Closed-Loop Recyclable and Totally Renewable Liquid Crystal Networks with Room-Temperature Programmability and Reconfigurable Functionalities.

Abstract

Dynamic covalent liquid crystal networks (DCv-LCNs) with straightforward (re)programmability, reprocessability, and recyclability facilitates the manufacture of sophisticated LCN actuators and intelligent robots. However, the DCv-LCNs are still limited to heat-assisted programming and polymer-to-polymer reprocessing/recycling, which inevitably lead to deterioration of the LCN structures and the actuation performances after repeated programming/processing treatments, owing to the thermal degradation of the polymer network and/or external agent interference. Here, a totally renewable azobenzene-based DCv-LCN with room-temperature programmability and polymer-to-monomers chemical recyclability is reported, which was synthesized by crosslinking the azobenzene-containing dibenzaldehyde monomer and the triamine monomer via the dynamic and dissociable imine bonds. Thanks to the water-activated dynamics of the imine bonds, the resultant DCv-LCN can be simply programmed, upon water-soaking at room temperature, to yield a UV/Vis light-driven actuator. Importantly, the reported DCv-LCN undergoes depolymerization in an acid-solvent medium at room temperature because of the acid-catalyzed hydrolysis of the imine bonds, giving rise to easy separation and recovery of both monomers in high purity, even with tolerance to additives. The recovered pure monomers can be used to regenerate totally new DCv-LCNs and actuators, and their functionalities can be reconfigured by removing old and introducing new additives, by implementing the closed-loop polymer-monomers-polymer recycling.