Modification of epoxy resin through the self-assembly of a surfactant-like multi-element flame retardant

In order to develop a multi-element, synergistic, flame-retardant system, the combination of DOPO, POM and POSS was achieved using the classical Kabachnik-Fields reaction. The as-designed POSS-bisDOPO was characterized by FT-IR, H-1 NMR, C-13 NMR, P-31 NMR, 2D NMR, and MS. POSS-bisDOPO was introduced into epoxy resins to obtain flame-retardant materials. The LOI value can reach 34.5% when the content of POSS-bisDOPO is 20 wt%. The TGA results showed that the char yield was significantly improved in cured POSS-bisDOPO/EP. The ATR-FTIR results, optical images and SEM analyses indicated that the residual char had a compact and coherent appearance in the inner layer, while the outer structure was intumescent and multi-porous. Therefore, by isolating heat and oxygen more efficiently, the char played an important role in improving the thermal stability and flame retardancy of cured POSS-bisDOPO/EP. The three-point bending test results showed that the mechanical strength of POSS-bisDOPO/EP was higher than those of pure EP and POSS-NH2/EP due to the outstanding reinforcement effect of the unique nanostructure of POSS-bisDOPO assembled in the EP matrix. These data indicated that POSS-bisDOPO not only obviously enhances the flame retardancy, but also improves the mechanical properties of epoxy resins.