Preparation of High-Performance Thermosetting Polyurethanes for Rapid Degradation and Recycling via Quadruple Boron–Oxygen Bonds

Degradable and recyclable thermosets can be prepared by introducing dynamic bonds, but the introduction of dynamic bonds often reduces the mechanical properties as well as the thermal stability of the materials, and a balance between degradability, mechanical properties, and thermal stability cannot be achieved. For this reason, in this paper, a thermosetting polyurethane (BPU1.5) with multiple excellent properties was prepared by a simple and rapid method using 1,4-phenylenebisboronic acid to introduce quadruple boron–oxygen bonds into polyurethanes. 1,4-Phenylenebisboronic acid, as a dynamic cross-linking agent, on the one hand, provided an excellent cross-linking structure for BPU1.5, which resulted in the stable mechanical properties of BPU1.5 (high tensile strength up to 34.0 MPa) and excellent thermal properties (5% weight loss temperature of 337.0 °C); on the other hand, due to the quadruple boron–oxygen bonds, the polyurethane not only possesses excellent recycling properties but also has the ability to be degraded rapidly (complete degradation in 106 min at 0.1 M HCl/tetrahydrofuran). In addition, a strain sensor based on BPU1.5 was prepared by introducing a conductive filler for detecting finger bending, and the conductive filler can also be recycled due to the swelling property of BPU1.5, which is important for the protection of the environment and resource conservation.