Synthesis of nitrile-containing reactive phenolphthalein polyaryletherketone and synergistic toughening research on the toughening of epoxy resin—phase structure, mechanical and thermal properties

Abstract

The introduction of reactive groups capable of participating in epoxy cross-linking into the molecular chains of conventional thermoplastic toughening agents effectively enhances the interfacial compatibility between thermoplastic and thermosetting resins, resulting in a significant improvement in system impact toughness. Building on this approach, this study innovatively incorporates polar nitrile groups into the molecular chains of thermoplastic polyaryletherketone agents containing terminal reactive groups, thereby exploring the synergistic mechanism between reactive and nitrile groups. A systematic investigation is conducted to examine how variations in the nitrile group content and the addition level of the toughening agent influence the toughening effect of epoxy resin. Additionally, the influence of different epoxy system phase structures on mechanical properties is assessed. Experimental results reveal that when the toughening agent PEKCN-OH is added at less than 10 parts per hundred resin (phr), the epoxy system exhibits a sea-island morphology, with the impact strength decreasing with increasing nitrile group content. When no nitrile groups are present (using PEKC-OH resin), the impact strength reaches 23.5 kJ m⁻², representing a 97% increase compared to the control without the toughening agent. For addition levels exceeding 10 phr, the system transitions to a bicontinuous structure. In this regime, the impact strength initially increases before decreasing as the nitrile group content increases. At a nitrile group content of 50% (using PEKCN-OH-2 resin), the impact strength reaches 25.8 kJ m⁻², representing a 117% increase. Importantly, the addition of these toughening agents not only prevents a reduction in the service temperature of the epoxy resin but also enhances its thermal stability. In conclusion, the PEKCN-OH developed in this study serves as a highly efficient, easily prepared reactive thermoplastic toughening agent suitable for industrial production. It holds great promise for use in demanding industrial applications, including aerospace, electronics and electrical appliances, and automotive manufacturing. The findings are expected to make significant contributions to material innovation and product performance optimization in these sectors.