Fabrication of poly(ionic liquid) functionalized COFs via surface-initiated polymerization for improved tribological performance

Recently, covalent organic frameworks (COFs) have been extensively studied due to their abundant active sites for functionalization and the derived various applications. Herein, we prepared poly(ionic liquid) functionalized COFs via mechanochemical reaction to bond with initiator and the following surface-initiated polymerization. Firstly, the initiator 2-bromo-2-methylpropionyl bromide bonded with the hydroxyl group of DT-COF through ball milling driven mechanochemical reaction, then the ionic liquid monomer (IL-Cl) can grow on COF skeleton from the active sites of initiator via surface-initiated atom transfer radical polymerization (SI-ATRP) to obtain the poly(ionic liquid) functionalized COF (PIL-Cl@DT-COF). The as-prepared PIL-Cl@DT-COF as well as the PIL-PF₆@DT-COF sample after anion exchange with PF₆⁻ served as oil-based lubricant additives, significantly reducing the friction coefficient and wear volume of base oil PAO10, especially PIL-PF₆@DT-COF can reduce the average friction coefficient from 0.169 to 0.094 and decrease the wear volume by 82.9 %. The outstanding tribological properties mainly benefited from the tough protective tribo-film, which was built via tribological reaction on the friction interface, containing the absorbed PIL-PF₆@DT-COF, ferric oxides and anti-wear F, P compounds.