Diethanolamine Phenylborate-Containing Polymer Micelles as Green Lubricant Additives for Enhanced Load-Bearing Capacity

Abstract Adverse friction and wear between moving mechanical parts create safety risks by dissipating substantial energy and causing mechanical failure. The most common method for reducing friction and wear and improving energy efficiency is the lubrication of mechanical parts. However, conventional sulfur- and phosphorus-based lubricant additives have raised serious toxicological and ecological issues, which are incompatible with contemporary sustainable development goals. In this work, diethanolamine phenylborate (DEAB)-containing polymer micelles have been constructed in situ in a lubricating base oil via dative interactions (B–N) between diethanolamine-functionalized block copolymers and phenylboronic acid derivatives. The resulting polymer micelles have a poly(stearyl methacrylate) corona and a DEAB core, conferring long-term colloidal stability in the base oil. Ball-on-disc reciprocating tribological studies showed that the polymer micelles achieved a 52% reduction in friction coefficient (from 0.25 to 0.12) and an 89% decrease in wear volume (from 1.02 × 106 to 1.12 × 105 μm3) compared to the unmodified base oil. Moreover, the micelles exhibited high load-bearing capacity up to 1200 N, which was much higher than those of diethanolamine- (450–650 N) and boron-containing block or random copolymers (700–900 N) alone. This enhanced load-carrying capability was attributed to the in situ formation of B2O3 and h-BN at the rubbing steel interfaces via tribochemical reactions. This work provides a platform for developing environmentally friendly lubricant additives through rational combination of functionalized block copolymers and triboactive molecular units.