Zirconium‐Embedded Polyhedral Oligomeric Silsesquioxane Containing Phosphaphenanthrene‐Substituent Group Used as Flame Retardants for Epoxy Resin Composites

A zirconium hybrid polyhedral oligomeric silsesquioxane derivative (Zr–POSS–bisDOPO) is synthesized by the corner‐capping and Kabachnik–Fields reactions. It is characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR), and then used as a flame retardant in diglycidyl ether of bisphenol A (DGEBA) to endow epoxy resin (EP) with flame retardancy. The flame retardancy, thermal stability, and mechanical properties of the cured EP/Zr–POSS–bisDOPO composites are investigated. The results show that when Zr–POSS–bisDOPO is added by 5–7 wt%, the EP/Zr–POSS–bisDOPO composites pass the UL‐94 V‐0 rating test. In addition, they have a better flame‐retardant effect than pure EP. The combination of Zr atom embedded in the SiO cubic cage and the two phosphaphenanthrene substituent groups in one corner of cubic cage is expected to realize the Zr/Si/P ternary intramolecular hybrid synergistic effect and achieve the possibility of dispersing metal–POSS cages at a sub‐micrometer‐scale level into polymer matrix. It also proves that Zr–POSS–bisDOPO produces phosphorus‐containing free radicals and terminates the chain reactions in gas phase. Meanwhile the SiOSi and ZrO units are retained in the solid phase, which promote the char formation and enhance the flame retardancy. This kind of Zr‐doped POSS will be helpful for developing the new metal–POSS hybrid flame‐retardant and polymer composites. A zirconium hybrid polyhedral oligomeric silsesquioxane (Zr–POSS–bisDOPO) is synthesized by the corner‐capping and Kabachnik–Fields reactions, and then used as a flame retardant to endow epoxy resin (EP) with good performance. Zr–POSS–bisDOPO can produce phosphorus‐containing free radicals and terminate the chain reactions in the gas phase during combustion. The SiOSi and ZrO units are preserved in the solid phase, promoting the char formation.