Optimization of the performance of UV light-responsive curing of polyurethane-urea adhesive formulations

UV-light curing polyurethane-urea adhesives (PU-urea) were formulated from 4,4′-methylenediphenyl diisocyanate (MDI), 1,5-pentanediol (PD), 1,5-pentanediamine (cadaverine, CAD), and acetone as the adhesive carrier. The UV light-triggered curing process of these PU-urea formulations was controlled by blocking hydroxyl and amine functional groups of PD and CAD, respectively, with 6-nitroveratryloxycarbonyl (NVoc) as a photo-labile protecting group. The adhesive formulation was proven to undergo a dual curing procedure, integrating the UV light-induced polymerization and the release of the volatile adhesive carrier. This study highlights the critical role of the urethane:urea linkage ratio in the synthesis of photo-triggered adhesives to achieve optimal performance. Hence, the formulation with a NCO:OH:NH₂ molar ratio of 2.6:1.0:0.5 and a 96 % acetone content exhibited the most appropriate mechanical response in PETG-adhesive-PETG joints. Upon 60 min of photo-curing process (180 mW cm⁻²) shear strength values of around 6.11 MPa, in combination with the concomitant substrate failure of the adhesive joint, were observed. From this research, the potential implementation of the formulated PU-urea systems as competitive adhesive alternatives was proven. It was shown that the temporally controlled UV-induced functional group release is essential for achieving optimum adhesion performance.