Shape programming of liquid crystal elastomers by two-stage wavelength-selective photopolymerization.

Reversible shape memory polymers are a topic of great interest in research focusing on materials for soft robotics and haptic technologies. In particular, liquid crystal elastomers (LCEs) programmed by two-stage crosslinking procedures have been increasingly reported in the past decade. These methods often include a base-catalyzed first crosslinking step, which limits the processibility of the material. Here, a two-stage crosslinking procedure based on the orthogonal wavelength-selective photo-initiation of free-radical and cationic ring-opening polymerizations is reported. Using a bifunctional acrylate-oxetane crosslinker, thermally responsive LCEs capable of reversible actuation are produced. The improved processibility of this method compared to base-catalyzed procedures is demonstrated through lithography-based production of actuators, as well as 4D-printed actuators with an additional shape programming step. The reported method opens up new manufacturing possibilities for the development of complex shape-programmed materials that were unattainable through previously known procedures.