Cyanate esters (CEs) are an important class of materials among high-temperature-performance thermosets. They are used in aerospace launch vehicles, heat sinks, booms, trusses of satellites, etc., due to their high glass transition temperatures (>220 °C), excellent thermal stability, and low flammability. Current approaches to improve the thermal stability of CEs include incorporation of siloxanes or phosphorus-based flame retardants. In this work, we have explored boron-based hydroxy (PD)- and epoxy (EP)-functionalized carborane additives to improve the thermal properties of CEs. Carborane fillers were solvent-blended at various mass loadings in the resin and cured to study their effect on thermal properties. PD and EP carboranes react with CEs to form iminocarbonates and oxazolidinone linkages, respectively. Cure kinetic studies at different wt % loadings explained that carboranes catalyze the curing reaction by reducing the curing activation energy by about 54 and 26% for 10 wt % loadings of PD and EP carboranes, respectively. In addition, carborane-filled CE nanocomposites demonstrate an exceptionally high thermal stability as compared to the pristine resin in air and inert environments. Our thermogravimetric analysis (TGA) experiments show that the ultimate char yield of the resin can be increased from 0% to as high as 76 and 82% with 30 wt % PD and EP carborane loadings, respectively, at 1000 °C in air. The initial degradation temperature T_d,5 of the composites decreased with increasing carborane loadings in both air and argon. For instance, T_d,5 values for CE were 465 and 471.6 °C in argon and air, while those for P20 were 437.4 and 452.1 °C, respectively. Modulated TGA studies gave evidence of the effect of carboranes on degradation mechanism and kinetics in air and inert environments. The effect of bonding between carboranes and CEs at various loadings on the thermal expansion of the matrix was also studied using a thermomechanical analyzer. PD carborane reduced the T_g for P20 to about 225 °C, while CE had T_g > 350 °C.

中文翻译：

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含碳硼烷的耐高温氰酸酯复合材料

氰酸酯 (CE) 是高温性能热固性材料中的一类重要材料。由于其高玻璃化转变温度（>220°C）、优异的热稳定性和低可燃性，它们被用于航天运载火箭、散热器、吊臂、卫星桁架等。目前提高 CE 热稳定性的方法包括加入硅氧烷或磷基阻燃剂。在这项工作中，我们探索了基于硼的羟基 (PD) 和环氧 (EP) 功能化碳硼烷添加剂，以改善 CE 的热性能。碳硼烷填料在树脂中以不同的质量负载进行溶剂共混并固化，以研究它们对热性能的影响。PD 和 EP 碳硼烷分别与 CE 反应形成亚氨基碳酸酯和恶唑烷酮键。不同重量百分比负载下的固化动力学研究解释说，对于 10 重量 % 的 PD 和 EP 碳硼烷，碳硼烷通过将固化活化能降低约 54% 和 26% 来催化固化反应。此外，与原始树脂相比，碳硼烷填充的 CE 纳米复合材料在空气和惰性环境中表现出极高的热稳定性。我们的热重分析 (TGA) 实验表明，在空气中 1000 °C 下，当 PD 和 EP 碳硼烷负载量为 30 wt% 时，树脂的最终焦化率可以从 0% 增加到高达 76% 和 82%。初始降解温度 与原始树脂相比，碳硼烷填充的 CE 纳米复合材料在空气和惰性环境中表现出极高的热稳定性。我们的热重分析 (TGA) 实验表明，在空气中 1000 °C 下，当 PD 和 EP 碳硼烷负载量为 30 wt% 时，树脂的最终焦化率可以从 0% 增加到高达 76% 和 82%。初始降解温度 与原始树脂相比，碳硼烷填充的 CE 纳米复合材料在空气和惰性环境中表现出极高的热稳定性。我们的热重分析 (TGA) 实验表明，在空气中 1000 °C 下，当 PD 和 EP 碳硼烷负载量为 30 wt% 时，树脂的最终焦化率可以从 0% 增加到高达 76% 和 82%。初始降解温度复合材料的T _d,5随空气和氩气中碳硼烷含量的增加而降低。例如，CE 的T _d,5值在氩气和空气中分别为 465 和 471.6 °C，而 P20 的T _d,5值分别为 437.4 和 452.1 °C。调制 TGA 研究提供了碳硼烷对空气和惰性环境中降解机制和动力学影响的证据。还使用热机械分析仪研究了不同负载下碳硼烷和 CE 之间的键合对基体热膨胀的影响。PD 碳硼烷将P20的T _g降低至约 225 °C，而 CE 的T _g > 350 °C。