Nitroxide‐Mediated Polymerization of Methyl Methacrylate Using an SG1‐Based Alkoxyamine: How the Penultimate Effect Could Lead to Uncontrolled and Unliving Polymerization

Guillaneuf, Yohann; Gigmès, Didier; Marque, Sylvain R. A.; Tordo, Paul; Bertin, Denis

doi:10.1002/macp.200600125

Cited by 116 publications

(156 citation statements)

References 52 publications

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“…However, no ambiguous discussions were provided on the origin of this effect. At a first glance, although this led to apparently contradictory measurements [10,15,16], such small differences in k d may look unimportant, but nevertheless, we have recently shown that the fate of NMP [11,12,17] and the occurrence of side-reactions [18] depends on such small differences.…”

Section: Introductionmentioning

confidence: 97%

“…During the last decade, the effect of the penultimate unit on the C-ON bond was poorly investigated, and seemingly contradictory results were published concerning polystyryl-TEMPO alkoxyamines. Until recently, it has been shown [10] that the penultimate unit may exert a dramatic effect on the C-ON bond homolysis and, consequently, on the fate of NMP [11,12]. Georges and colleagues [13] measured the C-ON bond homolysis in the diastereoisomers of styryl dyads of TEMPO-based alkoxyamines 7 ( Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO

et al. 2010

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Abstract:The rate constants k d of the homolysis of the C-ON bond in styryl dyads TEMPO-based alkoxyamines have recently been published (Li et al. Macromolecules 2006, 39, 9201). The diastereoisomers exhibited different values which were higher than for the unimer TEMPO-styryl alkoxyamine 1. At a first glance, the localization of the steric strain was not obvious. To decipher this problem, diastereoisomer models 2 (RR/SS) and 3 (RS/SR), as well as the released alkyl radicals, were calculated at the \B3LYP/6-31G(d) level. It was revealed that the increase in k d from 1 to 3 was due to the compression (buttressing effect) of the reactive center by the second styryl moiety. The difference in k d for the diastereoisomer was clearly an activation entropy effect S ≠ because the alkyl fragment of the RS/SR diastereoismer exhibited the same conformation as the released radical whereas the conformation for the RR/SS diastereoisomer was quite different and thus required the rotation of several bonds to reach the correct TS, which cost S ≠ , and thus lowers k d .

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO

et al. 2010

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“…As it was shown by Tordo and co-workers [38], the correct calculation of NMP could be done only by taking account of the k d and k c dependence on the length of the polymer chain. Therefore, k d and k c values implemented in the phase diagrams À2 mol/l, k p = 1298 l mol À1 s À1 , k t = 3.21 · 10 7 l mol À1 s À1 (see [8]), values of k c1 and k d from Table 3.…”

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confidence: 97%

2,5‐Dihydro‐1H‐imidazole‐Based Nitroxides as Prospective Mediators in Living Radical Polymerization

Zubenko

Kirilyuk

Roshchupkina

et al. 2006

Helvetica Chimica Acta

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Dedicated to the memory of Professor Hanns FischerA number of spectroscopic methods were applied to obtain kinetic parameters of reactions modelling the 2,5-dihydro-1H-imidazole 1-oxide mediated living polymerization of acrylates. The homolysis rate constants of alkoxyamines based on five nitroxides were measured by EPR spectroscopy at different temperatures. The recombination rate constants k c between the corresponding alkyl radicals and the nitroxides were measured by means of laser flash photolysis. The time-resolved chemically induced dynamic nuclear polarization (TR-CIDNP) experiments revealed the negligible contribution of disproportionation in the recombination reaction. In addition, the thermodecomposition of alkoxyamines in the NMR probe showed the absence of intramolecular elimination of hydroxylamines from the corresponding alkoxyamines. Analysis of the kinetic parameters showed that the 2,5-dihydro-1H-imidazole 1-oxide type radicals are promising mediators for the living polymerization of acrylates and methacrylates.Introduction. -Nitroxide-mediated polymerization [1] [2] (NMP) is a fine synthetic technique, which allows for the design of new types of homo-and copolymers with welldefined architectures and narrow molecular-mass distributions [3]. The principal mechanism of NMP (Scheme 1) involves the reversible dissociation of a dormant nitroxide end-capped polymer chain with rate constant k d , the propagation of C-centered radicals with rate constant k p , the cross-coupling reaction between the nitroxide and the growing polymer chain with rate constant k c , and simultaneous irreversible self-termination reactions of the C-centered radicals with rate constant k t .

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“…However, it has appeared in the literature that values of k c may play an important role in the fate of the polymerization [19] [20]. Siegenthaler and Studer [20] have shown that the polymerization was ca.…”

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confidence: 98%

Re‐formation Reaction of Cyclic Nitroxide‐Based Alkoxyamines: Steric and Polar/Stabilization Effects

Fischer

Marque²,

Nesvadba

2006

Helvetica Chimica Acta

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Dedicated to Professor Hanns Fischer for his invaluable contribution in the fields of nitroxide-mediated polymerization and radical chemistryIn nitroxide-mediated radical polymerization, the polymerization times decrease with the increasing re-formation rate constant of the CÀON bond (! alkoxyamine) between the growing polymer chain and the nitroxide radical. The factors influencing the re-formation rate constant are of considerable interest, but up to now, the polar/stabilization effects have not been addressed thoroughly. The combination of new data with previously reported data now showed that the re-formation rate constant k c increases with the increasing polar character of the substituents attached to the nitroxide moiety. The polar/stabilization effects are weaker for the re-formation than for the homolysis of the CÀON bond, and may be mainly attributed to the relocation of the odd electron onto the O-atom of the NÀO moiety, i.e., the stabilization of the nitroxide moiety. Hence, it is possible to predict the values of k c by combining both the polar/stabilization (s I ) and steric effects (E , nitroxide-mediated radical polymerization (NMP) has often been used for the synthesis of living polymers and copolymers with narrow polydispersities and controlled molecular masses and architecture [4 -6]. The mechanism of NMP outlined in Scheme 1 involves the cleavage of capped chain molecules (dormant species) into propagating alkyl and persistent nitroxide radicals (k d ). The propagating radicals grow by monomer addition (k p ) and form longer dormant chains by cross-coupling with the nitroxide radicals (k c ). Simultaneously, the usual self-termination (k t ) of the propagating radicals into unreactive polymer products takes place. This removes the propagating radicals and increases the concentration of nitroxide radicals over time; the cross-coupling reaction (k c ), therefore, dominates over self-termination [7] [8]. For an extended time range, a quasi-equilibrium of the reversible cleavage exists which is characterized by weakly time-dependent radical concentrations and a large excess of the persistent radicals over the propagating radicals.For the well-controlled and living radical polymerization of a given monomer with propagation and termination rate constants k p and k t , the rate constants of the reversible cleavage k d and k c must fall into proper ranges [7 -9]. In general, one aims at rela-

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Nitroxide‐Mediated Polymerization of Methyl Methacrylate Using an SG1‐Based Alkoxyamine: How the Penultimate Effect Could Lead to Uncontrolled and Unliving Polymerization

Cited by 116 publications

References 52 publications

Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO

Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO

2,5‐Dihydro‐1H‐imidazole‐Based Nitroxides as Prospective Mediators in Living Radical Polymerization

Re‐formation Reaction of Cyclic Nitroxide‐Based Alkoxyamines: Steric and Polar/Stabilization Effects

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