Multifunctional Tunable Polymethacrylates for Enhanced Shear Stability and Wear Prevention

Abstract

This paper describes the design, synthesis, and characterization of linear, polar, and nonpolar polymethacrylates designed for use as lubricant viscosity index (VI) improvers with enhanced shear and antiwear resistance. The polymers were prepared via reversible addition–fragmentation chain transfer to obtain relatively low and narrow molecular weights, with random polar moieties. The resulting polymers were evaluated as oil solutions to determine their VI, shear stability performance, and antiwear characteristics. The polymers had molecular weights (Mw) ranging from 120 to 170 kDa, and the resulting VIs, in general, tracked the Mw. Although the VIs were modest (140–189), all polymers displayed higher values than a commercial product designed for similar applications, both at 2% (w/w) and when kinematic viscosities (KVs) were normalized to the lowest KV100 of ∼6 cSt. One of the imidazole-containing polymers displayed an anomalously high VI for a low apparent Mw. As hypothesized, many of the polar polymers demonstrated substantial wear reduction compared to the nonpolar homopolymers or a commercial benchmark. The low-molecular weight imidazole-containing polymer produced less than 4% of the wear displayed by the commercial standard. The higher molecular weight polymers containing imidazole, hydroxy group, and amino group also produced as little as 10% of the wear shown by the benchmark. The strategy demonstrated the benefit of low and narrow molecular weight polymers to achieve good shear stability in viscosity modifiers while minimizing wear, rendering them suitable for fluid power applications.