Catalytic action of metallic salts in autoxidation and polymerization. IV. Polymerization of methyl methacrylate by cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide or dioxane hydroperoxide

Polymerization of methyl methacrylate was carried out by four initiating systems, namely, cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide (t-Bu HPO) or dioxane hydroperoxide (DOX HPO). Dioxane hydroperoxide systems were much more effective for the polymerization of methyl methacrylate than tert-butyl hydroperoxide systems, and cobaltous acetylacetonate was more effective than cobaltic acetylacetonate in both hydroperoxides. The initiating activity order and activation energy for the polymerization were as follows: Co(acac)₂–DOX HPO (E_a-9.3 kcal/mole) > Co (acac)₃–DOX HPO (E_a = 12.4 kcal/mole) > Co(acac)₂–t-Bu HPO (E_a = 15.1 kcal/mole) > Co(acac)₃–t-Bu HPO (E_a-18.5 kcal/mole). The effects of conversion and hydroperoxide concentration on the degree of polymerization were also examined. The kinetic data on the decomposition of hydroperoxides catalyzed by cobalt salts gave a little information for the interpretation of polymerization process.     

Catalytic Action of Metallic Salts in Autoxidation and Polymerization. VII. Polymerization of Methyl Methacrylate by Cobalt(ll) or (III) Acetylacetonate-Dioxane Hydroperoxide

Abstract

Polymerization of methyl methacrylate by Co(II or III) acetylacetonate-dioxane hydroperoxide [abbreviated as Co(acac)2, Co(acac)₃, and DOX HPO, respectively] was carried out in dioxane solvent, and the differences in polymerization rate and the degree of polymerization between two initiating systems were compared. Co(acac)₂-DOX HPO for the initiation of the polymerization system was more effective than Co(acac)₃-DOX HPO. The polymerization rate equations for both initiating systems obtained from kinetic data were as follows. For Co(acac)₂-DOX HPO initiating system: R_p=k [M]^3/2[Co(acac)₂]^1/7[DOX HPO]^?     

Cleavage of poly(vinyl alcohol) in the presence of tert-butyl hydroperoxide and biologically active metal complexes

The cleavage of poly(vinyl alcohol) in dimethyl sulfoxide at 42°C has been measured viscometrically in the presence of tert-butyl hydroperoxide and metal complexes. Phthalocyanine complexes of copper(II), iron(III), cobalt(II), and vanadium as VO(II) as well as hemin, hematin, chlorophyllin, and cytochrome c were used. The rates of decomposition of tert-butyl hydroperoxide in the presence of these metal complexes were measured idometrically. These data are compared to results obtained with other metal complexes in similar reactions.     

Synthesis of poly(arylene ethylene) oligomeric hydroperoxides and their use as initiating agents of radical polymerization

The oxidation to hydroperoxide of poly(arylene ethylenes) (PAE) by oxygen carried out in solutions at 80–110°C. The effect of initiating additions and the nature of solvent relative to the content of hydroperoxide groups in oxidized PAE were investigated. The oxidation to hydroperoxides in PAE occurs at the methylene groups, and the synthesized hydroperoxides are secondary peroxides. The decomposition of PAE hydroperoxides in toluene and chlorobenzene at concentrations of 0.006–0.03 mole/l. for hydroperoxide in the presence and absence of N-phenyl-α-naphthylamine (PNA) was studied. The decomposition of one hydroperoxide has been studied in the presence of cobaltous and manganese resinates and of PNA in chlorobenzene at 30–50°C. The addition of PNA to a chlorobenzene solution of PAE hydroperoxide containing cobaltous or manganese resinate accelerates the hydroperoxide decomposition, reduces the activation energy, and changes the reaction order from the second-order to first-order. The synthesized hydroperoxides initiate the radical polymerization of styrene and methyl methacrylate. The initiating activity of one of the synthesized hydroperoxides of PAE for polymerization of styrene (60°C) in the presence and absence of activating addition of manganese resinate was also evaluated.     

Titanium(IV) <Emphasis Type="Italic">tert</Emphasis>-Butoxide-<Emphasis Type="Italic">tert</Emphasis>-Butyl Hydroperoxide System as Oxidant for C-H Bonds in Hydrocarbons and Oxygen-containing Compounds

The system Ti(IV) tetra-tert-butoxide-tert-butyl hydroperoxide in mild conditions (20°C) oxidizes C-H bonds of methyl (toluene), methylene (hexane, ethylbenzene, benzyl ethyl ether), and methine (1, 1-diphenylethane, triphenylmethane) groups. The role of oxidant is played by the oxygen generated by the system. The process involves free radicals and produces hydroperoxides and Ti(IV) peroxides. The latter decompose both with preservation and decomposition of the hydrocarbon skeleton.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 545–551.Original Russian Text Copyright © 2005 by Stepovik, Gulenova, Martynova.     

Controlled radical polymerization of methacrylates of various structures in the presence of the AIBN-FeCl3-N,N-dimethylformamide catalytic system

The controlled radical polymerization of methyl methacrylate, 2-ethoxyethyl methacrylate, and tert-butyl methacrylate conducted via atom-transfer radical polymerization in the presence of the AIBN-FeCl₃· 6H₂O-N,N-dimethylformamide catalytic system is studied. For all the systems under study, the rate of reaction is first order with respect to the monomer concentration. The number-average molecular mass of the polymers linearly increases with conversion, and their polydispersity indexes are below 1.6. The rate of polymerization decreases in the following sequence: 2-ethoxyethyl methacrylate > methyl methacrylate > tert-butyl methacrylate. The presence of ω-terminal chlorine atoms in polymer macromolecules is confirmed by ¹H NMR spectroscopy and through the block copolymerization of methyl methacrylate with a poly(ethoxyethyl methacrylate)-based macroinitiator.     

Effect of thiourea on the radical polymerization of vinyl monomers. Part III. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with various organic peroxides as initiator

The effect of diphenyl thiourea (DPTU) on the radical polymerization of methyl methacrylate (MMA) has been studied in benzene solution at 50°C. with the use of cumene hydroperoxide (CHP), p-menthane hydroperoxide (PMHP), tert-butyl perbenzoate (tBPBz), di-tert-butyl peroxide (DBP), and dicumyl peroxide (DCP) as initiators. In the CHP-initiated polymerization, the rate of polymerization increased appreciably on addition of DPTU with a linear dependence on the square root of DPTU concentration up to a maximum which was observed when the ratio of the concentration of CHP to DPTU was 2.5. Then the rate decreased gradually with increasing DPTU concentration in the range greater than the above ratio. It was found from kinetic studied that the overall polymerization rate R_p was expressed by the equation: R_p = K[peroxide]^1/2 [DPTU]^1/2[MMA], where K is the rate constant, α = 1.2 for CHP and α = 1.0 for tBPBz. It was thought that the acceleration effect observed was due to a redox reaction caused by the interaction of a peroxide–monomer and/or a peroxide–solvent complex with DPTU, and the decrease in the polymerization rate which was observed over a certain concentration of DPTU was due to the action of the oxidized product of DPTU as a transfer agent. The effect of substituents was studied by using para and meta-substituted DPTU. It was found that the polymerization rate increased as electron-donating substituents are added to the benzene ring of DPTU with considerable dependence on Hammett's equation (p = ?0.36). The acceleration effect is also observed for PMPH-and tBPBz-initiated polymerizations, whereas the DCP- and DBP-initiated systems show no effects on the polymerization rate.     

Hydroperoxide-initiated copolymerization of sulfur dioxide and cyclohexene. I. Characterization of charge-transfer complex and initiation

The copolymerization of cyclohexene and sulfur dioxide to form an alternating copolymer was initiated by tert-butyl hydroperoxide. The enthalpies and entropies of formation of the cyclohexene-sulfur dioxide charge-transfer complex, which is present during the copolymerization, were determined in two solvents by means of ultraviolet spectroscopy. The reduction of ultraviolet absorption during copolymerization afforded a convenient means of investigating reaction kinetics. No evidence of the direct involvement of the complex in polymerization initiation was found. The observation that the use of unpurified cyclohexene led to spontaneous initiation appears to point to adventitiously formed hydroperoxide rather than the charge-transfer complex as providing initiating radicals which are produced by the redox reaction of the hydroperoxide with sulfur dioxide. A competing heterolytic scission reaction was found to result in the formation of tert-butyl peroxide and sulfuric acid. This reaction caused the polymerization reaction to stop after a short period of time due to a time-dependent decrease in initiator concentration.     

Anionic polymerization of vinyl monomers with xanthates

The polymerization of vinyl monomers with various xanthates (potassium tert-butylxanthate, potassium benzylxanthate, zinc n-butylxanthate, etc.) were carried out at 0°C in dimethylformamide. N-Phenylmaleimide, acrylonitrile, methyl vinyl ketone, and methyl methacrylate were found to undergo polymerization with potassium tert-butylxanthate; however, styrene, methyl acrylate, and acrylamide were not polymerized with this xanthate. In the anionic polymerization of methyl vinyl ketone with potassium tert-butylxanthate, the rate of the polymerization was found to be proportional to the catalyst concentration and to the square of the monomer concentration. The activation energy of methyl vinyl ketone polymerization was 2.9 kcal/mole. In the polymerization, the order of monomer reactivity was as follows: N-phenylmaleimide > methyl vinyl ketone > acrylonitrile > methyl methacrylate. The initiation ability of xanthates increased with increasing basicity of the alkoxide group and with decreasing electronegativity of the metal ion in the series, lithium, sodium, and potassium tert-butylxanthate. The relative effects of the aprotic polar solvents on the reactivity of potassium tert-butylxanthate was also determined as follows: diethylene glycol dimethyl ether > dimethylsulfoxide > hexamethylphosphoramide > dimethylformamide > tetrahydrofuran (for methyl vinyl ketone); dimethyl sulfoxide > hexamethylphosphoramide > dimethylformamide ? diethylene glycol dimethyl ether (for acrylonitrile).     

Polymerization of propadiene. II. Catalyst systems based on 3d transition metals and various stabilizing ligands

A variety of catalyst systems based on 3d transition metals, i.e., V(III), Cr(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and various stabilizing ligands, i.e., propadiene, methylacetylene, phenylacetylene, and 1,4-butadiene, were prepared. The activity of these catalytic systems towards the polymerization of a series of monomers (propadiene, methylacetylene, phenylacetylene, 1,4-butadiene, ethene, and propene) is investigated. Optimum conditions for the preparation of 1,2-polyallene, polymethylacetylene and polyphenylacetylene are given.     

Free-radical polymerization of methyl methacrylate and p-fluorostyrene in the presence of the Mn(acac)3–AlEt3 catalyst system

Methyl methacrylate and p-fluorostyrene were polymerized with manganese (III) acetylacetonate–aluminum triethyl catalyst at 60°C in a benzene medium. Maximum activity was found at Al/Mn ratio of 4. Maximum percent conversion of polymer was obtained when the aging time of the catalyst was 10 min. The rate of polymerization was first order with respect to monomer. The rate of polymerization with respect to catalyst and cocatalyst were found to be 0.5 and 1.5, respectively. The overall energy of activation for the polymerization of methyl methacrylate and p-fluorostyrene were found to be 52.6 and 57.0 kJ/mole, respectively. A free-radical mechanism is postulated.     

Synthesis of graft copolyimides via controlled radical polymerization of methacrylates with a polyimide macroinitiator

The atom-transfer radical polymerization of methyl methacrylate and tert-butyl methacrylate with a polyimide multicenter macroinitiator in the presence of a CuCl-2,2′-bipyridine catalytic system is investigated. The kinetic features of the process, the molecular-weight characteristics of the formed side chains, and the post-polymerization of methyl methacrylate with graft polyimides containing polymethacrylate side chains are studied. The conditions of controlled polymerization yielding graft copolyimides with narrowly dispersed living poly(methyl methacrylate) or poly(tert-butyl methacrylate) side chains of variable lengths are determined.     

Determination of lipids and their oxidation products by IR spectrometry

We proposed a procedure for the IR spectrometric determination of lipid hydroperoxides in biological systems. The main bands in the IR absorption spectra of linoleic acid and its hydroperoxide were identified, and analytical bands suitable for the determination of both compounds in their mixtures were selected. It was demonstrated that tert-butyl hydroperoxide can be used as an external standard for determining fatty acid hydroperoxides. Using the external standard method (calibration curve) for tert-butyl hydroperoxides, we calculated the concentration of linoleic acid hydroperoxide in its mixture with linoleic acid; it agreed with the specified values. Using the developed procedure, we estimated the concentration of hydroperoxide groups in natural cardiolipin. The results were compared to those obtained by an independent method (activated chemiluminescence).     

Mechanism of initiation of methyl methacrylate with lithium tert-alkoxides

An investigation of the solution polymerization of methyl, butyl, isobutyl, sec-butyl, and tert-butyl methacrylates and the polymerization of methyl and butyl methacrylates in the presence of methyl, butyl, and tert-butyl isobutyrate and methyl pivalate showed that the complex order of the initiation reaction with respect to the monomer (about 2) has its cause in the ability of the ester group in the monomer and of methyl or butyl isobutyrate to activate lithium tert-alkoxide. Owing to conjugation, the ester group in the monomer is less active than the ester group in isobutyrate. Steric hindrances of the formation of a complex between lithium tert-alkoxide and ester were also investigated, because this complex is intermediate product necessary for the formation of an activated lithium tert-alkoxide, capable of initiating the polymerization of alkyl methacrylates of the type CH₂?(CH₃)COOCH₂R.     

Metallo esters. VII. Stabilizing effect of sodium tert-butoxide on the growth center in the anionic polymerization of methacrylic esters

The growth center in the anionic polymerization of methacrylic esters is stabilized with alkaline alkoxides, sodium tert-butoxide in particular. The lifetime of the growth center was investigated in the polymerization of methyl methacrylate by evaluating yield and molecular weight distribution of the polymer formed when the monomer was added in two doses. The average lifetime of the original growth center stabilized by sodium tert-butoxide at 20°C under the given conditions was longer than several minutes. The stabilization of the growth center was also used in the stepwise copolymerization of n-butyl methacrylate and methyl methacrylate. The copolymer thus obtained in high yield was characterized as a block copolymer on the basis of its solubility, nuclear magnetic resonance (NMR) spectra, and measurements of the complex shear modulus.     

Styrene epoxidation over a SBA-15-supported Mn(III) Schiff-base complex

2,4-Di-tert-butyl-6-((E)-(propylimino)methyl)phenol as a Schiff-base ligand was immobilized onto an amino-functionalized SBA-15 through the reaction between di-tert-butyl-salicylaldahyde and the tethered amino group. The Mn(III) metal complex of the immobilized Schiff-base ligand was proven to be an active catalyst for the epoxidation of styrene withtert-butyl hydroperoxide as a terminal oxidant. The catalysts behaved as an oxidation catalyst in the epoxidation and could be used many times without structural degradation, leaching of active manganese species and significant activity loss. It has been concluded that the reversible redox cycles of the metal center play a key role during the epoxidation reaction, as well as in the reusability of the catalysts.     

Heterogeneous initiators for the synthesis of polymer nanocomposites

Nanocomposites are obtained by the radical polymerization of styrene and methyl methacrylate on the surface of a dispersed filler containing chemisorbed compounds of quaternary ammonium, which catalyze decomposition of cumene hydroperoxide. The heterogeneous catalysts of hydroperoxide decomposition are obtained via the adsorption of cetyltrimethyl ammonium bromide and acetylcholine chloride on sodium montmorillonite, cellulose, and chitosan. The highest rate of the polymerization of both monomers is provided by the cellulose–cetyltrimethyl ammonium bromide catalyst. For a more hydrophilic methyl methacrylate, the rate of radical initiation is significantly lower at the same concentrations of the catalyst and hydroperoxide compared with hydrophobic styrene; however, the rate of polymerization is higher than for styrene because of a higher activity of methyl methacrylate in chain-propagation reactions. Relatively high rates of radical generation upon contact of cellulose–cetyltrimethyl ammonium bromide and cellulose–acetylcholine with hydroperoxides open the possibility to create cellulose-based disinfecting and medical materials.     

Reactivity of tert‐butylperoxyl radical with manganese(III), cobalt(II), and nickel(II) salicylidene Schiff base chelates

Salicylidene Schiff base chelates (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminomanganese(III) chloride, (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminocobalt(II), N,N′‐bis(salicylidene)‐ethylenediaminocobalt(II), N,N′‐bis(salicylidene)ethylenediaminonickel(II), and N,N′‐bis(salicylidene)ethylenediaminoaquacobalt(II), as well as (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)1,2‐cyclohexanediamine, were kinetically examined as antioxidants in the scavenging of tert‐butylperoxyl radical (tert‐butylOO^?). Absolute rate constants and corresponding Arrhenius parameters were determined for reactions of tert‐butylOO^? with these chelates in the temperature range ?52.5 to ?11°C. High reactivity of tert‐butylOO^? with Mn(III) and Co(II) salicylidene Schiff base chelates was established using a kinetic electron paramagnetic resonance method. These salicylidene Schiff base chelates react in a 1:1 stoichiometric fashion with tert‐butylOO^? without free radical formation. Ultraviolet–visible spectrophotometry and differential pulse voltammetry established that the rapid removal rate of tert‐butylOO^? by these chelates is the result of Mn(III) oxidation to Mn(IV) and Co(II) oxidation to Co(III) by tert‐butylOO^?. It is concluded that removal of alkylperoxyl radical by Mn(III) and Co(II) salicylidene Schiff base chelates may partially account for their biological activities. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 431–439, 2007     

Photo-controlled/living radical polymerization of tert-butyl methacrylate in the presence of a photo-acid generator using a nitroxide mediator

The photo-controlled/living radical polymerization of tert-butyl methacrylate was performed using a (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) initiator and a 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) mediator in the presence of a (4-tert-butylphenyl)diphenylsulfonium triflate photo-acid generator. The bulk polymerization was carried out at 25 °C by irradiation with a high-pressure mercury lamp. Whereas the polymerization in the absence of MTEMPO produced a broad molecular weight distribution, the MTEMPO-mediated polymerization provided a polymer with a comparatively narrow molecular weight distribution around 1.4 without elimination of the tert-butyl groups. The living nature of the polymerization was confirmed on the basis of the linear correlations for the first-order time–conversion plots and conversion–molecular weight plots in the range below 50% conversion. The block copolymerization with methyl methacrylate also supported the livingness of the polymerization based on no deactivation of the prepolymer.     

The microdetection of particulates from organometallic compounds : I. Metal acetylacetonate chelates

The new technique of organic particulate analysis (OPA) has been employed to evaluate the thermal decomposition of metal acetylacetonate chelates. Of the 23 compounds thus evaluated, 13 were found to give organoparticulation signals at temperatures <190 °C as indicated by their effect on the output current of an ion chamber detector. In some instances, very strong particulation was observed, particularly with the transition metal acetylacetonates, such as Co(II), Co(III), Fe(III), Cr(III), and Mn(III).In an attempt to characterize the nature of the particulates derived from these compounds, mass-spectral data were obtained on the effluent species arising from the thermal decompositions of the strongest particulate emitting metal acetylacetonates. The results showed that acetylacetone was the major component identified in both particulate and vapor effluents. With the exception of Cr(III) acetylacetonate, no metal was detected in these effluents.The OPA technique enabled the relative thermal stabilities of the metal acetylacetonates to be ascertained. Zn acetylacetonate was found to have the lowest thermal stability and the alkaline earth compounds the highest; the transition metal acetylacetonates exhibit intermediate thermal stabilities.Since a certain critical minimum particulate size (i.e., 25 Å) seems to be necessary to produce a response on the ion chamber detector instrument, vapor-phase association of acetylacetone molecules may be occurring. This association would most probably occur through H-bonded species involving the enol form of the 1,3-diketone.