Design and Performance of Epoxy-Terminated Fluorinated Hyperbranched Poly(ether ether ketone) for the Synergistic Optimization of Multiple Properties of Epoxy Resins

To improve the toughness, dielectric properties, and surface hydrophobicity of epoxy resins, an epoxy-terminated fluorinated hyperbranched poly(ether ether ketone) (HPEEK-EO) was designed and synthesized, and then introduced as a reactive modifier into a bisphenol A epoxy resin cured with 4,4′-diaminodicyclohexylmethane (PACM). Composite specimens containing different amounts of HPEEK-EO were prepared by solution blending followed by thermal curing, and their mechanical, thermal, dielectric, and surface properties, as well as fracture morphology, were systematically investigated. The results showed that an appropriate amount of HPEEK-EO effectively improved the overall properties of the cured system. At a loading of 3wt.%, the tensile strength, flexural strength, and impact strength reached 89.4 MPa, 136.4 MPa, and 44.45 kJ/m², respectively, corresponding to a 123.9% increase in impact strength compared with the unmodified PACM/E44 system. Thermogravimetric analysis and differential scanning calorimetry showed that the 5% weight-loss temperature of all composite specimens remained around 340℃, while the highest glass transition temperature reached 94.3℃, indicating that good thermal stability was retained after toughening. Dynamic mechanical analysis further revealed that the incorporation of an appropriate amount of HPEEK-EO improved the storage modulus in the glassy region and the modulus retention at elevated temperatures. In terms of dielectric performance, the dielectric constant decreased from 3.96 to 2.80 at 1 MHz, and the dielectric loss was reduced in the medium-to-high frequency range. In terms of surface properties, with increasing HPEEK-EO content, the water contact angle increased from 77.32° to 102.67°, whereas the surface free energy decreased from 38.38 to 30.02 mJ/m², indicating markedly enhanced hydrophobicity. SEM observations revealed rougher fracture surfaces, crack deflection, and local tearing features in the modified specimens, suggesting greater energy dissipation during fracture. These results demonstrate that HPEEK-EO, as a fluorinated reactive hyperbranched modifier, enables the synergistic tuning of the mechanical, thermal, dielectric, and surface properties of epoxy resins, providing a useful molecular design strategy for the multifunctional modification of high-performance epoxy materials.