Polyacrylate Backbone Promotes Photoinduced Reversible Solid-To-Liquid Transitions of Azobenzene-Containing Polymers

The development of polymers with efficient photoinduced reversible solid-to-liquid transitions is desirable for the design of healable materials, reconfigurable devices, and switchable adhesives. Herein, we demonstrate that an azobenzene-containing polyacrylate P-H exhibits more efficient photoinduced reversible solid-to-liquid transitions than its polymethacrylate analogue P-Me. The side chain of P-H or P-Me contains a hexamethylene spacer, a photoresponsive azobenzene group, and an n-decyl tail. Both P-H and P-Me show reversible cis–trans photoisomerization. Solid transP-H and P-Me change to liquid cis ones via UV-light-induced trans-to-cis isomerization; liquid cisP-H and P-Me revert to solid trans ones via visible-light-induced cis-to-trans back isomerization. Differential scanning calorimetry and rheology measurements revealed that photoinduced reversible solid-to-liquid transitions occur because P-H and P-Me have photoswitchable glass transition temperatures. Although P-Me exhibits a slightly faster rate for trans-to-cis photoisomerization than P-H due to fewer aggregates in solid state, cisP-H flows 20 times faster than cisP-Me because P-H has a more flexible polymer backbone. The low viscosity of cisP-H makes photoinduced solid-to-liquid transition efficient and enables the design of rapidly healable coatings. Our study shows that the design of a flexible backbone is a new strategy to develop rapidly healable polymers with more efficient photoinduced solid-to-liquid transitions.