Diphenolic Acid-Derived Hyperbranched Epoxy Thermosets with High Mechanical Strength and Toughness

Diglycidyl ether of bisphenol A (DGEBA) is a kind of widely used epoxy resin, but its thermosets normally show high brittleness and poor impact resistance due to the intrinsic rigid aromatic rings, which limit its application greatly. To avoid this drawback, we proposed a method to prepare a series of hyperbranched epoxies (HBEPs) with different molecular weights. After HBEPs were cured with methyl tetrahydrophthalic anhydride (MTHPA), characterizations were carried out to evaluate the properties of the cured HBEP samples. Testing results indicate that the hyperbranched thermosets can achieve excellent mechanical strength and toughness (tensile strength: 89.2 MPa, bending strength: 129.6 MPa, elongation at break: 6.1%, toughness: 4.5 MJ m^-3, and impact strength: 6.7 kJ m^-2), which are superior to those of the thermosets of commercial DGEBA (tensile strength: 81.2 MPa, bending strength: 108.2 MPa, elongation at break: 3.0%, toughness: 1.5 MJ m^-3, and impact strength: 4.2 kJ m^-2). In addition, HBEP with the highest molecular weight and degree of branching shows the best comprehensive mechanical properties. All hyperbranched thermosets exhibit high glass-transition temperatures (T _g) and thermostability, which further illustrates the potential application value of HBEPs.