The effects of moisture on a polymerized monomeric reactant (PMR)-type polyimide (TriA X) and associated composites were investigated. Water uptake tests were performed on the polyimide at various temperatures and relative humidity levels to investigate moisture absorption behavior. Two-stage moisture absorption was observed, in which the first stage was diffusion controlled, whereas the second stage was moisture plasticization controlled. As exposure temperature increased, the equilibrium moisture content of the polyimide decreased, indicating an exothermic absorption process. The Arrhenius temperature dependence and moisture saturation as functions of temperature and humidity in the neat polymer were determined using curve fitting based on the published mathematical models. Long-term hydrothermal aging at 95°C was conducted on the neat polyimide and associated carbon fiber composites. Reversible hydrolytic reactions and a trace of irreversible hydrolysis were observed in the long-term exposure. The tensile ductility of the neat polyimide and the short-beam shear strength of the composites decreased with increasing aging time, while the tensile strength and modulus and thermal properties of the polyimide exhibited little change after 2000-h aging, demonstrating hydrothermal stability. The decrease in the ductility of the neat polymer after long-term moisture exposure was attributed to the network structure change, driven by hydrolysis and moisture plasticization.

中文翻译：

---

苯乙炔封端均苯四甲酸二酐型不对称聚酰亚胺及其复合材料的吸湿和水热老化

研究了水分对聚合单体反应物 (PMR) 型聚酰亚胺 (TriA X) 和相关复合材料的影响。在不同温度和相对湿度水平下对聚酰亚胺进行吸水测试，以研究吸湿行为。观察到两阶段吸湿，其中第一阶段是扩散控制，而第二阶段是水分塑化控制。随着暴露温度升高，聚酰亚胺的平衡水分含量降低，表明存在放热吸收过程。Arrhenius 温度依赖性和水分饱和度作为纯聚合物中温度和湿度的函数，使用基于已发表数学模型的曲线拟合来确定。在纯聚酰亚胺和相关碳纤维复合材料上进行了 95°C 的长期水热老化。在长期暴露中观察到可逆水解反应和微量不可逆水解。纯聚酰亚胺的拉伸延展性和复合材料的短梁剪切强度随着老化时间的增加而降低，而聚酰亚胺的拉伸强度、模量和热性能在 2000 小时老化后几乎没有变化，表现出水热稳定性。长期暴露于水分后纯聚合物延展性的降低归因于由水解和水分增塑驱动的网络结构变化。纯聚酰亚胺的拉伸延展性和复合材料的短梁剪切强度随着老化时间的增加而降低，而聚酰亚胺的拉伸强度、模量和热性能在 2000 小时老化后几乎没有变化，表现出水热稳定性。长期暴露于水分后纯聚合物延展性的降低归因于由水解和水分增塑驱动的网络结构变化。纯聚酰亚胺的拉伸延展性和复合材料的短梁剪切强度随着老化时间的增加而降低，而聚酰亚胺的拉伸强度、模量和热性能在 2000 小时老化后几乎没有变化，表现出水热稳定性。长期暴露于水分后纯聚合物延展性的降低归因于水解和水分增塑驱动的网络结构变化。