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: A method of treating the surface of a mold to improve its release characteristics is disclosed. A coating of a polyamic acid solution comprising the reaction product of 2,2-bis[4-(aminophenoxy)phenyl]hexafluoropropane and an aromatic tetracarboxylic acid or dianhydride or ester derivative thereof is applied to the mold surface. The coating is cured at elevated temperatures to remove the solvent and form the corresponding polyimide.

Abstract: Described is a way of sealing a carbon body such as monolithic graphite tooling so that it retains its vacuum integrity through numerous thermal cycles typical of thermoplastic processing. This is accomplished by (a) applying to the body surface a coating formulation composed of a carbon-filled solution of a polyamic acid formed by reaction between pyromellitic acid dianhydride and 2,2-bis[4-(aminophenoxy)phenyl]hexafluoropropane, and (b) heat curing the coated body to cause the polyamic acid to imidize into a thermally cured polyimide.