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 (1H 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.