Reversibly Cross-Linked Liquid-Free Ionic Conductive Elastomers for Closed-Loop Recyclable Temperature Sensors with Ultrahigh Sensitivity

The fabrication of liquid-free ionic conductive elastomers (ICEs) that can function as flexible temperature sensors with high sensitivity, fast response time, and efficient recyclability is a great challenge. In this study, novel liquid-free ICEs are conveniently fabricated through the complexation of 4-carboxybenzaldehyde-grafted poly(vinyl alcohol) (CPVA) with well-designed solid quaternary ammonium (QA) molecules bearing bifunctional hydrogen-bonding moieties. The resulting CPVA-QA elastomers, which are highly elastic and adhesive to diverse surfaces, exhibit a tensile strength of 6.6 MPa, a toughness of 14.7 MJ m⁻³, and a Young’s modulus of 0.15 MPa. These elastomers have a hydrogen-bonded network structure where the bifunctional QA molecules significantly suppress polymer chain entanglements. Benefitting from the thermally sensitive hydrogen bonds and the substantially reduced chain entanglements, the CPVA-QA elastomers show a high chain mobility upon temperature elevation, which facilitates ion transport within the CPVA-QA elastomers. Consequently, the CPVA-QA elastomer-based temperature sensors show an outstanding temperature resolution (0.05 °C), a fast response time over a wide temperature range, and a record-high thermosensitivity of 10.8% K⁻¹. Importantly, the CPVA-QA sensors can be depolymerized under mild conditions to recover their original components in high purity and yields (>96%), enabling closed-loop recycling of the sensors.