Search results for " function"
showing 10 items of 9395 documents
Enhancing the mechanical performance of polymer based nanocomposites by plasma-modification of nanoparticles
2012
Abstract The possibility of enhancing the mechanical performance of two different polymer-based nanocomposites using polyamide 6 (PA6) and poly[ethylene-co-(vinyl acetate)] (EVA) as matrices was investigated. The nanofillers used were, respectively, either carbon nanotubes (CNTs) or an organically modified montmorillonite (Cloisite 15A), both previously modified by plasma treatment to introduce polar moieties. The nanofillers were fully characterized by Raman spectroscopy, XPS, FT-IR and XRD, demonstrating their effective modification with oxygenated groups. The nanocomposites were prepared by melt processing in order to obtain films and fibres. The mechanical tests carried out on the nanoc…
Functionalization of aliphatic polyesters by nitroxide radical coupling
2014
Functionalized poly(butylene succinate) (PBS) samples were prepared by a post-polymerization method based on the coupling reaction between TEMPO derivatives bearing different functionalities and PBS macroradicals generated by H-abstraction using a peroxide. 4-Benzoyloxy-2,2,6,6-tetramethylpiperidine-1- oxyl (BzO-TEMPO) and 4-(1-naphthoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO), a pro-fluorescent nitroxide, were successfully grafted on PBS, as revealed by MALDI TOF MS and UV-Vis spectroscopy. The functionalization degrees were accurately determined by UV-Vis analysis and confirmed by 1H-NMR spectroscopy. The grafting site was identified by combining theoretical calculations with e…
Reactivity of the carbon-carbon double bond towards nucleophilic additions. A dft analysis
2004
Abstract The global and local electrophilicity indexes have been used to characterize the reactivity pattern of the CC double bond towards nucleophilic addition reactions. A wide family of molecules including ketones, esters, anhydrides, nitriles and nitrocompounds containing appropriate substitution on the CC double bond have been classified within an unique scale of reactivity. The predictive capability of the theoretical model is tested against a series of benzylidenemalononitriles and substituted α-nitrostilbenes.
A DFT study of the molecular mechanisms of the nucleophilic addition of ester-derived lithium enolates and silyl ketene acetals to nitrones: Effects …
2006
9 pages, 6 schemes, 3 figures, 2 tables.
The nucleophilic addition of nitrones to carbonyl compounds: insights on the nature of the mechanism of the l-proline induced asymmetric reaction fro…
2004
Abstract The mechanism of the l -proline induced asymmetric nitrone–aldol reaction of N -methyl- C -ethylnitrone with dimethyl ketomalonate has been studied by using density functional theory at B3LYP/6-31G** level. The reaction was initialized by the addition of l -proline to the nitrone to form an aminal, which by elimination of the hydroxylamine gave a chiral enamine. The nucleophilic addition of this chiral enamine to dimethyl ketomalonate corresponds to stereoselective C–C bond-formation step. Further nucleophilic addition of hydroxylamine to the zwitterionic intermediate formed in the enamine addition gave a second aminal, which by l -proline elimination afforded the corresponding β-h…
The triplet excited state of the biocative compound thiabendazole. Characterization and suitability as reporter for cyclodextrin complexation
2012
Fluorescence spectroscopy, laser flash photolysis (LPF), and density functional theory calculations have been performed to characterize the photobehavior of thiabendazole (1). Direct LFP of 1 results in the generation of a transient absorbing at λmax = 570 nm identified as the triplet excited state (31∗). The intersystem crossing quantum yield is 0.91, and the triplet energy is 288 kJ mol−1. The singlet–triplet energy gap is 84 kJ mol−1. The behavior of thiabendazole within CDs results in a marked enhancement of the triplet lifetime, this change is attributed to the mobility restrictions of included 1 imposed by the cyclodextrin cavities.
Calculation of the Phase Behavior of Lipids
1998
The self-assembly of monoacyl lipids in solution is studied employing a model in which the lipid's hydrocarbon tail is described within the Rotational Isomeric State framework and is attached to a simple hydrophilic head. Mean-field theory is employed, and the necessary partition function of a single lipid is obtained via a partial enumeration over a large sample of molecular conformations. The influence of the lipid architecture on the transition between the lamellar and inverted-hexagonal phases is calculated, and qualitative agreement with experiment is found.
A bonding evolution theory study of the mechanism of [3+2] cycloaddition reactions of nitrones with electron-deficient ethylenes
2015
The mechanism of zw-type [3+2] cycloaddition (32CA) reactions of nitrones with electron-deficient (ED) ethylenes has been studied using density functional theory (DFT) methods at the MPWB1K/6-31G(d) level of theory. An exploration of the potential energy surfaces associated with the four competitive reactive channels of the 32CA reaction between C-phenyl-N-methyl nitrone and acrolein indicates that the cycloaddition reaction takes place through a one-step mechanism. This cycloaddition reaction presents a moderate meta regioselectivity and a complete endo stereoselectivity, which is diminished in dichloromethane. Analysis of the DFT reactivity indices of the reagents allows an explanation of…
Scaling theory of star polymers and general polymer networks in bulk and semi-infinite good solvents
1988
Theorie d'echelle utilisant l'equivalence entre la fonction generatrice du nombre total de configuration et la fonction de correlation a plusieurs spins du modele de Heisenberg classique a n composantes dans la limite n→0
A Flory–Huggins thermodynamic approach for predicting sorption equilibrium in ternary polymer systems
1989
The Flory–Huggins theory as modified by Pouchlý has been applied to calculate preferential (λ) and total (Y) sorption coefficients for a ternary polymer system. The ternary interaction function (ϕ1ϕ2ϕ3GT(u1, ϕ3)) is described as the product of three independent binary functions. This expression allows prediction of λ and Y from binary interaction parameters χ, χ, g, g, and g12(ϕ10). Three ternary polymer systems are used to check the validity of the expression. Moreover for polymer systems in which the parameters g and/or g are unknown, a procedure to evaluate them has been developed and verified on systems for which sufficient experimental information is available.