Photoplastic Self-Healing Polyurethane Springs and Actuators

Typical crosslinked polymer networks have rubbery elasticity and do not exhibit thermoplasticity like linear polymers. However, thermodynamically crosslinked polymer networks exhibit a certain thermoplasticity that allows for thermal processing. Here, we introduce a new concept of photoplasticity, i.e., under light illumination, the covalently-crosslinked polymer elastomers become flexible and plastic like linear polymers. A novel class of photoplastic polyurethane (PPU) elastomers based on dynamically cova-lent crosslinker hexaarylbiimidozole (HABI) and permanent crosslinker glycerol, are designed and synthesized. Under the dual ac-tions of light and stretching, the photoplastic elastomer exhibits reversible elongation and contraction like springs. Due to the photo-induced reversible dissociation/recombination of HABI, two cut samples of solvent-free elastomers can be healed under irradiation at room temperature. Under asymmetric illumination, the photoplastic elastomer exhibits the appreciative phototro...