Multifunctional boron nitride nanosheets/fluorinated‐polyimide composites with ultra‐low dielectric constant and high thermal conductivity

Thermally conductive polymeric composites with low dielectric constant are highly promising for the packaging materials in the field of modern communication. Therefore, the synergistic improvement of low dielectric constant and high thermal conductivity has become a current research hotspot. In this work, we propose a one‐step alkylation of boron nitride nanosheet (BNNS) with ultrasonic stratification using 1‐hexanol, and then hot press the films to make Alkyl‐BNNSs orient in the fluorinated polyimide (f‐PI). The resulting Alkyl‐BNNS/f‐PI composite successfully realizes the synergistic improvement of thermal property and dielectric properties, exhibiting a high heat conductivity coefficient of 2.36 Wm−1 K−1 with a filler content of 4.99 wt.%. Moreover, the permittivity and dielectric loss of the film are as low as 1.76 and 0.0065 at 1 MHz, respectively. This work provides a facile strategy for breaking the bottleneck of making polyimide composites simultaneously with high thermal conduction and low dielectric performance. Highlights The composite exhibits a high heat‐conducting coefficient of 2.36 Wm−1 K−1. Ultra‐low dielectric constant of 1.76 was achieved by the modification of film. Excellent breakdown resistance and flexibility were endowed with the composites. The one‐step alkylation method was used to surface modify BNNS. And Alkyl‐BNNS/f‐PI composite films were prepared by in‐situ dispersion method using Alkyl‐BNNS and fluorinated polyimide resin. The prepared composite film has ultra‐low dielectric constant, high thermal conductivity and excellent mechanical properties.