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91.
92.
Y. Grohens P. Carriere L. Hamon G. Castelein Y. Holl J. Spevacek 《Macromolecular Symposia》2001,166(1):59-70
In this work local chain conformation, polymer/solvent interactions and particle size of different PMMA/solvent or PMMA/surfactant/solvent systems were investigated by dynamic light scattering, infrared spectroscopy and capillary viscosimetry. Aggregation can be forced, in the chlorinated solvents, through mixing with a small amount of PEG non‐ionic surfactants. Nano‐gel particles can also be formed by stereocomplexation of i‐ and s‐PMMA in certain solvents. The adsorption of stereoregular PMMA on silica was investigated by 1H NMR. The strong relative lowering of the peak ascribed to isotactic sequences has provided evidence of a stereospecific adsorption of the isotactic segments. The conformation and the secondary structure induced by the PMMA stereoregularity may, therefore, be considered as a significant factor in the adsorption process. According to the miscibility of the components, PMMA/PEG mixtures are shown to increase the amount of polymer adsorbed and also to modify the stereoselectivity of the adsorption. Aggregative adsorption is assumed to deeply influence the organisation of the polymer at the silica/solvent interface. Finally, adsorption of aggregates of stereocomplexes can be used to pattern surfaces in thin films. 相似文献
93.
94.
G. J. Alner R. E. Ansorge B. ?sman C. N. Booth L. Burow P. Carlson C. DeClercq R. S. DeWolf A. Drees B. Eckart G. Ekspong I. Evangelou A. Eyring J. -P. Fabre L. Fr?bel C. Fuglesang J. Gaudaen C. Geich-Gimbel B. Holl G. von Holtey R. Hospes K. Jon-And Th. Kokott F. Lotse N. Manthos R. Meinke D. J. Munday J. E. V. Ovens W. Pelzer J. J. Reidy J. G. Rushbrooke H. Schmickler F. Triantis L. Van hamme Ch. Walck C. P. Ward D. R. Ward C. J. S. Webber T. O. White G. Wilquet N. Yamdagni UA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1986,32(2):153-161
Data on antiproton-proton cross sections at the c.m. energies 200 and 900 GeV are presented. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode in which the same beams were accelerated and decelerated between beam energies of 450 and 100 GeV. The properties of the machine determine the ratio of the luminosities at the two energies to about 1% and thus an accurate measurement of the ratioR of the inelastic cross sections could be made. We findR (=σ 900/σ 200)=1.20±0.01±0.02, where the first error is statistical and the second systematic. Interpolating existing data to estimateσ ine1(200 GeV) this measurement ofR leads toσ ine1(900 GeV)=50.3+0.4+1.0 mb. Using an extrapolated value ofσ e1/σ tot we estimate the total cross section at 900 GeV to be 65.3±0.7±1.5 mb. Both the inelastic and total cross sections are compatible with a ln2 s dependence. Comparisons are made with different fits to the total cross section energy dependence. 相似文献
95.
96.
Schneider KS Nicholson KT Orr BG Holl MM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(6):2250-2256
Scanning tunneling microscopy data of a mixed monolayer comprised of a 40:60 ratio of H8Si8O12 and C6H13-H7Si8O12 clusters on gold are presented. The images display a composite monolayer surface with well-defined domain regions of the individual components. Holes present at face-centered cubic (fcc) sites of the starting Au/H7Si8O12 adsorbate layer indicate the location of active sites for impinging C6H13-H7Si8O12 clusters. Adsorption of a C6H13-H7Si8O12 cluster likely yields a mobile hydrogen atom available to recombine with and desorb an adjacent H8Si8O12 cluster. Hydrogen atom diffusion along substrate [121] directions is the proposed pattern formation mechanism of the mixed monolayer. Imaging of the spherosiloxane cluster domains identifies a novel terrace-based active site located in the fcc regions of the Au(111) 23 x square root3 surface reconstruction. 相似文献
97.
Spirocyclic Pentaalkylphosphorane, Alkoxy tetraalkylphosphorane and a Monocyclic Covalent Fluorotetraalkylphosphorane Methylation of the spiro-phosphonium salt (CH2)4P(CH2)4⊕Cl? by CH3Li at ?60°C affords the bicyclic pentaalkylphosphorane , a colourless distillable liquid of characteristic odour. The corresponding bicyclic methoxytetraalkylphosphorane is obtained from the same phosphonium salt with NaNH3 followed by CH3OH. The reaction is assumed to occur via the unstable bicyclic ylide. From 1-methyl-1-methylene-phospholane and NH4F the liquid and distillable, covalent fluorotetraalkylphoshorane (CH2)P(CH3)2F is formed. A complete 1H-, 13C-, 19F- and 31P-NMR study has been carried out for these three compounds. Due to a pronounced fluxional behaviour, none of the fixed standard geometries (TBP, SP) can be assigned. 相似文献
98.
An osmotic ensemble hyperparallel tempering technique has been developed to study the solubility of ethylene in amorphous linear low-density polyethylene of different chain architectures. The NERD united-atom force field (Nath, Escobedo, and de Pablo revised united-atom force field) is used in all simulations. We have investigated the effect of polyethylene chain length and branching on ethylene solubility. In this study, we have considered short-chain branching of amorphous linear low-density ethylene-1-hexene copolymers under typical polymerization reactor conditions. It is observed that, in the polymer, ethylene prefers to reside in the vicinity of polymer chain ends. This clustering causes a decrease in ethylene solubility with polymer chain length. When short-chain branches are introduced to a linear polymer chain, however, the chain-end clustering effect is counteracted by a higher density, thereby leading to an ethylene solubility almost identical to that in the linear polymer. 相似文献
99.
Connections between the calculated and measured electrophoretic mobilities (nu(ep)) determined by capillary electrophoresis as well as connections between the measured and calculated diffusion coefficients of anti-tumor peptides have been investigated in background electrolytes (BGEs) containing different organic solvents (acetonitrile, methanol, ethanol and isopropanol). Comparison of the electrophoretic mobility (nu(ep)) values revealed discrepancies between the measured and calculated values. However, no change in the migration order or selectivity could be expected from the calculated nu(ep) values, variation of both properties was observed applying organic solvents as BGE modifiers. Experimental determination of the diffusion coefficient suggested that the effect of the organic solvents is not restricted to the change of the BGE viscosity. The reason for the discrepancy between the measured and calculated mobility values might be the possible conformation and/or solvation changes of the peptide caused by the different organic solvents. 相似文献
100.
Klapötke TM Krumm B Piotrowski H Polborn K Holl G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(3):687-694
The first hexabenzylhexaazaisowurtzitane cage compounds with trifluoromethyl and azide groups, as well as those with fluorine atoms in the 3- and 4-positions, have been prepared and fully characterized. A study of the substituent influence on the benzene ring regarding the formation of the hexaazaisowurtzitane polycycle in either the 2- or 4-position with CF(3), F, and N(3) revealed an interesting difference. In all cases with CF(3), F, and N(3) substituents in the 4-position, the corresponding hexabenzylhexaazaisowurtzitanes were isolated. The corresponding hexabenzylhexaazaisowurtzitanes were also formed when these substituents were in the 2-position; however, in addition with azide in 2-position a novel type of polycycle was isolated and identified. (15)N NMR data and crystal structures of hexabenzylhexaazaisowurtzitane derivatives were obtained and are discussed in detail. 相似文献