Search results for "solution"
showing 10 items of 5638 documents
Ferrochirality: A simple theoretical model of interacting dynamically invertible helical polymers, 1. The basic effects
1994
The effect of interaction between reversible helical polymers of the poly(hexyl isocyanate) type is investigated by using a molecular field model. It is shown that for interacting helices a critical temperature exists below which they must adopt a common helix-sense spontaneously, even in the absence of any external or intrinsic chiral force
Phase Behavior of the System Linear Polyglycerol + Methanol + Carbon Dioxide
2011
To compare the phase behavior of linear and hyperbranched polymers, the phase envelopes of the ternary system linear polyglycerol + methanol + carbon dioxide were determined for polymers of varying molar mass. Phase changes were detected by a static synthetic method using the Cailletet setup for temperatures between 331 K and 421 K and pressures up to 13.1 MPa. Besides the vapor–liquid and liquid–liquid equilibria, also the vapor–liquid to vapor–liquid–liquid and vapor–liquid–liquid to liquid–liquid phase boundaries are reported. The experimental results are similar to systems with hyperbranched polymers (rather than linear polymers). For the systems with linear polymers, however, the bubbl…
Prediction of maxima and minima in the curve of total sorption parameter in ternary polymer systems. Influence of ternary interaction parameter
1993
Flory-Huggins theory modified by Pouchly has been applied to predict maxima and minima in the curve of total sorption in ternary polymer systems formed by a polymer and two liquids. In this work, different diagrams based on experimental magnitudes easily obtained such as the difference in affinities of liquids, solvents and non solvents, and the solvent molar volume ratio. Total sorption parameter has been considered to be the decisive magnitude to define extrema conditions in both cosolvent and cononsolvent ternary polymer systems. The theoretical prediction is not altered by the inclusion of ternary interactions. Different examples of ternary systems dealing with vinyl polymers and polydi…
Manganese(III)-mediated oxidative carbon-carbon bond cleavage of the 1,10-phenanthroline-5,6-dione ligand
1999
[EN] A new manganese(III)-1,10-phenanthroline-5,6-dione (phendione) complex possessing a putative Mn-2(mu-O) (mu-O2CMe)(2) core has been found to undergo a Ligand-based oxidative cleavage of the C(5)-C(6) bond in weak acid aqueous MeOH under aerobic conditions at room temperature to yield 2,2'-bipyridyl-3,3'-dicarboxylate with co-reduction to the corresponding Mn-II-phendione species.
Influence of gamma-irradiation on thermally-induced mesoscopic gelation of degalactosylated xyloglucans
2014
Thermoresponsive degalactosylated xyloglucans have been already proposed as in situ gelling scaffolds for tissue engineering, due to their reversible macroscopic thermal gelation at body temperature and biodegradability. The highly branched, hydroxyl group-rich molecular structure renders xyloglucans interesting raw materials also in the form of micro/nanoparticles for application as nanoscalar drug delivery devices in cosmetic and pharmaceutical formulations. Owing to their natural source, xyloglucans show high average molecular weight, broad molecular weight distribution and poor water solubility, as large and compact aggregates usually form via inter-molecular hydrogen bonding. Co-60 gam…
Studies of network organization and dynamics of e-beam crosslinked PVPs: From macro to nano
2012
Abstract In this work the influence of poly(N-vinyl pyrrolidone) (PVP) concentration in water on the organization and dynamics of the corresponding macro-/nanogel networks has been systematically investigated. Irradiation has been performed at the same irradiation dose (within the sterilization dose range) and dose rate. In the selected irradiation conditions, the transition between macroscopic gelation and micro-/nanogels formation is observed just below the critical overlap concentration (∼1 wt%), whereas the net prevalence of intra-molecular over inter-molecular crosslinking occurs at a lower polymer concentration (below 0.25 wt%). Dynamic–mechanical spectroscopy has been applied as a cl…
Palladium-catalyzed reaction of boronic acids with chiral and racemic alpha-bromo sulfoxides.
2004
Palladium-catalyzed cross-coupling reactions of racemic alpha-bromo sulfoxides with boronic acids are carried out in either aqueous or nonaqueous medium with formation of a new C sp(3)-C sp(2) bond. The arylation of chiral alpha-bromo sulfoxides occurs without racemization. The cross-coupling reaction is general and gives high yields with arylboronic acids substituted with either donor or acceptor groups but gives poor results with heteroarylboronic acids. The best yields are obtained using degassed solvents and CsF instead of aqueous base. The use of aqueous base and the presence of oxygen favor the homocoupling side reaction.
Telechele des methylpropens durch kationische polymerisation
1986
Amorcage par des hydrocarbures aromatiques et aliphatiques contenant des groupes terminaux chlorure d'isopropyle, associes a du trichlorure de bore. Mecanisme. Recyclage du coamorceur et du solvant
Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls
1995
Summary Methyl methacrylate was polymerized with tert-butyl lithium in the presence of triethylaluminum or triisobutylaluminium at -78~ in toluene. As indicated by GPC and MALDI-TOF mass spectrometry, the polymerization is accompanied by side reactions. The lower oligomers were fractionated by distillation and characterised by NMR, FT-IR, UV and electron impact (EI) mass spectrometry. All these data show that part of the polymer chains are carrying exactly one tert-butyl isoprenyl ketone unit. In order to avoid the formation of tert-butyl isoprenyl ketone a molar ratio of A1/Li > 2 is necessary.
γ-radiation-initiated polymerization of vinylidene fluoride in dense carbon dioxide
2002
The γ-ray-initiated batch polymerization of vinylidene fluoride (VF2) has been investigated in dense carbon dioxide under relatively mild operative conditions (T ≤ 40 °C and P < 25 MPa). When the initial VF2 molar concentration was increased from 3.4 to 6.4 mol/L, monomer conversion increased from 20 to 73%; a similar trend was observed for the number-average molecular weight and the molecular complexity of synthesized poly(vinylidene fluoride) (PVDF) as determined from rheological measurements. Under all adopted experimental conditions, a synthesized PVDF polymer was collected in the form of a white powder. Despite the inherent heterogeneous character of the polymerization process, a homog…