Hot-Melt Adhesive Based on Dynamic Oxime-Carbamate Bonds

Polyurethane hot-melt adhesives featured with high adhesion strength and environmental friendliness possess broad applications in many fields. However, their practical application is hindered by existing drawbacks such as low adhesion strength and poor recyclability for thermoplastic polyurethane and reactive polyurethane hot-melt adhesives, respectively. Achieving high adhesion strength and efficient recycling for hot-melt adhesives simultaneously is challenging. Herein, reversible covalent bonds (oxime-carbamate) were introduced to construct a three-dimensional dynamically cross-linked polyurethane system which has the merits of favorably reworkable thermoplastic polyurethane hot-melt adhesives and high adhesive reactive polyurethane hot-melt adhesives to accomplish efficient bonding-debonding conversion on demand. Such a structure provided a high cross-linked covalent network and a fast reversible adhesive property, and hence improved the overall performance of holt-melt adhesives. As a result, the adhesive exhibited an impressive initial and ultimate adhesion strength of 5.96 +/- 0.61 MPa (5 min curing) and 9.02 +/- 1.36 MPa (10 days curing), respectively. More remarkably, favorable repeated adhesive capability was realized even after it was completely broken four times, while still retaining all above 4.40 +/- 0.92 MPa. In addition, this adhesive also possessed excellent solvent resistance and good durability. Our work emphasized the importance of molecular design and a general method for strong and efficient adhesive systems.