Effects of star‐shaped poly(alkyl methacrylate) arm uniformity on lubricant properties

Robinson, Joshua W.; Zhou, Yan; Qu, Jun; Erck, R.A.; Cosimbescu, Lelia

doi:10.1002/app.43611

Cited by 16 publications

(13 citation statements)

References 29 publications

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“…Star polymers are highly functional materials due to their compact, spatially defined, three-dimensional structure that leads to unique physical properties and increased opportunity for functionalization. They are currently used industrially as viscosity modifiers and lubricants, while potential applications in areas as varied as drug nanocarriers and interfacial stabilizers are also being investigated. − Star polymers consist of linear arms that radiate from a central core and can be synthesized using a variety of controlled radical polymerization methods. Synthesis via reversible addition–fragmentation chain transfer (RAFT) polymerization has received significant attention and can be performed using either an arm-first or core-first approach .…”

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confidence: 99%

Highly Living Stars via Core-First Photo-RAFT Polymerization: Exploitation for Ultra-High Molecular Weight Star Synthesis

et al. 2019

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Star polymers are highly functional materials that display unique properties in comparison to linear polymers, making them valuable in a wide range of applications. Currently, ultra-high molecular weight (UHMW) star polymers synthesized using controlled radical polymerization are prone to termination reactions that have undesirable effects, such as star–star coupling. Herein, we report the synthesis of the largest star polymers to date using controlled radical techniques via xanthate-mediated photo-reversible addition–fragmentation chain transfer (RAFT) polymerization using a core-first approach. Polymerization from xanthate-functionalized cores was highly living, enabling the synthesis of well-defined star polymers with molecular weights in excess of 20 MDa.

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confidence: 99%

Highly Living Stars via Core-First Photo-RAFT Polymerization: Exploitation for Ultra-High Molecular Weight Star Synthesis

et al. 2019

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“…The tetra‐armed star‐shaped styrenic copolymers having pyrene side groups [ (S1‐S3)‐Pyr ] were prepared using core‐first approach (Scheme ), by which the number of arms of the star polymer could be clearly defined and would be equal to the number of the functional units on the polymerization‐initiating compound . Besides, this method provides good control on the macromolecular architecture .…”

Section: Resultsmentioning

confidence: 99%

Pyrene‐functional star polymers as fluorescent probes for nitrophenolic compounds

Taşcı

Aydın

Görür

et al. 2018

J of Applied Polymer Sci

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Novel tetra-armed star-shaped styrenic copolymers with pyrene side groups [(S1-S3)-Pyr] were prepared and employed as fluorescence sensing probe for fast and sensitive determination of nitroaromatic compounds. (S1-S3)-Pyr depicted characteristic pyrene monomer emission signals as well as broad excimer bands in their fluorescence emission spectra due to close proximity of the pyrene groups on the polymer chains and the ratio of monomer to excimer emission intensities gradually decreased as the pyrene content of the star polymers were increased from S1-Pyr to S3-Pyr. The highest quenching efficiency in the presence of 25 equivalent nitroaromatics was observed for 2,4,6-trinitrophenol/picric acid (99.4%) followed by 2,4-dinitrophenol (84.2%), 4-nitrophenol (82.6%), 2,4,6-trinitrotoluene (44.0%), 2,4-dinitrotolunene (32.6%), and 4-nitrotoluene (28.8%). Superior quenching efficiencies of nitrophenolic compounds were ascribed to their strong binding affinity for (S1-S3)-Pyr due to the acidity of phenolic hydroxyl units. Besides, quenching ratios of S1-Pyr, S2-Pyr, and S3-Pyr were measured to be very close to each other. Thus, (S1-S3)-Pyr are considered to be highly selective and sensitive fluorescence probes for phenolic nitroaromatic compounds.

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“…To increase the resilience against shear-induced degradation, polymers with a branched architecture are preferred. The viability of this strategy has been verified both experimentally and by simulation studies, where polymers with varying architectures (linear, star, ring, H-, and comb-shaped) were subjected to high-shear conditions. ,− Although the presence of branch points enhances mechanical stability, they also introduce conformational constraints on the swelling behavior. The viscosity-improving performance of a given additive is, therefore, a trade-off between thickening efficiency and resilience against mechanical degradation or additive lifetime.…”

Section: Introductionmentioning

confidence: 99%

“…recently developed polymeric additives combining bulk viscosity improvement with friction-reducing properties. The (hyper)branched structures based on poly(alkyl methacrylate) and poly(ethylene) chemistries were evaluated, and the authors suggested the beneficial effect of branched architecture for (boundary) lubrication purposes. ,,, Particular attention was given to the incorporation of hydrophilic moieties into the polymer backbone to facilitate surface adsorption and formation of lubrication layers. However, the presence of hydrophilic fragments negatively impacted the bulk viscosity improving performance which can be attributed to a lower tendency to undergo temperature-induced swelling when dissolved in highly apolar base oils. , …”

Section: Introductionmentioning

confidence: 99%

Triple Function Lubricant Additives Based on Organic–Inorganic Hybrid Star Polymers: Friction Reduction, Wear Protection, and Viscosity Modification

Ravensteijn¹,

Zerdan²,

Seo³

et al. 2018

ACS Appl. Mater. Interfaces

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Polymer-based lubricant additives for friction reduction, wear protection, or viscosity improvement have been widely studied. However, single additives achieving all three functions are rare. To address this need, we have explored the combination of polymer topology with organic–inorganic hybrid chemistry to simultaneously vary the temperature- and shear-dependent properties of polymer additives in solution and at solid surfaces. A topological library of lubricant additives, based on statistical copolymers of stearyl methacrylate and methyl methacrylate, ranging from linear to branched star architectures, was prepared using ruthenium-catalyzed controlled radical polymerization. Control over the polymerization yielded additives with low dispersity and comparable molecular weights, allowing evaluation of the influence of polymer architecture on friction reduction, wear protection, and bulk viscosity improvement in a commercial base oil (Yubase 4). Structure–performance relationships for these functions were assessed by a combination of a high-speed surface force apparatus (HS-SFA) experiments, wear track profilometry, quartz crystal microbalance analysis, and solution viscometry. The custom-built HS-SFA provides a unique experimental environment to measure the boundary lubrication performance under extreme shear rates (≈107 s–1) for prolonged times (24 h), mimicking the extreme conditions of automotive applications. These experiments revealed that the performance of the additives as boundary lubricants and wear protectants scales with the degree of branching. The branched architectures prohibit ordering of the additives in thin films under high-load conditions, leading to a thicker absorbed polymer brush boundary layer and therefore enhanced film fluidity and lubricity. Additionally, star polymers with increasing arm number lead to bulk viscosity modification, reflected by a significant increase in the viscosity index compared to the commercial base oil. Although outperformed by linear polymers for bulk viscosity improvement, the (hybrid) star polymers successfully combine the three distinct lubricant additive functions: friction reduction, wear protection, and bulk viscosity improvementin a single polymeric structure. It should also be noted that, judging from HS-SFA experiments, hybrid stars carrying a silicate-based core outperform their fully organic analogues as boundary lubricants. The enhanced performance is most likely driven by attractive forces between the silicate cores and the employed metallic surfaces. Combining three function in one minimizes formulation complexity and thus opens a route to fundamentally understand and formulate key design parameters for the development of novel multifunction lubricant additives.

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Effects of star‐shaped poly(alkyl methacrylate) arm uniformity on lubricant properties

Cited by 16 publications

References 29 publications

Highly Living Stars via Core-First Photo-RAFT Polymerization: Exploitation for Ultra-High Molecular Weight Star Synthesis

Highly Living Stars via Core-First Photo-RAFT Polymerization: Exploitation for Ultra-High Molecular Weight Star Synthesis

Pyrene‐functional star polymers as fluorescent probes for nitrophenolic compounds

Triple Function Lubricant Additives Based on Organic–Inorganic Hybrid Star Polymers: Friction Reduction, Wear Protection, and Viscosity Modification

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