Search results for "styrene"

Über eine Beziehung zwischen Verdünnunasentropie und Verdünnungsenthalpie in Lösungen von Polystyrol und Polymethylmethacrylat

1973

Durch Lichtstreuungsmessungen wurde der Entropieanteil und der Enthalpieanteil des 2. osmotischen Virialkoeffizienten (A2) von athermischen und exothermischen Losungen von Polystyrol (PS) und Polymethylmethacrylat (PMMA) bei 25°C und Normaldruck bestimmt. Zur Auffindung von athermischen und exothermischen Losungsmitteln fur diese Polymeren wurde die Temperaturabhangigkeit des STAUDINGERindex verwendet. Die ermittelten thermodynamischen Grosen A2, A2,S und A2,H ergeben zusammen mit fruheren Messungen eine beziehung, die nahezu unabhangig vom speziellen System ist. The second osmotic virial coefficient A2 and its entropic and enthalpic parts of athermal and exothermal solutions of polystyrene…

Endogenous Role of Microsomal Epoxide Hydrolase

2005

The specific activities of microsomal epoxide hydrolase with 16α,17α-epoxyandrosten-3-one (androstene oxide) as substrate were measured in various metabolically important and in various steroidogenic organs of the male and female rat and compared with the activities of 16α,17α-epoxyestratrienol (estroxide) and benzo[a]pyrene 4,5-oxide. Androstene oxide was an exceptionally good substrate. The specific activities differed widely between organs but the ratio of the activities towards these substrates was constant in all organs investigated. The ratios compared to benzo[a]pyrene 4,5-oxide were 2.5 for estroxide, and 8.6 for androstene oxide. The ontogenetic development of specific epoxide hydr…

ChemInform Abstract: Novel Prolinamide-Supported Polystyrene as Highly Stereoselective and Recyclable Organocatalyst for the Aldol Reaction.

2008

A new prolinamide derivative anchored to a polystyrene support has been straightforwardly prepared and employed as heterogeneous catalyst in the direct asymmetric aldol reaction with good results in terms of yield and stereoselectivity. The optimal reaction conditions were found when a 1:2 (v/v) water/chloroform mixture was used. This mixture was the best compromise between the good swelling properties of chloroform and the formation of a concentrated organic phase due to the presence of water. Noticeably, the enantioselectivities obtained employing acetone as ketone were, to the best of our knowledge, the highest achieved with a supported proline derivative. This catalyst can be easily rec…

A Photoredox-Catalyzed Four Component Reaction for the Atom-Efficient Synthesis of Complex Secondary Amines

2020

The one-pot sulfonylation/aminoalkylation of styrene derivatives furnishing highly substituted gamma-sulfonylamines was accomplished through a photoredox-catalyzed four-component reaction. Apart from one molecule of water and the sodium counterion of the sulfinate, all atoms of the starting materials are transferred to the final product, rendering this process highly atom-efficient. The operationally simple protocol allows for the simultaneous formation of three new single bonds (C–S, C–N, and C–C) and therefore grants rapid access to structurally diverse products. The reaction proceeds under mild conditions in aqueous acetonitrile and shows a broad scope, including natural products and dru…

Synthetic methods for the preparation of polystyrene resins containing chiral polyamine chains

1998

Abstract The preparation of functionalized polystyrene-divinylbenzene resins containing functional groups derived from polyamine aliphatic chains has been studied. Best results are always obtained by direct alkylation of the polyamine with Merrifield's polymers, but double alkylation at both end of the polyamine is observed. The procedure is useful for the preparation of polymer containing different chiral and non-chiral polyamine functionalities.

Polymer Retention Mechanism in GPC on Active Gels

1980

Abstract The elution behaviour of low molecular weight polystyrene (PS) down to the monomer on spherosil gel in several eluents has been studied. In the medium range of molecular weights the elution behaviour is similar to that followed by high molecular weight PS, the differences in elution volumes among different eluents increasing monotonically with decreasing molecular weight and partition rather than adsorption probably being responsible for the shifts in retention volumes. However, at the total permeation limit, the situation is alike to that found in liquid-solid chromatography, the elution volumes of solutes with molecular sizes very close to that of styrene being determined by solv…

Single Particle Motion of Hard-Sphere-Like Polymer Micronetwork Colloids Up to the Colloid Glass Transition

1997

Polymer micronetwork spheres swollen in a good solvent can be regarded as colloids which require no special stabilisation to avoid aggregation. Their interactions can be timed by changing the degree of internal crosslinking. The phase behaviour and the static structure factor demonstrate that crosslink density of 1:10 (inverse number of monomer units between crosslinks) is sufficient to achieve hard sphere behaviour. We designed a host-tracer system consisting of core-shell micronetwork spheres (core: polystyrene; shell: poly-t-butylacrylate) in a host of refractive-indexmatched poly-t-butylacrylate micronetwork colloids. Employing a crosslink density of 1:10 and tuning the polydispersity s…

QENS from polymeric micelles in supercritical CO[sub 2]

2000

We report QENS measurements from PS-b-PFOA aggregates in supercritical CO2. These consist of dense cores of CO2-insoluble polystyrene surrounded by a ‘corona’ of PFOA surfactant molecules whose CO2-philic groups interface with supercritical CO2. Lineshapes are dominated by localized diffusive modes and segmental dynamics of the anchored, finite-length PFOA chains. For Q∼0.6 A−1, we obtain effective diffusion coefficients of ≈0.8×10−6 cm2/sec. At higher Q, a single component is not sufficient as shown by excess intensity on the flanks. For Q>1.5 A−1, the wings reflect contributions due to a distribution of faster, more localized chain modes.

1991

Telechelic α,ω-macrozwitterions — narrowly distributed polystyrene chains oppositely charged at each end — were synthesized via anionic polymerization using direct functionalization with the initiator and the termination agent. The resulting products were purified (zwitterion content ≥ 0,95) and characterized with gel permeation chromatography, viscometry, static and dynamic light scattering and small-angle neutron scattering. In unpolar solvents as toluene, the polymeric zwitterions form clusters with molecular weights depending on concentration. In the dilute case, the clusters are relatively small and consist of approximately 8 zwitterions. The structure of these clusters is discussed by…

Nachweis und chemische umsetzungen von endgruppen in polystyrolen

1955

Bei der Losungspolymerisation van Styrol mit dem Eisen-Redox-System Brombenzoylperoxyd/Fe/Benzoin werden Brombenzoesaure-Ester-Gruppen in das Makromolekul eingebaut; diese lassen sich quantitativ verseifcn. Dabei entstehen Polymere mit alkoholischen Endgruppen; diese konnen mit Dichlorphenylisocyanat umgesetzt und quantitativ bestimmt werden. Mit Brombenzopersaure/Fe/Benzoin erhaltene Polystyrole enthalten keine Brombenzoesaure-Esterendgruppen sondern alkoholische Endgruppen, die ebenfalls mit Dichlorphenylisocyanat umgesetzt wurden. Die alkoholischen und esterartjgen Endgruppen lassen sich ultrarotspektroskopisch nachweisen. In the solutionpolymerisation of styrene with the iron-redox-syst…