Synthesis of Alkyl Sulfur‐Functionalized Oleic Acid‐Based Polymethacrylates and Their Application as Viscosity Index Improvers in a Mineral Paraffinic Lube Oil
Résumé
This work describes the synthesis of alkyl sulfur‐functionalized polymethacrylate‐based Viscosity Index Improvers (VII) derived from oleic acid (OLA) for mineral paraffinic lubricating oils. In this strategy, OLA was first quantitatively ramified by alkyl thiols containing long aliphatic chains through thiol‐ene coupling as demonstrated by 1H NMR spectroscopy with the complete consumption of OLA internal double bonds. The resulting alkyl sulfur‐functionalized OLA‐based derivatives were methacrylated through Steglich esterification in order to afford highly suitable hydrophobic OLA‐based monomers which, as far as we know, have not been described yet in the current literature. High polymethacrylate molecular weights were reached through radical polymerization despite the long alkyl pendant chains contained in their backbones. Finally, the resulting alkyl sulfur‐functionalized OLA‐based polymethacrylates have been blended in a mineral paraffinic oil (MPO) of reference at 5 wt% and evaluated as VII. Rheological measurements revealed that polymer thickening powers were significantly improved in oil with temperature and promoted by increasing the pendant alkyl thiol contained in polymer backbones. Moreover, the viscosity index of MPO was significantly improved with the addition of both synthesized homopolymers which confirmed their efficiency as VII. In the meantime, these results have been compared with a previously reported polymer, the poly(2‐[methacryloyloxy]ethyl oleate) (PMAEO), which demonstrated a lower VII efficiency compared with its analogous polymethacrylates containing an additional alkyl chain in their pendant chains.
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