Preparation and Properties of Fluorinated Polyimide Aerogels by Ternary Copolymerization

ABSTRACT To address the high moisture absorption and inadequate mechanical properties of conventional polyimide (PI) aerogels under extreme conditions, a ternary‐copolymerized fluorinated polyimide aerogel (PIF) was prepared by incorporating 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB). Its melamine‐crosslinked derivative (PIF‐M) was subsequently obtained by reaction with melamine. The introduction of TFMB markedly improved hydrophobicity, as indicated by water contact angles of 130° for PIF and 127° for PIF‐M. At a solid content of 3%, the compressive moduli of PIF and PIF‐M were 0.0252 and 0.0515 MPa, respectively. After 10 compression cycles, the corresponding values decreased to 0.0158 and 0.0450 MPa, indicating superior structural stability. At the same solid loading, the glass transition temperature increased from 319°C to 334°C, thereby improving high‐temperature structural stability. The dielectric constant and dielectric loss of 3% PIF‐M were slightly higher than those of 3% PIF. In addition, 3% PIF‐M exhibited an ultralow thermal conductivity of 0.030 W/(m·K), demonstrating excellent thermal‐insulation performance. The dielectric behavior was attributed to the CF 3 groups, whose strong electronegativity and large free volume resulted in higher dielectric constant and greater dielectric loss for PIF‐M than for PIF. Low moisture uptake also maintained stable dielectric performance under high‐humidity conditions. Overall, the combined fluorination and melamine‐crosslinking strategy produced polyimide aerogels with high hydrophobicity, excellent mechanical properties, and stable thermal and dielectric performance, supporting their use in high‐reliability applications.