An Environmentally Friendly Supramolecular Glue Developed from Natural 3,4-Dihydroxybenzaldehyde

Liquid adhesive suffers from the emission of volatile organic compounds (VOCs) that have detrimental effects on human beings. Herein, an environmentally friendly glue containing a novel supramolecule dissolved in non-toxic ethanol is developed. Poly (ether amine) (PEA) and 3,4-dihydroxybenzaldehyde (dhba) is utilized to synthesize catechol-terminated PEA, and subsequent complexation by Fe³⁺ results in the supramolecular component (PEA-dhba-Fe³⁺). The Fourier transform infrared (FTIR) spectrum together with the UV-vis spectrum reveal the existence of quinone converted from catechol. Raman spectra prove the existence of a successful complex of catechol-terminated PEA with Fe³⁺. The tri-complex is found to be the predominant mode and can successfully form into clusters, serving as a physical cross-linking network. The PEA-dhba-Fe³⁺ exhibits strong adherence to metal substrates compared to polymeric substrates, with its shear strength reaching as high as 1.36 ± 0.14 MPa when the pH of the glue is adjusted to 8. The obvious improvement of adhesion originates from the formation of interfacial coordination bonds between quinone/catechol and metal atoms, as well as their cations, as revealed by X-ray photoelectron spectroscopy (XPS) and theoretical calculations. With consideration of its merits, including strong adhesion and the minor emission of VOCs compared to commercial epoxy and acrylic adhesives, this environmentally friendly supramolecular glue has a range of cutting-edge applications as an adhesive for metal substrates.