TITLE:
Compositionally Driven Viscometric Behaviors of Poly (Alkyl Methacrylates) in Lubricating Oils
AUTHORS:
Reid A. Patterson, Christopher P. Kabb, David M. Nickerson, Eugene Pashkovski
KEYWORDS:
Viscosity Index, Shear Stability Index, Polymethacrylates, Lubricating Oils
JOURNAL NAME:
Advances in Chemical Engineering and Science,
Vol.12 No.2,
March
23,
2022
ABSTRACT: Viscosity index (VI) and shear stability index (SSI)
are standard methods used in the lubricant industry to determine
temperature-viscosity dependency and resistance to product degradation,
respectively. A variety of oil-soluble polymers, including poly(alkyl
methacrylates) (PAMAs) are routinely used to control these properties in
fully-formulated liquid lubricants. In this report, we use reversible addition-fragmentation
chain transfer (RAFT) polymerization to precisely target identical degrees of
polymerization in a family of PAMAs with varying lauryl, hexyl, butyl, ethyl,
and methyl groups. Then, expanding on previous methodology reported in the literature,
we establish structure property relationships for these PAMAs, specifically
looking at how intrinsic viscosity [η]
and Martin interaction parameters KM relate to VI and SSI
characteristics. While the intrinsic viscosity [η] is associated with the volume of macromolecules at infinite
dilution, the parameter KM reflects the hydrodynamic
interactions of polymer chains at actual polymer concentrations in lubricating
oils. In this paper, we show that the dependence of VI on the non-dimensional
concentration c/c* (or c[η]) can be presented in a form of master
curve with shift factors proportional to KM that decreases
with increasing size of alkyl groups. This finding implies that even in the
dilute regime, the coil-expansion theory used to explain the effect of
macromolecules on VI should be complemented with the idea of hydrodynamic
interactions between polymer molecules that can be controlled by the choice of
alkyl chains in the family of PAMAs.