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A ceramifiable and flame‐retardant silicone sealant was prepared by adding aluminum oxide and crosslinkers, coupling agents, and catalysts into hydroxy silicone oil. After ablation at 1000°C for half an hour, a ceramic shell with a certain strength was obtained. The impacts of the viscosity of the hydroxy silicone oil and the content of aluminum oxide on the flame‐retardant properties, mechanical properties, surface properties, and ceramification compressive strength of the composite material were studied. The composite with the highest aluminum oxide content could reach an FV‐1 vertical flame rating and a limiting oxygen index of 29.6%, and the ceramification compressive strength could reach 0.15 MPa. This ceramifiable has a wide range of application prospects in industries such as building decoration and wire and cable. [ABSTRACT FROM AUTHOR]

Polysilsesquioxanes (PS) powder was synthesized from methyltrimethoxysilane and vinyltrimethoxysilane by hydrolytic condensation method in aqueous phase. The prepared PS powder was characterized using Fourier transform infrared spectroscopy, particle size, and polydispersity of the powders was determined using dynamic light scattering technique. Polydimethylsiloxane (PDMS) nanocomposites and the sealant were synthesized using different weight percentage (1–4 wt %) of PS powder and hydrophobic fumed silica. Tensile strength and thermal stability of the nanocomposites showed perceptible enhancement on increasing the filler ratio when compared to pristine PDMS composites. The surface morphology and the extent of filler dispersion were visualized from the scanning electron microscopy images. Dielectric strength of the composites also showed significant improvement on increasing the filler loading. Poly(methyl/vinyl)silsesquioxane (PMVS) (4 wt %) reinforced composites showed a considerable enrichment in properties when compared to other formulations. Adhesive strength of silicone sealant on both the alumina and mild steel substrate was studied by conducting lap shear test. PMVS‐loaded nanocomposites exhibited more adhesive strength on both the substrates and hence it can be used as a sealant in electronic assemblies. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47228. [ABSTRACT FROM AUTHOR]