Concentrated prepolymer composition useful for forming polyimide articles

A method for forming a homogeneous, concentrated, prepolymer composition, and a method of using the concentrated prepolymer composition to uniformly coat fibers is described. The prepolymer mixture is formed by dissolving a dialkyl, trialkyl, or tetraalkylester of biphenyltetracarboxylic acid in a solvent comprising ethyl acetate and methanol in a molar ratio of from about 1:3 to about 1:60, to form an ester solution. Diamine and end cap compound are added to the ester solution to form a monomer mixture solution. The end cap compound is a divalent compound characterized by (i) at least one unsaturated moiety, (ii) capable of reacting with the diamine or the ester to form an end cap radical that precludes further reaction of the diamine with the ester, and (iii) capable of undergoing addition polymerization. A portion of the solvent is evaporated from the monomer solution to form the substantially homogeneous, concentrated, prepolymer composition. The concentrated prepolymer composition is used to uniformly coat fibers by heating the composition to an elevated temperature to form a prepolymer melt and applying the prepolymer melt to fibers. An article of manufacture comprising fibers and polyimide can be formed by heating the prepolymer coated fibers to the cross-linking temperature of the prepolymers.