Universally Correlating the High-Frequency Dielectric Properties with Structural Parameters of Polyimides with Diversified Functional Groups

With the increasing demand for high-frequency signal transmission and chip miniaturization, conventional insulating materials face significant limitations. Among various low-loss materials, polyimide (PI) stands out for its excellent processability, stability, and diverse chemical structure. In this study, 54 PIs incorporating various functional groups, including ether, ester, fluorine, amide, and sulfone, were analyzed for their effects on the dielectric constant (D_k) and dissipation factor (D_f). A combination of theoretical simulation and experimental methods is adopted to investigate the dielectric behavior of PIs. Density functional theory (DFT) was employed to calculate the polarizability, while molecular dynamics (MD) simulations were used to evaluate realistic chain conformations and volumetric properties. The PI film’s refractive index is measured for calculating its electronic polarizability (α_e). The analysis further distinguishes between electronic and dipolar contributions to the DFT-calculated total polarizability (α_t). It examines their correlations to the D_k and D_f values across different frequencies, demonstrating the complementarity between the semitheoretical (α_e) and theoretical (α_t) methods. Based on local chain stiffness, a correction factor for the fraction of free volume (FFV) derived from MD simulations is proposed to enhance the predictive relationship between volumetric polarizabilities (Nα_t or Nα_e) and dielectric properties. Results show that at higher frequencies, the semitheoretical (Nα_e) and theoretical (Nα_t) regressions exhibit a better correlation, indicating that this FFV-modified regression parameter is more suitable for predicting dielectric properties in high-frequency systems. The combination of DFT and MD calculations can generate theoretical parameters for correlating the PI’s D_k and D_f values at high frequencies; the corresponding parameters are the ratio or product between volumetric total polarizability and free volume fraction, respectively. This study offers a comprehensive approach, combining structural modeling and frequency-dependent experimental validation to provide a predictive and practical framework for designing low-dielectric polymers for advanced electronic and communication applications.