Facile method for fabricating low dielectric constant polyimide fibers with hyperbranched polysiloxane
High-performance fibers with a low dielectric constant and good mechanical properties as well as excellent thermal stability are in demand for the next generation of advanced radar-wave-transparent composites. In this study, an effective method is proposed to prepare amine-functionalized hyperbranched polysiloxane (NH2-HBPSi) reinforced polyimide (PI) composite fibers with exceptional dielectric behavior, mechanical and thermal properties. The amino-functionalized NH2-HBPSi were grafted to PI chains during in situ polymerization, promoting the uniform dispersion of the NH2-HBPSi nanoparticles and forming strong interfacial interactions between NH2-HBPSi and the PI matrix. The composite fiber containing 10 wt% NH2-HBPSi exhibited a 10% and 26% increase in tensile strength and modulus compared to the pure PI fiber. Owing to the dielectric confinement effect from NH2-HBPSi, the dielectric constants of the NH2-HBPSi/PI composites were reduced drastically and the value could reach as low as 2.2 at 108 Hz. The composite fiber demonstrated better specific strength, specific modulus and lower dielectric constant than the commonly used E-glass, S-glass and quartz fibers. These results provide useful information for designing molecular architecture and fabricating high-performance reinforcing fibers in the future radomes.