Poly(alkylimidazolium bis(trifluoromethylsulfonyl)imide)-Based Polymerized Ionic Liquids: A Potential High-Performance Lubricating Grease

Abstract Polymers prepared from ionic liquids are widely called polymerized ionic liquids (PILs). Compared to monocationic and dicationic ILs, PILs have higher molecular weights, charge, and greater intermolecular interactions, which make PILs have a higher possibility to generate better lubricity. PILs of poly‐alkylimidazolium bis(trifluoromethylsulfonyl)imide (PImC 6 NTf 2 ) is studied herein. Dicationic ILs of 1,1′‐(pentane‐1,5‐diyl)‐bis(3‐butylimidazolium) bis(trifluoromethylsulfonyl)imide (BIm 5 ‐(NTf 2 ) 2 ) is used as additive to decrease the crystallization temperature of PImC 6 NTf 2 . Lubricity of PImC 6 NTf 2 and PImC 6 NTf 2 +BIm 5 ‐(NTf 2 ) 2 , as well as BIm 5 ‐(NTf 2 ) 2 for comparison is evaluated under severe conditions, i.e., 3.0 to 3.5 GPa and 200 °C. The rheological study suggests that PImC 6 NTf 2 can be classified into grease. Tribological test results show that PImC 6 NTf 2 has much better antiwear property than BIm 5 ‐(NTf 2 ) 2 , especially at 3.5 GPa. Adding 4% BIm 5 ‐(NTf 2 ) 2 to PImC 6 NTf 2 is able to reduce friction under high pressure. At 200 °C, PImC 6 NTf 2 exhibits excellent lubricity. The mixture of 96%PImC 6 NTf 2 +4%BIm 5 ‐(NTf 2 ) 2 shows even better antiwear property than neat PImC 6 NTf 2 and exhibits the highest friction reducing property among the ILs at 200 °C. It is speculated that the robust strength of PILs and strong adhesion between PILs and solids are key factors in achieving the excellent antiwear property.