Lignin‐Based Macromolecular Photoinitiator for Non‐Migration, Self‐Adhesive, and Water‐Resistant Eutectogels toward Underwater Reliable Communication

Abstract Hydrophobic conductive gels have attracted much attention in underwater sensing as the soft robots and wearable sensors. Among the various methods for preparing conductive gels, UV‐initiated polymerization shows advantages of rapid curing and significant energy savings. However, traditional commonly used photoinitiators in UV‐initiated polymerization often migrate or diffuse within conductive gels, especially with prolonged use or underwater, posing potential environmental and health risks. Herein, a novel lignin‐based macromolecular photoinitiator (L‐BF) is first designed by incorporating benzoylformate into the lignin backbone, demonstrating excellent UV absorption, high radical initiation efficiency, and hydrophobicity. Subsequently, hydrophobic eutectogels (HEG) are prepared via UV‐initiated polymerization using L‐BF as photoinitiator. The HEG shows excellent mechanical properties (toughness of 5.67 MJ m⁻³ and strain of 941%) and scarcely L‐BF migration underwater. Moreover, the hydrophobic network of L‐BF endowed HEG with hydrophobicity (water contact angle exceeds 110°; swelling ratio is <5.8%), superior underwater adhesion (255 kPa), even maintained excellent sensing performance (gauge factor of 4.69), and long‐term reproducibility (20 000 cycles) in air and underwater. Validation confirms the potential of HEG as an effective wearable sensor for underwater posture monitoring and communication, advancing the use of lignin and low‐migration conductive gels in marine exploration.