Photoswitchable Adhesives of Spiropyran Polymers

Photoswitchable polymer adhesives enable strong bonding and on-demand debonding with minimal damage to adherends due to the high spatiotemporal resolution and therefore promise to contribute to material recycling as complex architectures consisting of dissimilar materials are being developed in various fields. In a variety of photosystems, the photoisomerization between noncharged spiropyran (SP) and zwitterionic merocyanine (MC) with large polarity changes is a primary candidate because molecular polarity is a dominant factor to generate adhesion force. However, SP has not been chemically incorporated into polymer adhesives. In this study, we developed photoswitchable adhesives of SP homopolymers with different molecular mobility of the SPs, which were located in the side chains and linked to the main chains through alkyl spacers with different lengths. Photoswitching of the adhesion strength by the polarity changes between SP and MC was demonstrated on both hydrophilic and hydrophobic substrates.