Thermoplastic polyimide with low dielectric properties enabled by the 2,2′‐spirobifluorene group

Abstract Thermoplastic polyimides (TPIs) have melt‐processability and adhesive ability, besides the intrinsic advantages of polyimides. To meet the requirements of applications in high‐frequency communication, TPIs with low dielectric constant ( D k )/dielectric loss factor ( D f ) at high frequency are also desirable. Enhancing the rigidity of polymer chains and simultaneously intermolecular interaction are effective ways to ensure low D k / D f , which also benefit to heat resistance. However, it is not conducive to thermoplasticity, due to limited movement of polymer chains. To balance the trade‐off between them, we introduce noncoplanar 2,2′‐spirobifluorene groups to modify the rigidity of polymer chains and regulate the twist between electron‐donor moieties (diamine units) and electron‐acceptor moieties (dianhydride units). It leads to rigid polymer chains, which benefits to good heat resistance and dielectric properties. Meanwhile, the resultant irregular chain structure is difficult to crystallize, which results in thermoplasticity.