Achieving low dielectric constant and high thermal conductivity polymer composites by using larger POSS functionalized boron nitride nanosheets

Abstract

Low dielectric constant (low-k) polymer composites with high thermal conductivity hold significant potential for applications in high-frequency communication and high-power-density electronic devices. The incorporation of fillers with high thermal conductivity can effectively enhance the thermal conductivity of polymers, but it often leads to an increase in the k value. Herein, a series of novel nanofillers were developed by chemically grafting polyhedral oligomeric silsesquioxanes (POSSs) with different cage sizes (i.e., T₈, T₁₀, and T₁₂ POSSs) onto the surface of boron nitride nanosheets. These fillers were then uniformly dispersed into poly(dicyclopentadiene) (PDCPD) via reactive blending, resulting in the fabrication of thermally conductive yet low-k polymer nanocomposites. The results demonstrate that increasing the filler content, particularly the POSS cage size, enhances the material's free volume, resulting in a reduction in the k value. Additionally, the materials exhibit significantly improved thermal conductivity and comprehensive properties. Consequently, a material with a low k value of 2.39, a dielectric loss of 0.0035, a thermal conductivity of 2.34 W m⁻¹ K⁻¹ (a remarkable enhancement by 780% compared to pure PDCPD), a coefficient of thermal expansion of 48.1 ppm °C⁻¹, excellent thermal stability, and hydrophobicity was achieved. This study not only provides new insights for addressing the well-known trade-off between low k and high thermal conductivity but also offers promising materials for future electronic packaging.