Synthesis and Tribological Properties of Polyoxometalate-Based Miktoarm Star Copolymers

Both organomolybdenum complexes and nanoparticles have been widely used as high-performance lubricant additives for friction and wear reduction. Polyoxometalates (POMs) are intermediate between them and similarly show excellent lubricating properties. In this work, a series of polyoxometalate-based poly(stearyl methacrylate) (PSMAn)–poly(ethylene glycol) (PEGm) miktoarm star supramolecular copolymers (SEMo-1–4) are prepared by coupling a Keggin-type polyoxometalate of Na3[α-PMo12O40] with 1,2,3-triazolium bridged block copolymers of PSMAn-b+-PEGm (n = 38, 52, 63, 80; m = 45) via electrostatic interactions. The resulting POM-based miktoarm star copolymers self-assemble in base oil to form spherical micelles with a PEG core and a PSMA corona, wherein the POM cluster of [α-PMo12O40]3– is implanted at the core–corona interface. Moreover, the spherical micelles exhibit long-term colloidal stability in the oil. Compared with the base oil, the POM-based stars as lubricant additives demonstrated remarkable reductions in coefficient of friction (∼61%) and wear volume (∼97%). The POM-containing polymers with enhanced lubricity may represent a class of macromolecular alternatives to conventional organomolybdenum complexes as lubricant additives for lowering friction and wear.