• A novel biobased poly(ether ketone) was successfully synthesized from a bifuran-based monomer via Friedel–Crafts polymerization. • PBFK1 exhibited high thermal stability, surpassing its single-furan analogue. • Inherent, reversible solid-state halochromism was discovered in the polymer matrix. • Macroscopic color shifts are primarily driven by pH-dependent fluorescence emission rather than UV–vis absorption changes. • PBFK1-based smart coatings achieved high surface hardness (5H) and functioned as repeatable pH-sensing materials. Developing biobased engineering plastics from biomass remains a significant challenge, particularly in the integration of “smart” stimuli-responsive functionalities into traditionally inert robust polymer frameworks. In this study, a novel biobased poly(ether ketone) ( PBFK1 ) was successfully synthesized via Friedel–Crafts polymerization using aluminum chloride and incorporating a strategic bifuran unit derived from inedible resources. To evaluate the unique structural influence of this bicyclic conjugated scaffold, PBFK1 was compared against its single-furan ( PFK ) and benzene-based ( PPhK ) analogues. Thermal analysis revealed that PBFK1 possesses high thermal stability, surpassing PFK , though its α-relaxation temperature was uniquely lower than both analogues. A central highlight is the discovery of inherent, reversible solid-state halochromism (pH-responsiveness). Spectroscopic investigations confirmed that macroscopic color transitions between blue, green, and pale yellow are driven by pH-dependent shifts in fluorescence emission rather than UV–vis absorption changes. Leveraging this synergy of robustness and optical responsiveness, PBFK1 enabled smart functional coatings with exceptional pencil hardness (5H on glass) and repeatable pH-sensing composite films. These findings position the bifuran unit as a strategic building block for multifunctional biobased materials, effectively bridging the gap between passive engineering plastics and advanced sensing capabilities.
Arakawa et al. (Wed,) studied this question.