Robust and Programmable Liquid Crystal Elastomers through Catalytic Control of Dynamic Aza-Michael Reactions
Elina Ghimire, Charlie A. Lindberg, Tyler D. Jorgenson, Chuqiao Chen, Juan Pablo, Neil D. Dolinski, Stuart J. Rowan
Abstract
A strategy to efficiently synthesize thermally reprogrammable but mechanically stable liquid crystalline elastomers (LCEs) is reported by investigating the catalytic effects of para-substituted phenols on dynamic aza-Michael reactions. The synthesis of aza-Michael LCEs was optimized based on a study of catalyzed small-molecule aza-Michael reactions, where the presence of an electron-withdrawing substituent significantly improved the reactivity of the aza-Michael system. The catalysts were then screened to study their effects on the dynamic exchange of aza-Michael adducts. Catalysts with electron-withdrawing substituents were efficient in inducing the dynamic exchange of aza-Michael bonds, thus influencing the mesogen alignment and actuation. After programming the mesogen alignment, the catalyst was washed away to dramatically reduce the dynamic activity and improve the creep resistance of the material while preserving the postsynthetic alignment. This approach represents a straightforward and accessible methodology for efficiently obtaining thermally programmable as well as mechanically stable actuators from dynamic aza-Michael LCEs.