Exploiting Polymer Architecture and Molecular Composition Towards Performance Enhancing Lubricant Additives

Exploiting Polymer Architecture and Molecular Composition towards Performance Enhancing Lubricant Additives

Lelia Cosimbescu^‡*, Joshua W. Robinson^‡, Jun Qu^†, Yan Zhou^†, J. Timothy Bays^‡,

^‡Pacific Northwest National Laboratory, Richland, WA

^†Oak Ridge National Laboratory, Oak Ridge, TN

Abstract

Lubricant packages are comprised of a myriad of additives and are responsible for up to 30 wt % of the blended oil. Generally, each additive plays a mono-functional role and are formulated together to increase engine oil performance. Additives also increase the overall cost of lubricants which requires a careful critique of the cost-benefit relationship. Combining the beneficial effects of 2 or more lubricity enhancing additives would reduce formulation challenges and cost. Viscosity modifiers and/or viscosity index improvers reduce the natural thinning effect that lubricants experience with increasing temperature. These additives are typically polymeric in nature and exploit principles of polymer dynamics to mitigate viscosity losses of the lubricant at elevated temperatures thereby maintaining desirable lubricity such as in the reduction of friction. Friction modifiers are generally relatively small compounds/molecules that interact more directly with internal surfaces and reduce friction via thin film formations. By exploiting modern polymer preparation techniques in regards to architecture and molecular composition, we have designed and investigated these additives as viscosity and friction modifiers. Our polymeric structures encompass beneficial characteristics of these two separate additives providing the first duel-functional lubricant additive that may increase fuel economy by reducing friction on two fronts within an internal combustion engine. We investigated several promising polymer classes ranging from hyperbranched polymers to comb-burst hyperbranched analogs, modified polyethylene-based polymers and finally hybrid star polymers. The latter topologies appear to be the most promising in providing the VII properties required of an engine oil additive. We will discuss synthetic methodologies as they pertain to controlling the topology of the polymers, characterization and the effects of structure and topology on viscosity and friction.