Azobenzene-Containing Block Copolymers as Light-Induced Reworkable Adhesives: Effects of Molecular Weight, Composition, and Block Copolymer Architectures on the Adhesive Properties

We previously reported that ABA-type triblock copolymers with azobenzene-containing terminal blocks can be utilized as a light-induced reworkable adhesive that enables repeatable bonding and debonding on demand. The reworkability was based on the photoisomerization of the azobenzene moiety and concomitant softening and hardening of the azo blocks. Our aim in this study is to investigate the effect of the composition, molecular weight, and block copolymer architectures on the reworkable adhesive properties. For this purpose, we prepared AB diblock, ABA triblock, and 4-arm (AB)(4) star-block copolymers consisting of polymethacrylates bearing an azobenzene moiety (A block) and 2-ethylhexyl (B block) side chains and performed adhesion tests by using these block copolymers. As a result, among the ABA block copolymers with varied compositions and molecular weights, the ABA triblock copolymers with an azo block content of about 50 wt % and relatively low molecular weight could achieve an appropriate balance between high adhesion strength and low residual adhesion strength upon UV irradiation. Furthermore, the 4-arm star-block structure not only enhances the adhesion strength, but also maintains low residual adhesion strength when exposed to UV irradiation. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 806-813