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

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 (Tm) in the range of 51-251 degrees 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 Tms or glass transition temperatures (Tgs) above room temperature, whereas cis-polymers are red liquids with Tgs below -20 degrees 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. Azobenzene-based polyesters (azopolyesters) from copolymerization of azobenzene-based epoxides with cyclic anhydrides possess remarkable intrinsic crystallinity and novel photoinduced reversible solid-to-liquid transition abilities, owing to photoinduced trans-cis isomerizations of azobenzenes being inlaid with soft alkyl side-chain. This represents a new design strategy for the synthesis of reversible adhesives.image