Temperature-Invariant Large Broadband Polyimide Dielectrics with Multimodal Porous Networks

Herein, we describe sponge-like polymeric materials with multimodal porous networks with stable ultralow dielectric properties over broad frequency and temperature ranges. A hierarchically porous polyimide (PI) film was prepared via nonsolvent-induced phase separation (NIPS), followed by stepwise thermal imidization. Through the swelling and the subsequent liquid-liquid phase separation, highly insulating interconnected pores of the internal layer and the water-vapor impermeable, closed-cell skin of the outer layer were directly formed on the PI film. The grafting of porous PI onto amino-functionalized mesoporous silica (AMS) to further adjust the overall thermal stability and dielectric constant has become a valid strategy. The porous PI-grafted-AMS (PPI-g-AMS) exhibited uniform micropores, which were regularly shaped with an average diameter of 16.3 ± 0.6 μm. The glass transition temperature (T_g) of PPI-g-AMS increased considerably from 367 °C to as high as 398 °C because of the formation of interchain cross-linking bridges in the AMS. Outstanding dielectric constant (D_k) and dissipation factor (D_f) of 1.84 and 0.0018 at a frequency of 1 MHz, respectively, were achieved for PPI-g-AMS-1 with the addition of AMS with 1% wt. Moreover, stable and ultralow D_k (∼1.84 at 1 MHz) and D_f (∼0.001 at 1 MHz) values were achieved over a broad temperature range from −20 to 200 °C. These findings indicate the broad application potential of polymeric materials as interlevel insulation materials in the next-generation 5G/6G infrastructure.