Mechanical robustness, reprocessability and functionality of nanocomposites of polyurethane with Fe3O4 enabled by compatibilizing and crosslinking through dynamic boronic ester bonds

A new approach to the nanocomposites of polyurethane with Fe₃O₄ was reported through simultaneous compatibilizing and crosslinking with dynamic boronic ester bonds; the nanocomposites featured robust mechanical strengths, reprocessing and functional properties. First, a linear PU was synthesized, which carries a plethora of 1,3-diol structural moieties in the main chain. In the meantime, Fe₃O₄ nanoparticles were surface-modified with boronic acid groups. The unique functionalization allowed the generation of boronic ester bonds between the linear PU and Fe₃O₄ nanoparticles. Furthermore, the mixtures of linear PU with the Fe₃O₄ nanoparticles were crosslinked with a diboronic acid, generating the nanocomposites which feature dynamic boronic ester bonds. Compared to the linear PU, the nanocomposites displayed the improved thermal and mechanical properties. Attributable to the exchange of dynamic boronic ester bonds, the nanocomposites were recyclable or reprocessable. The crosslinking further imparted shape memory properties to the materials, featuring the reconfigurability. In terms of recovery and fixity of shapes, it was judged that the shape memory properties were significantly improved due to the incorporation of Fe₃O₄ nanoparticles. In addition to the robust mechanical strengths, the functional properties such as photothermal and magnetothermal properties were bestowed on the nanocomposites, which can be exploited to trigger the self-healing and shape recovery of the nanocomposites.