Thiol-acrylate Catalyst Enabled Post-Synthesis Fabrication of Liquid Crystal Actuators

Synthesizing orientated liquid crystal elastomers (LCEs) via the two-stage thiol-acrylate Michael addition and photopolymerization (TAMAP) reaction is extensively used. However, excess acrylates, initiators, and strong stimuli are inevitably involved in the second stage crosslinking. Herein, we simplify the strategy through taking advantage of a volatile alkaline (originally added to catalyze the thiol-acrylate addition in the first crosslinking stage). Without excess functional groups, the residual catalyst after annealing is still enough to trigger reactions of dynamic covalent bonds at a relatively mild temperature (80 °C) to program the alignment of LCEs. The reversible reaction switches off by itself after this process since the catalyst gradually but totally evaporates upon heating. The obtained soft actuators exhibit robust actuation during repeated deformation (over 1000 times). Many shape-morphing modes can be achieved by rationally designing orientation patterns. This strategy not only facilitates the practical synthesis of LCE actuators, but also balances the intrinsic conflict between stability and reprogrammability of exchangeable LCEs. Moreover, the method of applying volatile catalysts has the potential to be extended to other dynamic covalent bonds (DCBs) applied to crosslinked polymer systems.