Photoresponsive Adhesives Based on Arylazoisoxazoles-Containing Polymers

Adhesives exist in many forms and are essential in the daily life, in industrial processes, and in healthcare, calling for continuous improvements in terms of application fields, strength, biocompatibility, recyclability, and reversibility. Regarding the last two points, embedding photoresponsive molecules into the adhesive allows the use of light to attach or detach reversibly different surfaces. Photoresponsive adhesives can be removed without the use of high temperature or solvents, which is ideal for delicate environments. To date, azobenzenes are the most explored chromophore to prepare smart adhesive formulations. Here, the synthesis of polymer containing arylazoisoxazoles (AIZs) -- azobenzene analogs containing a heterocycle -- and their application as adhesives is described. Mechanical tests demonstrate an enhancement of the adhesion strength from 0.39 to 2.79 MPa, passing from low molecular weight monomer to selected AIZs acrylate polymer. Irradiation with UV induces the formation of the cis isomer with a consequent drop of more than 70% in the adhesion strength. The different compounds result as possible candidates as adhesives on the basis of the increased load that can be held, together with the possibility to obtain joints that can be either stable or detachable under light irradiation.