Ultra‐light fluorinated polyimide foams with excellent thermal insulation, low dielectric loss and high heat resistance

Abstract High efficiency thermal insulation materials are highly desirable in aerospace industry, whereas combining low density and low thermal conductivity of thermal insulation materials still remains a challenge. In this work, a series of fluorinated polyimide foams (PIFs) based on 4,4‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) were successfully prepared by microwave‐assisted powder foaming. The modification of fluorination decreased the melt strength while simultaneously enhanced the thermal properties of fluorinated PIFs through the high bonding energy of CF bond. Thus, fluorinated PIFs exhibited one of the lowest densities of reported PIFs, among them, the density of PIF 6FDA‐DMBZ was as low as 9.34 kg m −3 . The glass transition temperature of all fluorinated PIFs was greater than 295°C. Microwave‐assisted foaming optimized the cell structure effectively, resulting in the thermal conductivity of PIF 6FDA‐ODA as low as 0.029 W m −1 K −1 . The incorporation of hexafluoroisopropylidene groups reduced the polarization and enhanced the free volume of fluorinated PIFs, leading to hydrophobic characteristics (CA >105°) and ultra‐low dielectric loss properties (tan δ <0.001 at 20 GHz). PIF 6FDA‐ODA demonstrated the most excellent comprehensive performance. The excellent comprehensive performance of fluorinated PIFs indicated their potential application as thermal insulation and wave‐transparent materials in aerospace, railway, and shipbuilding industries.