Ultrastretchable and Tough Poly(ionic liquid) Elastomer with Strain-Stiffening Ability Enabled by Strong/Weak Ionic Interactions

Polymer ionic conductors have shown great promise as iontronic sensors for flexible wearable devices and intelligent machines. A series of exquisitely designed hydrogels, ionogels, and ionic elastomers have good mechanical properties, such as super stretchability and high elasticity. However, most gels tend to exhibit softening or linear mechanoresponsive behavior when subjected to stress, which is completely different from the strain-stiffening behavior of the biological tissues. Therefore, designing polymer ionic conductors with good mechanical properties and strain-stiffening ability remains a challenge, which is critical in improving the reliability and durability of iontronic sensing. Here, we propose a strong/weak ionic interaction strategy to develop poly(ionic liquid) elastomers (PILEs) through the copolymerization of imidazolium ionic liquid monomers and acrylate monomers. The design allows weak ionic interactions to impart softness to the polymer network, while strong ionic interactions stiffen the network during stretching. The resulting transparent PILE possesses ultrastretchability, immense strain stiffening, good elasticity, high toughness, and puncture resistance. The PILE also shows antibacterial ability and good adhesion due to high-content charge groups in the polymer network. These combined properties make the PILE an excellent candidate for iontronic sensors, with excellent stability and sensitivity to temperature and strain, demonstrating great potential in wearable devices and human–machine interfaces.