Grafting Poly(Ionic Liquid)s on Covalent Organic Frameworks via Surface-Initiated Ring-Opening Metathesis Polymerization for Enhancing Lubrication Performance

Recently, a variety of functionalization methods have emerged to enhance the application efficiency of covalent organic frameworks (COFs) across diverse fields. Herein, poly(ionic liquid)-functionalized COF-LZU1 was successfully synthesized via a mechanochemical reaction followed by surface-initiated ring-opening metathesis polymerization (SI-ROMP). At first, a ROMP initiator (5-norbornene-2-methylamine) was grafted onto the aldehyde-terminated COF-LZU1 via Schiff base reaction induced by mechanical force input through ball milling; subsequently, the ionic liquid monomer (NM-MIm-PF6) can grow onto the surfaces of COFs from the active sites of the initiator through SI-ROMP, resulting in the formation of a poly(ionic liquid)-functionalized COF (PNM-MIm-PF6@LZU1). The as-prepared PNM-MIm-PF6@LZU1 exhibited outstanding tribological performance when served as an oil-based lubricant additive. Compared to base oil 500SN, the average friction coefficient of the lubricant with PNM-MIm-PF6@LZU1 decreased from 0.162 to 0.105, accompanied by a 74.3% reduction in wear volume. The excellent lubricating performance is mainly attributed to the formation of a continuous and tough friction protective film through tribochemical reaction on the friction interface.