Programmable liquid crystal elastomers with dynamic covalent siloxane bonds based on a dual self-catalytic strategy

The exchange reaction of preparing the siloxane-based liquid crystal elastomers (Si-LCEs) always require the acid or base catalysts, which will increase the complexity of the operation and reduces the stability of the Si-LCE materials. In this paper, a novel and simple dual self-catalytic strategy for producing Si-LCEs with dynamic covalent siloxane bonds was proposed. A readily available compound-1,3-bis (aminopropyl) tetramethyldisi-loxane (BATS) acts as chain extender and crosslinker for elastomers and provides dynamic covalent bonds (DCBs) as well. More importantly, amino groups of BATS play the role of dual self-catalyst, not only accelerating the thiol Michael addition reaction and aza Michael addition reaction simultaneously during producing Si-LCEs, but also promoting dynamic covalent siloxane bonds exchange reaction at an elevated temperature after the for-mation of the cross-linked network. With this ingenious design, the obtained fully cured polydomain Si-LCEs possess excellent self-healing and processing abilities enabled by DCBs and outstanding mechanical properties facilitated by hydrogen bond, which can be easily aligned, programmed and recycled. By exploiting these dy-namic features, a series of multi-functional soft actuators were realized by simple welding, showing a local fast response and precise control by light and heat. Furthermore, soft robots fabricated with a bilayer structure of Si-LCEs can perform crawling and coiling actuation controlled by near-infrared (NIR) light facilely. These results manifest that the self-catalytic dynamic covalent siloxane bonds strategy is a facile and effective approach for preparing Si-LCEs and provides a new solution for the exploitation of multi-functional liquid crystal elastomers with fast response to various stimulus.