电熔刚玉和锆刚玉中变价态氧化物存在价态的ESR分析

对影响刚玉、电熔锆刚玉 (FCAZS)中变价态氧化物存在价态的因素之一的熔炼气氛 ,以及变价态氧化物存在价态的测定方法进行了研究。研究结果证实 ,致密电熔刚玉和还原法生产的FCAZS制品中 ,变价态氧化物确实是以低价态存在的 ,而电子自旋共振法 (ESR)是定性或半定量分析变价态氧化物杂质存在价态的有效手段。     

Fourier transform near‐infrared and electron spin resonance studies on the crosslinking reaction of liquid carboxylated poly(acrylonitrile‐co‐butadiene) rubber with dicumyl peroxide in dioxane

The crosslinking reaction of liquid carboxylated poly(acrylonitrile‐co‐butadiene) [or nitrile rubber (NBR); acrylonitrile = 10 wt %] with dicumyl peroxide (DCPO) was studied in dioxane by means of Fourier transform near‐infrared spectroscopy (FT‐NIR) and electron spin resonance spectroscopy (ESR). Among the three butadiene units (1,2, cis‐1,4, and trans‐1,4 units) of NBR, only the pendant vinyl group of the 1,2 unit showed an absorption at 6110 cm^?1 from the FT‐NIR examination of dioxane solutions of NBR, 1‐octene, 3,3‐dimethyl‐1‐butene, trans‐2‐octene, cis‐5‐octen‐1‐ol, poly‐cis‐1,4‐butadiene, and poly‐1,2‐butadiene. The crosslinking reaction was followed in situ in dioxane by the monitoring of the disappearance of the pendant vinyl double bond with FT‐NIR. The initial disappearance rate (R₀) of the vinyl group was expressed by R₀ = k[DCPO]^0.9[NBR]^?0.2 (120°C). The overall activation energy of the reaction was calculated to be 20.7 kcal/mol. This unusual rate equation suggests unimolecular termination due to degradative chain transfer and depressed reactivity of the vinyl group caused by crosslinking. ESR study of the reaction mixture revealed that an allyl‐type polymer radical was formed in the reaction, and its concentration increased with time and was then saturated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2095–2101, 2003     

Location of Mn in MnAPO‐11: influence of synthesis from aqueous and non‐aqueous media

MnAPO11 samples were synthesized from aqueous (MnAPO11(A)) and ethylene glycol (MnAPO11(NA)) media. The crystallinity of the samples was more when the synthesis was carried out in ethylene glycol. Chemical and thermogravimetric analyses reveal greater incorporation of Mn in the framework of MnAPO11(NA) than in MnAPO11(A). At least five different types of Mn(II) species are detected in the samples by ESR. The studies suggest that Mn is more homogeneously distributed in MnAPO11(NA) than in MnAPO11(A).     

Inhibitor radicals in styrene polymerization

Stable radicals derived from inhibitor molecules were detected in the process of styrene polymerization. N‐(1,4‐dimethylpentyl)‐4‐nitroso‐aniline and 2,4‐dinitrophenol inhibitors were shown to produce nitroxyl radicals. Phenoxyl radicals come from 4‐benzylidene‐2,6‐di‐tert‐butyl‐cyclohexa‐2,5‐dienone. The radical structures were determined. The kinetics of radical formation was studied. These radicals can participate in the process of living radical polymerization and significantly affect the kinetics of polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1599–1603, 2004     

The study of poly(styrene‐co‐p‐(hexafluoro‐2‐hydroxylisopropyl)‐α‐methylstyrene)/poly(ethylene oxide) blends

Different hydroxyl content poly(styrene‐co‐p‐(hexafluoro‐2‐hydroxylisopropyl)‐α‐methylstyene) [PS(OH)‐X] copolymers were synthesized and blends with 2,2,6,6‐tetramrthyl‐piperdine‐1‐oxyl end spin‐labeled PEO [SLPEO] were prepared. The miscibility behavior of all the blends was predicted by comparing the critical miscible polymer–polymer interaction parameter (χ_crit) with the polymer–polymer interaction parameter (χ). The micro heterogeneity, chain motion, and hydrogen bonding interaction of the blends were investigated by the ESR spin label method. Two spectral components with different rates of motion were observed in the ESR composite spectra of all the blends, indicating the existence of microheterogeneity at the molecular level. According to the variations of ESR spectral parameters T_a, T_d, ΔT, T_50G and τ_c, with the increasing hydroxyl content in blends, it was shown that the extent of miscibility was progressively enhanced due to the controllable hydrogen bonding interaction between the hydroxyl in PS(OH) and the ether oxygen in PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2312–2317, 2004     

Thermally induced homolytic scissions of interunitary bonds in a softwood lignin solution: A spin‐trapping study

Unstable chemical species, that is, radicals generated by the thermal treatment of a dimethyl sulfoxide (DMSO) solution of the lignin of a softwood, Yezo spruce (Picea jezoensis Carr.), were studied in detail with an electron spin resonance (ESR) method combined with a spin‐trapping technique. An unstable secondary carbon radical (～CH ·) in the solution was trapped as a stable nitroxide spin adduct [R? (N? O ·)? CH～ (R = tert‐butyl benzene)] when the DMSO solution was heat‐treated in the presence of a spin‐trapping reagent [2,4,6‐tri‐tert‐butylnitrosobenzene (BNB)] at about 40°C. This meant that alkyl phenyl ether bonds (～CH? O‐phenyl), known as interunitary lignin bonds, were homolytically scissioned by the thermal treatment in the lignin solution. A detailed analysis of the ESR spectrum revealed that three kinds of radicals—primary (～CH₂ ·), secondary (～CH ·), and tertiary (～C ·) carbon radicals—were trapped as stable spin adducts at about 60°C, although the phenoxy radical (Ph? O ·) was not trapped by the BNB spin trap as the counter radical of the secondary carbon radical. This suggested that a fairly large steric hindrance existed between the so‐called guaiacoxy radical with a methoxy group in the ortho position and the BNB molecule bearing two butyl groups as bulky moieties in the ortho positions. However, the phenoxy radicals in the lignin solution were stable up to about 60°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2136–2141, 2004     

Mechanism of copper(II) adsorption by polyvinyl polyacrylate

The mechanism of copper adsorption by polyvinyl polyacrylate (PVPA) was examined using ESR and magnetic measurements. The copper adsorption by PVPA obeyed Langmuir adsorption isotherm with the maximum adsorption amounts of 4.17 mmol g^?1 adsorbent, being larger than those of uranium adsorption. Though copper in the solution was completely adsorbed by the resin above pH 4, the ESR intensity was remained low level and only increased above pH 8. The ESR spectrum of Cu(II) ion in PVPA are axial type with tetragonally distorted octahedral symmetry, having parameters of g_⊥ = 2.361, g_? = 2.057, |A_⊥| = 14.0 m cm^?1 (pH 5), and g_⊥ = 2.329, g_? = 2.058, |A_⊥| = 16.2 m cm^?1, |A_?| = 2.7 m cm^?1 (pH 9). The absorption peaks originated from Cu(II)–Cu(II) dimer was also observed (pH 5). The paramagnetic susceptibility of PVPA adsorbed Cu(II) ion at pH 5 explained by the dimer model with |J| = 220 K. These results suggested that most of copper was adsorbed and formed dimer in PVPA, being similar to that in Cu(II)‐acetate monohydrate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5372–5377, 2006     

Comparison of cupric ion location and adsorbate interactions in Cu(II)-exchanged H-SAPO-5 and H-SAPO-11 molecular sieves determined by electron spin resonance and electron spin echo modulation spectroscopies

The locations and interactions of cupric ion exchanged into H-SAPO-11 and H-SAPO-5 molecular sieves with water, methanol, ethanol, ammonia, ethylene and pyridine have been compared by electron spin resonance and electron spin echo modulation spectroscopies. After dehydration, equilibration with ethylene and pyridine adsorbates was slower compared with that for more polar adsorbates. One major difference between these two molecular sieves in cupric ion coordination to adsorbates is that two waters are coordinated in CuH-SAPO-11 while three waters are coordinated to cupric ion in CuH-SAPO-5. This indicates different coordination sites for the cupric ion in these two molecular sieves of rather similar structure. By considering a particular location of the cupric ion, these coordination numbers can be understood, however. Another major difference involves coordination to ammonia; four ammonias are coordinated to cupric ion in CuH-SAPO-11 consistent with the cupric ion being located in the center of a 10-ring channel, while only three ammonias are coordinated in cupric ion to CuH-SAPO-5. This indicates a different coordination site for cupric ion between these two molecular sieves also with ammonia adsorbate. The coordination site in the SAPO-5 material for cupric ion is suggested to be the same for ammonia coordination and water coordination and is different from the site for water coordination in the SAPO-11 material.     

Synthesis and characterization of soluble hyperbranched polymer via initiator‐fragment incorporation radical polymerization of divinylbenzene with dimethyl 2,2′‐azobisisobutyrate

The homopolymerization of divinylbenzene (DVB) as an excellent crosslinker (0.20 mol/L) with dimethyl 2,2′‐azobisisobutyrate (MAIB) proceeded homogeneously without any gelation at 80°C in benzene when the MAIB concentrations as high as 0.30–0.50 mol/L were used, yielding soluble polymers. In the polymerization at the concentrations of [DVB] = 0.20 mol/L and [MAIB] = 0.50 mol/L, the polymer yield increased with time and leveled off over 90 min. The molecular weight and molecular weight distribution increased with polymer yield. The vinyl groups of DVB were observed to be almost completely consumed in about 80 min, by FT near‐IR spectroscopic analysis. The homogeneous polymerization system involved ESR‐observable polymer radical, the concentration of which increased with time up to 3.4 × 10^?5 mol/L. The polymer formed in the polymerization for 2 h consisted of 46 mol % of DVB unit and 54 mol % of the methoxycarbonylpropyl group as MAIB fragment, indicating that an initiator‐fragment incorporation radical polymerization proceeds in the present polymerization. The polymer was soluble in benzene, tetrahydrofuran, ethyl acetate, chloroform, acetone, and N,N‐dimethylformamide, while it was insoluble in n‐hexane, acetonitrile, dimethyl sulfoxide, methanol, and water. The results of the multiangle laser light scattering and viscometric measurements revealed that the individual polymer molecules were formed as hyperbranched polymer nanoparticles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 664–670, 2006     

Cu,Co, Ag-Containing Pillared Clays as Catalysts for the Selective Reduction of NOx by Hydrocarbons in an Excess of Oxygen

Thermally stable Al- and Zr-PILC loaded with copper and cobalt cations and silver nanoparticles were synthesized. The structural and surface features of these nanosystems were studied and compared with those of bulk analogs – partially stabilized ZrO₂ loaded with the same active components. Specificity of the catalytic properties of nanocomposites in SCR of NO _x by propane, propylene and decane in the excess of oxygen appears to be determined both by distribution of active components on the catalytic surface and degree of their interaction with supports. Formation of ads.-NO _x , nitroxyl-hydrocarbon C _x H _y NO₂ and isocyanate NCO intermediates was observed by ESR and IR spectroscopy in situ.