Preparation of Hydroxyl-Terminated Phenolphthalein Polyether Sulfone and Its Application in Toughening Epoxy Resin

The introduction of reactive groups that participate in epoxy cross-linking into the molecular chain of conventional thermoplastic tougheners can improve interfacial compatibility between thermoplastic and thermoset resins, thereby improving the impact toughness of the system. In this work, a series of hydroxyl-terminated phenolphthalein polyether sulfone (PESC-OH) and chlorine-terminated phenolphthalein polyether sulfone (PESC-Cl) resins were prepared, and the molecular structure, molecular weight, and thermal properties of the polymers were characterized by proton nuclear magnetic resonance ( 1 H NMR), gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry (DSC). To assess the toughening effect on epoxy, different molecular weights and different quantities of PESC-OH were incorporated into the epoxy resin/methyltetrahydrophthalic anhydride (E51/MTHPA) system, respectively. The curing process of the E51/MTHPA/PESC-OH blend was examined using DSC, and the curing mechanism was investigated. Subsequently, the thermal and mechanical properties of the toughened system were characterized, with a scanning electron microscope employed to elucidate the phase structure and toughening principle. After curing, phase separation was observed within the system, and also the presence of hydroxyl end-groups enhanced the interface compatibility between PESC and E51/MTHPA, thereby improving the system’s impact strength. In summary, PESC-OH emerges as a reactive thermoplastic toughening agent that is feasible to prepare and has potential practical applications.