Iodoform as a transfer agent in radical polymerizations

Barson, C.A.; Bevington, J. C.; Hunt, B. J.

doi:10.1016/s0032-3861(96)00411-9

Cited by 14 publications

(10 citation statements)

References 7 publications

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“…Both compounds may act as initiators and strong chain‐transfer agents. Although the values of C CHI3 or C CI4 are not available from VC telomerization literature, it is still expected20 that C CuX2 > C CI4 > C CHI3 > C CBr4 > C CCl4 . Moreover, at elevated temperatures, elemental iodine may be generated from the thermolysis of the initiator 20.…”

Section: Resultsmentioning

confidence: 99%

“…Although the values of C CHI3 or C CI4 are not available from VC telomerization literature, it is still expected20 that C CuX2 > C CI4 > C CHI3 > C CBr4 > C CCl4 . Moreover, at elevated temperatures, elemental iodine may be generated from the thermolysis of the initiator 20. At 130 °C in the presence of Cu(0)/bpy, CHI 3 affords PVC with a high molecular weight but a broad polydispersity ( M n = 45,000, M w / M n = 1.57) or a low molecular weight PVC and a narrow molecular weight distribution ( M w / M n = 1.21, M n = 3300).…”

Section: Resultsmentioning

confidence: 99%

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From metal‐catalyzed radical telomerization to metal‐catalyzed radical polymerization of vinyl chloride: Toward living radical polymerization of vinyl chloride

Asandei

Percéc

2001

J. Polym. Sci. A Polym. Chem.

122

116

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The metal-catalyzed radical polymerization of vinyl chloride (VC) in orthodichlorobenzene initiated with various activated halides, such as ␣,␣-dihaloalkanes, ␣,␣,␣-trihaloalkanes, perfloroalkyl halides, benzyl halides, pseudohalides, allyl halides, sulfonyl halides, ␣-haloesters, ␣-halonitriles, and imidyl halides, in the presence of Cu(0)/2,2Ј-bipyridine, Fe(0)/o-phenantroline, TiCp 2 Cl 2 , and other metal catalysts is reported. The formation of the monoadduct between the initiator and VC was achieved with all catalysts. However, propagation was observed only for metals in their zero oxidation state because they were able to reinitiate from geminal dihalo or allylic chloride structures. Poly(vinyl chloride) with molecular weights larger then the theoretical limit allowed by chain transfer to VC were obtained even at 130°C. In addition, the most elemental features of a living radical polymerization, such as a linear dependence of the molecular weight and a decrease of polydispersity with conversion, were observed for the most promising systems based on iodine-containing initiators and Cu(0), that is, IOCH 2 OPhOCH 2 OI/Cu(0)/bpy (where bpy ϭ 2,2Ј-bipyridyl), at 130°C. However, because of the formation of inactive species via chain transfer to VC and other side reactions, the observed conversions were in most cases lower than 40%. A mechanistic interpretation of the chain transfer to monomer in the presence of Cu species is proposed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

From metal‐catalyzed radical telomerization to metal‐catalyzed radical polymerization of vinyl chloride: Toward living radical polymerization of vinyl chloride

Asandei

Percéc

2001

J. Polym. Sci. A Polym. Chem.

122

116

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“…One of the oldest method is iodine transfer polymerization (ITP), discovered by Tatemoto. − Indeed, this process has been used in the eighties for the polymerization of vinylidene fluoride. ,− Despite this precedence, only a few studies dealing with ITP have been reported in the literature. Works of Matyjazsewski et al in 1995 , reactivated the interest for this type of polymerization in studying different monomers: styrene, − n- butyl acrylate, vinyl chloride, − vinylidene chloride, and last, vinyl acetate . ITP permits controlling molecular weights for a wide range of monomers, such as acrylates and vinyl acetate, and appears with RAFT, the most universal technique.…”

Section: Introductionmentioning

confidence: 99%

Reverse Iodine Transfer Polymerization (RITP) of Methyl Methacrylate

et al. 2006

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The polymerization of methyl methacrylate (MMA) initiated by 2,2‘-azobis(isobutyronitrile) (AIBN) as radical initiator in the presence of iodine (I2) was studied at different temperatures (T = 70 °C and 80 °C). This process, called reverse iodine transfer polymerization (RITP), is based on the direct reaction of radicals with molecular iodine. RITP efficiently controls the molecular weight (determined by size exclusion chromatography, SEC) and the structure of the polymer chains (confirmed by 1H and 13C NMR spectroscopy). For instance, PMMA samples of M n,SEC = 2300 g mol-1 and polydispersity index PDI = M w/M n = 1.5 (M n,theoretical = 2300 g mol-1), M n,SEC = 4600 g mol-1 and PDI = 1.6 (M n,theoretical = 4700 g mol-1), M n,SEC = 9600 g mol-1 and PDI = 1.6 (M n,theoretical = 10 000 g mol-1), and M n,SEC = 19 200 g mol-1 and PDI = 1.5 (M n,theoretical = 18400 g mol-1) were successfully prepared by RITP. The polymerization was followed by on-line 1H NMR spectroscopy, and the conversion of iodine was followed by titration with a thiol (thioglycolic acid). It was shown by SEC, titration of iodine, gas chromatography, and NMR analyses that RITP was split into two different periods: a first “inhibition” period during which iodine is consumed to form very short ω-iodotelomers, and a second period where the polymerization follows the kinetics of a conventional free radical polymerization governed by degenerative chain transfer. The degenerative chain transfer constant was estimated to be C ex ≈ 2.6 at T = 80 °C. Last, the iodine-end-capped structure of the polymers was demonstrated by different analytical techniques, and the iodine functionality of the PMMA chains was up to 95%.

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“…For this VC polymerization process, CT constants to iodo‐alkanes are not known, but for other olefin polymerizations they are much higher than the bromo or chloro derivatives. For example, for free‐radical styrene polymerization the CT constant to iodoform was C T,HCI3 = 10.10, whereas for bromoform it was C T,HCBr3 = 0.12 73. Other iodo‐alkanes were used as CT agents in olefin radical polymerization 74, 75.…”

Section: Resultsmentioning

confidence: 99%

DFT Calculations Suggest a New Type of Self‐Protection and Self‐Inhibition Mechanism in the Mammalian Heme Enzyme Myeloperoxidase: Nucleophilic Addition of a Functional Water rather than One‐Electron Reduction

Sicking

Somnitz

Schmuck

2012

Chemistry A European J

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The mammalian heme enzyme myeloperoxidase (MPO) catalyzes the reaction of Cl(-) to the antimicrobial-effective molecule HOCl. During the catalytic cycle, a reactive intermediate "Compound I" (Cpd I) is generated. Cpd I has the ability to destroy the enzyme. Indeed, in the absence of any substrate, Cpd I decays with a half-life of 100 ms to an intermediate called Compound II (Cpd II), which is typically the one-electron reduced Cpd I. However, the nature of Cpd II, its spectroscopic properties, and the source of the additional electron are only poorly understood. On the basis of DFT and time-dependent (TD)-DFT quantum chemical calculations at the PBE0/6-31G* level, we propose an extended mechanism involving a new intermediate, which allows MPO to protect itself from self-oxidation or self-destruction during the catalytic cycle. Because of its similarity in electronic structure to Cpd II, we named this intermediate Cpd II'. However, the suggested mechanism and our proposed functional structure of Cpd II' are based on the hypothesis that the heme is reduced by charge separation caused by reaction with a water molecule, and not, as is normally assumed, by the transfer of an electron. In the course of this investigation, we found a second intermediate, the reduced enzyme, towards which the new mechanism is equally transferable. In analogy to Cpd II', we named it Fe(II'). The proposed new intermediates Cpd II' and Fe(II') allow the experimental findings, which have been well documented in the literature for decades but not so far understood, to be explained for the first time. These encompass a) the spontaneous decay of Cpd I, b) the unusual (chlorin-like) UV/Vis, circular dichroism (CD), and resonance Raman spectra, c) the inability of reduced MPO to bind CO, d) the fact that MPO-Cpd II reduces SCN(-) but not Cl(-), and e) the experimentally observed auto-oxidation/auto-reduction features of the enzyme. Our new mechanism is also transferable to cytochromes, and could well be viable for heme enzymes in general.

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Iodoform as a transfer agent in radical polymerizations

Cited by 14 publications

References 7 publications

From metal‐catalyzed radical telomerization to metal‐catalyzed radical polymerization of vinyl chloride: Toward living radical polymerization of vinyl chloride

From metal‐catalyzed radical telomerization to metal‐catalyzed radical polymerization of vinyl chloride: Toward living radical polymerization of vinyl chloride

Reverse Iodine Transfer Polymerization (RITP) of Methyl Methacrylate

DFT Calculations Suggest a New Type of Self‐Protection and Self‐Inhibition Mechanism in the Mammalian Heme Enzyme Myeloperoxidase: Nucleophilic Addition of a Functional Water rather than One‐Electron Reduction

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