Effect of Copolymer Structure on Rare‐Earth‐Element Chelation Thermodynamics

Archer, William R.; Thompson, Tiffany N; Schülz, Michael

doi:10.1002/marc.202000614

Cited by 9 publications

(19 citation statements)

References 35 publications

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“…Each polymer–REE interaction was endothermic, and we observed relatively large values for |− T Δ S| . These entropy–driven interactions are largely the result of releasing bound water molecules surrounding the polymer and REE ion, consistent with previous observations in both polymer–metal and protein–metal binding thermodynamics. ,− Interestingly, we observed larger |Δ H | and |− T Δ S | values for the more isotactic PMAAs (Figures and A,B), with only slight variations in Δ G across the series.…”

Section: Resultssupporting

confidence: 91%

Polymer Tacticity Effects in Polymer–Lanthanide Chelation Thermodynamics

Archer,

Chen,

Vaissier Welborn

et al. 2023

Macromolecules

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Metal-chelating polymers are critical components in numerous applications. However, despite the known influence of polymer tacticity on both bulk and solution properties, most materials used in metal-chelation applications are atactic. Here, we investigate the relationship between polymer tacticity and polymer–lanthanide interactions in aqueous solution. We synthesized a series of five poly(methacrylic acid)s with systematic variations in tacticity (20–99% m diads) and used isothermal titration calorimetry to measure the thermodynamics of lanthanide binding to each material (ΔH, ΔG, ΔS, K a, and stoichiometry). We observed enthalpy–entropy compensation across this tacticity series, finding that both |ΔH| and |ΔS| decreased with decreasing m diad content while ΔG remained similar. Molecular dynamics simulations of the polymer–metal interactions revealed that the observed differences in binding thermodynamics may be largely ascribed to differences in polymer flexibility. These combined experimental and computational results demonstrate that metal binding can be influenced by altering the polymer stereochemistry, ultimately influencing the design of more efficient metal-chelating materials.

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Section: Resultssupporting

confidence: 91%

Polymer Tacticity Effects in Polymer–Lanthanide Chelation Thermodynamics

Archer,

Chen,

Vaissier Welborn

et al. 2023

Macromolecules

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“…The thermodynamic profiles at these different ionic strengths ( Figure ) are consistent with our previous work [ 31–33 ] and other studies on polyelectrolyte binding, [ 44,45,54–57 ] showing an entropically favored binding interaction, presumably driven by the release of bound water molecules. As expected, the Gibbs free energy (ΔG) varies consistently with the binding affinity.…”

Section: Resultssupporting

confidence: 91%

Effect of Ionic Strength and Anion Identity on Rare‐Earth Element Chelation by Poly(acrylic acid)

Gallagher,

Schulz

2023

Macro Chemistry & Physics

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Rare‐earth elements (REEs) are critical components of many modern technologies, but their efficient separation and purification continue to pose significant challenges. Metal‐binding polymers may enable the development of promising alternative approaches to conventional separation techniques (e.g., solvent extraction), and insights into the interactions between the metal ions and polymers in solution are crucial to such development. In this work, we investigate the effect of ionic strength on the chelation of REEs by poly(acrylic acid) using isothermal titration calorimetry (ITC) to measure the metal‐binding thermodynamics. ITC experiments revealed that when ionic strength increases from increasing the sodium acetate buffer strength, polymer‐REE binding becomes increasingly disfavored. However, when ionic strength is increased by the addition of sodium chloride, binding again becomes increasingly disfavored, but to a lesser extent than when ionic strength increases from increasing the buffer strength. Additionally, the reduction in binding affinity was enthalpically driven when ionic strength was raised with sodium chloride, while it was entropically driven when raised with sodium acetate buffer, suggesting competive binding by the acetate ions. These results highlight the importance of ionic strength in polymer‐metal binding thermodynamics and will guide the development of new processes for the purification of critical metals.This article is protected by copyright. All rights reserved

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“…We used Eu 3+ as a representative lanthanide ion to study polymer-metal binding, having previously observed similar binding thermodynamics across a subset of lanthanide ions with poly(acrylic acid). 9 We conducted isothermal titration calorimetry (ITC) experiments by titrating small aliquots of a Eu 3+ solution into each polymer solution (pH 5 NaOAc-HOAc buffer) (Fig. S9-S13, ESI †).…”

Section: Resultsmentioning

confidence: 99%

“…[5][6][7] To probe these complexities, the thermodynamics (DG, DH, and DS) of the polymer-metal interaction have been studied: Binding is entropy driven, suggesting the critical role of water in REE chelation. 8,9 However, the intricate interactions among metal, polymer, and water make designing effective metalchelating materials a challenge. 10,11 Thus, understanding and ultimately controlling these interactions will enable more efficient and selective REE-extracting materials.…”

Section: Introductionmentioning

confidence: 99%