Synthesis and characterization of trifluoromethyl-containing polyimide-modified epoxy resins

Two series of epoxy resins modified with trifluoromethyl-containing poly(amic acid)s and polyimides, respectively, were prepared. The effects of trifluoromethyl group and imide unit on the properties of epoxy resins were investigated. The epoxy resins modified with poly(amic acid)s exhibited better performance because poly(amic acid)s serve as amine curing agent in epoxy resins and form chemical bond with epoxy matrix, thus having higher miscibility with epoxy resin than the epoxy resins modified with polyimides. The glass transition temperatures of the modified epoxy resins were in the range of 88.9-168.2 A degrees C. Compared with unmodified epoxy resin, the modified epoxy resins exhibited better thermal stability with char yield at 800 A degrees C ranging from 18 to 55 %, lower hydrophilicity with water absorption in the range of 0.47-0.95 %, and water contact angle of 94.9-105.0A degrees. The introduction of trifluoromethyl group decreases the surface free energy and hydrophilicity of the modified epoxy resins. The SEM images of the fracture surfaces of the modified epoxy resins showed tough fracture features, indicating the enhancement of toughness of these resins in which imide unit had been introduced.