Rate Constants for the Trapping of Various Carbon-Centered Radicals by Nitroxides:  Unimolecular Initiators for Living Free Radical Polymerization

Skene, W. G.; Scaiano, Juan C.; Listigovers, Nancy A.; Kazmaier, Peter M.; Georges, Michaël K.

doi:10.1021/ma991753c

Cited by 60 publications

(70 citation statements)

References 54 publications

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“…Furthermore, the substituent at C-4 is too far away to influence the kinetics. This result is consistent with an earlier report about the substituent of benzoyloxy at the 4-position of TEMPO does not influence the trapping kinetics [6]. The nature of the chain ends for polymers derived from Ini2 and Ini3 as these units were probed by observing the 1 H-NMR spectra of the resultant polymers R2 and R3.…”

Section: Polymerization Of Styrenesupporting

confidence: 91%

One-step formation of two new unimolecular initiators on the basis of styrene and HO-TEMPO

Yin¹,

Wang²,

Бауер³

et al. 2005

Designed Monomers and Polymers

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2005) One-step formation of two new unimolecular initiators on the basis of styrene and HO-TEMPO, Designed Monomers and Polymers, 8:3, 211-221To link to this article: http://dx.Abstract-Two kinds of modified unimolecular initiators for nitroxide-mediated radical polymerization were formed in a one-step and one-pot BPO initiated reaction of styrene with 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HO-TEMPO) involving an additional oxidation reaction. Their ability to initiate and to control the radical polymerization of styrene was verified and the newly produced initiators did not show any differences compared to the well-known TEMPO-based initiator. 1 H-NMR spectra of the resultant polymers showed the presence of the end-group in the functionalized polymers. HO-TEMPO used in a bimolecular initiator system gave similar results as the significantly more expensive TEMPO, but in general the use of unimolecular initiators gives a better control over the molecular weight of the polymers synthesized.

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Section: Polymerization Of Styrenesupporting

confidence: 91%

One-step formation of two new unimolecular initiators on the basis of styrene and HO-TEMPO

Yin¹,

Wang²,

Бауер³

et al. 2005

Designed Monomers and Polymers

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“…Alkyl radicals were generated by photolysis of the corresponding symmetric ketones, and their decay was monitored at the absorption maximum of 315 nm. 41 In the absence of nitroxides,…”

Section: Scheme 1 Simplified Reaction Scheme Of Nmp Chart 1 Structumentioning

confidence: 99%

pH-Sensitive C–ON Bond Homolysis of Alkoxyamines of Imidazoline Series with Multiple Ionizable Groups As an Approach for Control of Nitroxide Mediated Polymerization

et al. 2011

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Recently, a new concept of pH-switchable agents for reversible addition-fragmentation chain transfer (RAFT) polymerization has been introduced by Benaglia et al. (J. Am. Chem. Soc.2009, 131, 6914-6915). In this paper we extended the concept of pH-switchable mediators to nitroxide mediated polymerization (NMP) by employing nitroxides with basic or acidic groups as controlling agents. Four alkoxyamines, the derivatives of 2-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-2-(pyridin-4-yl)-2,5-dihydro-1H-imidazol-1-oxyl and 2-(2-carboxyethyl)-5,5-diethyl-2,4-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl, have been prepared. The influence of pH on alkoxyamine homolysis rate constants (k(d)) and on the nitroxide-alkyl radical recombination rate constants (k(c)) was studied. All alkoxyamines under study as well as the parent nitroxides have several basic groups, which under pH variation can undergo consecutive protonation. It was shown that the k(d) value under basic conditions are significantly (up to 15-fold) higher than in acidic solution at the same temperature, whereas the k(c) value in basic solutions decrease by a factor of 2 only. The efficiency of NMP is known to be dependent on k(d) and k(c), both constants being dependent on the monomer structure; therefore the performance of NMP of different monomers in the controlled mode requires different conditions. It is shown that the pH value crucially affects the polymerization regime, changing it from the controlled to the uncontrolled mode. The controlled regime of NMP of different hydrophilic monomers (sodium 4-styrenesulphonate and acrylamide) in aqueous solution under mild conditions (90 °C) can be achieved using the same alkoxyamine by the variation of the pH value. The chain length of polymers depends on pH value during the polymerization.

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“…181 However, Scheme 16 DTBN is thermally robust and has been used in NMPs. [182][183][184][185][186][187][188] One might also propose the loss of the tbutyl cation from oxammonium intermediate 65. This is also unlikely, as DTBN has been used catalytically in the oxammonium-mediated oxidations of alcohols.…”

Section: Proposed A-hydrogen Nitroxide Decomposition Mechanismmentioning

confidence: 99%

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Nilsen

Braslau

2005

J. Polym. Sci. A Polym. Chem.

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ABSTRACT:Nitroxides bearing an a-hydrogen decompose upon heating in a bimolecular reaction. A new mechanism is proposed for the decomposition of t-butylisopropylphenyl nitroxide (TIPNO) involving the formation of a head-to-tail dimer, single electron transfer to form an oxammonium salt, epimerization to the corresponding nitrone, and elimination to form a conjugated oxime. This mechanism may provide insights into designing new nitroxides for use in controlled polymerization.

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Rate Constants for the Trapping of Various Carbon-Centered Radicals by Nitroxides: Unimolecular Initiators for Living Free Radical Polymerization

Cited by 60 publications

References 54 publications

One-step formation of two new unimolecular initiators on the basis of styrene and HO-TEMPO

One-step formation of two new unimolecular initiators on the basis of styrene and HO-TEMPO

pH-Sensitive C–ON Bond Homolysis of Alkoxyamines of Imidazoline Series with Multiple Ionizable Groups As an Approach for Control of Nitroxide Mediated Polymerization

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

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