Enhancing Toughness of Epoxy Crossing Network: The Role of Branched Reactive Polyethersulfone Ketone

ABSTRACT Thermoplastic toughening agents represent a prevalent category of epoxy resin modifiers. In practical applications, these agents can significantly enhance the mechanical properties of epoxy resins. However, due to the inherent phase separation characteristic of epoxy resins, the toughening effect is somewhat constrained. Recently, branched polymers have gained recognition for their effectiveness in toughening epoxy resins. Their low viscosity and abundant reactive groups facilitate superior toughening outcomes. This study leverages both the structural attributes of branched polymers and high‐performance polyethersulfone ketone (PESK). Through nucleophilic polycondensation reactions involving bisphenol monomers such as dihydroxydiphenylsulfone (BDS), difluorophenyl ketone (DFDBK), and trifunctional monomer 1,1,1‐tri(4‐hydroxyphenyl)ethane (THPE), we synthesized a series of long‐chain polyaryletherketones (LCBPESK) with varying degrees of branching. The fundamental properties of these materials were characterized, and they were employed for toughening modification within the epoxy resin/methyltetrahydrophthalic anhydride (E51/MTHPA) system. Characterization tests revealed that long‐chain branched polyethersulfone ketones possessing both branched structures and reactive end groups effectively mitigate phase separation between the toughening agent and the epoxy resin while significantly enhancing its toughness. Notably, when LCBPESK‐30 is incorporated at a loading level of 15 phr, there is a remarkable increase in impact strength by 133% in the epoxy system. In addition, we investigated the toughening mechanism of LCBPESK in E51. For polyaryl ether resins, a certain degree of branching and the presence of active end groups significantly influence their toughening effect in epoxy resins, which holds considerable industrial value and promising application prospects.