Molecular‐Level Interface Engineering and Additive‐Induced Crystallinity Tuning for High‐Performance Thermally Conductive Polymer Composites

To boost up the properties of thermally conductive polymer composites, it is essential to conduct comprehensive research focused on interface engineering between the polymer matrix and fillers. Hexagonal boron nitride (BN) or expanded graphite (EG) are commonly utilized as nanofillers to improve the thermal conductivity of polymer composites. However, the interfacial interactions between the polymer matrix and nanofillers are generally weak, making effective thermal conductivity challenging. To address this issue, we have designed and synthesized an electron‐rich and aromatic tetrathiafulvalene‐based reactive mesogen (TRM), which not only possesses high thermal conductivity but also exhibits excellent interfacial affinity with BN and EG at the molecular level. Systematic experiments including photophysical, thermodynamic, structural, and computational analyses reveal that the thermal conductivity of TRM‐based polymer composites is substantially enhanced due to effective interfacial interactions between TRM and fillers. The TRM composites experimentally show excellent thermal conductivity based on enhanced interfacial phonon transfer, and these results are supported by theoretical interpretations. These findings underscore the critical importance of interface engineering between the polymer matrix and fillers at the molecular level in maximizing the material properties of polymer composites.