The demand for increased energy efficiency continuously drives the development of new lubricants. Here we report the design and synthesis of hexahydrotriazine, triazine, and cyclen derivatives as friction modifiers (FMs) for enhanced fuel economy. This series of sulfur- and phosphorus-free oil-soluble heterocyclic ring-based molecules exhibits differing thermal and chemical stability depending on the degree of aromatization and number of linking spacers within the central heterocyclic ring. Thermally stable triazine and cyclen FMs significantly increase friction performance in the boundary lubrication regime. Cyclens in particular reduce friction by up to 70% over a wide temperature range. Detailed experimental investigations of the newly synthesized FMs at elevated temperatures demonstrate their favorable tribological performance under four operating conditions: variable-temperature sliding, linear speed ramping, reciprocating sliding, and rolling–sliding contact. These latest experimental findings suggest the potential of the application of “designer” heterocyclic FMs for reducing frictional loss in motor vehicles.
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