Synthesis of acid anhydride‐modified flexible epoxy resins and enhancement of impact resistance in the epoxy composites

Abstract Epoxy resins are key materials used in various applications, including coatings, adhesives, and composites. Tougheners, such as nanoparticles, soft polymers, elastomeric polyurethanes, and core/shell particles, have been widely applied to compensate for the brittleness of the epoxy matrix and to enhance the impact resistance. Modifying epoxy resin by reacting it with a flexible component is one of the representative methods to overcome the weakness of cured epoxy polymers upon impact. For introducing flexible parts, we synthesized three types of epoxy‐modified resins by reacting acid anhydride with glycidol, followed by reaction with bisphenol [F, S, or J] glycidyl ether to produce flexible modified epoxy resins. Mechanical tests, such as flexural strength and impact resistance tests, were performed by adding various amounts of the synthesized resin to the epoxy composites. The results of these tests suggest that the modified resins were effective in improving the toughness of the epoxy matrix.