Preparation of fluorescent UV-curable adhesives containing AIEgen-modified monomer

Epoxy acrylate (EA) is the most widely used prepolymer for an ultraviolet (UV)-curable adhesive. Its colorless and transparent appearance can meet some special application needs, but also bring some problems, such as the position and amount of adhesive cannot be well observed by the naked eye, and so that malposition, shortage, or leakage of adhesive may happen. The UV-curable EA adhesive with UV light-excited fluorescence can be used to locate the adhesive through simple visual observation, but would not interfere with the macroscopic appearance of the glued item under natural light. Here we introduced tetraphenylethylene (TPE), a typic structure having aggregation-induced emission (AIE) effect, into the adhesive system. TPE-modified methacrylate (TPE-MA) monomer was added to UV-curable EA adhesive to participate in the curing process. The concentration of TPE-MA added to the adhesive was optimized to 0.1 % of the amount of EA prepolymer in mol to give blue fluorescence under UV light. By comparing the cured products, we found that the one having TPE-MA to form covalent bonds with other components, has higher fluorescence intensity and better stability than the other one having TPE via simple blending. Finally, tensile lap-shear strength measurement and thermal analysis of the cured products revealed that the addition of a small amount of TPE-MA to the adhesive has no significant effect on the performance of the adhesive. In conclusion, due to the viscosity of the adhesive itself, the intramolecular movement of TPE is restricted even at dilute concentrations, resulting in blue fluorescence. We hope this study can open a new avenue for the preparation of fluorescent adhesives.