Fluoropolymers find applications in heat‐resistant cables, chemical‐resistant linings, electronic components, cladding materials, and weather‐resistant films. Therefore, it is imperative to improve their temperature resistance level and dielectric properties. In this study, a series of new fluorinated epoxy‐phthalonitrile resins with different mass ratios were prepared by adding phthalonitrile to the epoxy resin matrix, followed by a two‐step reaction of the amine with the epoxy resin at low temperature, and then by the reaction of the nitrile with the epoxy resin and the nitrile group at high temperature. The thermal stability and thermal oxidation stability of the cured products were improved; the initial decomposition temperature for 5% weight loss in air was 375.3°C, indicating good heat resistance performance. In addition, the glass transition temperature and storage modulus of the fluorinated epoxy‐phthalonitrile resins cured products increased with an increase in phthalonitrile content. The storage modulus remained above 1500 MPa until 150°C. The glass transition temperature of fluorinated epoxy‐phthalonitrile resins (at a mass ratio of 5:5) was 180°C, much higher than that of the epoxy resin (which was 140°C). Moreover, the dielectric constant of fluorinated phthalonitrile‐epoxy resin (5:5 mass ratio) was 2.01, which was 39.63% lower than that of fluorinated epoxy resin. The thermoset matrix has potential applications in the fabrication of a variety of low dielectric constant composites for electronic device related industries.

To improve the processability of biphenyl phthalonitrile resin, a flexible siloxane structure was introduced into the phthalonitrile monomer through molecular design, which was then blended with a biphenyl monomer to prepare phthalonitrile alloy resins. When the ratio of phthalonitrile monomer containing flexible siloxane to biphenyl phthalonitrile monomer was 1:1, the processing window widened from 58 to 110°C, as compared to that of biphenyl phthalonitrile. Due to the introduction of the biphenyl structure into the phthalonitrile alloy resins, the initial decomposition temperature of the silicon-containing phthalonitrile resin increased from 385 to 516°C. More importantly, the phthalonitrile alloy resin exhibited a high bending strength (66 MPa) and bending modulus (3762 MPa), indicating that it could be potentially applied as high temperature structural composite matrices. Furthermore, it provides a new strategy for processing phthalonitrile resins with a high melting point and narrow processing window.