Facile Fabrication of Degradable Polyurethane Thermosets with High Mechanical Strength and Toughness via the Cross-linking of Triple Boron-Urethane Bonds

Degradable polymers that play an increasingly important role in the development of sustainable society are highly expected to exhibit not only high mechanical strength, but also superior toughness. Herein, degradable polyurethane thermosets with high mechanical strength and toughness are synthesized by cross-linking isocyanate-terminated prepolymers with boric acids. The incorporation of triple boron–urethane bonds derived from the coupling between hydroxyl groups in boric acids and isocyanate groups in the prepolymers into polyurethanes brings about a significant enhancement in the mechanical properties of the polyurethanes. Typically, PTMEG-HDI-BA1.5 exhibits optimal mechanical performances with an ultimate strength of ∼53.9 MPa, tensile strain of ∼1865%, and toughness of ∼390 MJ m−3. The toughness of poly(boron–urethanes) is even better than that of spider dragline silk (∼180 MJ m−3). The labile nature of the boron–urethanes enables the polyurethane thermosets to be rapidly degraded under mild acid conditions. The PTMEG-HDI-BA1.5 samples can be entirely decomposed in 0.1 M HCl/THF solution in 3 h at room temperature. Meanwhile, the degraded polyurethane thermosets can be further recycled into linear PU oligomers. Based on the above results, a new approach to fabricate degradable polymeric materials with simultaneously high mechanical strength and toughness is provided in this study.