Abstract: The resin composition comprises, as essential components, (A) an epoxy resin, (B) a thermoplastic resin and (C) particles of a diaminodiphenylsulfone compound whose cross linking reactivity with the epoxy resin is prevented until the resin composition is subjected to molding or curing by a resin coating which is formed (i) by forming or adhering resin particles onto the surface of the diaminodiphenylsulfone particles or (ii) by forming a resin film on the diaminodiphenylsulfone particles, the coating resin used for forming the resin coating is not compatible with components included in the resin composition at the temperature up to the curing temperature of the resin composition.

Abstract: The resin composition which contains thermosetting resin as Component (A), a thermoplastic resin as Component (B), and at least one compound selected from the group consisting of an epoxy resin capable of dissolving the thermoplastic resin and a reactive diluent possessing at least one epoxy group as Component (C) in a ratio such that the proportions of Components (A), (B), and (C) fall respectively in the ranges of 30 to 96% by weight, 2 to 50% by weight, and 2 to 49% by weight, based on the total weight of the resin composition. The resin composition is capable of producing a molded article combining the highly satisfactory mechanical and thermal properties of a thermosetting resin and the highly satisfactory toughness of a thermoplastic resin.

Abstract: A prepreg for making a composite is disclosed. The prepreg comprising reinforcing fibers impregnated with a resin composition comprising (A) an epoxy resin, (B) a reaction product of an epoxy resin and a butadiene-acrylonitrile copolymer having carboxyl groups on at least both terminals of the molecular chain of the copolymer, and (C) 4,4'-diaminodiphenylsulfone as a curing agent. A composite produced by curing this prepreg is high in both tensile elongation and heat resistance and is used with advantage as primary and secondary structural materials in aircraft.