Abstract: Gel coating of thermoplastic particles, such as polyimide particles, with a polyketone or polyvinyl alcohol gel, and applying the gel coated particles to reinforcement, e.g. carbon, fibers to form a pre-preg. Such gel coated thermoplastic particles can be mixed with a thermosetting resin to form a pre-preg, which can be cured at elevated temperatures to form a composite having damage tolerance characteristics. The gel coating is applied to the thermoplastic particles by contacting such particles with a polymerizable material such as acetone in a weakly acidic solution to cause the acetone to undergo tautomerism, and in the presence of a polymerization promoter or catalyst, preferably certain anionic surfactants such as sulfated ammonium salts, to convert the tautomer to polyacetone gel of low molecular weight, which coats or encapsulates the thermoplastic particles.

Abstract: A process for increasing the damage tolerance in thermoset composites without loss of processibility or mechanical properties of the thermoset, by controlled solubility of a thermoplastic filler in the base thermoset. The process includes mixing spherical particles of a selected thermoplastic, such as polyimide, of particle size ranging from about 10 to 80 microns, with a hot thermoset resin, such as a bismaleimide, to form a uniform dispersion of the resin mixture, employing about 5 to about 40% of the thermoplastic by weight of the mixture of the two resins. The particles of thermoplastic are non-agglomerating and insoluble in the resin mixture. The hot resin dispersion is then applied to fiber reinforcement, such as carbon fiber tapes, to form pre-pregs. Upon curing the thermoset at elevated temperature, the thermoplastic particles dissolve in the thermoset resin, forming a composite with no definable boundary interfaces between the thermoplastic and thermosetting resins.