Azopolyesters with Intrinsic Crystallinity and Photoswitchable Reversible Solid‐to‐Liquid Transitions

Abstract Herein, we introduce a variety of azopolyesters (azobenzene‐based polyesters) with remarkable intrinsic crystallinity and photoinduced reversible solid‐to‐liquid transition abilities from copolymerization of azobenzene‐based epoxides with cyclic anhydrides. The length of the soft alkyl side‐chain inlaid with azobenzenes and stereoregularity of main‐chain of azopolymers have tremendous effects on crystallization properties of the resulting polyesters with melting temperature ( T m ) in the range of 51–251 °C. Moreover, some of azopolyesters possess excellently photoinduced reversible solid‐to‐liquid transition performance thanks to trans‐cis photoisomerization of azobenzenes. Trans ‐azopolyesters are yellow solids with T m s or glass transition temperatures ( T g s) above room temperature, whereas cis ‐polymers are red liquids with T g s below −20 °C. These azopolyesters could be applied as novel light‐switchable adhesives for quartz/quartz, wood/wood and quartz/wood adhesion, with the strength in the range of 0.73–0.89 MPa for trans ‐polymers. Conversely, the adhesion strength of liquefied cis‐ azopolyesters generated from the irradiation of trans ‐polymers by UV light was about 0.1 MPa, which shows light enable to control the adhesion process with high spatiotemporal resolution.