Robust and self-healable polybenzimidazole membranes via Diels–Alder chain extension

Despite the critical role of polybenzimidazole (PBI) in high-temperature membranes in fuel cells, its practical deployment remains hindered by inherent limitations including low molecular weight (<20 kDa), poor solution processability, and irreversible network formation upon conventional synthesis. To address these challenges, a dynamic covalent strategy was introduced, leveraging Diels–Alder (DA) chemistry for topological reconfiguration. By subjecting furan-functionalized PBI prepolymer (PBI-furan, Mn = 8.2 kDa) to bismaleimide chain extension, we achieve a fourfold increase in molecular weight (Mn = 32 kDa), yielding a reversibly crosslinked PBI-DA membrane. Compared to traditional PBI with the same molecular weight, this architecture synergistically integrates exceptional thermal stability (>450 °C onset decomposition), robust mechanical strength (tensile strength >80 MPa), suppressed phosphoric acid swelling (<10%) and elevated ionic conductivity. Crucially, the dynamic network enables cyclic reprocessability and autonomous self-healing, retaining >90% of the initial mechanical properties after three tensile cycles. Compared to static PBI networks, this system reduces irreversible chain entanglement, while maintaining performance parity. By deeply integrating dynamic covalent chemistry with PBI materials, this work not only advances the performance of high-temperature proton-exchange membranes but also establishes a novel framework for the sustainable design of green energy devices, presenting significant scientific merit and engineering application potential.