A promising low-dielectric-constant material with good comprehensive performance upon heating

The dielectric and other properties of low-dielectric-constant materials after heating are crucial to their performance and use, but rarely studied. In this article, sandwich-type porous polyimide (PI) film in which porous structures located on both upper and lower surfaces of flat PI film was prepared through the simple, low-cost and green microemulsion method. The porous structures were preserved after heating due to the usage of thermally stable fluorine-contained PI (FPI) and PI as skeleton and substrate of the porous structure, respectively, but with the increase of pore size because of the removal of thermally unstable surfactant on the inner surface of the pores. More importantly, 2.89%-5.57% of reductions in the dielectric constant with the maintenance of low dielectric loss and water absorption and high mechanical strength were observed after heating. Therefore, the low dielectric properties of heated films were well preserved upon high humidity treatment. Moreover, the structure and properties of the heated films could be adjusted via controlling the parameters in the microemuslion method. These excellent properties after the high-temperature treatment facilitate the application of the sandwich-type porous PI film as dielectric materials in high-temperature environment.