An ESR study of PMMA mechanoradicals and of their interaction with oxygen

Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicals? CH₂? C(CH₃)(COOCH₃) (I) and CH₂? C(CH₃)(COOCH₃)? CH₂ (II) produced by the breaking of the polymer chain, and secondary radicals ? CH₂? C(CH₃)(COOCH₃)? CH? C(CH₃)? (COOCH₃)? CH₂? (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).     

ESR spectra of C60 in concentrated sulfuric acid

On dissolution of C₆₀ in concentrated sulfuric acid, ESR spectra of paramagnetic species, which were identified as dimers (C₁₂₀ ⁺) or oligomers (nC₆₀)⁺, were recorded. The ESR spectra recorded upon the reaction of a toluene solution of C₆₀ with sulfuric acid were assigned to the radical cation C₆₀ ⁺. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2373–2376, November, 1998.     

甲基丙烯酸甲酯增长自由基ESR谱研究

利用高斯分布和构象叠加模型模拟了本体聚合反应全过程增长自由基ESR谱,获得了其构象构成及其随反应的变化,并对产生变化的原因即介质粘度和增长反应对谱的影响进行了讨论。     

ESR spectra of fullerence C70 in concentrated sulfuric acid

It was established by ESR spectroscopy that the reaction of C₇₀ with concentrated H₂SO₄ resulted in the formation of isomeric dimers C₁₄₀ ⁺, and the action of H₂SO₄ on a toluene solution of C₇₀ ⁺ gave the C₇₀ radical cation. The structure of dimers was discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 208–210, January, 1999.     

Determination of the orientation distribution function of anisotropic paramagnetic species from the angular dependence of the ESR spectra

A method for determination of the orientation distribution function of anisotropic paramagnetic species from the angular dependence of the ESR spectra based on simulation of the spectra was developed. The orientation distribution function is represented as a sum of orthonormal functions. The weight coefficients are determined by minimizing the deviations of the theoretical spectra from experimental ones. The method was numerically tested. The method is relatively insensitive to the presence of noise and foreign ESR signals not related to the sample orientation in the magnetic field.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2595–2601, December, 2004.     

ESR spectra of paramagnetic palladium complexes

Binuclear nitrosopalladium complexes Pd₂(μ-COOR)₂(η²-CH₂C₆H₄NO)₂ (R = Me, CF₃, or Ph) were studied by ESR spectroscopy. Analysis of parameters of ESR spectra of the polycrystalline samples and their toluene solutions suggests partial izomerization of the nitroso ligands to the nitroxide form to result in the oxidation of palladium(II) to palladium(III). __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1746–1751, August, 2005.     

A generation mechanism of triboelectricity due to the reaction of mechanoradicals with mechanoions which are produced by mechanical fracture of solid polymer

Mechanical fracture of solid polymer under vacuum at 77K can, in principle, produce both mechanoradicals and mechanoanions which are formed by homolytic and heterolytic scission of carbon-carbon bonds in the polymer main chain. The production of mechanoanions was claimed by a detection of tetracyanoethylene (TCNE) anion radical (TCNE^–), which was observed by electron spin resonance (ESR) spectroscopy using the electron trapping method with TCNE.A novel mechanism for generating triboelectricity is proposed. The charge carrer is an electron. The electron donor is the mechanoanion A^–, which is produced by heterolytic carbon-carbon bond scission of the main chain of polymer A. The electron acceptor is the mechanoradical B·, which is produced by homolytic carbon-carbon bond scission of the main chain of polymer B. Charge separation is due to an electron transfer from the mechanoanion to the mechanoradical when in contact. It is possible to speculate the sign of the charge induced by friction from the electron release potential of A^–, Pr(A^–), and the molecular electron affinity of B·, Ea(B·). The triboelectric series deduced from our mechanism is PMMA-PP-PE-PVDF-PTFE, in which polymers having a relatively low Pr(A^–) to high Pr(A^–) or polymers having a relatively low Ea(B·) to high Ea(B·) are arranged. This order is identical with well-known triboelectric series.Dedicated to Professor Hans-Henning Kausch on the occasion of his 60th birthday     

Effect of dioxygen on ESR spectra of polyaniline

The effect of dioxygen on the width of ESR lines of powders and films of polyaniline was studied at 15–300 K. It was found that the line broadening can decrease or increase, which corresponds to strong or weak exchange, respectively. For dry polyaniline powders and films, maxdimum broadening was observed at 240 K. The findings were explained by spin exchange during collisions of a mobile polaron with immobile O₂ molecules bound to the polymer. The values of exchange interaction between the O₂ molecule and the polaron and the mobility of the polarons along the polymer chain were found. The mobility of polarons along the polymer chains decreases in the presence of H₂O, and dioxygen predominantly adds to the imine N atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2293–2297, December, 1999.     

Photochemical synthesis and ESR spectra of quintet meta-phenylenedinitrenes

Relationships between the molecular structures and zero-field splitting parameters of quintet m-phenylenedinitrenes formed during the photolysis of 1,3-diazidobenzenes in 2-methyltetrahydrofuran solutions frozen at 77 K were studied by ESR spectroscopy and B3LYP/6-31G* calculations. Simulations of the W₋₂/W₋₁, W₊₂/W₊₁, W₋₁/W₀, W₊₁/W₀, and W₊₂/W₀ (Δm _s = 2) transitions were performed for the first time and all signals in the ESR spectra of quintet m-phenylenedinitrenes were unambiguously assigned. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1085–1089, July, 2006.     

Effect of chain aggregation on the conductivity and ESR spectra of polyaniline

Solutions of polyaniline in m-cresol with and without camphorsulfonic acid (CSA), as well as films cast from these solutions were studied by ESR spectroscopy at 133–423 K and by optical spectroscopy in the range λ = 350–1100 nm. An analysis of the optical and ESR spectra shows that in the solutions and films without CSA polyaniline is fully doped but the conductivity of these films is low (∼10⁻⁸ S cm⁻¹; cf. 100 S cm⁻¹ for the films with CSA). Compared with the CSA-containing samples, the samples without CSA are characterized by broader ESR lines and higher contribution of the Curie spins to the magnetic susceptibility. These facts indicate a weak aggregation of polyaniline chains without CSA, which leads to low conductivity. A formula was proposed, which describes the temperature dependence of the polyaniline ESR linewidth and allows the interchain distance and the mobility of electrons moving along polymer chains to be determined. The conductivity of polyaniline films is affected by moderate heating (363–388 K) of the films and solutions from which the films were cast. It was found that the interchain distances correlate with the conductivity of the films and with the broadening of their ESR lines caused by the effect of O₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2701–2711, December, 2005.     

Study of ESR spectra of fullerene C60 doped with magnesium and mercury

An increase in the intensity of the ESR signal and of its g value was observed in the course of annealing of the diamagnetic product of the reaction between magnesium amalgam and a toluene solution of C₆₀. The formation of a crystalline substance Mg_rC₆₀ with semiconductor properties was assumed. The ESR spectra of the products of vapor-phase synthesis of MgC₆₀ and Hg_rC₆₀ were recorded.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2256–2258, September, 1996.     

The ESR spectra of the spin-adducts of branched perfluorinated σ-radicals with fullerene-60

The ESR spectra of the radical adducts of the^.CF=CFC(CF₃)₃ and^.C(O)CF(CF₃)₂ radicals with C₆₀ are characterized by hyperfine interaction with the nucleus of the δ-fluorine atom located above the five-membered cycle in the fullerenyl radical. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1222–1224, June, 1997.     

Correlations between magnetic resonance parameters of ESR and NMR spectra

Empirically established correlations between magnetic resonance parameters of free radicals (g-factors, isotropic hyperfine coupling constans) and isostructural molecules (chemical shifts, isotropic spin-spin coupling constants) or structurally similar ligands in paramagnetic transition metal complexes (isotropic chemical shifts) are systematized and critically discussed. Quantum-chemical analysis of the suggested spin distribution damping coefficients in model systems and structurally similar chemical compounds is performed. Based on the results obtained, physicochemical interpretation of the observed correlations between the parameters of ESR and NMR spectra is given. Dedicated to the memory of Academician V. V. Voevodskii (to the 80th anniversary). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1575–1583, September, 1997     

Surface characterization and radical decay studies of oxygen plasma‐treated PMMA films

Polymethylmethacrylate (PMMA) films were modified by RF oxygen plasma with various powers applied for different periods, and the effects of these parameters on the surface properties such as hydrophilicity, surface free energy (SFE), chemistry, and topography were investigated by water contact angle, goniometer, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy, and the types of the created free radicals and their decay were detected by electron spin resonance spectroscopy (ESR). SFE and contact angle results varied depending on the plasma parameters. Oxygen plasma treatment (100 W–30 min) enhanced the hydrophilicity of PMMA surface as shown by decreasing the water contact angle from 70° to 26°. XPS analysis showed the change in the amounts of the present functionalities as well as formation of new groups as free carbonyl and carbonate groups. The roughness of the surface increased considerably from ~2 nm to ~75 nm after 100 W–30 min oxygen plasma treatment. ESR analysis indicated the introduction of peroxy radicals by oxygen plasma treatment, and the intensity of the radicals increased with increasing the applied power. Significant decrease in radical concentration was observed especially for the samples treated with higher powers when the samples were kept under the atmospheric conditions. As a conclusion, RF plasma, causes changes in the chemical and physical properties of the materials depending on the applied parameters, and can be used for the creation of specific groups or radicals to link or immobilize active molecules onto the surface of a material. Copyright © 2012 John Wiley & Sons, Ltd.     

ESR spectra of endohedral metallofullerene Ce@C82 radical anions in dimethylformamide and pyridine

Endohedral metallofullerene Ce@C₈₂ dissolved in dimethylformamide or pyridine is reduced to the radical anion. Analysis of hyperfine coupling with the topologically different ¹³C nuclei indicates the electronic structure with bivalent cerium and the paramagnetic carbon framework Ce²⁺@C₈₂ ^·3–. The ESR spectra of the radical anions of the functionalized Ce@C₈₂ derivatives are detected.     

Anomalous line broadening in the ESR spectra of copper(ii) dithizonate

The structure of the copper(ii) complex with dithizone (H₂Dz) was studied by ESR spectroscopy. The lines of the ESR spectra of the Cu(HDz)₂ complex in solutions are so broad that the superhyperfine structure (SHFS) from the ligand atoms is unobservable and even the hyperfine structure (HFS) from the copper nuclei is poorly resolved. In polycrystalline magnetically dilute powders with the ratio Ni(HDz)₂ : Cu(HDz)₂ = 60 : 1, the SHFS from the N atoms is well resolved in both perpendicular and parallel orientations. The copper(ii) complex with dithizone has a square-planar structure in both liquid solutions and Ni(HDz)₂ matrix. Reasons for the unusual linewidths in the ESR spectra of Cu(HDz)₂ are discussed.     

ESR analysis of the kinetic alkalinity of pseudophedrine

The kinetics of protonation of pseudoephedrine by 3,6-di-tert-butyl-2-hydroxyphenoxyl have been analyzed by the ESR technique. It was shown that protolysis of the radical produced closed ionic pairs with the pseudoephedrine cation in a dimer state.A. N. Nesmeyanov Institute of Elementoorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2007–2011, September, 1992.     

ESR spectra of trifluoromethyl radical formed during the solid-phase photodecomposition of long-lived perfluoro-2,4-dimethyl-3-ethylpentyl-3 radicals

The products of photolysis of the long-lived radical [(CF₃)₂CF]₂C^·C₂F₅ at 77 K were studied by ESR. The mechanism of photodecomposition to form ^·CF₃ radicals was proposed. The ESR spectra of the trifluoromethyl radicals stabilized at 77 K in a glassy hexafluoropropylene trimer matrix were simulated, and the parameters À = 25.15 mT, À = 9.1 mT, and g = l.9996, g = 2.0056 were determined.     

Melt-electrospinning of PMMA

<正>The melt electrospinning of PMMA was investigated.The averaged fiber diameter thus obtained was reduced from 34.0μm to 19.7μm by adding di-(2-ethylhexyl)phthalate to reduce viscosity of the molten PMMA,and it further lowered down to 4.0μm when a KCl/ice-water solution was used as collection media.A comparison study on the PMMA fibers made through melt electrospinning and done by solution electrospinning was made.It was found that solution electrospinning was capable of fabricating very thin fibers as small as to a nanometer size,but resulted in a much wider fiber diameter range than melt-electrospinning did.In general,within some extent an increase in applied voltage and amount of the additive or a decrease in collection distance can give rise to a decreased fiber diameter and improved mechanical performance for the PMMA fibers by melt electrospinning.It was also indicated that the mechanical properties of the PMMA fibers made through melt-electrospinning were superior to those by solution elctropspinning.     

Temperature dependence of ESR spectra of nitroxide spin probe in glassy polymers

Temperature dependencies of ESR spectra of nitroxide spin probes in glassy polymers near and below glass transition temperature were examined in detail. Three temperature ranges, each characterized by specific changes in spectral shape, were defined. (i) In the low temperature range, ESR spectra of nitroxide radical in glassy polymer matrix weakly depend on temperature and remain qualitatively the same. (ii) In the intermediate temperature range, significant changes in the shape of spectra are observed. (iii) A new phenomenon was revealed near and below glass transition temperature: narrowing of linewidths occurs while the ratio of amplitudes of different components varies insignificantly. Analysis of molecular rotational mobility was carried out by means of commonly used empirical approaches. It was shown that widely used formulas and empirical approaches are not applicable for characterization of molecular mobility in glassy polymers. Mechanisms of rotational molecular movements in glassy polymers are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 563–575, 2009