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Polyhedral oligomeric silsesquioxane (POSS) is a hybrid material composed of an organic substituent shell and inorganic skeleton core. To study the influence of different shells and cage‐shaped cores on dielectric and mechanical properties, four kinds of epoxy resin composites (EPs) fabricated with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), DOPO‐containing polyhedral oligomeric silsesquioxane (DOPOPOSS), octaphenyl polyhedral oligomeric silsesquioxane (OPS), and epoxy phenyl polyhedral oligomeric silsesquioxane (EPOSS) with the addition of 5 and 10 wt% were prepared, respectively. The dispersion, transparency, glass transition, dielectric, mechanical tensile, flexural, and impact properties of these epoxy resins were studied. Dielectric constant and loss of EPs were significantly reduced through introduction of three POSSs owing to their inherent hollow cores, and dielectric constant of the resins was further decreased with additional increase. Compared with three POSSs, DOPOPOSS had the best compatible shell, and its composites exhibited favorable transparency similar to pure EP and the obvious reduction in dielectric constant and loss, due to its nano‐dispersion in matrix. EPOSS was dispersed in a perfect spherical shape and uniformly embedded in matrix, and the composites showed good mechanical tensile, flexural, and impact strength. OPS was disorderly dispersed in resins, but its eight phenyl rings symmetrical shell had the advantage of nonpolar molecule structure, which endowed epoxy resin lower dielectric loss over the high‐frequency range (105–106 Hz). Compared with DOPOPOSS, DOPO was effective in reducing dielectric constant and loss of epoxy resin due to its reactive addition, however, it decreased the glass transition temperature, mechanical tensile, flexural, and impact strength of epoxy resin either.

An intercalated organic montmorillonite DOPO-MMT was prepared through the melting method using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as a modifier. Epoxy resin (EP) composites were prepared with DOPO-MMT, DOPO, MMT, and the physical mixtures of DOPO+MMT as flame retardants. The microstructure of the flame retardants and EP samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The flame retardant properties, thermal stability, and residual char structure of the EPs were studied by the limited oxygen index (LOI) test, the UL-94 vertical burning test, thermogravimetric analysis (TGA), the differential scanning calorimeter (DSC) test, the cone calorimeter (CONE) test as well as other characterization methods. The results showed that the intercalated organic montmorillonite DOPO-MMT can be successfully prepared by the melting method and that the MMT is evenly dispersed in the EP/DOPO-MMT composite in the form of nanosheets. The EP/DOPO-MMT nanocomposites showed the optimal flame retardancy (LOI, UL-94, PHRR, etc.) among the EPs with DOPO, MMT, and the physical mixture of DOPO+MMT. The flame-retardant grade of the material reached V-0.

The ease of undesirable agglomeration and a low efficiency are two problems that restrict the application of graphite nanoplatelets (GNPs) in epoxy resins (EP). Herein, a new strategy with melamine (MEL) as the precursor to functionalize GNPs chemically, which form a bonding layer that is compatible with epoxy matrix, is reported.The MEL fragments with secondary amine groups were grafted uniformly on the GNPs surface by covalent junctions to exploit the diazonium chemistry. This behavior led to a better dispersion and a stronger interaction with the epoxy matrix and resulted in an enhanced glass transition temperature and bending strength, compared with the pure EP. When only 1 wt% functionalized GNPs (f-GNPs) was used, the Tg of the modified EP raised of about 15 C compared with pure EP, and the bending strength increased by approximately 39%. The dielectric constant of the EP with f-GNPs was impacted slightly, and the dielectric loss decreased. At 10 5 Hz, the dielectric loss of the EP with 1 wt% f-GNPs decreased by approximately 11% compared with pure EP. Therefore, diazotization modification of the GNPs is a useful approach to improve the compatibility in nanoparticle networks. K E Y W O R D S compatibility, epoxy resins, graphite nanoplatelets

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