Optical, Dielectric, and Thermal Properties of Bio‐Based Polyimides Derived from An Isosorbide‐Containing Diamine

The need for functional polymers derived from plant-based materials has increased from a carbon-neutral perspective. Herein, six different semialicyclic isosorbide-containing diamine-based polyimides (ISSD-PIs) are synthesized by incorporating isosorbide (ISS), which is a D-glucose derivative, into the diamine moiety to investigate the relationship between the chemical structure and optical, thermal, and dielectric properties. Compared with the conventional fully aromatic PIs, such as Kapton, the as-prepared ISSD-PIs demonstrate excellent optical transparency, low refractive indices (1.554-1.633), low birefringence (0.0084-0.0348) at 1310 nm, and low dielectric constants (2.93-3.36) with moderate dissipation factors (0.0112-0.0267) at 10 GHz. They also exhibit excellent thermal stability, with glass transition temperatures exceeding 250 °C and 5% thermal decomposition temperatures exceeding 400 °C. The chirality of the ISS skeleton remains intact, displaying characteristic circular dichroism. This study shows that the incorporation of ISS into PI chains enhances their optical and dielectric properties while maintaining thermal stability by increasing the free volume and reducing intermolecular interactions. In addition, the physical properties of the ISSD-PIs are more dependent on the rigidity of the dianhydride moiety, which directly affects the molecular packing of the PI chains, rather than that of the diamine moiety.