Investigation of the structure–dielectric relationship of polyimides with ultralow dielectric constant and dissipation factors using density functional theory

Polyimides (PIs) possessing both low dielectric constant (Dk) and dissipation factor (Df) remain an intriguing study for the ever-increasing demand for the high frequency transmission of signals. In this study, the relationship between the chemical structures and the dielectric properties of PIs were comprehensively investigated. 35 kinds of PIs with different types of functional groups such as ester, fluorine and ether were prepared via the polyaddition and the subsequent thermal imidization. Their chemical structures and physical properties including the mechanical and dielectric properties were systematically studied. We found that the additive group contribution method failed to provide an effective correlation on the PIs with low Dk and Df values, and it is incapable of distinguishing geometry isomers of PIs. Herein, by utilizing the density functional theory simulation, we successfully remedied those issues. The Dk and Df values of PIs provided strong correlations with volumetric polarizability and volumetric dipole moment. The results elaborated the effect of the interchain behavior to the Dk values and the impact of the chain rigidity on the Df values of PIs. Combining with the molar volume derived from the film density, and a correction factor expressing the polymer rigidity, we eventually established a confident correlation of Dk and Df values with the structure parameters of PIs, respectively. In the meantime, this study interprets the guidelines for the design on PIs molecular structure which sheds light on the development of the insulating materials at high frequencies.