Novel melamine-based engineering thermosets: Facile synthesis, extraordinary thermostability, high strength and toughness

Extreme temperature resistance, high strength and toughness are desired properties for polymeric engineering materials used in fields like aerospace, military and superconductivity industries. In this study, via facile route, two new transparent thermosetting resins were synthesized by ingenious combination of melamine (M) and 1,6-hexamethylenediamine (H), endowing the MH resin with extraordinary thermostability and peculiar mechanical properties. Particularly, the decomposition temperature (T5%) of MH resin was measured to be above 460 °C, superior to most resinous materials. Different from typical thermosets which are strong but brittle, the MH resin appeared to be strong and tough. Obvious yield was observed in compression strength tests and the yield strengths above 160 MPa were achieved at room temperature and cryogenic temperature (−196 °C) with high strain as 21 ∼ 25 %. Further, tensile strength around 70 MPa was obtained with high elongation (12 %) at break. For another resin which includes urea (U) as the third monomer, namely MHU, similar mechanical properties were achieved. As structural adhesives, the two resins exhibited excellent bonding performance to different substrates at room temperature and extreme temperature, which is comparable or superior to polyurethane (PU) and epoxy resins.