyamic acid resin or polyimide precursor from which the polyimide is formed on curing. The bond is tenacious. Even after heating to 800.degree. F. the bond was stronger than two different polyimide films. Interposing between the polyimide film and the substrate a strip or patch of a prepreg made from polyimide precursor solutions composed of monomers, solvent and polyamide acid, and applying heat to cure the resin in situ while keeping the components in intimate contact by application of slight pressure is a preferred way of applying and utilizing the adhesives. Such prepregs are also useful for bonding metal to metal or to various other substrates.