Single-Component High-Performance Adhesives Enabled by Synergistic Supramolecular and Covalent Polymerization
Yan Shao, Wen Li, Massimo Cametti, Zoran Džolić, Zeyang Ding, Zairan Yang, Ying Xie, Shimei Jiang
Abstract
The development of high-strength supramolecular adhesives from a single small molecule is a highly compelling research goal, as it offers the potential for lightweight, reversible, and stimuli-responsive bonding systems. However, achieving such adhesives presents significant challenges. Herein, we present a novel tripodal multifunctional molecule, BTA-C7, designed to exploit a synergistic supramolecular and covalent polymerization strategy to achieve a remarkable adhesive performance. BTA-C7 features a central benzene-1,3,5-tricarboxamide (BTA) core from which cyanostilbene moieties extend, each terminating in a benzo-crown-ether macrocycle. Under ambient conditions, while the highly directional hydrogen bonding between tripodal amide groups induces one-dimensional (1D) stacked arrays, the terminal benzo-crown-ether macrocycles facilitate the assemblies of the 1D chains, thereby promoting the formation of supramolecular networks exhibiting a baseline adhesion of 2.28 MPa as measured by lap-shear tests. Notably, under ultraviolet (UV) irradiation, the supramolecular networks undergo additional covalent photo-cross-linking through a [2 + 2] cycloaddition reaction, facilitated by the supramolecular confinement of cyanostilbene moieties. This process significantly enhances the adhesion strength to 5.18 MPa. Comparative studies with model compounds BTA-O7 (devoid of crown ether moieties, replaced by acyclic glycol chains) and BTE-C7 (with amide units replaced by ester groups) reveal that amide and crown ether units are indispensable for both supramolecular networks and covalent cross-linking.