Preparation and Properties of Light-Controlled Reversible Adhesives of Azopolymers

A reversible adhesive PAzo-PEG, with a main chain structure of methyl methacrylate and a side chain of azobenzene(Azo) having six methylene spacer groups and a short polyethylene glycol(PEG) chain as a tail group, can undergo solid to liquid transformation under UV and visible light irradiation. It was prepared by atom transfer radical polymerization (ATRP). The azobenzene group undergoes reversible trans-to-cis isomerization under UV and visible light irradiation, and the process is reversible. The reversible photoisomerization process of solid materials was studied by UV-Vis absorption spectroscopy. The solid-to-liquid transition was studied by differential scanning calorimetry (DSC). Results showed that the solid-liquid transition is due to the different glass transition temperatures (T_g) of the cis and trans isomers, and T_g of trans is higher than room temperature while T_g of cis is lower than room temperature, so PAzo-PEG macroscopically exhibits reversible solid-to-liquid transition under light irradiation. The different adhesion capabilities of solid and liquid states of PAzo-PEG endow it with reversible adhesive properties. The solid state exhibits better adhesion properties, with an adhesion strength of 0.97 MPa measured experimentally, while the adhesion strength of PAzo-PEG in the cis state is reduced to 0.03 MPa. After three cycles of adhesion, the adhesive strength maintained 80% of the original strength.