Hyperbranched Poly(octadecyl Acrylate)s as Lubricant Additive Studied by Resonance Shear Measurement

Polymer additives are commonly used in lubricants, yet previous studies have predominantly focused on those with linear chain structures. Generally, low viscosity lubricants are effective in the hydrodynamic lubrication regime, but they lead to increased friction and wear in the boundary lubrication regime. In this study, hyperbranched poly(octadecyl acrylate)s (HBPs) were proposed as a novel class of lubricant additives, and their performance was compared to that of linear polymers. HBPs with controlled macromolecular structures were synthesized by the organotellurium-mediated radical polymerization and evaluated as additives in a poly(α-olefin) (PAO) base oil. Viscosity measurements showed that HBP solutions maintained low fluid resistance comparable to PAO itself, unlike linear polymers, which increased in viscosity. Resonance shear measurements demonstrated superior nanoscopic lubrication efficiency for HBPs, HBPs > linear polymers > PAO, and macroscopic friction tests confirmed a significant reduction in the coefficient of friction in the boundary lubrication regime. These results revealed that HBPs offered effective lubrication for both the hydrodynamic and boundary lubrication regimes.