Polymer Architecture: Does It Influence Shear Stability?

Abstract

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.

Tailor-Made Functional Polyolefins of Complex Architectures: Recent Advances, Applications, and Prospects

“…Dendrimers, hyperbranched polymers, and starlike architectures are potential candidates for emerging applications such as rheology modifiers and processing aids due to their desirable properties, including solubility and considerably low melt and solution viscosity. , Li et al described a new synthetic approach for preparing polysiloxane brushes with dendritic polyethylene ( M w = 5 to 28 kg mol –1 ) as the pendant group . This functional polyolefin was synthesized via CWP to obtain vinyl-terminated DPE followed by a thiol–ene coupling reaction with (3-mercaptopropyl) methyl dimethoxysilane (MPTDMS).…”

Facile Synthesis of Functionalised Hyperbranched Polymers for Application as Novel, Low Viscosity Lubricant Formulation Components

“…Rather, additional additives, including polymers, are used to reduce friction [6]. However, there are concerns related to polymeric additive shear stability in this context [7]. Traditionally, these additives are amphiphilic molecules, i.e., they contain both a straight-chain hydrocarbon "tail" group and a polar "head" group, such as amines, amides, carboxylic acids and phosphoric/phosphonic acids.…”

Core-Crosslinked Star Copolymers as Viscosity Index Improvers for Lubricants

“…Among these, PMAs hold a special position due to the availability of a large number of methacrylic monomer alkyl groups of different chain lengths, which enabled a variety of copolymers to be prepared with tuned solubility, thickening efficiency, and VIs. − Moreover, a wide variety of architectures can be easily obtained using controlled or “living” radical polymerizations. − In this context, it is important to notice that although linear polymers are characterized by high thickening efficiency and a marked effect on VIs, polymers with branched architectures, including comb, star-shaped, and dendritic polymers, represent the best compromise between VI improvement and capability to resist chain breaking processes . In particular, star-shaped polymers, thanks to their globular structure, present a high shear stability even at a high molecular weight. − …”