Flexible rubber with metal-like thermal conductivity achieved via hydrogen bonding engineering

The ideal electronics packaging for next-generation wearable devices and integrated circuits would be a flexible material with high thermal conductivity of a metal. We report a liquid-metal polyurethane composite (LiMPuC) with a thermal conductivity of 23.42 W m^-1 K^-1 while retaining extreme stretchability. The performance arises from interfacial-chemistry-guided ordering of the polyurethane matrix and improved liquid-metal wetting. By modulating hydrogen-bond donor/acceptor densities in the thermoplastic polyurethane and grafting -NH₂ groups onto eutectic gallium-indium (EGaIn) droplets, we create anchored, reconfigurable interfaces that (i) increase matrix chain alignment and intrinsic heat transport and (ii) promote stable, strain-tolerant thermal near-percolation of the liquid metal. Under large tensile strain, these coupled effects preserve high conductivity and deliver a flexibility figure of merit > 100. This chemistry-to-microstructure pathway, linking hydrogen-bond engineering with LM surface functionalization, provides a general strategy for designing flexible, high- $\kappa$ composites for advanced thermal management in emerging electronics.