Polymer Architecture: Does It Influence Shear Stability?

Hyperbranched and linear poly­(alkyl methacrylate)­s with and without polycaprolactone segments were designed and prepared via a core-first strategy, and then evaluated with respect to their rheology and shear stability performance. The focus of this work was to study the effect of architecture on mechanical shear stability, as it relates to lubricant performance. The polymers were prepared from functionalized macroinitiators subsequently subjected to atom transfer radical polymerization (ATRP)/activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) conditions with dodecyl methacrylate and 2-ethylhexyl methacrylate mixtures. As expected, most compounds displayed an increased viscosity index along with increasing molecular weight. The inclusion of polycaprolactone appears to have enhanced the viscosity index in select samples. Although the hyperbranched polymers studied here varied in the number of arms from about 20 to 1 (linear), the data presented supports the empirical understanding that shear stability is mainly influenced by molecular weight and not architecture or topology. The polymers with caprolactone blocks and shorter methacrylate pendants demonstrated a positive effect on the shear stability, as in possessing the lowest permanent shear stability index, 4 times lower than other compounds included in this study as well as the benchmark.