Role of Architecture on Thermorheological Properties of Poly(alkyl methacrylate)-Based Polymers

Abstract

Oil-soluble poly(meth)acrylate-based polymers play a vital role in the thermorheological modification of a wide variety of lubricants and formulated consumer products, where increased viscosity at elevated temperatures ensures sufficient viscosity over a broad temperature range. The assumed mechanism of viscosity modification for many such polymers is based on temperature-induced swelling due to marginal solvent quality. Although this mechanism is widely accepted, direct and consistent experimental proof is limited due to a lack of structural characterization over a wide temperature range. Additionally, the effect of polymer architecture on the temperature-dependent solution behavior is not fully understood, despite the trend toward branched polymers in recent years. Here, we provide a comprehensive set of data relying on detailed temperature-dependent viscosity measurements, dynamic light scattering (DLS), and small-angle neutron scattering (SANS) experiments to confirm the existence of temperature-induced coil expansion for industrially relevant poly(stearyl methacrylate-co-methyl methacrylate) (p(SMA-co-MMA)) polymers with various architectures including linear, randomly branched, and star-shaped topologies. Compared to the linear and randomly branched polymers, the degree of coil expansion for the star-shaped additives is significantly lower. Regardless of the polymer architecture, the propensity to undergo temperature-induced chain swelling proved to be highly specific toward the type of base oil, underlining the sensitive interplay between polymer and oil chemistry required for designing successful thermorheological modifiers.