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Lubricating oil multifunctional additives on the base of alkyl methacrylate and maleic anhydride terpolymers

Introduction: Terpolymers of dodecyl methacrylate (DMA), octadecyl methacrylate (OMA) and maleic anhydride (MA) were synthesized and evaluated for the use as a lubricating oil additive. The synthesis was performed by reacting three monomers in mineral base oil solutions using the free radical polymerization initiation. The terpolymerization process conditions were optimized by virtue of a series of experiments. The overall conversions of the monomers were estimated by the 1H NMR spectroscopy method while molecular weights by the SEC method. Results and discussion: The properties of the prepared polymer additive solutions in mineral base oil were evaluated for terpolymeric additives with up to 10 mol. % of MA, which was limited by polymer solubility in mineral oil. The viscosity, viscosity index, shear stability and pour point were determined. The results are compared with pure methacrylate additive (PAMA, methyl methacrylate, MMA instead of MA). All terpolymer solutions in the base oil exhibited high kinematic viscosity and viscosity index values proving high thickening efficiency. It has been found that the kinematic viscosity does not significantly alters with terpolymer composition change and shows the ordinary linear dependence on molecular weight. The increase of MA content in the additive resulted in a slight decrease of viscosity index, whereas the shear stability index also decrease, reflecting the higher stability of MA copolymers. The molecular interaction parameters between polymeric additives and base oil were determined with the assistance of dilute solution viscometry measurements and the mechanism of action was proposed. (Figure 1: Viscosity index of semi-diluted, 5 wt. % polymeric additive solutions in mineral base oil. Figure 2: Viscosity loss (shear stability) of 5 wt. % polymeric additive solutions in mineral base oil.) Conclusion: The obtained results show that terpolymers of maleic anhydride, DMA and OMA could serve as advanced viscosity index improvers of lubricating mineral oils. Their properties are fully comparable with conventional methacrylate additives ; besides, they show better shear stability, as well as disperse properties.

lubricating mineral oil; multifunctional additives; alkyl methacrylate and maleic anhydride terpolymers

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