A reusable and high shear strength hot melt adhesive with oxime-urethane bonds

Adhesives are widely used to bond various materials and surfaces, hot melt adhesives (HMAs) have conquered almost every industry area due to their solvent-free volatilization and ease of use. However, preparing reusable HMAs with high shear strength is still extremely challenging. Here, we show a simple way to prepare a reusable HMA, OPU (oxime-based polyurethane), with high lap shear strength based on oxime-urethane bonds. Cu(II) ions were introduced to further enhance the bulk strength to form ligand bonds. The relationship between the ligand bond content and the material properties was also investigated. Increasing ligand bond content limited the degree of crystallinity and shear strength. And the breaking stress and toughness of the coordinated material were significantly increased. The initial shear strengths of OPU for 304 stainless steel (after this referred to as "steel") and aluminum reached 12.6 MPa and 9.3 MPa, respectively, which is the highest shear strength available for oxime-urethane-based polyurethane HMAs. After 10 repetitions, the OPU still retains its high shear performance. By analyzing the relationship between shear strength and the amount of Cu(II), it is found that the shear strength is strongly related to chain mobility and Young's modulus. This work demonstrates a useful way of synthesizing reusable HMAs with high lap shear strength.