PNNL

Abstract

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. These additives were designed with a comparable number of repeating units per arm and the number of arms was varied between 3 and 6. Well-defined star-shape PAMAs were synthesized by atom transfer radical polymerization (ATRP) via a core-first strategy from multi-functional head-groups. 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 over other structural features. Star-shape PAMAs, as oil additives, effectively reduce the friction coefficient in both mixed and boundary lubrication regimes. Several analogs outperformed commercial VIIs in both viscosity and friction performance. Unfortunately, increased wear rates were observed for these star-shape PAMAs in the boundary lubrication regime suggesting pressure sensitive conformations may exist.