Abstract: A determined amount of at least C.sub.8 dicarboxylic functional unsaturated anhydride or acid, excluding polymeric anhydrides and acids, is incorporated in an unsaturated polyester resin which comprises (1) a condensation polymer which is the reaction product of: (a) dicarboxylic acid, at least a portion of which contains ethylenic unsaturation, with (b) dihydric alcohols; and (2) an alpha-beta-ethylenically unsaturated copolymerizable monomer, to provide modified polyester resins for curable polyester resin systems having improved cohesive and adhesive strengths of the cured resin and improvement in adhesion of such systems to a wide range of substrates, especially substrates considered extremely difficult to bond to, viz., hot dipped galvanized steel, stainless steel, copper, bronze, tin, aluminum, solder, brass and glass (silicon oxide), while also reducing or effectively eliminating retardation of cure by the presence of galvanized (zinc) coated steel or the like.