Abstract: To further enhance the ablation resistance properties of thermosetting phenolic resin matrix composites, in this work, bifunctional alkalic heptaphenyltrisilanol sodium salt polyhedral oligomeric silsesquioxane was utilized to catalyze the synthesis of boron phenolic resin and provide silicon source to obtain boron-silicon hybrid phenolic resin (BPOSSPR) with excellent ablative resistance. BPOSSPR possesses a low curing activation energy (101.4 kJ/mol) and excellent thermal properties (initial decomposition temperature was 453.0 °C and char yield at 1000 °C was 72.7%). The mechanical and thermal insulation properties of carbon fiber reinforced BPOSSPR composites (CF/BPOSSPR) and high silica fiber reinforced BPOSSPR composites (HSF/BPOSSPR) are significantly enhanced. The linear ablation rate and mass ablation rate of CF/BPOSSPR are as low as 0.003 mm/s and 0.0354 g/s; those of HSF/BPOSSPR are 0.119 mm/s and 0.0264 g/s. The ablation-resistance mechanism of BPOSSPR composites is mainly due to the formation of ceramic thermal barrier layers under high temperature conditions, such as B₂O₃, SiO₂, borosilicate glass, SiC, which might play an effective role in protecting against heat flow erosion. As a result of these excellent properties, the innovative heat shielding BPOSSPR composites could offer the ability to tolerate harsher environment in future aerospace applications.

Key words: Ceramicized composites, High-temperature properties, Ablation behavior, Bifunctional-POSS catalyst