Shape-Memory Ideal Polymer Networks with Giant Tunable Thermal Conductivity

Since polymer networks are conventionally known as thermal insulators, strategies to enhance their thermal conductivity offer promising solutions to complicated thermal management problems. Thermally conductive polymer fibers and films have been processed by thermal drawing to achieve heightened measured thermal conductivities that match those of metals. However, dramatic thermal transport enhancement has only been shown using irreversible processing. Here we report ideal polymer networks that achieve giant tunable thermal conductivity. The thermal conductivity enhances by over four times its initial value in the stretched direction, from 0.3 Wm^-1K^-1 to 1.5 Wm^-1K^-1. This thermal conductivity change is reversible and can be tuned over many cycles. Crosslinks enable the material to quickly stretch and retract above the glass transition temperature, and the ideal-network architecture promotes chain alignment and stretchability. This shape-memory material retains the structure of the deformed configuration and becomes semicrystalline when cooled to room temperature. Structural characterization and molecular simulation indicate that stretching facilitates alignment of crystalline domains that contributes to bulk heat transport. These findings provide important steps towards realizing tunable, polymeric thermal switches for advanced applications of building materials, electronics, flexible devices, and heat exchangers.