Presence Of Radical Initiator Research Articles

Functional copolymer/organo-MMT nanoarchitectures. II. Dynamic mechanical behavior of poly(MA-co-BMA)s-organo-MMT clay nanocomposites

Functional copolymer/organo-silicate [N,N′-dimethyldodecyl ammonium cation surface modified montmorillonite (MMT)] layered nanocomposites have been synthesized by interlamellar complex-radical copolymerization of preintercalated maleic anhydride (MA)/ organo-MMT complex as a ‘nano-reactor’ with n-butyl methacrylate (BMA) as an internal plasticization comonomer in the presence of radical initiator. Synthesized copolymers and their nanocomposites were investigated by dynamic mechanic analysis, X-ray diffraction, SEM, and TEM methods. It was found that nanocomposite dynamic mechanical properties strongly depend on the force of interfacial MA…organo-MMT complex formation and the amount of flexible n-butyl ester linkages. An increase in both of these parameters leads to enhanced intercalation and exfoliation in situ processes of copolymer chains and the formation of hybrid nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Lipid Oxidation in Water-in-Olive Oil Emulsions Initiated by a Lipophilic Radical Source

The lipophilic 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) was used to study thoroughly the oxidation reaction in a model water-in-olive oil emulsion system. This radical species decomposes thermally generating a constant flux of radicals in the oil phase. The dissociation constant k(d) in olive oil at 40 degrees C for AMVN was calculated as 2.5 x 10(-4) min(-1) and the rate of initiation of the oxidation reaction, R(i) was calculated by using vitamin E as antioxidant. The olive oil oxidation in emulsion was monitored by measuring the hydroperoxide concentration by a sensitive fluorimetric method. The DPPP (diphenyl-1-pyrenylphosphine) was used as a probe because it reacts stoichiometrically with hydroperoxides to yield a fluorescent product, the diphenyl-1-pyrenylphosphine oxide (DPPP-O). Oxidation data together with emulsion droplet size data showed that in the presence of radical initiator and a large interface, the oxidation reaction is accelerated in W/Olive oil emulsion with respect to whole oil. The mediation of the surface area of water droplets is surely involved in this process because the addition of saturated solutions of ascorbic acid (AA) dispersed in the oil brings about the strong reduction of the oxidation rate even in the presence of the highest AMVN quantity.

EPR/Spin‐trapping study of free radical intermediates in the photolysis of trifluoromethyl ketones with initiators

Photolysis of trifluoromethyl ketones (TFMKs) 1a-1e versus the non-fluorinated ketones 2a-2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2-methyl-2-nitrosopropane (MNP) and 2,4,6-tri-tert-butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t-butylperoxide, short-chain TFMKs, such as 1,1,1-trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long-chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one alpha-methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a gamma-hydrogen to the carbonyl group.

Catalytic and Thermal 1,2-Rearrangement of (α-Mercaptobenzyl)trimethylsilane

The mechanisms of catalytic and thermal 1,2-rearrangement of (alpha-mercaptobenzyl)trimethylsilane were studied by using density functional theory (DFT) at the MP2/6-31+G(d,p)//B3LYP/6-31G(d) levels. The results show that (alpha-mercaptobenzyl)trimethylsilane rearranges to (benzylthio)trimethylsilane through a trimethylsilyl group migration from C to S atom via a transition state of pentacoordinate Si atom with or without radical initiators. The low reaction activation energy (15.1 kcal/mol) is responsible for the fast rearrangement in the presence of radical initiators. Both radical and nonradical thermal rearrangement mechanisms were suggested, and the radical mechanism dominates through its self-catalyzing. These results are consistent with the experiment results. The activation energy (DeltaH(act) = 15.1 kcal/mol) for the rate-determining step within the self-catalytic cycle is low enough to make (trimethylsilylbenzyl)thiyl radical be a reasonable catalyst for the thermal rearrangement. The catalytic and thermal 1,2-rearrangement mechanisms of (alpha-mercaptobenzyl)trimethylsilane, especially the self-catalytic radical mechanism, were revealed for the first time. The comparison of the rearrangement mechanisms between (alpha-mercaptobenzyl)trimethylsilane and silylmethanethiol discloses the factors in determining the reaction mechanism of such kinds of mercaptoalkyl-functionalized organosilanes. The phenyl group is found to be favorable for the radical rearrangement, thus making (alpha-mercaptobenzyl)trimethylsilane instable.

Further kinetics studies of intermediates formed by flash photolysis of Mo(CO) 6

Kinetics studies of the behavior of Mo(CO) 5(CH) in the presence of radical initiators were conducted in cyclohexane (CH) solution by laser flash photolysis with time-resolved infrared detection. Activation parameters were determined for reactions of Mo(CO) 5(CH) with toluene and with photochemical radical generator dibenzylketone (DBK) in the presence of excess CO.

New Stimuli Responsive Poly(1‐vinylpyrrolidin‐2‐one) Bearing Pendant Activated Disulfide Groups

AbstractSummary: A novel functionalised poly(1‐vinylpyrrolidin‐2‐one) (PVP) derivative, carrying a pre‐determined amount of 2‐(2‐pyridinyldithio)ethylamine moieties as side substituents, P(VP‐co‐VP‐SS‐Py), has been prepared from carboxylated VP copolymers, in turn obtained by copolymerising 1‐vinylpyrrolidin‐2‐one with 3,3‐di‐(ethoxycarbonyl)‐1‐vinylpyrrolidin‐2‐one in the presence of radical initiators. Using reaction solvents acting in the mean time as chain transfer agents could control its molecular weight. P(VP‐co‐VP‐SS‐Py) proved to be extremely reactive towards exchange reactions with molecules containing mercapto functions, including bioactive peptides. The exchange derivative with reduced glutathione, chosen as a model compound, was easily prepared. magnified image

Self-immobilized and polymerized miscellaneous metallocene catalysts for ethylene polymerization

Metallocene complexes with an allyl group (η 5-C 3H 5C 5H 4)(η 5- t BuC 5H 4)ZrCl 2 ( 2), (η 5-C 3H 5C 5H 4)(η 5- t BuC 5H 4)ZrCl 2 ( 3) and (η 5-C 3H 5C 5H 4)(η 5- t Bu 2C 5H 3)ZrCl 2 ( 4) have been synthesized and characterized. The polymerized metallocene catalyst 5 is prepared by the copolymerization of 3 with styrene in the presence of radical initiator. In the presence of MAO, 2– 5 can be used as catalysts for ethylene polymerization with high activities.

Hydrophosphination of Unactivated Alkenes, Dienes and Alkynes: A Versatile and Valuable Approach for the Synthesis of Phosphines

The last years have seen many advances in the field of organometallic catalysis. Motivating much of the work has been the potential for discovering new catalytic reactions, which can be used for the synthesis of bulky chemicals and fine chemical intermediates. Since the efficiency and the selectivity of the catalyst mainly rely on the structure of the ligand, there is a great interest in the design and the synthesis of new ligands (amines, aminoalcohols, thioether, phosphines etc). From all of them, phosphine derivatives are the most widely used with transition metal catalysts. Different approaches have allowed to prepare phosphine derivatives: nucleophilic substitution of a P-chloro derivative, nucleophilic substitution using metal phosphide, C-P cross coupling etc. A greener way to phosphines is the addition of a P-H bond to a multiple bond since no atom loss is observed (atom economy concept). These reactions are mainly carried out in the presence of radical initiators or under basic conditions. Acidic and neutral media were also proposed. A few recent examples reported the use of a metal activation. This review is designed to remember some of the early aspects of hydrophosphination reactions using phosphines, protected or not, and unactivated or slightly activated alkenes, dienes and alkynes and to focus on the more promising results obtained in this field for the last 15 years. The reactions involving pentavalent phosphorus derivatives (phosphine-oxide, thiophosphines, phosphonate and phosphate derivatives etc.) are not concerned by this chapter. Keywords: AIBN activation, radical catalysis, functionalised dendrimers, Vinylpyridines, polyhedral oligosilsesquioxane (POSS), Cyclotrimerisation

Original SF5-Containing Fluorinated Copolymers Based on Vinylidene Fluoride

The radical co- and terpolymerization of fluorinated monomers bearing an SF5 group, XYCCZSF5 (where X, Y, and Z represent either H or F atoms) with 1,1-difluoroethylene (vinylidene fluoride, VDF or VF2) and hexafluoropropene (HFP), is presented. Although these SF5 monomers do not homopolymerize under radical initiation, they do copolymerize (and terpolymerize) in solution, in the presence of radical initiators with VDF (and with VDF and hexafluoropropylene (HFP)), hence leading to original copolymers bearing SF5 side groups. NMR characterizations and yields enabled one to compare the relative reactivities of F2CCFSF5, HFP, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether in the copolymerization of VDF with these fluoroolefins. The degree of fluorine substitution on the ethylenic unit of the SF5 monomers had an influence on their reactivity, on their relative incorporation in the copolymers, and on the molar masses of the resulting terpolymersthe higher the fluorine in the SF5 monomer, the higher molecular weight. Interestingly, the greater the degree of fluorine substitution of the SF5-containing monomer, the greater the yield of the reaction. The yield also increased as the amount of initiator was increased. The relative concentrations of the comonomers in each copolymer were assessed by 19F and 1H NMR spectroscopy. The thermal properties (thermal stability and glass transition temperature) of these resulting SF5-containing fluoropolymers were also examined.

Bamboo fiber (BF)-filled poly(butylenes succinate) bio-composite – Effect of BF-e-MA on the properties and crystallization kinetics

Abstract Effects of bamboo fiber (BF)-esterified with maleic anhydride (MA) (BF-e-MA) on the properties of BF-filled poly(butylene succinate) (PBS) bio-composites were investigated. Adding 5% BF-e-MA increased the tensile strength of the PBS/BF (70/30) composite from 21 MPa to 28 MPa in the presence of radical initiator (0.5%). Melt viscosity was also increased by adding BF-e-MA. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. At the same crystallization temperature, all composites showed lower values for the Avrami and Ozawa exponents than pure PBS. Furthermore, the values for the PBS/BF-e-MA composite were smaller than those for the PBS/BF composite. Equilibrium water-sorption amount (M ∞) were highest for the composite without BF-e-MA, followed by the composites with BF-e-MA and finally pure PBS. The diffusion coefficient (D) was smaller for the composites with BF-e-MA than without. Scanning electron microscopy revealed that interfacial adhesion between BF and PBS matrix was improved after addition of BF-e-MA.

Synthesis and potential radical copolymerization of new monomers based on diallylguanidine

AbstractMethods were elaborated for the synthesis of new monomers, derivatives of diallylguanidine. These monomer salts (acetate and trifluoroacetates) have the ability to polymerize in water and organic solvents in the presence of radical initiators. Radical copolymerization of diallylguanidine and diallyldimethylammonium chloride was investigated. High biocide ability of obtained copolymers was demonstrated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 439–444, 2004

Polymer immobilized silane bridged metallocene catalysts for ethylene polymerization

Ansa-zirconocene complex with an allyl substituted silane bridge [(CH 2CHCH 2)CH 3Si(C 5H 4) 2]ZrCl 2 ( 1a) has been synthesized and characterized. The molecular structure of 1a has been determined by X-ray crystallographic analysis. The polymer immobilized metallocene catalyst 1b is prepared by the co-polymerization of 1a with styrene in the presence of radical initiator. The result of ethylene polymerization showed that the polymer immobilized metallocene catalyst kept high activity for ethylene polymerization and was a potential supported catalyst for olefin polymerization.

Preparation of Partially Degraded Copolymers of Acrylamide with (Acrylamidopropyl)trimethylammonium Chloride in the Presence of Radical Initiators

Chain degradation of copolymers of acrylamide with (acrylamidopropyl)trimethylammonium chloride at 25-50°C in aqueous solutions under the action of radical degradative agents was studied viscometrically. The effiency of controlling the molecular weight of the copolymers was evaluated.

Quantitative assessment of antioxidant properties of natural colorants and phytochemicals: carotenoids, flavonoids, phenols and indigoids. The role of β‐carotene in antioxidant functions

AbstractReactive oxygen species are potentially damaging molecules. An important function of antioxidants is to intercept harmful triplet states, in order to prevent the formation of singlet oxygen, or to quench singlet oxygen directly. However, antioxidants are also reactive towards other active oxygen species such as the hydroxyl radical, the superoxide anion and the non‐excited oxygen ground state in the presence of radical initiators. It is well known that flavonoids and carotenoids show strong antioxidant properties. Polyenes and carotenoids are the best known among the compounds that quench singlet oxygen by efficient energy transfer. A large number of modified, synthetic analogues and derivatives have been synthesised to prepare even better quenchers than the natural carotenoids. Phenols are also excellent chain‐breaking antioxidants. Recently, many indigoid dyes (including bacterial indigoids) were studied, with the remarkable result that most, but not all, members of this class of chromophores quench singlet oxygen at the diffusion limit and some of them are excellent radical traps. It has been shown in this study that a quantitative assessment of antioxidant properties of flavonoids, carotenoids, phenols and natural indigoids can be achieved using the following three assays: (1) oxygen pressure dependence; (2) peroxide formation; (3) singlet oxygen quenching. Reactivities towards both excited states and ground state radicals can be properly described by these assays. The remarkable role of β‐carotene as an ‘unusual antioxidant’ (Burton GW and Ingold KU,Science224: 569–573 (1984)) in reactions using various oxygen pressures becomes clearer. The so‐called ‘pro‐oxidant effects’ concern primarily the antioxidant itself and its degradation, since no or very little damage to the substrate occurs in this type of experiment. Three main categories of antioxidants may be classified: (1) excellent antioxidants that perfectly quench excited states as well as ground state radicals (eg actinioerythrol, astaxanthin); (2) good antioxidants that strongly inhibit peroxide formation but are less efficient in quenching excited states (eg flavonols, tocopherols) or lead to considerable degradation of the antioxidant itself (eg β‐carotene, lycopene); (3) moderate antioxidants that fail to excel in both reactivities (eg ζ‐carotene, flavone).© 2001 Society of Chemical Industry

New Camphor Derivatives Functionalized at C3 and C10

Base-catalyzed condensation of 10-methylenecamphor with diethyl oxalate gave the corresponding (Z)-3-ethoxycarbonyl(hydroxy)methylene derivative which was converted into methyl ether and acetate. The Z-methyl ether undergoes isomerization into the E-methyl ether on treatment with N-bromosuccinimide in the presence of radical initiator [azobis(isobutyrodinitrile)]. (Z)-3-Ethoxycarbonyl(hydroxy)methylene-10-methylenecamphor smoothly reacts with N-bromosuccinimide to afford stereoisomeric 3-bromo derivatives.

The reactions of hypochlorous acid, the reactive oxygen species produced by myeloperoxidase, with lipids.

Myeloperoxidase (MPO), an abundant enzyme in phagocytes, has been implicated in the pathogenesis of various inflammatory diseases including atherosclerosis. The major oxidant produced by MPO, hypochlorous acid (HOCl), is able to modify a great variety of biomolecules by chlorination and/or oxidation. In this paper the reactions of lipids (preferentially unsaturated fatty acids and cholesterol) with either reagent HOCl or HOCl generated by the MPO-hydrogen peroxide-chloride system are reviewed. One of the major issues has been whether the reaction of HOCl with lipids of low density lipoprotein (LDL) yields predominantly chlorohydrins or lipid hydroperoxides. Electrospray mass spectrometry provided direct evidence that chlorohydrins rather than peroxides are the major products of HOCl- or MPO-treated LDL phosphatidylcholines. Nevertheless lipid peroxidation is a possible alternative reaction of HOCl with polyunsaturated fatty acids if an additional radical source such as pre-formed lipid hydroperoxides is available. In phospholipids carrying a primary amino group such as phosphatidylethanolamine chloramines are the preferred products compared to chlorohydrins. Cholesterol can be converted by HOCl to great variety of oxysterols besides three isomers of chlorohydrins. For the situation in vivo it appears that the type of reaction occurring between HOCl and lipids would very much depend on the circumstances, e.g. the pH and the presence of radical initiators. The biological effects of lipid chlorohydrins are not yet well understood. It has been shown that chlorohydrins of both unsaturated fatty acids as well as of cholesterol may cause lysis of target cells, possibly by disruption of membrane structures.

Radical addition of iodine monochloride to vinylidene fluoride

The radical addition of iodine monochloride to 1,1-difluoroethylene or vinylidene fluoride (VDF) leading to a ClCF 2CH 2I ( I)/ClCH 2CF 2I ( II) mixture is described. Four different ways of initiation (thermal, photochemical, presence of radical initiators or redox catalysts) were used and all of them led to a high amount (≥98%) of isomer ( I). The percentages of ( I) and ( II) isomers were determined by 19F NMR and they were also deduced from those of ClCF 2CH 3 and ClCH 2CF 2H obtained by selective reduction of the iodine atom of the product mixture, by tributylstannane. The reactivity of ICl to VDF and the high proportion of isomer ( I) were interpreted by means of a thermodynamical approach from the enthalpy of formation of ( I) and ( II), respectively, determined by semi-empirical computations. In addition, heats of formation of both isomers and interactions between the SOMO of radicals and the HOMO of the fluoroolefin show that the mechanism of such a reaction occurs via the addition of I to the less fluorinated side of VDF.

Mechanism of Free Radical-Induced Hemolysis of Human Erythrocytes: Comparison of Calculated Rate Constants for Hemolysis with Experimental Rate Constants

We previously developed a simple competitive reaction model between lipid peroxidation and protein oxidation in erythrocyte membranes that accounts for radical-induced hemolysis of human erythrocytes. In this study, we compared the rate constants calculated from the hemolysis curves of erythrocytes in the presence of radical initiators with those obtained from experiments using erythrocyte ghosts treated with radicals. 2,2′-Azobis(amidinopropane) dihydrochloride and 2,2′-azobis(2,4-dimethylvaleronitrile) were used as radical initiators. Plots of the logarithm of concentration of the radical initiator against the logarithm of the rate constant gave straight lines. The slope of the lines for the calculated lipid peroxidation was nearly equal with the experimental value. Similar results were obtained for oxidation of membrane proteins, except for band 3 oxidation. The values for the rate constants calculated from hemolysis curves seem to be accurate. The slope of the lines for the calculated rate constants for proteins was larger than the experimental value for band 3 oxidation, because band 3 oxidation is accompanied by aggregation or redistribution of band 3 proteins to form hemolytic holes. These results indicate that the competitive reaction model may be useful for analyzing radical-induced hemolysis.

Synthesis and properties of polystyrene-organoammonium montmorillonite hybrid

Styrene monomer was mixed with quaternary ammonium montmorillonites(org-MMTs) and polymerized in the presence of radical initiator. The resulting materials showed an expansion of interlayer distance. These hybrid materials exhibited higher thermal stability compared with the virgin polystyrene(PS) or PS/pristine-MMT microcomposite. PS/Bz-MMT, containing benzyl-unit similar to styrene in org-MMT, exhibited higher decomposition temperature even for MMT loading as low as 0.3wt.% compared with other PS/org-MMT hybrids. It was found that the structural affinity between styrene monomer and the organic group of org-MMT plays an important role in the structure and the properties of hybrid materials.

Radical addition of iodine monochloride to trifluoroethylene

The addition of iodine monochloride to trifluoroethylene (TrFE) leading to a ClCF 2CFHI ( I)/ClCFHCF 2I ( II) mixture is described. Four different ways of initiation (thermal, photochemical, presence of radical initiator, or redox catalyst) were used and all of them led to a high amount (>89%) of isomer ( I). The amounts of ( I) and ( II) isomers were determined by 1H and 19F NMR and also they were deduced from those of ClCF 2CFH 2 and ClCFHCF 2H obtained by selective reduction of the iodine atom of the former mixture, in the presence of tributylstannane. The reactivity of ICl to TrFE and the high proportion of isomer ( I) were interpreted by means of a thermodynamical approach from the enthalpy of formation of ( I) and ( II), respectively, determined by semi-empirical computations. In addition, heats of formation of both isomers and interactions between SOMO of radicals and HOMO of fluoro-olefin enable to show that the mechanism of such a reaction occurs via the addition of I to the less fluorinated side of TrFE.