Dielectric Properties of Silicone Resins from Substituent Effects to High-Temperature Structural Evolution

Silicone resins are highly desirable matrix materials for high-temperature wave transparent applications. However, the evolutionary correlations spanning from ambient substituent architectures to dynamic high-temperature structural transitions remain elusive, and their precise atomic-level links to macroscopic dielectric responses have yet to be fully unraveled. Herein, we innovatively establish a closed-loop investigative framework integrating multiscale simulations (DFT and ReaxFF MD) with experiment characterizations, which explicitly decoupled the structural origins of these dielectric behaviors: the dielectric constant (ε) under ambient condition is fundamentally dominated by the fractional free volume (FFV), whereas the dielectric loss tangent (tan δ) is governed by side-group localized motion friction. Consequently, the vinyl-substituted resin exhibits exceptionally low dielectric parameters (∼3.16), driven by its maximized FFV (15.26%) for spatial dilution and flexible side groups. Furthermore, the high temperature dielectric degradation mechanisms are discovered for the first time. Specifically, the progressive transformation of the siloxane backbone from low-polarizability D units (C2SiO2/2, 0.37) into highly polarizable inorganic Q units (SiO4/2, 0.52) directly drives the continuous elevation of ε. Concurrently, the sharp surge in tan δ above 800 °C stems from the aggregation of free carbon into continuous conductive pathways, which elevates electrical conductivity from 10–11 to nearly 10–2 S/cm and severely intensify conductive dissipation. This study provides robust theoretical guidance for designing reliable structural-functional integrated aerospace dielectric materials.