Boosting Dielectric Properties of Polyimide/Hollow Silica Nanospheres@Polyimide Composites via Electrospinning-Coating Integrated Strategy

While polyimide (PI) is widely employed in microelectronics, its utilization at high frequencies such as fifth generation (5G) is critically bottlenecked by its high dielectric constant (∼3.0 to 3.9) and significant dielectric loss. Herein, hydrophobic fluoride-free polyimide/hollow silica nanospheres@polyimide (PI/SiO2@PI) composite films with superior dielectric properties, excellent thermal stability, and good mechanical properties were developed via an electrospinning-coating integrated strategy. These composite films were synthesized by electrospinning polyamic acid (PAA)/hollow silica nanospheres (SiO2) mixed dispersion prior to imidization, and further reimidizating the PAA dip-coated PI/SiO2 nanofibrous membrane. By this means, not only the resulting composite films trap more air in the pores but also the relaxation and directional polarization of PI chains along with electron migration are suppressed, leading to a significant reduction in the dielectric constant and dielectric loss. The composite films demonstrate an ultralow dielectric constant of 1.99–2.34 and a dielectric loss of 0.001–0.014 in the high-frequency range (8.2–12.4 GHz). Meanwhile, the PI/[email protected]% demonstrated a satisfactory dielectric strength (124.3 kV mm–1) and mechanical properties (51.9 MPa). All of the composite films exhibited excellent thermal stability (Td5% ≥ 554 °C; Tmax ≥ 602 °C) and meanwhile retained hydrophobic properties even without any fluorinated substance. This study proposes an electrospinning-coating integrated method for preparing high-performance PI/SiO2@PI composites suitable for high-frequency applications such as 5G telecommunication even under harsh environments.