Decreasing the dielectric constant and water uptake of co-polyimide films by introducing bulky spirobifluorene and cross-linked tetrafluorostyrol groups

With the diminishing gap between the internal components of chips, the signal transmission delay poses a substantial threat to chip performance. To enhance the transmission speed of electrical signals, the development of materials with a low dielectric constant (Dk) becomes imperative. Polyimide (PI), categorized as a specialized engineering material, exhibits a high Dk (≥3), posing challenges in meeting the requirements of electronic and communication industries. Consequently, a new diamine monomer named BTVFD, characterized by spirobifluorene and cross-linkable tetrafluorostyrol groups, was synthesized. It was copolymerized with 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine (TFDB) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) to synthetize cross-linkable polyimides (TBPIs) with different BTVFD content. The cross-linked TBPIs (CL-TBPIs) were obtained by thermal cross-linking reaction. The study results demonstrate the Dk of PIs is significantly reduced through this effective strategy. Notably, CL-TBPI-2 exhibits outstanding comprehensive performance with low Dk (1.88@10 MHz) and dielectric loss (0.00513@10 MHz), low water uptake (0.125 %), high thermal decomposition temperature (5 % weight loss at 553 °C) and glass transition temperature (374 °C), excellent tensile strength (121.8 MPa) and nice transparency and flexibility.