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It’s Better with Salt: Aqueous Ring-Opening Metathesis Polymerization at Neutral pH

Foster, JC; Grocott, MC; Arkinstall, LA; Varlas, S; Redding, MJ; Grayson, SM; O'Reilly, RK; (2020) It’s Better with Salt: Aqueous Ring-Opening Metathesis Polymerization at Neutral pH. Journal of the American Chemical Society 10.1021/jacs.0c05499. (In press). Green open access

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Abstract

Aqueous ring-opening metathesis polymerization (ROMP) is a powerful tool for polymer synthesis under environmentally-friendly conditions, functionalization of biomacromolecules, and preparation of polymeric nanoparticles via ROMP-induced self-assembly (ROMPISA). Whilst new water-soluble Ru-based metathesis catalysts have been developed and evaluated for their efficiency in mediating cross metathesis (CM) and ring-closing metathesis (RCM) reactions, less is known with regards to their catalytic activity and stability during aqueous ROMP. Here, we investigate the influence of solution pH, the presence of salt additives, and catalyst loading on key parameters typically utilized to assess polymerizations such as monomer conversion, molecular weight, and molecular weight distribution. We find that ROMP in aqueous media is particularly sensitive to chloride ion concentration, and propose that this sensitivity originates from chloride ligand displacement by hydroxide or H_{2}O at the Ru center which reversibly generates an unstable and metathesis inactive complex. The formation of this Ru-(OH)n complex not only reduces monomer conversion and polymerization control but also influences polymer microstructure. However, we find that addition of chloride salts dramatically improves ROMP conversion and control. By carrying out aqueous ROMP in the presence of various chloride sources such as NaCl, KCl, or tetrabutylammonium chloride, we show that di- and triblock polymers can be readily synthesized in solutions with high concentrations of neutral H_{2}O (i.e., 90 v/v%) and relatively low concentrations of catalyst (i.e., 1 mol%). The capability to conduct well-controlled aqueous ROMP at neutral pH is anticipated to enable new research avenues, particularly for applications in biological media, where the unique characteristics of ROMP provide distinct advantages over other polymerization strategies.

Type: Article
Title: It’s Better with Salt: Aqueous Ring-Opening Metathesis Polymerization at Neutral pH
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/jacs.0c05499
Publisher version: https://doi.org/10.1021/jacs.0c05499
Language: English
Additional information: © 2020 American Chemical Society with CC-BY license (https://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html).
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10106461
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