Side-chain quadruple H-bonds empower self-healing e-skins with ultralow-temperature tolerance

• • S-UD elastomer achieves elongation at break of ~3257% at −78 °C, 3.4× higher than PDMS controls and ~32% higher than M-UD (~2474%), enabling extreme stretchability for robotic joints in polar conditions. • • Autonomous self-healing efficiency at −78 °C reaches ~75.9% for S-UD after 24 h, versus ~34.3% for M-UD, demonstrating superior crack recovery critical for durable e-skin operation in harsh environments. • • PDMS backbone with Tg = −127 °C and Tb = −150 °C remains unfrozen at polar temperatures, mitigating brittleness and preserving flexibility down to −78 °C, a key design parameter for ultralow-temperature elastomers. • • DFT analysis shows S-UD has a deeper potential well at 0° convergence angle, indicating stronger thermodynamic driving force for chain reconfiguration, which underpins its superior cryogenic self-healing.