透波复合材料用聚酰亚胺纤维的制备及其介电行为和力学性能的协同调控机制

The preparation of high-performance polymeric fibers with low dielectric constant and high tensile strength is expected to satisfy the requirements of new lightweight, broadband and multifunctional wave-transparent composites. Polyimide fibers always exhibit good mechanical property, high thermal stability and excellent UV-resistance compared to other polymer fibers. The key issue for the application polyimide fibers as the reinforcement in the wave-transparent composites is to simultaneously decrease the dielectric constant and maintain their excellent mechanical properties. To solve the problem of serious loss of mechanical properties when the dielectric constant of intrinsic polyimides is reduced, in this project, low polar hyperbranched polysiloxane nanoparticles (HBPSi) with different functional groups are designed and intended to be incorporated into polyimide matrix via the strong interfacial interaction to optimize the dielectric and mechanical properties of the polyimide fibers. Series of polyimide composite fibers with low dielectric constants and excellent mechanical properties are expected to be fabricated by exerting the dielectric confinement effect and reinforcing effect of these HBPSi nanoparticles and controlling the aggregation structures of fibers in the spinning process. In addition, the effects of interfacial property (interfacial strength, polarity, area) and crystalline structure (crystallinity and orientation) on the internal polarization and mechanical behaviors of the composite fibers will be well studied to reveal the synergistic regulation mechanism of fibers' dielectric and mechanical properties. Furthermore, the relationship between the stable production, microstructure and macro-property of PI composite fibers will be built. It is hoped to provide useful reference and database for the development of high-performance and functional polymeric fibers.

低介电、高强度有机高性能纤维的开发有望满足新型透波复合材料轻量化、宽频化的发展需求。聚酰亚胺纤维具有高强度、高耐热性和高耐候性等特性，在此基础上如何有效降低纤维的介电常数并保持其优异的力学性能，是该纤维应用于透波复合材料增强体的关键。为解决传统聚酰亚胺纤维在本征结构上难以兼顾低介电常数和高力学性能的难题，本项目拟以活性基团修饰的超支化聚硅氧烷为功能纳米粒子，与具有高强度特征的聚酰亚胺高效复合，充分发挥纳米粒子的介电限域效应和增强作用，并有效控制纤维的凝聚态结构，制备兼具低介电和高强度特性的聚酰亚胺复合纤维。深入研究界面作用强弱、界面极性及纤维的取向度、结晶度等因素对复合纤维内部极化行为和力学行为的影响规律，揭示界面作用和凝聚态结构对纤维介电和力学性能的协同调控机制，构建“稳定制备-微观结构-宏观性能”之间的相互关系，为高性能功能性聚合物纤维的设计和制备奠定理论和实验基础。

本项目针对新型透波复合材料的应用需求，开展兼具低介电常数、高强度、耐高温等特性聚酰亚胺复合纤维的研究。为解决传统有机高性能纤维在本征结构上难以兼顾低介电常数和高力学性能的难题，本项目设计合成了含氨基、氟原子等基团修饰的新型超支化聚硅氧烷纳米粒子，通过原位聚合将上述功能性纳米粒子与高强聚酰亚胺高效复合，从而将低极化率的Si-O-Si单元引入聚酰亚胺中；同时，聚酰亚胺的活性官能团与聚硅氧烷表面氨基形成化学键合，充分发挥“介电限域效应”，减弱了聚合物分子链运动能力，有效抑制了分子主链上电子云在外电场下的极化效应，降低极化率，减小介电常数和介电损耗；此外，两者间化学键合作用实现了强界面复合，有效提高了材料的力学性能。通过合适的纺丝工艺，制备兼具低介电、高强度等特征的聚酰亚胺复合纤维，实现了结构-功能一体化聚酰亚胺纤维的开发。目前，所制备的纤维的断裂强度为3.44-4.2 GPa，初始模量为110-145 GPa，在f=1 GHz时，复合纤维的介电常数由3.6（纯聚酰亚胺纤维）降至2.61，损耗角正切tan δ < 0.01，综合性能超过传统透波复合材料用Kevlar 49，E-玻纤、石英等增强纤维。本项目相关研究成果已经获授权国家发明专利4项，发表学术论文17篇，培养博士研究生1名，硕士研究生4名。