Extreme Thermal Stabilization of Carborane–Cyanate Composites via B–N Dative-Bonded Boroxine Barriers

Enhancing the thermal stability of cyanate ester (CE) resins is crucial for high-temperature aerospace applications. This study elucidates the degradation mechanisms of CE composites reinforced with carborane additives, focusing on the formation of boron–nitrogen (B–N) dative bonds and their role in improving thermal resistance. Using thermogravimetric analysis, we examined char formation and evolved gases at multiple degradation stages. Reaction sequences and char products were characterized via Fourier transform infrared spectroscopy (FTIR), solid-state 13C and 11B NMR, and evolved gas analysis using mass spectrometry and FTIR. The solid-state 11B NMR was instrumental in detecting various boron oxidation states and the formation of B–N dative bonds during decomposition. These bonds facilitate cross-linking in the char phase, enhancing material integrity at elevated temperatures. However, in inert environments, the volatility of boron additives like carborane limits their effectiveness. These findings advance the understanding of CE composite degradation mechanisms and offer critical insights for developing high-temperature-resistant materials for aerospace applications.. Authors: Goyal, Shailja [Iowa State Univ., Ames, IA (United States)] (ORCID:0000000308370084); Forrester, Michael J. [Iowa State Univ., Ames, IA (United States)] (ORCID:0000000330639975); Carnahan, Scott L. [Ames Lab., and Iowa State Univ., Ames, IA (United States)]; Coverdell, Danielle [Kansas City National Security Campus (KCNSC), Kansas City, MO (United States)]; Torres, Sabrina [Kansas City National Security Campus (KCNSC), Kansas City, MO (United States)]. DOE Contract: AC02-07CH11358; NA0002839. Subjects: Fourier transform infrared spectroscopy; boron; carborane; cyanate ester; dative-bond polymers; degradation; extreme-environment composites; nuclear magnetic resonance spectroscopy; solid-state NMR; thermogravimetric analysis; thermoset