It is Better with Salt: Aqueous Ring-Opening Metathesis Polymerization at Neutral pH.

Autor: Foster JC; School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom., Grocott MC; School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom., Arkinstall LA; School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom., Varlas S; School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom., Redding MJ; Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States., Grayson SM; Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States., O'Reilly RK; School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
Jazyk: angličtina
Zdroj: Journal of the American Chemical Society [J Am Chem Soc] 2020 Aug 12; Vol. 142 (32), pp. 13878-13885. Date of Electronic Publication: 2020 Aug 03.
DOI: 10.1021/jacs.0c05499
Abstrakt: 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). Although 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, little 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 ROMP monomer conversion and catalyst lifetime. 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 catalyst lifetime but also influences polymer microstructure. However, we find that the 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 diblock copolymers can be readily synthesized via ROMPISA 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 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.
Databáze: MEDLINE