Programmable actuation of liquid crystal elastomers: Via "living" exchange reaction

Liquid crystal elastomers (LCEs) have recently been intensively explored in various applications as soft actuating materials and opto-mechanical coupling materials. Since the orientation of mesogens in the elastomer largely determines its properties, various methods of programming the alignment of mesogens in LCEs have recently been developed. However, most of the methods either involve complex fabrication processes or have intrinsic limitations in their applicability. In this article, we synthesize a LCE with dynamic disulfide bonds and propose a facile room-temperature mechanical programming method via a "living" exchange reaction without requiring additional stimuli and catalysts. We also, for the first time, reveal the "living" exchange reaction of disulfide bonds at room temperature in a bulk polymer. Such a "living" exchange reaction relies on the significantly prolonged lifetime of free radicals generated during the breakage of disulfide bonds, which is counterintuitive and in contrast to most previous understandings. Thanks to the disulfide bond, the patterned orientation of the mesogens in the LCE is erasable and reprogrammable. In addition, the synthesized LCE also exhibits a shape memory effect, enabling the design of deployable soft actuating devices.