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11.
Tzanetos NP Dracopoulos V Kallitsis JK Deimede VA 《Langmuir : the ACS journal of surfaces and colloids》2005,21(20):9339-9345
A detailed study of the self-assembly ability of triblock coil-rod-coil copolymers containing a rigid di(styryl)-anthracene segment covalently linked to oxadiazole-based blocks and their binary blends with oxadiazole-based homopolymers is presented here. The self-organized microdomains seem to pack into a fascinating ordered hexagonal structure obtained at a critical concentration without any significant influence of the sample preparation method, based on evidence obtained by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy studies. The compatibilization efficiency of these coil-rod-coil copolymers in polymer blends composed of an electron-accepting polyoxadiazole and a luminescent polyanthracene-based pair was studied by atomic force microscopy (AFM). The common feature of all observed morphologies is the compatibilizing function of the rod-coil molecule, which intercalates between the incompatible domains to prevent the formation of well-defined phase separated nanostructured surfaces. 相似文献
12.
Patrina Paraskevopoulou Eleftheria Petalidou Nikos Psaroudakis Pericles Stavropoulos Konstantinos Mertis 《Monatshefte für Chemie / Chemical Monthly》2005,136(12):2035-2039
Summary. Primary phenylmethanols are selectively and efficiently oxidized to the corresponding aldehydes by the system C6H5IO/(C6H5)4PBr/CH2Cl2, T = 298 K under aerobic conditions. The use of the relatively stable iodosobenzene, an iodine(III) compound, in place of the
usually employed and potentially explosive iodine(V) reagents, the easy work-up procedure, and the facile recycling of solvent
and oxidant provides a convenient and environmentally benign oxidation method. 相似文献
13.
Ioanna Chalari Nikos Hadjichristidis 《Journal of polymer science. Part A, Polymer chemistry》2002,40(10):1519-1526
The synthesis of second‐generation (G‐2) dendritic polymers of isoprene (I) and styrene (S) was achieved with anionic polymerization high‐vacuum techniques and by performing the following steps: (1) selective reaction of a living chain with the chlorosilane group of 4‐(chlorodimethylsilyl)styrene (a dual‐functionality compound) to produce a macromonomer, (2) addition of a second living chain (same or different) to the double bond of the macromonomer, (3) polymerization of I with the anionic sites, and (4) reaction of the produced off‐center living species with trichloromethyl silane or tetrachlorosilane (CH3SiCl3 or SiCl4). The combined characterization results showed that the G‐2 dendritic macromolecules synthesized—(S2I)3, (SI′I)3, (I″I′I)3, (I′2I)4—have a high molecular and compositional homogeneity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1519–1526, 2002 相似文献
14.
Guldi DM Zilbermann I Anderson G Kotov NA Tagmatarchis N Prato M 《Journal of the American Chemical Society》2004,126(44):14340-14341
Novel organic (positively charged fullerene)-inorganic (negatively charged CdTe nanoparticle) nanoensembles were devised through electrostatic interactions and probed as versatile donor-acceptor hybrids. Photoirradiation of their homogeneous solutions, containing the electrostatically packed components, let to very long-lived (1.3 ms) charge separated states. 相似文献
15.
The effect of L-serine in supersaturated solutions of calcium phosphate was investigated under plethostatic conditions. The rates of crystal growth measured in the presence of L-serine at relatively high concentrations and in the range between 2x10(-3) and 1x10(-2) mol dm(-3) were appreciably reduced. The inhibitory effect of L-serine was found to be due to blocking of a portion of the active growth sites by adsorption. Kinetics measurements in the presence of L-serine as well as adsorption isotherm analysis suggested Langmuir-type adsorption of L-serine on the surface of hydroxyapatite (HAP) with a relatively low affinity for the substrate. Adsorption experiments showed that at pH 7.4 considerable adsorption of L-serine onto HAP takes place, whereas at pH 10.0 the adsorption was negligible, suggesting that electrostatic interactions are dominant. Attraction between the positively charged protonated amino group of the L-serine molecule and the negatively charged HAP surface contributed largely to the adsorption. This was corroborated by the fact that, in the presence of L-serine in the solution, a significant shift of zeta-potential of the HAP particles to less negative values was found at pH values close to 7.4. At pH values higher than 10.0 essentially no shift of zeta-potential takes place. On the basis of the experimental results, a model was proposed according to which L-serine absorbs on the surface of HAP through electrostatic attractions exerted between one negative site of the HAP surface, i.e., phosphate or hydroxyl ion, and the positively charged protonated amino group of one L-serine molecule, forming a surface ion pair. Copyright 2001 Academic Press. 相似文献
16.
Dimitris Pantazis Donald N. Schulz Nikos Hadjichristidis 《Journal of polymer science. Part A, Polymer chemistry》2002,40(10):1476-1483
The synthesis of a model cyclic triblock terpolymer [cyclic(S‐b‐I‐b‐MMA] of styrene (S), isoprene (I), and methyl methacrylate (MMA) was achieved by the end‐to‐end intramolecular amidation reaction of the corresponding linear α,ω‐amino acid precursor [S‐b‐I‐b‐MMA] under high‐dilution conditions. The linear precursor was synthesized by the sequential anionic polymerization of S, I, and MMA with 2,2,5,5‐tetramethyl‐1‐(3‐lithiopropyl)‐1‐aza‐2,5‐disilacyclopentane as an initiator and amine generator and 4‐bromo‐1,1,1‐trimethoxybutane as a terminator and carboxylic acid generator. The separation of the unreacted linear polymer from the cyclic terpolymer was facilitated by the transformation of the unreacted species into high molecular weight polymers by the evaporation of the reaction solvent and the continuation of the reaction under high‐concentration conditions. The intermediate materials and the final cyclic terpolymer, characterized by size exclusion chromatography, vapor pressure osmometry, thin‐layer chromatography, IR and NMR spectroscopy, exhibited high molecular weight and compositional homogeneity. Dilute‐solution viscosity measurements were used as an additional proof of the cyclic structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1476–1483, 2002 相似文献
17.
Ramanan Krishnamoorti William W. Graessley Achim Zirkel Dieter Richter Nikos Hadjichristidis Lewis J. Fetters David J. Lohse 《Journal of Polymer Science.Polymer Physics》2002,40(16):1768-1776
The unperturbed chain dimensions (〈R2〉o/M) of cis/trans‐1,4‐polyisoprene, a near‐atactic poly(methyl methacrylate), and atactic polyolefins were measured as a function of temperature in the melt state via small‐angle neutron scattering (SANS). The polyolefinic materials were derived from polydienes or polystyrene via hydrogenation or deuteration and represent structures not encountered commercially. The parent polymers were prepared via lithium‐based anionic polymerizations in cyclohexane with, in some cases, a polymer microstructure modifier present. The polyolefins retained the near‐monodisperse molecular weight distributions exhibited by the precursor materials. The melt SANS‐based chain dimension data allowed the evaluation of the temperature coefficients [dln 〈R2〉o/dT(κ)] for these polymers. The evaluated polymers obeyed the packing length (p)‐based expressions of the plateau modulus, G = kT/np3 (MPa), and the entanglement molecular weight, Me = ρNanp3 (g mol?1), where nt denotes the number (~21) of entanglement strands in a cube with the dimensions of the reptation tube diameter (dt) and ρ is the chain density. The product np3 is the displaced volume (Ve) of an entanglement that is also expressible as pd or kT/G. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1768–1776, 2002 相似文献
18.
Nikos Ekizoglou Nikos Hadjichristidis 《Journal of polymer science. Part A, Polymer chemistry》2002,40(13):2166-2170
Multiblock copolymers of ethylene oxide, with four and five different blocks, were synthesized by the sequential anionic polymerization of styrene, isoprene, 2-vinyl pyridine, t-butyl methacrylate, and ethylene oxide with benzyl potassium as an initiator. The monomer sequence was based on the relative nucleophilicity of the active centers. Characterization of the multiblock copolymers by size exclusion chromatography (with refractive-index and UV detectors), membrane osmometry, and NMR spectroscopy confirmed that benzyl potassium is an efficient initiator for the synthesis of well-defined multiblock multicomponent copolymers of ethylene oxide. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2166–2170, 2002 相似文献
19.
Nikos G. Tsierkezos 《Journal of solution chemistry》2007,36(10):1301-1310
The reduction of benzophenone (Bzph) in 3-pentanone (PEN), acetone (ACE), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (ACN) and dimethyl sulfoxide (DMSO) with n-tetrabutylammonium hexafluorophosphate (TBAPF6) as background electrolyte was studied using the technique of cyclic voltammetry at the temperature of 263.15 K. The half-wave
potentials (E
1/2) were extracted. The reduction of Bzph occurs in two successive one-electron steps to produce first the free radical anion
Bzph− and then the dianion Bzph2−. The results indicated that the radical anion Bzph− is reoxidized to Bzph in all investigated solvent media whereas the dianion Bzph2− is reoxidized to Bzph− only in THF. The heterogeneous electron-transfer rate constants (k
s
) were evaluated by employing the electrochemical rate equation proposed by Nicholson. The rate of electron transfer for the
Bzph/Bzph− couple was found to be relatively slow in all investigated solvent media. Consequently, the electron-transfer processes can
be recognized as quasi-reversible. The diffusion coefficients (D) of Bzph in the investigated solvent media have been calculated using the modified Randles-Sevcik equation. The effect of
the physical and chemical properties of the solvent medium on the electrochemical behavior of Bzph has been examined. 相似文献
20.
Five new CuII complexes of general formula [Cu2(Rdtc)tpmc](ClO4)3, (1)–(5), where tpmc and Rdtc
– refer to N,N,N,N-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of CuII ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the (C=N) and (C=S) vibrations which decrease in the order of the complexes: Pipdtc>N-Mepipdtc>Pzdtc>Morphdtc>Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The g
eff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria. 相似文献