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Disproportionation
Terms modified by Disproportionation Selected AbstractsKinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese(ii,ii) and -(ii,iii) Complexes of a Bridging Phenolate LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Lionel Dubois Abstract The dimanganese(ii,ii) complexes [Mn2(L)(OAc)2(CH3OH)]-(ClO4) (1a) and [Mn2(L)(OBz)2(H2O)](ClO4) (1b) as well as the dimanganese(ii,iii) complex [Mn2(L)(OAc)2(CH3OH)]-(ClO4)2 (2a), where HL is the asymmetric phenol ligand2-[bis(2-pyridylmethyl)aminomethyl]-6-{[(benzyl)(2-pyridyl-methyl)amino]methyl}-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first-order dependence on both the catalyst and H2O2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a. The same bis(,-oxo)dimanganese(III,IV) and (,-oxo)dimanganese(ii,iii) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase-like reaction revealed the accumulation of the magnetically uncoupled dimanganese(ii,iii) precursor of the active bis(,-oxo)dimanganese(III,IV) species which dominates the spectra in the case of 1a. This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H2O2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthetic and Mechanistic Aspects of Acid-Catalyzed Disproportionation of Dialkyl Diarylmethyl Ethers: A Combined Experimental and Theoretical StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2009Margherita Barbero Abstract The disproportionation reactions of various dialkyl diarylmethyl ethers have been carried out in the presence of a catalytic amount (10 mol-%) of o -benzenedisulfonimide as a Brønsted acid catalyst; the reaction conditions were mild, and the yields of the diarylmethane target products were good. The catalyst was easily recovered and purified, ready to be used in further reactions. The theoretical study confirmed that the reaction proceeds in two steps: The formation of a carbocation from the protonated ether followed by hydride transfer. Although the hydride transfer is the rate-determining step, it is the stability of the carbocation that determines the reaction rate and therefore the yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Stability of photocurable anhydrides: Methacrylic acid mixed anhydrides of nontoxic diacidsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2001Peter J. Tarcha Abstract Disproportionation of the liquid mixed anhydride dimethacrylic sebacic anhydride (m-SA) to methacrylic anhydride and polyanhydride oligomers, as well as vinylic polymerization, can occur on workup and storage at room temperature. Dimethacrylic 1,3-bis(p -carboxyphenoxy) propane, being a solid, can also disproportionate, but the propensity to do so is lower than for m-SA. These events can be suppressed with free-radical inhibitors, and the inhibitor 2+3- t -butyl-4-methoxyphenol is a more effective stabilizer than 4-methoxyphenol at 20 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4189,4195, 2001 [source] Sonochemical Disproportionation of Carbon Monoxide in Water: Evidence for Treanor Effect during Multibubble Cavitation,ANGEWANDTE CHEMIE, Issue 50 2009Sergey Nichtgleichgewichts-Sonochemie: Die Disproportionierung von CO in Wasser bei Ultraschallbehandlung führt zur Bildung eines hydratisierten Kohlenstoffsuboxid-Polymers (C3O2)n (siehe Bild), in dem das schwere Isotop 13C angereichert ist. Diese Beobachtung spricht für das Vorliegen von CO-Molekülen in angeregten Schwingungszuständen mit einer Treanor-Nichtgleichgewichtsverteilung im Bläscheninneren. [source] ChemInform Abstract: FeCl3·6H2O Catalyzed Disproportionation of Allylic Alcohols and Selective Allylic Reduction of Allylic Alcohols and Their Derivatives with Benzylic Alcohol.CHEMINFORM, Issue 37 2009Jialiang Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Understanding the Reactivity and Basicity of Zeolites: A Periodic DFT Study of the Disproportionation of N2O4 on Alkali-Cation-Exchanged Zeolite Y.CHEMINFORM, Issue 32 2008Pierre Mignon Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Highly Efficient RuCl3 -Catalyzed Disproportionation of (Diacetoxyiodo)benzene to Iodylbenzene and Iodobenzene; Leading to the Efficient Oxidation of Alcohols to Carbonyl Compounds.CHEMINFORM, Issue 50 2006Mekhman S. Yusubov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Approach of Charge Disproportionation in the Perovskite Oxide TlNiO3 from ab initio Electronic Structures.CHEMINFORM, Issue 43 2004S. F. Matar No abstract is available for this article. [source] Disproportionation of an Element in a Zeolite.CHEMINFORM, Issue 52 2003Part 2. Abstract For Abstract see ChemInform Abstract in Full Text. [source] Samarium(II)-Mediated Pinacol Coupling in Water: Occurrence of Unexpected Disproportionation and Action of Low-Valent Samarium as an Active Species.CHEMINFORM, Issue 32 2003Satoru Matsukawa Abstract For Abstract see ChemInform Abstract in Full Text. [source] Evidence of Ni(III) Disproportionation in the TlNiO3 Perovskite Lattice Through Neutron Powder Diffraction and Moessbauer Spectroscopy.CHEMINFORM, Issue 10 2003S. J. Kim Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Metal,Semiconductor Transition, Charge Disproportionation, and Low-Temperature Structure of Ca1-xSrxFeO3 Synthesized under High-Oxygen Pressure.CHEMINFORM, Issue 13 2001Takashi Takeda Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Experimentally Based DFT Calculations on the Hindered Disproportionation of [Al4Cp*4]: Formation of Metalloid Clusters as Intermediates on the Way to Solid Al Prevents the Decomposition of a Textbook Molecule,CHEMISTRY - A EUROPEAN JOURNAL, Issue 45 2009Michael Huber Dr. Clusters are the answer! The formation of metalloid clusters such as [Al50Cp*12] (Cp*=C5Me5) species are responsible for the kinetically hindered decomposition of [Al4Cp*4] to metallic aluminum; that is, metalloid clusters may be considered as nuclei for the formation of metals (see graphic). [source] Understanding the Reactivity and Basicity of Zeolites: A Periodic DFT Study of the Disproportionation of N2O4 on Alkali-Cation-Exchanged Zeolite YCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2008Pierre Mignon Dr. Abstract The disproportionation of N2O4 into NO3, and NO+ on Y zeolites has been studied through periodic DFT calculations to unravel 1),the role of metal cations and the framework oxygen atoms and 2),the relationship between the NO+ stretching frequency and the basicity of zeolites. We have considered three situations: adsorption on site,II cations with and without a cation at site,III and adsorption on a site III cation. We observed that cations at sites II and III cooperate to stabilize N2O4 and that the presence of a cation at site,III is necessary to allow the disproportionation reaction. The strength of the stabilization is due to the number of stabilizing interactions increasing with the size of the cation and to the Lewis acidity of the alkali cations, which increases as the size of the cations decreases. In the product, NO3, interacts mainly with the cations and NO+ with the basic oxygen atoms of the tetrahedral aluminium through its nitrogen atom. As the cation size increases, the NO3,,,,cation interaction increases. As a result, the negative charge of the framework is less well screened by the larger cations and the interaction between NO+ and the basic oxygen atoms becomes stronger. NO+ appears to be a good probe of zeolite basicity, in agreement with experimental observations. [source] Kinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese(ii,ii) and -(ii,iii) Complexes of a Bridging Phenolate LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Lionel Dubois Abstract The dimanganese(ii,ii) complexes [Mn2(L)(OAc)2(CH3OH)]-(ClO4) (1a) and [Mn2(L)(OBz)2(H2O)](ClO4) (1b) as well as the dimanganese(ii,iii) complex [Mn2(L)(OAc)2(CH3OH)]-(ClO4)2 (2a), where HL is the asymmetric phenol ligand2-[bis(2-pyridylmethyl)aminomethyl]-6-{[(benzyl)(2-pyridyl-methyl)amino]methyl}-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first-order dependence on both the catalyst and H2O2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a. The same bis(,-oxo)dimanganese(III,IV) and (,-oxo)dimanganese(ii,iii) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase-like reaction revealed the accumulation of the magnetically uncoupled dimanganese(ii,iii) precursor of the active bis(,-oxo)dimanganese(III,IV) species which dominates the spectra in the case of 1a. This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H2O2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Energetics of overall metabolic reactions of thermophilic and hyperthermophilic Archaea and BacteriaFEMS MICROBIOLOGY REVIEWS, Issue 2 2001Jan P. Amend Abstract Thermophilic and hyperthermophilic Archaea and Bacteria have been isolated from marine hydrothermal systems, heated sediments, continental solfataras, hot springs, water heaters, and industrial waste. They catalyze a tremendous array of widely varying metabolic processes. As determined in the laboratory, electron donors in thermophilic and hyperthermophilic microbial redox reactions include H2, Fe2+, H2S, S, S2O32,, S4O62,, sulfide minerals, CH4, various mono-, di-, and hydroxy-carboxylic acids, alcohols, amino acids, and complex organic substrates; electron acceptors include O2, Fe3+, CO2, CO, NO3,, NO2,, NO, N2O, SO42,, SO32,, S2O32,, and S. Although many assimilatory and dissimilatory metabolic reactions have been identified for these groups of microorganisms, little attention has been paid to the energetics of these reactions. In this review, standard molal Gibbs free energies (,Gr°) as a function of temperature to 200°C are tabulated for 370 organic and inorganic redox, disproportionation, dissociation, hydrolysis, and solubility reactions directly or indirectly involved in microbial metabolism. To calculate values of ,Gr° for these and countless other reactions, the apparent standard molal Gibbs free energies of formation (,G°) at temperatures to 200°C are given for 307 solids, liquids, gases, and aqueous solutes. It is shown that values of ,Gr° for many microbially mediated reactions are highly temperature dependent, and that adopting values determined at 25°C for systems at elevated temperatures introduces significant and unnecessary errors. The metabolic processes considered here involve compounds that belong to the following chemical systems: H,O, H,O,N, H,O,S, H,O,N,S, H,O,Cinorganic, H,O,C, H,O,N,C, H,O,S,C, H,O,N,S,Camino acids, H,O,S,C,metals/minerals, and H,O,P. For four metabolic reactions of particular interest in thermophily and hyperthermophily (knallgas reaction, anaerobic sulfur and nitrate reduction, and autotrophic methanogenesis), values of the overall Gibbs free energy (,Gr) as a function of temperature are calculated for a wide range of chemical compositions likely to be present in near-surface and deep hydrothermal and geothermal systems. [source] Kinetics and mechanism of the hydrolytic disproportionation of iodineINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2004Krisztina Seb, k-Nagy Kinetics of the hydrolytic disproportionation of I2 was studied by UV,VIS spectrophotometry at 298 K and at the ionic strength 0.2 M (NaClO4) in buffered solutions in the pH range 8.91,10.50 at different initial iodide concentrations. The characterization of this reaction is fundamental for modeling oscillatory and front reactions in the presence of iodine as reactant or intermediate as well as for drinking water treatment. A matrix rank analysis confirmed three absorbing species in the beginning of the reaction, whereas later assumption of two species is enough to describe the experimental data in the visible part of the spectrum. A reaction mechanism was proposed for disproportionation by using fitting/simulation with a multipurpose program package ZiTa, by simultaneous evaluation of 17,906 points in 79 experimental curves. A parameter set was suggested, which was obtained by absolute, relative, and orthogonal fittings of the experimental data. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 596,602, 2004 [source] Inorganic reactions of iodine(+1) in acidic solutionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2004Guy Schmitz We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H2OI+ , HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3. Our new value, K(H2OI+ , HOI + H+) , 2 M at 25°C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI , IO3, + 2I, + 3H+ in perchloric acid solutions from 5 × 10,2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M,1 s,1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI , I2O·H2O in the mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480,493, 2004 [source] Kinetics and mechanisms of transalkylation and disproportionation of meta -diethylbenzene by triflic acid catalystINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2003S. M. Al-Zahrani The kinetics of transalkylation and isomerization of meta -diethylbenzene in the presence of benzene using triflic acid as a catalyst has been investigated. High catalytic activity of the triflic acid catalyst was observed in homogeneous liquid-phase reactions. On the basis of the product distribution obtained, transalkylation, disproportionation, and isomerization reactions have been considered and the main product of the reaction was ethylbenzene. These reactions are conducted in a closed liquid batch reactor with continuous stirring under dry nitrogen and atmospheric pressure over the temperature range of 288,308 K. The main transalkylation, disproportionation, and isomerization reactions occurred simultaneously and were considered as elementary reactions. The apparent activation energy of the transalkylation reaction was found to be 35.5 kJ/mol, while that of disproportionation reaction was 42.3 kJ/mol. The reproducibility of the experimental product distribution occurred with an average relative error of ±2%. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 555,563, 2003 [source] Quantized Double-Layer Charging of Rhodium2057(Tridecylamine)321 Clusters Using Differential Pulse and Cyclic Voltammetry,ADVANCED MATERIALS, Issue 2 2007A. Kakade Rhodium nanoclusters show a series of quantized double-layer-charging events in solution-phase voltammetry at room temperature (see figure). The unusual variation in the FWHM for both the cathodic and anodic regions in differential pulse voltammetry experiments can be explained by several complex factors including reorganization and disproportionation of charged clusters coupled with electron-transfer processes pertaining to the Rh,Rh bonds. [source] Grafting itaconic anhydride onto polyethylene using extrusionJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010C. J. R. Verbeek Abstract Reactive extrusion was employed to graft itaconic anhydride (IA) onto polyethylene, using thermally induced peroxide decomposition. It was found that an increase in IA concentration lead to an increase in the degree of grafting (DOG), but only up to 6 wt % IA. Using di-cumyl peroxide (DCP) as the initiator resulted in a higher DOG compared to di- tert -butyl peroxide (DTBP) and required less reaction time to achieve the same DOG. However, raising the IA concentration also resulted in an increase in cross-linking. Increasing the initiator concentration from 0.2 to 2 wt % resulted in a higher DOG. However, 5 wt % initiator showed similar results compared to using 0.2 wt % due to termination by disproportionation, which has been shown to be more prevalent at high initiator concentrations. Degradation was clearly observed by the inability to form a continuous extrudate during extrusion as well as discolouration. A residence time of more than 50 seconds, using DCP and 120 s for DTBP didn't offer any further increase in the DOG and also resulted in more pronounced degradation. Optimizing grafting is therefore a trade-off between maximal DOG and minimizing side reactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Interfacial and foaming characteristics of milk whey protein and polysaccharide mixed systemsAICHE JOURNAL, Issue 4 2010Adrián A. Perez Abstract Protein-polysaccharide (PS) interactions find many applications in food engineering and new foam formulations. In this article, we have studied the effect of anionic nonsurface active PSs [sodium alginate (SA) and lambda-carrageenan (,-C)] in aqueous solution on interfacial and foaming characteristics of milk whey proteins [whey protein concentrate (WPC) and whey protein isolate (WPI)]. Whey protein concentration (1.0% wt), temperature (20°C), pH (7), and ionic strength (0.05 M) of the aqueous media were kept constant, while PS influence was evaluated within a 0.0,1.0% wt concentration range. The dynamic properties (dynamics of adsorption and surface dilatational properties) of WPC/PS and WPI/PS adsorbed films were considered in order to correlate the foaming characteristics of the biopolymer mixed systems. Foaming characteristics of the biopolymer mixed systems depended on the PS relative concentration in the aqueous phase and on the whey protein-PS interactions in solution and at the air,water interface. Dynamic surface properties of the adsorbed films at short adsorption time had a significant effect on foaming capacity. For a particular system, the overall foam destabilization (foam half-life time) and the individual destabilization processes (drainage, disproportionation, and bubble coalescence) depend on the nature of the PS, its relative bulk concentration, and whey protein-PS interactions in the vicinity of the air,water interface. The viscosity of the aqueous phase has an effect on the rate of drainage while the rate of disproportionation/collapse is more dependent on the interfacial characteristics of the adsorbed film. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Alkyl halides reactions with cathodes or with magnesium.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2006Grignard reagent studied with radical clocks. Abstract In the mechanism of reaction of Grignard reagent formation for alkyl halides (RX), it is generally assumed that the alkyl radical, formed by the electron transfer from the metal to this halide, reacts rapidly with the paramagnetic MgX, species. The previous comparisons of aryl halides reactivity toward magnesium and their reactivity toward a cathode strongly suggested that MgX, species are not, for the aryl halides, compulsory to rationalise the observed facts. The aryl radicals formed by electron transfer from the metal to the aryl halide would undergo a rapid second electron transfer to yield carbanions transformed into RMgX by reaction with MgX2. In contrast, for the alkyl halides, the reduction of the rapidly formed alkyl radicals into carbanions has seldom been discussed as a possible fate for these radicals, the main discussed fates being dimerisation, disproportionation, hydrogen abstraction from the solvent, rearrangement or coupling with MgX, radicals. Two main differences distinguish the reactivity of alkyl halides from their aryl halides counterpart. First, the radical anions of aryl halides may have a given lifetime whereas electron transfer to alkyl halides is concerted with the cleavage of the molecule. Second, the aryl radicals display far stronger oxidising properties than the alkyl radicals. The counterpart of this property is that aryl carbanions display weaker reducing properties than the alkyl ones. In this report, putting in perspective Grignard reaction and the experimental results obtained with identical radical clocks in electrochemistry, we tentatively provide an answer to the question raised in the title. The comparison of electrochemical patterns of reactivity of selected alkyl halides and the evolutions of yields in the preparation of Grignard reagent suggest a new explanation for the lower yields generally observed when alkyl iodides are the starting substrates. It involves an autocatalytic reaction where carbanionic species formed from the alkyl radicals and diffusing away from the metal surface, transfer one electron to the alkyl halide; the result would be the creation of two radicals leading to an increased amount of by-products. If the carbanionic mechanism were to be retained for the formation of alkyl Grignard reagent one would have to admit that the magnesium surface behaves as a cathode displaying high current densities reminiscent of microelectrodes. Copyright © 2006 John Wiley & Sons, Ltd. [source] The effect of ligand on the rate of propagation of Cu(0)-wire catalyzed SET-LRP of MA in DMSO at 25 °CJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2009Nga H. Nguyen Abstract The effect of initial ligand concentration on the apparent rate constant of propagation of single-electron transfer living radical polymerization (SET-LRP) of MA in DMSO at 25 °C was examined using various lengths of Cu(0) wire as catalyst. It was determined that unlike other parameters such as initiator concentration, solvent concentration, and deactivator concentration, no simple external rate-order for the ligand concentration could be determined. Rather, the response of the rate of SET-LRP to initial ligand concentration is complex and is likely determined by a competition of ligand-dependent extent of disproportionation as well as the role of ligand concentration in the surface mediated activation process. Results suggest that a minimum concentration of ligand is needed to achieve both acceptable reaction rate and reaction control, and therefore, ligand concentration must be considered in designing experimental conditions for SET-LRP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5629,5638, 2009 [source] Ultrafast SET-LRP of methyl acrylate at 25 °C in alcoholsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2008Gerard Lligadas Abstract Alcohols are known to promote the disproportionation of Cu(I)X species into nascent Cu(0) and Cu(II)X. Therefore, alcohols are expected to be excellent solvents that facilitate the single-electron transfer mediated living radical polymerization (SET-LRP) mediated by nascent Cu(0) species. This publication demonstrates the ultrafast SET-LRP of methyl acrylate initiated with bis(2-bromopropionyloxy)ethane and catalyzed by Cu(0)/Me6 -TREN in methanol, ethanol, 1-propanol, and tert -butanol and in their mixture with water at 25 °C. The structural analysis of the resulting polymers by a combination of 1H NMR and MALDI-TOF MS demonstrates the synthesis of perfectly bifunctional ,,,-dibromo poly(methyl acrylate)s by SET-LRP in alcohols. Moreover, this work provides an expansion of the list of solvents available for SET-LRP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2745,2754, 2008 [source] Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry investigations of polystyrene and poly(methyl methacrylate) produced by monoacylphosphine oxide photoinitiationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2007Faith J. Wyzgoski Abstract The chain-end-group composition was determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analyses of low-molecular-weight polystyrene (PS) and poly(methyl methacrylate) (PMMA) produced by free-radical polymerization with a monoacylphosphine oxide, (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO), as a photoinitiator. Gel permeation chromatography (GPC) fractionation of the PS and PMMA samples with initial polydispersities of 1.81 and 2.81, respectively, yielded improved MALDI-TOF MS spectra. Spectral analyses of the PS fractions showed distributions attributable to PS having two diphenylphosphinyl ends and PS having one diphenylphosphinyl end and/or one 2,4,6-trimethylbenzoyl end, indicating that a combination of PS radicals with the highly reactive diphenylphosphine oxide group at one end of the chains was the predominant mode of termination. MALDI-TOF MS results for PMMA fractions provided evidence for termination primarily by disproportionation, but structure determination was confounded by the presence of isobaric peaks. Discernible peaks were obtained by MALDI-TOF MS analyses of GPC fractions of TPO-initiated poly(methyl- d3 methacrylate- d5), in which the major product was PMMA with a diphenylphosphinyl end group and an abstracted deuterium end group, whereas the minor combination product had two diphenylphosphinyl chain ends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2161,2171, 2007 [source] Living radical polymerization of vinyl chloride initiated with iodoform and catalyzed by nascent Cu0/tris(2-aminoethyl)amine or polyethyleneimine in water at 25 °C proceeds by a new competing pathways mechanismJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2003Virgil Percec Abstract The first example of living radical polymerization of vinyl chloride carried out in water at 25 °C is reported. This polymerization was initiated by iodoform and catalyzed by nascent Cu0 produced by the disproportionation of CuI in the presence of strongly CuII binding ligands such as tris(2-aminoethyl)amine or polyethyleneimine. The resulting poly(vinyl chloride) was free of structural defects, had controlled molecular weight and narrow molecular weight distribution, contained two ,CHClI active chain ends, and had a higher syndiotacticity (62%) than the one obtained by conventional free-radical polymerization at the same temperature (56%). This novel polymerization proceeds, most probably, by a combination of competitive pathways that involves activation by single electron transfer mediated by nascent Cu0 and degenerative chain transfer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3283,3299, 2003 [source] Modeling the reversible addition,fragmentation transfer polymerization processJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2003Aileen R. Wang Abstract A kinetic model has been developed for reversible addition,fragmentation transfer (RAFT) polymerization with the method of moments. The model predicts the monomer conversion, number-average molecular weight, and polydispersity of the molecular weight distribution. It also provides detailed information about the development of various types of chain species during polymerization, including propagating radical chains, adduct radical chains, dormant chains, and three types of dead chains. The effects of the RAFT agent concentration and the rate constants of the initiator decomposition, radical addition, fragmentation, disproportionation, and recombination termination of propagating radicals and cross-termination between propagating and adduct radicals on the kinetics and polymer chain properties are examined with the model. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1553,1566, 2003 [source] Nanosized CdSe Particles Synthesized by an Air Pressure Solution Process Using Ethylene-Glycol-Based SolventJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Tao Wang Nanosized CdSe particles were synthesized at a temperature of 115°,175°C by a solution method with air pressure condition. Ethylene glycol (EG) was used as the main solvent and sodium selenite and cadmium nitrate-tetrahydrate as inorganic sources. The influence of refluxing temperature and time on growth morphology and crystallization was investigated by transmission electron microscope, high-resolution transmission electron microscope, and X-ray diffraction. The chemical reaction was deducted based on X-ray photoelectron spectra. The optical absorption property was measured by UV-vis. The CdSe nanoparticles synthesized through this EG solvent system was single wurtzite crystallization and had a nanoscale size below 15 nm diameter with a narrow size distribution. The reduction of Se4+,Se0,Se2,and the disproportionation of Se0 occurred during the synthetic process and dominated the chemical reaction. [source] Application of Nitroxide-Terminated Polymers Prepared by Sonochemical Degradation in the Synthesis of Block CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2006Martina Bartsch Abstract Summary: The ultrasonic irradiation of a polymer solution results in the breakage of macromolecular CC bonds. In the presence of radical scavengers the formed macroradicals are prevented from termination reactions as combination or disproportionation. Using nitroxides as trapping agents the polymer is transformed into a macroinitiator, which can be used in controlled free-radical polymerization to synthesize block copolymers. In this work several polymers were exposed to sonochemical degradation and terminated with various nitroxides, e.g. OH-TEMPO and TIPNO. In a second reaction step the prepared polymer-nitroxide-adducts were applied as macroinitiators in controlled free-radical polymerizations with styrene. The obtained products were mixtures of block copolymer and the corresponding homopolymers. The visco-elastic properties were investigated by rheological analysis. A special separation technique with selective solvents was applied to determine the content of block copolymer. Synthesis of block copolymers with sonochemically prepared macroinitiators. [source] | |||||||||||||||||||||||||||||||