Smart Responsive Azo-Copolymer with Photoliquefaction for Switchable Adhesive Application.

The development and utilization of switchable adhesives are considered to be an essential target to solve the problems of their separation and recycling in some specific service environments, such as the preparation or repair process of electronic devices. Intelligent materials with controllable phase transition are utilized to fabricate switchable adhesives because of the significantly diverse adhesion strengths in different phase states. Photoresponsive azobenzene and its derivatives usually possess different melting temperatures () or/and glass transition temperatures () of the cis-trans isomers, which are beneficial to making the photoinduced solid-liquid phase transition for switchable adhesive application possible. Here, a novel three-component azo-copolymer (PNIM-Azo) with fast and reversible photoinduced solid-liquid phase transition has been designed and synthesized. PNIM-Azo possesses reversible bonding/debonding processes, resulting from the different adhesion strengths between trans-configuration PNIM-Azo in the solid state and cis-configuration in the liquid state. Moreover, by incorporating commercialized 2-methoxyethyl acrylate and -isopropylacrylamide with O and N heteroatoms into the copolymer, the trans-configuration PNIM-Azo possesses the highest adhesion strength (∼11 MPa between two glass substrates) among all of the reported azobenzene-based switchable adhesives, which could be attributed to the increase in the entanglement effect because of the H-bond in the polymer chains formed by introducing heteroatoms. Our synthesized PNIM-Azo copolymer provides an alternative for designing and developing switchable adhesives with high adhesion strength for some electronic production processes.