TIPNO

Scheme 6.2 Examples of nitroxides 1, TEMPO [5k] 2, DDPO [5f] 3, DEPN [5g,i,j] 4, TIPNO [5h]...

St/MAh TIPNO Alternating and block/alternating copolymers Hawker et al. [104]... 

Scheme 3 Synthetic scheme of the two possible pathways towards PvTPA-/ -PPerAcr block copolymers via NMRP. Using PvTPA as a macroinitiator for the NMRP of PerAcr gave monomodal block copolymers whereas starting from PPerAcr as macroinitiator, a mixture of PPerAcr and the corresponding PPerAcr-/ -PvTPA block copolymer was obtained. o-DCB ortho-dichlorobenzene, TIPNO 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl...

Fig. 1 a Linear increase of the experimental molecular weight of PvDMTPA vs conversion (determined by 1H-NMR) for the NMRP of vDMTPA using a monomer-alkoxyamine-TIPNO ratio of 200 1 0.1. The extrapolated experimental molecular weight of 3.2kgmol 1 at conversion = 0% arises from calibration with polystyrene standards, b SEC curves of the elution volume of different well-defined PvDMTPA macroinitiators... 

TIPNO iV-ferf-Butyl-iV-[l-phenyl-2-(methylpropyl)] nitroxide... 

NMP [191-193] can be applied to a wide range of monomers such as styrenes, acrylates, acrylamides, acrylonitrile, and 1,3-dienes. Acyclic nitroxides such as 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) or Af-tert-butyl-iV-(l-diethyl phosphono-2,2-dimethylpropyl) nitroxide (DEPN) enables the reversible termination of the growing polymer chains. 

The hydroxylamine or N-hydroxy compounds can be easily oxidized to nitroxides by a large number of oxidizing agents. The most suitable for this purpose are lead, mercury, or silver oxides. Air, in combination with a catalyst or used alone, may also turn hydroxylamines into nitroxides. For example, the 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl (TIPNO) nitroxide (Table 2, 29) is obtained upon treatment of the corresponding hydroxylamine by a copper(II)-catalyzed oxidation at ambient temperature. When multiple-step synthesis must be carried out prior to oxidation, the hydroxylamine can be protected either by O-acetylation or O-silylation with tert-butylchlorodimethylsilane... 

Moon and Kang used the same nucleophilic substitution but prepared the hydroxylaminate anion of the TIPNO nitroxide by a one-electron reduction using potassium metal. Gigmes et a prepared alkoxyamines based on the 2,2-diphenyl-3-phenylimino-2,3-dihydroindol-l-yloxyl (DPAIO) nitroxide by a one-pot process combining the reduction of the nitroxide by addition of phenyl hydrazine, the preparation of hydroxylaminate anion by addition of tBuOK, and then the nucleophilic substitution by the alkyl halide. 

Water-soluble TIPNO derivatives 37b-38 were also devel-opped The polymerization of SS was successfully achieved at temperatures below 100 °C using 37b under its deprotonated form and led to well-defined polymers. Nitroxide 38 is water-soluble under its protonated form and presents another interesting feature, which is its strong polarity. However, despite a more pronounced instability compared to nPNO, nitroxide 38 is more efficient than TIPNO since no addition of free nitroxide is required for the controlled radical polymerization of nBA. This confirmed the result observed in the case of the polar SGI nitroxide (see Section 3.10.3.1.2 for details), namely the strong influence of the polarity of the nitroxide on the efficiency of NMP. 

Bisnitroxide 39 based on TIPNO was prepared by Ruehl et and allowed a pseudo-controlled polymerization at temperatures as low as 70 °C to be performed. Decomposition of the corresponding styryl bisalkoxyamine presented an unusual behavior since the homolytic cleavage occurred twice as fast as the monofunctional counterpart. According to the ESR analyses, the authors claimed that conformational constraint induced strong spin-spin interaction and the near-proximity of the two nitroxide moieties led to an enhanced rate of homolysis. Nevertheless, Marque and Siri showed that the analysis of Braslau could be erroneous due to both EJA compensation error effect (with the activation energy and A the frequency factor) and the need for diastereoisomers purification prior to analysis of the decomposition kinetics. 

Contrary to hydroxyl-TIPNO 40a, the hydroxy-functionalized SGI 55 developed by the group of Tordo did not exhibit H-bonding between the alcohol and the aminoxyl function but between the alcohol and the phosphoryl grorrp. Nevertheless, this interaction increased the fed value since the stabilization occurred only for the nitroxide and not for the alkoxyamine since very high steric hindrance arormd the ami-noxyl moiety should dismpt the intramolecular H-bonding. 

Although the homopolymerization of methacrylate monomers cannot be controlled by the most classical nitroxides used, the TEMPO-, TIPNO-, and SGl-mediated copolymerizations were shown to work quite well, in conditions where relatively low amounts of the methacrylate comonomer were used. " ... 

Molecular alkoxyamines based on TEMPO and detiva-tives or sgi also received great interest regarding miniemulsion NMP. For the polymerization of styrene initiated by the styryl-TEMPO alkoxyamine, adequate experimental conditions led to narrow molar mass distributions (PDI 1.3) and high monomer convetsions. With nBA at 135 C upon the addition of ascorbic add, the miniemulsion polymerization conducted to rather high PDls compared to previous results with the TIPNO-OH nitroxide. The more versatile SGl-based oil-soluble alkoxyamine (MONAMS)... 

Harth et al. took advantage of a radical approach to functionalize (macro) alkoxyamines. They used a nonself-polymerizable monomer (maleimide or maleic anhydride) as a radical trap and then succeeded in preventing multiple radical additions. This step is followed in situ by an elimination of the TIPNO nitroxide. Various other radical traps... 

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