Smectic liquid crystalline poly(ester imide)s with low dielectric dissipation factors for high-frequency applications

High-frequency electronic applications increasingly require polymer-based insulators with low dielectric constants (Dk) and dissipation factors (Df). Reducing molecular mobility effectively decreases the Df of polyimides (PIs), which are widely used as interlayer dielectrics in semiconductor integrated circuits. In this study, we reduced molecular mobility by synthesizing smectic liquid crystalline polyimides (LC-PIs) via the use of diamines with phenyl benzoate structures and alkyl chains, and promoting mesogen stacking in LC structures. Self-supporting films were fabricated, and their dielectric properties were evaluated, revealing significantly lower Df values than those of conventional PI. The functional groups responsible for increasing Df are visualized via molecular dynamics simulations performed by applying a virtual alternating electric field to 3D models of the LC-PIs whose structure was confirmed via wide-angle X-ray diffraction. This study highlights the potential of smectic LC-PIs in the molecular design of polymeric materials with lower Df. This study demonstrates the synthesis of smectic liquid crystalline polyimides (LC-PIs) with reduced dissipation factors (Df) by incorporating phenyl benzoate units and alkyl chains into the polyimide backbone to promote mesogen stacking. Compared to conventional polyimides derived from pyromellitic dianhydride and 4,4′-oxydianiline, the LC-PIs exhibited significantly lower Df. The functional groups responsible for increasing Df were visualized via molecular dynamics simulations, applying a virtual alternating electric field to 3D models of the LC-PIs, the structures of which were confirmed using wide-angle X-ray diffraction.