Preparation of reactive phenolphthalein poly(aryl ether ketone) for toughening epoxy resin: Synthesis, characterization, and performance evaluation

The advantage of thermoplastic heat-resistant tougheners lies in their ability to increase impact toughness without reducing the original high modulus and temperature resistance of a thermosetting system when they are incorporated into the system. However, the poor interfacial compatibility of the thermoplastic-thermoset phases during the curing process leads to phase separation, which decreases the mechanical properties of the system. In this study, two reactive resins with controllable carboxyl group content were prepared starting from phenolphthalin/3,5-dihydroxybenzoic acid and phenolphthalein, and the carboxyl groups participate in the epoxy curing reaction to improve the interfacial compatibility of the two phases, which in turn improves the mechanical properties of the epoxy resins. Both reactive resins have excellent thermal stability, and their glass transition temperatures are above 210 °C. The resin with a phenolphthalin structure has a larger free volume, and a superior toughening effect. Compared with the pure epoxy system, the impact strength is improved by 82% when the resin additive amount is 5 PHR, and the toughening effect is better than that of the PEK-C system without reactive groups. Meanwhile, the modulus and thermal properties of the blended system were not reduced. This study presents a superior toughener of reactive thermoplastic resins for epoxy.