A Reinforced Epoxy Network With Novel Long Chain Branched Polyaryl Ether Ketone to Improve Phase Separation Morphology

ABSTRACT The incorporation of a second thermoplastic component into epoxy resin is an effective method for the enhancement of toughness. However, practical applications are generally challenged by issues like phase separation and the mass addition of toughening agents. Branched polymers have become an upgraded toughening agent due to the advantages of low viscosity and diverse reactive groups, enabling remarkable toughening effects. In this study, long‐chain polyaryl ether ketones (LCBPEKCs) with varying branching degrees were synthesized via nucleophilic polycondensation from bisphenol monomer phenolphthalein (PHT), difluorodiphenyl ketone (DFDBK), and trifunctional monomer 1,1,1‐tri (4‐hydroxyphenyl) ethane (THPE). The fundamental properties of LCBPEKCs were characterized, and they were applied to toughen the epoxy resin/methyl tetrahydrophthalic anhydride (E51/MTHPA) system. The branched structure and reactive end groups of long‐chain branched polyaryl ether ketones could effectively reduce the phase separation between the toughening agent and epoxy resin, significantly enhancing the toughness of epoxy resin. Among the various additives, the addition of LCBPEKC‐30 at just 5 phr contributed to a remarkable 109% increase in the impact strength of the cured epoxy system, which significantly improved its mechanical properties. Additionally, a detailed analysis of the toughening mechanism of LCBPEKC within the cured E51 system confirmed that both branched structures and active end groups exhibited crucial functions in the improvement of the network's properties.