Synthesis and properties of fluorinated biphenyl-type epoxy resin

A novel fluorinated biphenyl-type epoxy resin (FBE) was synthesized by epoxidation of a fluorinated biphenyl-type phenolic resin, which was prepared by the condensation of 3-trifluoromethylphenol and 4,4'-bismethoxymethylbiphenyl catalyzed in the presence of strong Lewis acid. Resin blends mixed by FBE with phenolic resin as curing agent showed low melt viscosity (1.3-2.5 Pa s) at 120-122°C. Experimental results indicated that the cured fluorinated epoxy resins possess good thermal stability with 5% weight loss under 409-415°C, high glass-transition temperature of 139-151°C (determined by dynamic mechanical analysis), and outstanding mechanical properties with flexural strength of 117-121 MPa as well as tensile strength of 71-72 MPa. The thermally cured fluorinated biphenyl-type epoxy resin also showed good electrical insulation properties with volume resistivity of 0.5-0.8 x 10¹⁷ Ω cm and surface resistivity of 0.8-4.6 x 10¹⁶ Ω. The measured dielectric constants at 1 MHz were in the range of 3.8-4.1 and the measured dielectric dissipation factors (tan δ) were in the range of 3.6-3.8 x 10⁻³. It was found that the fluorinated epoxy resins have improved dielectric properties, lower moisture adsorption, as well as better flame-retardant properties compared with the corresponding commercial biphenyl-type epoxy resins.