Effect of Diamine Monomers with Varied Backbone Structures on Dielectric and Other Comprehensive Properties of Fluorinated Polyimide Films

Fluorinated polyimide (FPI), renowned for its exceptional low-dielectric properties, colorless transparency, high-temperature resistance, and flexibility, has emerged as an ideal material for addressing challenges in 5G/6G high-frequency signal transmission and flexible electronic substrates. Nevertheless, the structure-property relationship between molecular architectures and the dielectric characteristics of FPI films remains insufficiently understood, necessitating urgent elucidation of the underlying mechanisms. In this study, a diamine monomer containing bis-amide bonds, 4-amino-N-{4-[(4-aminobenzoyl)amino]phenyl}benzamide (PABA), was synthesized. Subsequently, six FPI films (FPAIs, FPEIs, and FPEsIs) with distinct structural features were prepared through homopolymerization of PABA and five other diamines (containing amide bonds, ether, and ester groups) with fluorinated dianhydride (6FDA). Systematic characterization of thermal, mechanical, optical, and dielectric properties revealed that these films exhibit excellent thermal stability (<i>T</i>_g: 296-388 °C), mechanical strength (<i>σ</i>: 152.5-248.1 MPa, <i>E</i>: 2.1-3.4 GPa), and optical transparency (<i>T</i>_{550 nm}: 82-86%). Notably, they demonstrated a low dielectric constant (<i>D</i>_k as low as 2.8) and dielectric loss (<i>D</i>_f down to 0.002) under both low- and high-frequency electric fields. Furthermore, molecular dynamics simulations and quantum chemical were employed to calculate critical physical parameters and HOMO-LUMO energy levels of the six FPIs. This computational analysis provides deeper insights into the structure-performance correlations governing dielectric behavior and optical transparency in FPIs. The findings establish valuable theoretical guidance for designing advanced PI films with tailored dielectric properties and high transparency.