Construction of Waterborne Thermoplastic Polymeric Adhesives Based on Hierarchical Hydrogen Bonds in Miniemulsions

Development of high-performance waterborne thermoplastic polymeric adhesives (TPAs) based on supramolecular interaction may meet the high-level requirements of green manufacture, sustainable development, and advanced applications. In this work, waterborne TPAs based on hierarchical hydrogen bonds were molecularly designed and synthesized through miniemulsion polymerization to harvest the above-mentioned properties. 2-Ureido-4[1H]-pyrimidinone (UPy) and carboxyl units, which can form strong quadruple hydrogen bonds and weak single hydrogen bonds, respectively, were adopted as the building blocks to construct the hierarchical hydrogen bond system of TPAs. The bonding performance of TPAs could be manipulated via the combination of hydrogen bonds with various bond energies. The strong quadruple UPy hydrogen bonds acted as the noncovalent “cross-linking” points to significantly enhance the intermolecular interaction of TPAs. The waterborne TPAs based on hierarchical hydrogen bonds displayed superior comprehensive bonding performance, substrate adaptability, and good cycling bonding capability. Furthermore, the bonding performance of TPAs with a high UPy content to a steel plate could be significantly enhanced by heat treatment at elevated temperatures to strengthen the interfacial interaction, and thus to simultaneously achieve high peel strength with adhesive failure (>17 N/25 mm) and high shear strength (>1.3 MPa), approaching some high-performance solvent-borne counterparts. This work provides inspiring insights into the design, green fabrication, and performance manipulation of advanced waterborne TPAs based on hierarchical hydrogen bonds.