Synthesis of chiral stationary phases with radical polymerization reaction of cellulose phenylcarbamate derivatives and vinylized silica gel

Cellulose phenylcarbamate derivatives having methacrylate groups were synthesized with regioselective and non-regioselective procedures. These derivatives were chemically immobilized onto a vinylized silica gel, respectively, via a radical co-polymerization reaction. The immobilization was efficiently attained using a small amount of AIBN. The chiral recognition abilities of the prepared chiral stationary phases (CSPs) were evaluated by HPLC resolution of test enantiomers. It was observed that most of the enantiomers were completely resolved with markedly high column efficiency of 30,000-40,000 plates per metre for the eluted peaks. The effect of the amount of methacrylolyl chloride used for preparation on resolution was investigated. A direct comparison of the chiral recognition ability was made on the regioselectively and non-regioselectively prepared CSPs. In addition, the chemically bonded-type of CSPs were found to be relatively stable with addition of solvents such as tetrahydrofuran (THF) and chloroform into the mobile phase, which can lead to the dissolution of cellulose derivatives on the coated CSPs. Thus the choice of solvents used as the mobile phase is greatly extended and better resolution of several test enantiomers was observed on the prepared CSPs with THF and chloroform as a composition in the mobile phase. The batch-to-batch and run-to-run reproducibility was also discussed on the newly prepared CSPs. (C) 2004 Elsevier B.V. All rights reserved.

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

Photodissociation dynamics of the CH3 radical at 212.5 nm has been investigated using the H atom Rydberg tagging time-of-flight method with a pure CH3 radical source generated by the photolysis of CH3I at 266 nm. Time-of-flight spectra of the H atom products from the photolysis of both cold and hot methyl radicals have been measured at different photolysis polarizations. Experimental results indicate that the photodissociation of the methyl radical in its ground vibrational state at 212.5 nm excitation occurs on a very fast time scale in comparison with its rotational period, indicating the CH3 dissociation at 212.5 nm occurs on the excited 3s Rydberg state surface. Experimental evidence also shows that the photodissociation of the methyl radical in the nu(2)=1 state of the umbrella mode at 212.5 nm excitation is characteristically different from that in the ground vibrational state. (C) 2004 American Institute of Physics.

Bluish-white emission from radical carbonyl impurities in amorphous Al2O3 prepared via the Pechini-type sol-gel process

Many efforts have been devoted to exploring novel luminescent materials that do not contain expensive or toxic elements, or do not need mercury vapor plasma as the excitation source. In this paper, amorphous Al2O3 powder samples were prepared via the Pechini-type sol-gel process. The resulting samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), photoluminescence (PL) excitation and emission spectra, kinetic decay, and electron paramagnetic resonance (EPR).

Novel spiro-fluorenes from tandem radical addition for liquid crystalline monodisperse conjugated oligomers

3'-Nonafluorobutylmethyl-4'-methyl-spiro[cyclopentyl-9,1']fluorenes were successfully synthesized via tandem radical-addition reactions between 9,9-diallylfluorenes and perfluorobutyl iodide in the presence of a radical initiator followed by reduction under mild conditions. Single crystal analysis indicates that two substituents at 3,4-positions of cyclopentane are in a maleinoid form. Accordingly, four oligo(fluorene-co-bithiophene)s with the same molecular length of similar to 10 nm (7 fluorene units and 12 thiophene units) containing one to three novel spiro-fluorene units were synthesized.

Theoretical studies on the reaction mechanism of oxidation of primary alcohols by Zn/Cu(II)-phenoxyl radical catalyst

The catalytic mechanism for the oxidation of primary alcohols catalyzed by the two functional models of galactose oxidase (GOase), M-II L (M = Cu, Zn; L = N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)1-2-diiminoquinone)), has been studied by use of the density functional method B3LYP The catalytic cycle of Cu- and Zn-catalysts consists of two parts, namely, substrate oxidation (primary alcohol oxidation) and O-2 reduction (catalyst regeneration). The catalytic mechanisms have been studied for the two reaction pathways (route 1 and route 2). The calculations indicate that the hydrogen atom transfer within the substrate oxidation part is the rate-determining step for both catalysts, in agreement with the experimental observation.

Free-Radical Solution Copolymerization of the Ionic Liquid Monomer 1-Vinyl-3-Ethylimidazolium Bromide with Acrylonitrile

Ionic liquid monomer 1-vinyl-3-ethylimidazolium bromide (ViEtIM(+)Br(-)) was first used to copolymerize with acrylonitrile (AN) successfully under various conditions. This was achieved with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The kinetics of this copolymerization were studied. The values of the monomer apparent reactivity ratios were calculated by the Kelen-Tudos method. The apparent reactivity ratios of ViEtIM(+)Br(-) (r(ViEtIM+Br-)) and AN (r(AN)) were similar at polymerization conversions of less than 10%, (r(AN) = 0.954, r(ViEtIM+Br-) = 0.976). The copolymers were obtained with high molecular weights and high hydrophilicides. The copolymers were characterized by H-1-NMR, differential scanning calorimetry, and thermogravimetric analysis. These copolymers may be potentially useful in the preparation of precursor fibers and carbon fibers.

Analysis of chemical calorific effect during reactive extrusion processes for free radical polymerization

In the reactive extrusion process for polymerization, the chemical calorific effect has a great influence on the temperature. In order to quantitatively analyze the polymerization trend and optimize the processing conditions, the phenomena of the chemical calorific effect during reactive extrusion processes for free radical polymerization were analyzed. Numerical computation expressions of the heat of chemical reaction and the reactive calorific intensity were deduced, and then a numerical simulation of the reactive extrusion process for the polymerization of n-butyl methacrylate was carried out. The evolutions of the heat of chemical reaction and the reactive calorific intensity along the! axial direction of the extruder are presented, on the basis of which reactive processing conditions can be optimized.

Investigation of the gel effect in reactive extrusion processes for free radical polymerization

The gel effect in the reactive extrusion process for free radical polymerization in a closely intermeshing co-rotating twin screw extruder was investigated. First the reaction kinetic model was constructed mainly on the basis of entanglement theory. Next, numerical calculation expressions for the initiator and monomer concentrations, monomer conversion, average molecular weight and apparent viscosity were deduced. Finally, the evolution of the above variables were shown and discussed for the example of butyl methacrylate. The simulated results of the monomer conversion are in good agreement with experimental results.