Epoxy resin flame retarded and toughed via flexible siloxane chain containing phosphaphenanthrene

In order to improve the flammability, and meanwhile increase the toughness of epoxy resin (EP), a flexible siloxane chain containing phosphaphenanthrene structure (KHDOPO) was chemically grafted onto epoxy resin macromolecules. Because of the polar phosphaphenanthrene group and the flexible siloxane chain interacting with the matrix, this modified epoxy resin (KHDOPO-EP) exhibited satisfactory flame retardancy and thermal stability. The thermal degradation and fire behaviors of KHDOPO-EP were systematically evaluated by thermo-gravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning (UL-94) and cone calorimeter (CC) tests. The results showed that KHDOPO-EP achieved V-0 rating in UL-94, with the LOI value of 33.1%. Furthermore, the introduced flexible siloxane chain effectively maintained the toughness of the flame retardant EP, whose tensile strength and impact strength were as high as 71.7 MPa and 15.56 kJ/m2 respectively, much higher than those of neat EP, showing the characteristics of simultaneous toughening and strengthening. As an efficient flame retardant and flexibilizer, KHDOPO-EP possesses promising prospect in modification field of EP material.