Synthesis and Rare-Earth-Element Chelation Properties of Linear Poly(ethylenimine methylenephosphonate)

Abstract

Rare-earth elements (REEs) are indispensable for modern technology; consequently, effective materials for REE extraction and separation are in demand. Polymeric chelators polymers with metal binding functional groupsare often used in these applications due to their low cost and high selectivity for target ions, with phosphonate-containing polymers often proving particularly effective. We synthesized linear poly(ethylenimine methylenephosphonate), a material previously made only with a branched architecture, and studied its rare-earth-element chelation properties as a function of molecular weight (7−680 kDa) and degree of phosphonation (0−85%) using isothermal titration calorimetry (ITC). ITC enabled the determination of the full thermodynamic profile (ΔG, ΔH, ΔS, K a , and stoichiometry) for each polymer−REE interaction in aqueous solution. We observed entropically driven metal−polymer binding with five REEs, independent of polymer molecular weight and degree of functionalization. Finally, we characterized the metal-ion-induced aggregation behavior of these polymers using dynamic light scattering.

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

“…Using ITC, we previously quantified the thermodynamics of REE binding to linear poly(ethylenimine methylenephosphonate) (PEI‐MP). [ 22 ] Here, we synthesized poly(acrylic acid‐ co ‐methyl acrylate) copolymers and examined the effect of copolymer composition on REE‐binding thermodynamics using ITC.…”

Exploring the role of polymer hydrophobicity in polymer–metal binding thermodynamics

“…[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.…”

Phosphonated Lower-Molecular-Weight Polyethyleneimines as Oilfield Scale Inhibitors: An Experimental and Theoretical Study

“…The water phase of the mixture reaction was then removed in vacuo, giving a phosphonated linear polyethyleneimine (linear PPEI-5000) as a pale yellow oil (2.1 g). 31 P NMR (D 2 O, 162.00 MHz): δ 19.78 ppm. For the synthesized branched PPEIs via the Moedritzer−Irani reaction, the percentage of all reactants (H 3 PO 3 , HCHO, and HCl) to aziridine monomer units was 3:1.…”

“…The synthesis route of PPEIs has been reported several times in the open literature under different synthetic approaches. 31,34,66,67 For example, Jensen et al synthesized a series of amino ethylenephosphonate-hyperbranched polyethyleneimines via the Michael addition reaction in the presence of a vinyl phosphonate monomer as a phosphonating agent. 67 The synthesized PPEIs were characterized and elucidated by The 31 P NMR chemical shifts of branched PPEI-600, 1200, and 2000 were recorded at δ 18.33, 17.67, and 15.40 ppm, respectively.…”