Enhanced purification and dispersion techniques for boron nitride nanotubes by introducing repulsive sites in polyethylene glycol block copolymer

Boron nitride nanotubes (BNNTs) possess outstanding thermal properties and biocompatibility, yet their limited dispersibility in polar media such as polyethylene glycol (PEG) hinders their processability and application in composite materials and biomedical fields. In this study, a modified PEG-based block copolymer incorporating a pyrrolidinium salt capable of interacting with BNNT surfaces to give a repulsion force between BNNTs was developed to address this challenge. Benzamide and PEG segments along the modified PEG backbone interact with BNNT surfaces, enabling selective adsorption, whereas the pyrrolidinium N⁺/Br⁻ ion pair imparts electrostatic repulsion and steric stabilization, thereby maintaining excellent dispersion stability for up to 7 days. The centrifugation enabled a high purification efficiency of up to 92 %, indicating successful removal of residual impurities. Notably, the concentrated BNNTs paste derived from the purified solution exhibited potential liquid crystalline behavior, suggesting a high degree of alignment and interaction between nanotubes. These results demonstrate a versatile and scalable strategy for producing high-purity, functionalized BNNTs, offering a promising platform for advanced applications in BNNT-based nanocomposites, including bioelectronics, thermal interface materials, and biomedical systems.