Light-induced bonding and debonding with supramolecular adhesives

Light-responsive supramolecular polymers were applied as reversible adhesives that permit bonding and debonding on demand features. A telechelic poly(ethylene-co-butylene) (PEB) was functionalized with either self-complementary hydrogen-bonding ureidopyrimidinone (UPy) motifs (UPy-PEB-UPy) or 2,6-bis(1'-methylbenzimidazolyl)-pyridine (Mebip) ligands (Mebip-PEB-Mebip), which can coordinate to metal ions (Zn(NTf2)2) and form a metallosupramolecular polymer with the sum formula [Znx(Mebip-PEB-Mebip)](NTf2)2x, with x ≈ 1. In the latter case, light-heat conversion is facilitated by the ultraviolet (UV) light-absorbing metal-ligand motifs, while in the case of UPy-PEB-UPy a UV absorber was added for this purpose. Single lap joints were prepared by sandwiching films of the supramolecular polymers of a thickness of 80-100 μm between two glass, quartz, or stainless steel substrates and bonded by exposure to either UV light (320-390 nm, 900 mW/cm(2)) or heat (80 or 200 °C for UPy-PEB-UPy and the metallopolymer, respectively). UPy-PEB-UPy and [Zn0.8Mebip-PEB-Mebip](NTf2)1.6 displayed a shear strength of 0.9-1.2 and 1.8-2.5 MPa, respectively. When lap joints were placed under load and exposed to light or heat, the samples debonded within seconds. They could be rebonded through exposure to light or heat, and the original adhesive properties were recovered.