(PNNL), Richland, WA (United States) Argonne National Lab. (ORNL), Oak Ridge, TN (United States) Pacific Northwest National Lab. Publication Date: Research Org.: Oak Ridge National Lab. Unfortunately, increased wear rates were observed for these star-shape PAMAs in the boundary lubrication regime suggesting pressure sensitive conformations may exist. Several analogs outperformed commercial VIIs in both viscosity and friction performance. Star-shape PAMAs, as oil additives, effectively reduce the friction coefficient in both mixed and boundary lubrication regimes. Observations of the polymer-oil blends suggest that stars with less than four arms are favorable as a viscosity index improver (VII), though molecular weight dominates viscosity related effects. Well-defined star-shape PAMAs were synthesized by atom transfer radical polymerization (ATRP) via a core-first strategy from multi-functional head-groups. These additives were designed with a comparable number of repeating units per arm and the number of arms was varied between 3 and 6. Star-shape poly(alkyl methacrylate)s (PAMAs) were prepared and blended into an additive free engine oil to assess the structure-property relationship between macromolecular structure and lubricant performance.
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