Phase-Structure Engineering of Addition-Cross-Linked Silicone-Hybridized Carborane-Phenolic Resins toward Ultrahigh-Temperature Thermal Protection up to 2500 °C

Silicone-phenolic hybrids (SiPRs) exhibit intrinsic self-ceramization behavior and unparalleled thermal-oxidative resistance, which endow them with significant potential in thermal protection engineering. However, obvious phase separation limits their practical use by causing an interfacial failure. In this study, 2-allylphenol and vinyltriethoxysilane were introduced into carborane and polysiloxane, respectively, to construct an unsaturated bond-modified organic–inorganic hybrid structure. Through regulation of the allyl groups in the resin matrix and utilization of addition cross-linking reactions, the hybrid resin achieves controlled transformation from a sea-island phase separation to a homogeneous phase. Benefiting from the molecular-scale homogeneity and tailored composition, the hybrids exhibited significantly enhanced thermo-oxidative stability and ablation resistance. Compared to phenolic resin (PR), SiCBPR 0.75 showed enhanced thermal stability in air atmosphere, with its initial decomposition temperature and 800 °C residual weight increasing by 147.7 °C and 42.33%, respectively. Its ablation resistance improved significantly, reducing linear (LAR) and mass ablation rates (MAR) by 17.46% and 33.33% versus PR. Importantly, the back temperature decreased significantly from 129.2 to 70.1 °C, further confirming the material’s improved thermal protection capability. This study provides an effective approach for synthesizing tailored homogeneous organic–inorganic hybrid materials, offering valuable insights for developing next-generation thermal protection systems with combined erosion and ablation resistance.