Temperature-Invariant Large Broadband Polyimide Dielectrics with Multimodal Porous Networks

• Published in: ACS applied polymer materials 2023-06, Vol.5 (6), p.4159-4169
• Main Authors: Khim, Seongjun, Hwang, Yun Chan, Choi, Jaewon, Park, Hyunjin, Nam, Ki-Ho
• Format: Article
• Language: English
• ISSN: 2637-6105; 2637-6105
• DOI: 10.1021/acsapm.3c00369

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.