Correlating the Molecular Structure of Polyimides with the Dielectric Constant and Dissipation Factor at a High Frequency of 10 GHz

The relationships between the structure and the dielectric properties of polyimides (PIs) were extensively studied to construct universal correlations of dielectric constant (Dk) and dissipation factor (Df) on the structural parameters. In this study, 36 kinds of PIs with a plethora of functional groups including ether, fluorine, amide, ester, ketone, sulfide, sulfone, and alkane groups were prepared by polyaddition and thermal imidization. Accordingly, their thermal, mechanical, and dielectric properties were systematically investigated. The experimental results showed highly correlated relationships between the Dk values and two structural parameters of fluorine content (F%) and volume polarizability (P/V) with a correlation coefficient of 0.98 and 0.90, respectively. Likewise, the Df value was highly correlated to the imide group content (Imide%) with a correlation coefficient of 0.95. However, a multiple positive trend was found in the relationship between the Df values and the volume dipole moment (μ/V) for the PIs. The discrepancy might be resulted from the difficulty to elucidate local molecular motions in the unit structure of PIs. Nevertheless, the Df values still presented a nontrivial relation to the orientational polarization and dipole moment of the unit structures. Collectively, our experimental results revealed the structure–dielectric properties relationships of the PIs by rational definition on a series of structural parameters and warrant further investigation. Meanwhile, this work provides systematic guidelines for molecular structure design of PIs which are promising for high frequency applications on the fifth-generation (5G) mobile communications technology.