Base Oil-Mediated One-Pot Synthesis of a P(LMA-MMA-ST) Viscosity Index Improver

Viscosity index improvers (VIIs) are indispensable polymer additives in modern lubricating oil formulations. In this work, a one-pot in situ free-radical polymerization strategy is proposed for the synthesis of poly(lauryl methacrylate-methyl methacrylate-styrene) (P(LMA-MMA-ST)) terpolymer VII in base oil, eliminating solvent removal and complex post-treatment steps. The results showed that the maximum thermal decomposition temperature, glass transition temperature, particle size, and dispersity of terpolymers are 346 °C, −33.64 °C, 16 nm, and 2.17, respectively, confirming that the copolymer has a uniform molecular structure and adequate thermal stability. The terpolymer exhibits favorable rheological properties in base oil. At a content of 7.5 wt %, the viscosity index reaches 225 with a pour point of −29 °C, and when increasing the content to 9.1 wt %, the viscosity index further improves to 244 without deterioration of low-temperature performance. The tribological performance shows that the maximum reduction of the friction coefficient is up to 14.89%. Compared with other VIIs, the P(LMA-MMA-ST) delivers competitive efficiency. All the results demonstrated that the base oil-mediated one-pot strategy has industrialization potential and practical application in the synthesis of poly(methacrylate)-type VIIs.