Synergistic effects of P and Si on the flame retardancy in a polymethylsilsesquioxane aerogel prepared under ambient pressure drying

Polymethylsilsesquioxane (PMSQ) aerogels have been developed for diverse applications owing to their excellent flexibility and hydrophobicity. PMSQ aerogels, however, are limited by their flammability and low thermal stability. In this study, transparent and robust PMSQ aerogels were synthesized using an environmentally friendly flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane (DOPO) in a facile one-pot manner and successfully dried under ambient pressure without cracks. Briefly, methyltrimethoxysilane (MTMS) and another synthesized precursor, DOPO-vinyltrimethoxysilane (DOPO-VTMS), where DOPO and VTMS were covalently bonded, were used to prepare a DOPO-VTMS MTMS aerogel via co-hydrolytic condensation. The DOPO-VTMS MTMS aerogel showed excellent flame retardancy with a peak heat release rate of 23.48 W g −1 , which is 60% lower than that of the MTMS aerogel. It also exhibited enhanced thermal stability, as confirmed by thermogravimetric analysis, originating from the synergistic effect of P and Si. Furthermore, the compressive strength of the DOPO-VTMS MTMS aerogel was 26 times higher than that of the MTMS aerogel. With superior thermal properties and mechanical robustness, the preparation strategy employed in this study can contribute to the development of PMSQ aerogels for various applications such as thermal insulation for buildings, flame-retardant airspace dust collectors, or fire preventive coatings for fabrics.