Toughening agent for epoxy resin with low dielectric constant as well as preparation method and application of toughening agent

The invention discloses a flexibilizer for low-dielectric-constant epoxy resin as well as a preparation method and application of the flexibilizer. The preparation method comprises the following steps: mixing epichlorohydrin, eugenol and a surfactant for reaction, adjusting the pH value, extracting, washing with water, and evaporating to remove the epichlorohydrin to obtain an epoxy modified eugenol compound; and mixing the toughening agent with hydrogen-containing silicone oil, heating, adding a catalyst solution, carrying out heating reaction, and mixing the toughening agent with a resin raw material to prepare a cured epoxy resin with a low dielectric constant. Epoxy modified eugenol is utilized to improve the compatibility and interface state of silicone rubber and epoxy, the polymer alloy performance is effectively improved, meanwhile, end hydrogen-containing silicone oil is adopted as a flexible chain, the length of the flexible chain between two epoxy groups is adjusted, and the toughening effect of th