Low-dielectric polyimide constructed by integrated strategy containing main-chain and crosslinking network engineering

Polyimide (PI) is widely used as a mainstream antenna material for fourth-generation communication technology (4G) due to its excellent dielectric properties and mechanical properties. However, the relatively high dielectric constant and dielectric loss make traditional polyimide unable to meet the requirement of the fifth-generation communication technology. The molecular engineering strategy is an effective method to improve the dielectric properties and control the comprehensive performance of the polyimide. In this work, an m-phenylenediamine containing tetrafluorostyrol pendant group [(4-(2,3,5,6-tetrafluoro-4-vinylphenoxy) benzene-1,3-diamine (TFVPDM)] has been designed. On the one hand, the rigid m-phenylene and biphenyl structure in TFVPDM is beneficial for balancing the solubility and thermal properties of the TFVPDM-based polyimides. On the other hand, the tetrafluorostyrol pendant group can provide cross-linkable sites and help construct the hydrophobic network in the TFVPDM-based cross-linked fluorinated polyimides (CL-FPIs: CL-FPI-10; CL-FPI-20; CL-FPI-30), which can improve their dielectric properties and water resistance. The CL-FPIs films were obtained through polymerization of TFVPDM, 2,2′-bis(trifluoromethyl) benzidine (TFDB), and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and subsequent cross-linking reaction. Among CL-FPIs, the CL-FPI-30 shows the best comprehensive performance including low dielectric constant (2.29 at room temperature and 2.03 at 200 °C), low dielectric loss (0.0051 at 1 MHz), high glass transition temperature (Tg) (346.9 °C), low coefficient of thermal expansion (CTE) (44.1 ppm °C−1), low water absorption (0.128%) and good stability of dielectric constant in a humid environment.