Intrinsically flame-retardant polysilsesquioxane epoxy resin with excellent mechanical and dielectric properties

Due to the poor flame retardancy and high dielectric constant, the application of epoxy resins (EP) in high-performance materials has been limited. It is vital for meeting increasing performance demands to develop a novel thermosetting resin. In this study, an epoxy-containing polyhedral oligomeric silsesquioxane (EPHPOSS) was synthesized as the epoxy monomer, and the polysilsesquioxane epoxy resin (EPHPOSS30) was successfully prepared at room temperature. On the one hand, the EPHPOSS30 showed higher thermal behavior than that of traditional epoxy resin (EP-257), the thermal initial decomposition temperature, the char residues and the glass transition temperature were obviously increased. On the other hand, the EPHPOSS30 resin showed intrinsic flame retardancy, the limiting oxygen index (LOI) value reached 28.3 %, the peak heat release rate (p-HRR), total heat release (THR), carbon monoxide production (COP), and maximum smoke density were 60.3 %, 34.1 %, 86.1 % and 69.3 % lower than that of EP-257, respectively. Similarly, the EPHPOSS30 demonstrated excellent bending strength and impact strength, the bending strength and impact strength reached 103.4 MPa and 16.67 KJ/m², which were 73.1 % and 60.1 % higher than that of the EP-257, respectively. Notably, the EPHPOSS30 exhibited low dielectric constant, which was lower than 3.08, and the dielectric loss was lower than 0.023 at the high operating frequency range of 7–18 GHz. This strategy overcame the key limitations of epoxy resins in processing temperature, flame retardancy, mechanical and dielectric properties, making it a promising alternative to the commercial epoxy resins.