Properties of epoxy-amine networks containing nanostructured ether-crosslinked domains

Epoxy-amine networks with a nanodomain toughener—soft nanostructured ether-crosslinked domains (NECDs), which could increase the fracture and tensile toughness of the networks, were simply obtained when a mixture of diglycidyl ether bisphenol A (DGEBA) epoxy resin and 4,4′-methylene dianiline (MDA) hardener was heat-cured in the presence of varying amounts of the imidazole derivatives (called imidazoles)—1-methylimidazole (1-MI) or 2-methylimidazole (2-MI). Under these conditions, the epoxide groups in DGEBA underwent not only polyaddition with the aromatic amine of the MDA to form a hard epoxy-amine networked matrix but also anionic ring-opening polymerization by itself to build soft NECDs connected to the epoxy-amine matrix. The curing chemistry of the DGEBA/MDA mixture, both with and without the imidazoles, was studied using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The morphology of the networks dispersed with 5–30-nm-sized NECDs was investigated by atomic force microscopy (AFM). When the optimum amount (∼0.15–0.30 wt%) of imidazoles was added, the NECDs were effective in significantly increasing the tensile and fracture toughness and the thermal stability of the epoxy-amine networks without markedly sacrificing the glass transition temperature (Tg). The novel toughening mechanism and thermal behavior of the epoxy-amine networks were discussed.