Toughened, fiber-reinforced thermosetting resin matrix prepregs and composites made therefrom

A curable thermosetting resin system for forming a toughened single phase cured matrix resin, said resin system consisting essentially of:

• A. a base resin system consisting essentially of
• (i) one or more thermosetting resin monomers selected from the group consisting of the bismaleimide resins, epoxy resins, cyanate resins, and mixtures thereof:
• (ii) at least one curing agent
• (iii) optionally catalysts;
• and
• (iv) optionally at least one dissolved thermoplastic in an amount effective to assist the toughness of the single phase cured matrix resin;
• B. optionally, particulate engineering thermoplastics in an amount of from 10 to 30 weight percent based on the total resin system weight;
• and
• C. from about 1 percent to about 10 percent by weight relative to the total system weight of preformed functionalized, lightly crosslinked elastomer particles having a T.sub.g of less than 10.degree. C., and a particle size of from about 2 .mu.m to about 70 .mu.m wherein said elastomer particles remain in substantially particulate form.