Silicon-Containing Semi-Aromatic Polyimides incorporating Double-Decker Silsesquioxane for low dielectric properties

The rapid advancement of 5G and emerging 6G communication technologies demands polymer dielectrics that minimize transmission loss at GHz frequencies. Conventional fully aromatic polyimides (PIs) exhibit high electronic and orientational polarizabilities, resulting in dielectric constants (D_k) and dissipation factors (D_f) that remain insufficient for next-generation signal integrity. To overcome these limitations, we designed semi-aromatic PIs incorporating cyclohexyl-substituted double-decker-shaped silsesquioxane (C-DDSQ) units. The rigid silsesquioxane cage possesses a large molar volume, intrinsic rigidity, and low polarizability, thereby suppressing both electronic and dipolar polarization. Moreover, the cage architecture inhibits chain stacking and increases free volume, further reducing the dielectric response. The resulting PI film exhibited a D_k of 2.57 and an ultralow D_f of 0.0019 at 10 GHz under 30% relative humidity (RH). Even at 60% RH, only a slight increase in D_k and D_f was observed, indicating stable dielectric performance in humid environments. Thermogravimetric analysis confirmed excellent thermal stability, with T_d-10 values above 470 °C. These results demonstrate that C-DDSQ-containing semi-aromatic PIs are promising low-loss dielectric materials in next-generation high-frequency applications.