Facile synthesis of transition metal containing polyhedral oligomeric silsesquioxane complexes with mesoporous structures and their applications in reducing fire hazards, enhancing mechanical and dielectric properties of epoxy composites

[Display omitted] •Mesoporous M@POSS–COOH was synthesized by thiol–ene click reaction and coordination reactions.•The unique structure of M@POSS–COOH offered no visible phase separation between M@POSS–COOH and EP.•M@POSS–COOH was incorporated to EP to decrease its fire hazards.•Mechanical and dielectric properties of EP composites were improved by carboxyl groups and mesopores of M@POSS–COOH. Transition metal (Co or Fe) containing polyhedral oligomeric silsesquioxane complexes (M@POSS–COOH) were prepared from octa carboxyl polyhedral oligomeric silsesquioxane (OC–POSS). The structures of OC–POSS and M@POSS–COOH were characterized by FT–IR, NMR, MALDI–TOF MS and XRD. Fe@POSS–COOH and Co@POSS-COOH possess mesoporous structures, whose Brunauer–Emmett–Teller surface areas (SBET) are 58.7 m2/g and 46.3 m2/g, respectively. The remaining carboxyl groups of M@POSS–COOH that can react with epoxy groups along with the mesoporous structure increase the network strength of the epoxy resin (EP), and play a significant role in improving the mechanical properties, dielectric properties and thermal properties of the composites. Furthermore, the elemental composition of transition metal and silicon oxygen in the M@POSS–COOH structures significantly increases the amount of char residues of EP composites during the combustion of the material through elements catalysis and surface enrichment, which significantly reduces the toxic smoke density and fire hazards of EP composites. The structural and elemental merits of M@POSS–COOH significantly improve the overall performance of epoxy resin and occupy broad application space.