Impact resistant vinyl ester resin and process for making same

A process for preparing a thermosettable resin having improved impact resistance in the thermoset state which comprises [simultaneously] reacting the epoxide moieties of a polyepoxide having an average of more than one epoxide group per molecule with the acid moieties of an unsaturated monocarboxylic acid and a liquid carboxy terminated polydiene rubber wherein the combined acid equivalents of said unsaturated acid and said polydiene ranges from about 0.8 to 1.2 equivalents per epoxide equivalent and wherein at least about 80 percent of said acid equivalents comprises said unsaturated acid and the balance between 0.01 and 20 percent comprises said polydiene, provided that the polydiene rubber content is at least about 4 weight percent and wherein said resin is prepared by the simultaneous reaction of said polyepoxide, said polydiene rubber and said monocarboxylic acid or by the sequential reaction wherein said polyepoxide and said polydiene rubber are reacted followed by addition and reaction of said monocarboxylic acid with the product of that first reaction .