High-Performance Polyimides Derived from Biomass: Design, Synthesis, and Properties

The development of sustainable polyimides (PIs) from abundant renewable biogenic feedstocks has been limited by the bio-based content and the lack of mechanical and thermal properties. This study synthesized a series of daidzein-based PIs with a high bio-based content of up to 53%, which was significantly higher than the reported bio-based content (approximately 40%). The mechanical and thermal stability of the obtained polymer is comparable with that of commercial PIs, with the tensile strength of 148.6 MPa and the glass transition temperature (Tg) of 318.2 °C. Additionally, the daidzein-based PIs showed excellent fluorescence characteristics with a maximum fluorescence efficiency of 45.18 ns and an absolute fluorescence quantum yield of 14.1%. Such a performance combination has not been reported in bio-based PIs, even petrochemical PIs. Interestingly, the integration of experiments and density functional theoretical calculations revealed an effective intermolecular and intramolecular conjugation and the inhibition effect of intramolecular charge transfer by "enone and ether bonds" in daidzein-derived PIs. This work provides a possible route for the design and synthesis of multifunctional PIs with high bio-based content.