Breaking the Thermal Conductivity-Adhesion-Viscosity Trade-off in Thermally Conductive Adhesive via Hyperbranched Networks and Multi-Scale Fillers.

Thermally conductive adhesives are essential for thermal management in high-power optoelectronic systems, where they provide both efficient heat dissipation and strong mechanical bonding. However, achieving high thermal conductivity alongside strong adhesion and low viscosity remains a fundamental challenge due to conflicting material requirements. Herein, a molecularly engineered thermally conductive adhesive is reported that uniquely and simultaneously overcomes these trade-offs by integrating amino- and phenylboronic acid-functionalized hyperbranched polysiloxane into a polydimethylsiloxane matrix filled with multi-scale aluminum fillers. A coupled dynamic-covalent network originating from the hyperbranched polysiloxane enhances both bulk and interfacial dissipation through reversible boronic-ester exchange, while the multi-scale aluminum architecture increases maximum packing and connectivity yet suppresses viscosity growth, enabling ultra-high filler loading without sacrificing bonding. The resulting thermally conductive adhesive achieves a thermal conductivity of 6.21 W m-1 K-1, an adhesion strength of 5.13 MPa, and a low viscosity of 253.0 Pa s. Device-level validation confirms its excellent dispensability, ability to lower operational temperature and relieve thermomechanical stress, thereby establishing a distinct design paradigm that links molecular structure, filler architecture, and thermo-mechanical reliability in one coherent framework.