Lightweight and Highly Heat‐Resistant Microcellular Polyetherimide/Barium Titanate/Carbon Nanotube Nanocomposites with High Dielectric Permittivity and Low Dielectric Loss

Dielectric materials with lightweight, high heat resistance, high dielectric permittivity, and low dielectric loss are highly desirable for dielectrics. Herein, lightweight and highly heat‐resistant microcellular polyetherimide/barium titanate/multiwalled carbon nanotube (PEI/BaTiO 3 /MWCNT) nanocomposites with high dielectric permittivity and low dielectric loss are fabricated via the efficient physically microcellular foaming method. The resultant microcellular PEI/BaTiO 3 /MWCNT nanocomposites with the BaTiO 3 /MWCNT content of 8 wt% exhibit a high dielectric permittivity of 18.7 and a low dielectric loss of 0.35 with a low relative density of 0.26. Owing to the heterogeneous cell nucleation effect, the microcellular PEI/BaTiO 3 /MWCNT nanocomposites present much more uniform cellular structures with larger cell density and smaller cell size compared with the microcellular PEI. The physically microcellular foaming slightly decreases the dielectric permittivity and dramatically decreases the dielectric loss of the nanocomposites. Compared with the solid and microcellular PEI/BaTiO 3 nanocomposites, the microcellular PEI/BaTiO 3 /MWCNT nanocomposites exhibit dramatically increased dielectric permittivity with low filler content. The results indicate that the lightweight and highly heat‐resistant microcellular PEI/BaTiO 3 /MWCNT nanocomposites with high dielectric permittivity and low dielectric loss have excellent potential for dielectrics in areas such as aerospace, electronics, and military engineering.