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991.
A versatile nonaqueous emulsion polyaddition process for the one-step fabrication of spherical polyurethane nanoparticles
is presented. Three different emulsion systems were used consisting of N,N′-dimethylformamide (DMF) dispersed in n-hexane, acetonitrile dispersed in cyclohexane, and acetonitrile dispersed in tetradecane. After successful stabilization
of the emulsion systems by using a poly(isoprene)-poly(methylmethacrylate) block copolymer, the fabrication of the polyurethanes
was carried out within the dispersed polar phase. The polyurethane particles showed average diameters as small as 35 nm. Additionally,
infrared (IR) characterization revealed that the formation of any urea, which decreases the mechanical properties of the polyurethanes,
was prevented during the polyaddition. This was attributed to the anhydrous reaction conditions. Gel permeation chromatography
(GPC) analysis demonstrated the average molecular weights (M
n) of the polyurethanes to be as high as 16,500 g/mol, corresponding to conversions of 0.98. Comparable molecular weights and
conversions have not previously been achieved without the formation of urea. 相似文献
992.
A new (E,E)-dioxime, (6Z,7Z)-15,16-dihydro-14H-dibenzo[b,h][1,10,4, 7]dithiadiazacyclotride-cine-6,7(5H,8H)-dionedioxime (H
2
L) has been synthesized by reacting cyanogen-di-N-oxide (2) with 2,2′-[propane-1,3-diylbis(thio)]dianiline (1). Mononuclear complexes (4) and (5) of this ligand have been synthesized by reacting the vic-dioxime (H2L) with NiCl2 · 6H2O and CoCl2 · 6H2O, respectively. The BF
2
+
capped Ni(II) and Co(III) complexes (6) and (7) of the dioxime have been synthesized from (4) and (5). The new compounds were characterized by a combination of elemental analysis, 1H- and 13C-n.m.r, i.r. and m.s. spectral data. 相似文献
993.
Stefan Mecking 《Colloid and polymer science》2007,285(6):605-619
By contrast to traditional free radical emulsion polymerization, catalytic polymerization allows for polymer microstructure
control. In terms of polymerizable monomers, both techniques are largely complementary. Since the beginning of this decade,
an increasing number of reports on polyolefin, polybutadiene, polyalkenamer, polynorbornene, polyketone, and polyacetylene
dispersions prepared by catalytic polymerization in disperse aqueous systems has appeared. This contribution reviews the preparation
of these dispersions, their colloidal properties, particle formation mechanisms, particle morphologies, and polymer microstructures. 相似文献
994.
Irina F. Catta Preta Solange K. Sakata G. Garcia J. P. Zimmermann F. Galembeck Claudia Giovedi 《Journal of Thermal Analysis and Calorimetry》2007,87(3):657-659
Polyacrylonitrile
(PAN) polymers are used as precursors for carbon fiber production. This process
requires an oxidative stabilization step, which can be studied by differential
scanning calorimetry (DSC). In this sense, thermal behavior of PAN based terpolymers
by different polymerization processes, compositions and itaconic acid concentrations
in the reaction media were investigated. The obtained results showed that
the addition of itaconic acid and methyl acrylate as comonomers resulted a
lower heat flow during the process comparing to the PAN homopolymer. It suggested
that these comonomers aid the oxidative stabilization stage for all studied
process. The redox system polymerization at 40°C resulted in a lower heat
flow. Itaconic acid decreases slightly initial and peak temperatures of the
terpolymer and heat flow until concentration of 3y. The cyclization temperature
decreases when MAis incorporated into the terpolymer compared to the MMA terpolymer
and increases when MAA is the acidic monomer. Among terpolymers the AN/MA/AA
polymer showed the best thermal behavior for carbon fiber producing. 相似文献
995.
Hans-Christian Mez Günther Rist Jaroslav Kalvoda Otto Ermer Ljubinka Lorenc Mihailo Lj. Mihailovi 《Helvetica chimica acta》1976,59(4):1273-1293
X-ray structure determination of the p-bromobenzoate 2b of one of the (E/Z)-isomeric 3β-hydroxy-5,10-seco-1(10)-cholesten-5-ones confirmed the (E)-configuration proposed previously and showed the cyclodecenone ring to adopt an extended crown conformation of type A 1 (Fig. 9). Analysis of the 1H- and 13C-NMR. spectra of acetate 2a revealed that in solution the ten-membered ring of this steroid exists in at least two distinct forms, the predominant (about 85%) corresponding to the solid-state conformation of 2b (= A 1), and the minor most likely to B 2 (Fig. 9). From NMR. data the energy difference between the two species and the relevant activation energy were estimated. A number of conformational force field calculations using a simplified partial structural model was performed; but the computed energy differences between the various possible conformations do not reproduce the effective situation, neither in solution nor in the crystal lattice, indicating that additional effects such as the transannular interaction of the double bond with the carbonyl group may strongly influence the thermodynamic stability of the system. The conformations deduced were used to rationalize the stereochemical course of different chemical reactions of 2a . 相似文献
996.
It was shown in previous papers, that many titrimetric problems can be solved by observing the pressure change of a closed system above the solution titrated at the equivalence point. This principle was made the basis of a gasometric titration method in which the end-point is found graphically. The titrant is added to the sample solution in measured increments at fixed intervals of time and the corresponding gas pressure or volume of the system is recorded and then plotted against the volume of added titrant. Half a dozen readings are sufficient to establish the end-point of a titration, which is found at the intersection of two straight lines. This graphical method was applied to cerimetry and chlorometry, as well as to some other analytical reactions (determination of nitrite, nitrate, hydroxide and carbonate) already described in previous papers on the gas pressure end-point technique. The results are comparable in precision and accuracy to the values obtained by the conventional visual end-point titrations. A gasometric titration takes about 10 minutes. The presence of other substances in the sample capable of reacting with the titrant does not necessarily cause interference. 相似文献
997.
To build a kinetic model of a cell with diffusion one has to solve a coupled nonlinear partial differential equation system consisting of several hundred equations. (Several hundred chemical components undergoing several hundred reactions.) To solve this formidable mathematical problem the division of the model cell into compartments (most biochemical reactions take place in a certain part of the cell) was suggested.1 Solving the differential equation system in one compartment, the results can be used as input at other compartments until mutually consistent solutions are achieved. To test this suggestion 10 coupled chemical reactions with diffusion were investigated in a model that contains three compartments. The results in the case of pure diffusion are in excellent agreement with and without compartmentalization. After this the full problem was treated by compartmentalization using for the solution of the differential equation system a discretization of the concentrations as functions of space and time and the Newton–Raphson iterative procedure. The results obtained give reasonable space and time dependence for the concentrations of all 10 components. 相似文献
998.
In the present work, corrosion resistance of surface-coated galvanized steel was quantitatively determined by an analysis
of the alternating current (AC) impedance spectra measured on the salt-spray-tested specimen. To evaluate the corrosion resistance
of the surface-coated galvanized steel, AC impedance spectroscopy was performed on the salt-spray-tested specimen previously
exposed to salt-sprayed corrosive environment. From the analysis of the impedance spectra, the area fraction transient of
white rust θ
2(t) was theoretically derived from the equivalent circuit equation by using two fitting parameters. The values of the two fitting
parameters were determined by fitting the empirical transient equations to the area fraction of the resin coating layer and
to the total resistance obtained from the impedance spectra measured, respectively. From the analyses of θ
2(t) for four kinds of surface-coated galvanized steels with various resin coating layers, it is indicated that as the values
of the two fitting parameters decrease in the order of CP, GI, OD and OM (commercial trade names) specimens, the corrosion
resistance increases in that order as well. Furthermore, from the quantitative comparison of the two fitting parameters with
the polarization resistance of the upper resin coating layer R
p determined from the potentiodynamic polarization curve, it is suggested that the two fitting parameters decrease in value
as well with increasing R
p. 相似文献
999.
Rollie J. Myers 《Journal of solution chemistry》2007,36(3):395-403
We have measured the second acid dissociation constant, K
2a
, at several ionic strengths for hydrogen telluride (H2Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe− and Te2−. Since it is produced in our solutions, we have also determined the spectra of Te2
2− both in the uv and in the visible regions. At 25 ∘C, K
2a
= (1.28 ± 0.02) × 10−12 by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm-3 was estimated to be (8.7 ± 0.2) × 10−12. The solution thermodynamics of these species are also discussed and comparisons are made to related acids. 相似文献
1000.
Martin Winterwerber Rouzita Geiger Hans-Hartwig Otto 《Monatshefte für Chemie / Chemical Monthly》2006,137(10):1321-1347
Summary. Cyanomethanesulfonyl chloride was reacted with amines yielding cyanomethanesulfonamides which could be transformed into alkoxymethylidene
and aminomethylidene derivatives. The reaction of alkoxymethylidene derivatives with phenylhydrazine resulted in the formation
of 5-aminopyrazol-4-sulfonamides, whereas from cyanomethanesulfonamides via the N-hydroxyamidine derivatives and their reaction with esters 1,2,4-oxadiazol-3-methanesulfonamides became accessible. Nitrosation
of cyanomethanesulfonamides yielded 2-hydroxyimino derivatives which were then transformed into 2-hydroxyimino N-hydroxyamidine derivatives, and finally cyclized into 4-amino-1,2,5-oxadiazol-3-sulfonamides. On the other hand diazotation
of cyanomethanesulfonamides gave the 2-arylhydrazono derivatives, which after transformation into N-hydroxyamidine derivatives gave by reaction with POCl3 5-amino-1,2,3-triazol-4-sulfonamides. Finally, the reaction between cyanomethanesulfonamides and formamidinium acetate opened
an easy access to 4-aminopyrimidine-5-sulfonamides, which could be transformed by trialkyl orthoformiates into substituted
pyrimidino[4,5-e][1,2,4]thiadiazine derivatives. All intermediates as well as transformation products of the heterocyclic systems were isolated
and well characterized. Mechanisms were discussed, and the stereochemistry, when necessary and possible, was elucidated. 相似文献