Abstract: A curing agent for a polyepoxide has the formula: ##STR1## wherein R.sub.1 is a divalent aryl radical such as phenylene and wherein R.sub.2 is a tetravalent aryl radical such as a tetravalent benzene radical. An epoxide is cured by admixture with the curing agent. The cured epoxy product retains the usual properties of cured epoxides and, in addition, has a high char residue after burning, on the order of 45% by weight. The high char residue is of value in preventing release to the atmosphere of carbon fibers from carbon fiber-epoxy resin composites in the event of burning of the composite.

Abstract: A composition for making polyimide resin-reinforced fibers or fabric. The composition is of the type disclosed in U.S. Pat. No. 3,745,149 and includes a polyfunctional ester, a polyfunctional amine, and an end-capping agent. The composition is impregnated into fibers or fabric and heated to form prepreg material. The tack retention characteristics of this prepreg material are improved by incorporating into the composition a liquid olefinic material compatible with the other ingredients of the composition. The prepreg material is heated at a higher temperature to effect formation of the polyimide resin and the monomeric additive is incorporated in the polyimide polymer structure.