Building Crosslinking Network via Catalytic Furan-to-Pyrrole Conversion

To address the limitations of conventional furan resins, which rely on furfural derivatives for synthesis and exhibit constrained performance, this work presents a catalytic polycondensation strategy that synthesizes high-performance resins directly from furfural and amines. Catalyzed by NH₄Cl, the process transforms furan rings into pyrrole rings via a Schiff base intermediate, proceeding through aromaticity disruption, nitrogen-atom incorporation, and aromaticity reconstruction. This unreported mechanism constructs a multi-substituted pyrrole cross-linked network, which demonstrates exceptional thermal stability (450°C decomposition), flame retardancy (limiting oxygen index of 31.7%), superior mechanical strength (tensile strength of 70 MPa, flexural strength of 131 MPa), excellent fatigue resistance (a resin spring surviving 10 000 compression cycles at 95% strain), and robust adhesion to diverse substrates, particularly on stainless steel across an extremely broad temperature range (-196°C-200°C). The solvent-free, atom-economical method, coupled with dynamic covalent bonds enabling reprocessing, offers a sustainable pathway for biomass-based furfural utilization and establishes a general strategy for furan-to-pyrrole conversion with potential in engineering plastics, structural adhesives, and coatings.