Flexible-Bridged Mechanophores Balance Toughness and Thermomechanical Actuation in Main-Chain Liquid Crystal Elastomers

Abstract

Improving the toughness of liquid crystal elastomers (LCEs) without compromising their reversible actuation remains a central challenge for mechanically robust soft actuators. Here, we introduce HBDEC, a flexible-bridged nonscissile mechanophore chain extender, into main-chain LCE networks to expand their deformation and energy-dissipation capacity. HBDEC contains C6-bridged fused cyclobutane units that can be covalently incorporated into polymer backbones through thiol-ene addition. Linear-polymer mechanochemical tests support force-responsive ring opening of the fused cyclobutane units, consistent with a nonscissile hidden-length mechanism. In aligned LCE networks, HBDEC incorporation produces a composition-dependent toughness–actuation balance. Increasing HBDEC content enlarged the deformation range and improved tensile toughness by approximately 3.8-fold, while an intermediate HBDEC loading enabled the best combination of toughness and thermomechanical actuation. The optimized LCE-H10 composition achieves a tensile strength of 6.98 MPa, an elongation at break of 358%, a toughness of 9.55 MJ m–3, and an actuating stress of 2.18 MPa, together with reversible thermomechanical contraction. A macroscopic impact-buffering test further shows that LCE-H10 withstands transient loading more effectively than the HBDEC-free LCE, exhibiting larger deformation, greater kinetic energy reduction, and retained film integrity. This molecular design provides a practical route to tougher single-network LCE actuators for impact-tolerant and lightweight buffering applications.