Search results for "Styrene"
showing 10 items of 561 documents
Phase Distribution Chromatography (PDC) of Polystyrene
1971
Abstract Phase distribution chromatography is a new chromatographic method of fractionating polymers. The separation is achieved by partitioning the sample between the solvent and a polymer phase, in the case a noncross-linked polystyrene of very high molecular weight, which is coated as a thin layer on small glass beads. The temperature must be held below the θ-temperature of the sample. The separation increases sharply with decreasing temperature. The theory of this method is presented and compared with experimental results. The agreement is very good.
The kinetics of anionic polymerization of styrene in 1,2-dimethoxiethane
2007
Kinetic measurements in a flow apparatus in combination with conductance measurements, permit the determination of the two equilibrium constants Kes and Kdiss* and the three propagation rate constants k(±)c, k(±)s and k(−) as a function of temperature. The great differences in the polymerization rate in various solvents are mainly caused by their influence on the equilibrium constants. The influence of the solvent on the rate constants is not greater than in other chemical reactions.
Zur polymerisation und copolymerisation des natriumvinylsulfonats
1959
Natriumvinylsulfonat (VS-Na) zeigt in konzentrierten wasrigen Losungen eine ausgepragte Polymerisationsneigung. Die Polymerisationsgeschwindigkeit und der erreichte Umsatz hangen stark von der Aciditat der Losungen ab. Es wurde gefunden, das mit der Polymerisationsdauer und mit wachsendem Umsatz auch die Molekulargewichte der Polymerisate ansteigen. Wasserunlosliche oder nur begrenzt losliche ungesattigte Verbindungen wie Styrol, Vinylacetat und andere konnen in Dimethylsulfoxyd in homogener Losung mit VS-Na copolymerisiert werden. Sodiumvinylsulphonate (VS-Na) shows a strong tendency for polymerization in concentrated aqueous solutions. The rate of polymerization and the conversion depend …
Die thermische diffusion von polystyrol in verschiedenen lösungsmitteln
1969
Es wird uber Messungen von thermischen Diffusionskoeffizienten und LUDWIG-SORET-Koeffizienten von Polystyrol in den Losungsmitteln Toluol, Methylathylketon, Butylacetat und Cyclohexan berichtet. Es zeigte sich, das der rein thermisch bedingte Diffusionsprozes in Butylacetat und im Θ-Losungsmittel Cyclohexan unabhangig vom Molekulargewicht ist, wie as fur Toluol bereits fruher nachgewiesen werden konnte. Fur Methylathylketon wurde eine schwache, aber deutliche Abhangigkeit von D' vom Molekulargewicht zu D' ∼ M−0,12 gefunden. Bemerkenswerterweise verhalten sich die beiden in Bezug auf Polystyrol thermodynamisch sehr ahnlichen Losungsmittel Butylacetat und Methylathylketon in dieser Hinsicht s…
Polystyrene-supported organocatalysts for α-selenenylation and Michael reactions
2011
Abstract Three different resin-supported catalysts have been prepared by using the well established post-modification approach by means of thiol-ene coupling reaction. Two catalysts were tested for the first time in the asymmetric α-selenenylation of propanal, while the third catalyst was used in the Michael addition reaction. While the preliminary results are not encouraging in the case of supported Jorgensen’ catalyst, interesting data have been collected with both for the supported MacMillan and prolyl-prolinol catalysts. In fact, these catalysts displayed good activity and selectivity. A reversed enantioselectivity in the α-selenenylation was observed by changing the polarity of the sol…
Anwendung der gelchromatographie auf cellulosenitrate
1970
Es wird uber gelchromatographische Untersuchungen von Cellulosenitrat und Polymethylmethacrylat in Aceton als Losungsmittel berichtet. Das gunstigste Trennverhalten fur die Fadenmolekule sehr grosen Durchmessers wurde mit hochvernetzten fur Aceton gepackten Styrolgelen erzielt. Als universelle Trennparameter versagten die in Tetrahydrofuran haufig anwendbaren Kombinationen von [η] und M. Am besten stimmen noch die mittels Lichtstreuung gemessenen Tragheitsradien als Funktion des Elutionsvolumens fur die beiden Polymeren uberein. Gelchromatographic measurements of cellulosenitrate and polymethylmethacrylate in the solvent acetone are reported. For coiled molecules of very large diameters hig…
Polymer-Functionalised Nanograins of Mg-Doped Amorphous Calcium Carbonate via a Flow-Chemistry Approach
2019
Calcareous biominerals typically feature a hybrid nanogranular structure consisting of calcium carbonate nanograins coated with organic matrices. This nanogranular organisation has a beneficial effect on the functionality of these bioceramics. In this feasibility study, we successfully employed a flow-chemistry approach to precipitate Mg-doped amorphous calcium carbonate particles functionalized by negatively charged polyelectrolytes&mdash
Potent Aroma Compounds of Two Red Wine Vinegars
2000
Gas chromatography olfactometry (GCO) was used to determine key aroma compounds of two red wine vinegars. Sensory analysis was performed to choose the best neutralization agent of acetic acid (NaOH or MgO) and to test representativeness of four extracts obtained by different methods (dichloromethane extraction, XAD-2, mixture of XAD-2 and XAD-7, and Extrelut resins extraction). Neutralization with NaOH followed by dichloromethane extraction was selected to extract volatile compounds of vinegars. Key odorant compounds were determined by GCO based on detection frequency with 13 people. In the two red wine vinegars, 13 odors were perceived by at least 70% of the panelists, and 8 compounds amon…
Phase behaviour of poly(vinyl methyl ether)-cross-polystyrene semi-interpenetrating networks
1990
Semi-interpenetrating polymer networks of varying composition are prepared by crosslinking polystyrene containing a small number of maleic anhydride groups (4.8 mol% of MA units) with hexamethylene-diamine (HMDA) in the presence of linear poly(vinyl methyl ether) (PVME). Lightly crosslinked samples are homogeneous at room temperature and show a phase behaviour similar to uncrosslinked blends, i.e. lower critical solution temperature (LCST) behaviour. The influence of crosslinking on the phase behaviour has been studied by small angle light scattering (SALS) and turbidity measurements. The cloud point strongly depends on the heating rate. The presence of the network reduces the stable single…
Epoxide Hydratase: Purification to Apparent Homogeneity as a Specific Probe for the Relative Importance of Epoxides among Other Reactive Metabolites
1977
Aromatic and olefinic compounds can be metabolized by microsomal monooxygenases to epoxides which chemically represent electrophilic species (for reviews, see refs. 1–5). Spontaneous binding of such epoxides to DNA, RNA, and protein has been observed (6–10). Accordingly, such metabolites have been suggested and, in some instances, shown to disturb the normal functions of cells, leading to such effects as mutagenesis (11–14), malignant transformation (15–19), or cell necrosis (20). However, aromatic and olefinic compounds are biotransformed to a vast array of metabolites (cf. refs. 21–27), possibly including a considerable number of reactive metabolites other than epoxides. The relative impo…