Altering the effectiveness of radical traps in atom transfer radical coupling reactions of polymer chains

Wu, Jessica P.; Pan, Ching W.; Heiler, Katherine E.; Ching, Megan E.; Tillman, Eric S.

doi:10.1016/j.polymer.2017.08.046

Cited by 10 publications

(14 citation statements)

References 33 publications

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“…β‐CD as the reducing agent provided an interesting test, as β‐CD is known to encapsulate the nitroso radical trap used in these systems . There is even evidence that β‐CD may lead to higher amounts of the active monomeric form of MNP, which exists in an equilibrium with inactive aggregates . However, as can be visualized in Figure (bottom), the extent of coupling in the presence of β‐CD was far lower compared to the other two reducing agents (Table , trials 7–9).…”

Section: Resultsmentioning

confidence: 99%

Atom transfer coupling reactions performed with benign reducing agents and radical traps

Xia

Rubaie²,

Johnson³

et al. 2019

J. Polym. Sci. Part A: Polym. Chem.

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Monobrominated polystyrene (PSBr) was prepared by ATRP, and the resulting chain ends were activated in the presence of radical traps to induce chain end-coupling. In atom transfer radical coupling (ATRC) with radical trap assistance, to achieve significant coupling requires excess metal catalyst, ligand, and a reducing agent that is often additional metal. In this work, activators generated by electron transfer (AGET) and radical trap assistance are used in the ATRC sequence to successfully lead to chain-end coupling without the need for the oxidatively unstable copper (I) and with environmentally friendlier agents in place of copper metal. High extents of coupling (Xc) were achieved using ascorbic acid (AA) as the reducing agent and copper(II) bromide as the oxidized version of the catalyst, and when combined with AGET ATRP to prepare the PSBr precursor, only a fraction of the total metal was required compared to traditional atom transfer reactions, while still retaining similar Xc values.

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Section: Resultsmentioning

confidence: 99%

Atom transfer coupling reactions performed with benign reducing agents and radical traps

Xia

Rubaie²,

Johnson³

et al. 2019

J. Polym. Sci. Part A: Polym. Chem.

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“…Two radical traps, MNP and nitrosobenzne (NBz) were added in varying equivalents to redox active solutions of PSBr. Previous research by our group has shown that both MNP and/or NBz act as radical traps in ATRC‐like reactions leads to high amounts of coupling for end‐halogenated polystyrene (PS), poly(methyl methacrylate), and poly(methyl acrylate), producing either coupled polymer dimers or cyclic polymers. This so‐called RTA‐ATRC is summarized in Scheme , along with the desired nitroxide‐capped intermediate (boxed).…”

Section: Resultsmentioning

confidence: 99%

“…The combination of GPC, UV–vis, and EPR spectroscopy provided the most compelling evidence of the end group transformation, while 1 H NMR was not found to be useful as both the precursor (PSBr) and nitroxide‐capped polymer product showed only the characteristic signals of polystyrene. Our group has previously shown that coupled chain ends resulting from the reaction shown in Scheme contains the mid‐chain alkoxyamine as a consequence of the radical trap using MALDI‐TOF …”

Section: Resultsmentioning

confidence: 99%

“…As shown in Figure and tabulated in Table 3 , a substantial amount of the PS‐nitroxide did not participate in the coupling reaction and remained in the reaction mixture of the product, with the extent of coupling ( X c ) not exceeding 30%. The relative ineffectiveness of the nitroxide‐capped polymer to trap another polymer radical, when it is well known to do so in RTA‐ATRC sequences, suggests that not all the nitroxide label was active. This may be consistent with the EPR spectrum in Figure , which showed unusual fine detail not necessarily expected in nitroxide‐labeled macromolecules.…”

Section: Resultsmentioning

confidence: 99%

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Synthesis of Nitroxide End‐Labeled Polymers by Capturing Polystyrene Radicals with Spin Traps

Heiler

Pan

Heiler

et al. 2018

Macro Chemistry & Physics

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Atom transfer radical polymerization is used to synthesize brominated polystyrene, and the alkyl halide chain end is transformed into a nitroxide radical by the addition of excess nitrosobenzene to a redox active reaction mixture. The nitroxide group at the chain is verified using gel permeation chromatography, UV–vis, and electron paramagnetic resonance spectroscopy, showing the addition of the nitroso group does not result in a doubling of molecular weight, with the resulting polymer possessing new absorptions in the 300–400 nm range and an unpaired electron. The nature of the radical trap plays a role in halting the reaction at the end‐capped nitroxide polymer, rather than undergoing dimerization via atom transfer radical coupling‐type pathways. The polymeric nitroxide radical can be used to trap a second polymer radical in a subsequent reaction, simply by reacting with a second bromine‐capped polymer and adjusting the redox activity of the solution.

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“…Note that the magnitude of K ATRP plays a role in the rate of coupling in both cases, but plays a greater role in ATRC reactions lacking a radical trap. Furthermore, the ability of 2‐methyl‐2‐nitrosobenzene (MNP) to trap a polymer radical, ( k 1 in Scheme ), is tied to the polarity of the solvent, which alters the aggregation and reactivity of the radical trap toward the alkyl radicals …”

Section: Introductionmentioning

confidence: 99%

Effect of Aromatic Co‐Solvents on the Efficiency of Atom Transfer Radical Coupling Reactions of Fluorinated and Non‐Fluorinated Vinyl Aromatic Polymers

Ching

Lee

et al. 2019

Macro Chemistry & Physics

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Monobrominated versions of poly(pentafluorostyrene) (PPFSBr), polystyrene (PSBr), and poly(methyl acrylate) (PMABr) are prepared by atom transfer radical polymerization (ATRP) and employed in a variety of atom transfer radical coupling (ATRC)‐type reactions to observe the impact of external aromatic faces on the extent of coupling (Xc). In ATRC reactions assisted with the radical trap 2‐methyl‐2‐nitrosopropane (MNP), Xc is nearly unchanged when the electron‐rich benzene co‐solvent (50% v/v with THF) is replaced with the electron‐poor hexafluorobenzene (HFB) for PSBr and PMABr. In the case of PPFSBr, the addition of benzene to the reaction mixture results in far lower extents of coupling (Xc < 0.2). 1H NMR spectra of the radical trap MNP in HFB show greater aggregation to the inactive form, compared to the spectra obtained in benzene. To remove the effect of the radical trap interacting with the aromatic co‐solvent and altering the rate of coupling, traditional ATRC reactions are performed with the same co‐solvent systems and, in this case, HFB results in higher Xc values across all polymer types. This is consistent with HFB pushing the position of the KATRP further toward the active radical, while benzene increases the reactivity of the MNP radical trap.

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Altering the effectiveness of radical traps in atom transfer radical coupling reactions of polymer chains

Cited by 10 publications

References 33 publications

Atom transfer coupling reactions performed with benign reducing agents and radical traps

Atom transfer coupling reactions performed with benign reducing agents and radical traps

Synthesis of Nitroxide End‐Labeled Polymers by Capturing Polystyrene Radicals with Spin Traps

Effect of Aromatic Co‐Solvents on the Efficiency of Atom Transfer Radical Coupling Reactions of Fluorinated and Non‐Fluorinated Vinyl Aromatic Polymers

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