Search results for "Mass distribution"

Die Fällungschromatographie als exakte Methode zur Bestimmung der Molekulargewichtsverteilung von Hochpolymeren Zur Theorie der Fällungschromatograph…

1965

Bei der Fallungschromatographie wird ein Gemisch Hochpolymerer durch kombinierte Wirkung eines Losungsmittel-Fallungsmittel- und eines Temperaturgradienten in Fraktionen zerlegt, aus denen man nach einem fruher beschriebenen Verfahren die Verteilungskurve der Molekulargewichte erhalt. Eine so bestimmte Verteilungsfunktion ist dann exakt, wenn die Uneinheitlichkeit der Fraktionen (Ufr) klein gegen die Uneinheitlichkeit des zu analysierenden Polymeren (U) ist. Die Uneinheitlichkeit der bei der Fallungschromatographie erhaltenen Fraktionen ist nach Gleichung (20) durch drei Grosen bestimmt: 1 Die Breite der idealisierten Fraktionen, gemessen durch den Abstand ΔP der mittleren Polymerisationsgr…

Molekulargewichtsbestimmungen an verschieden scharf fraktionierten polymethacrylsäuremethylestern

1954

Aus drei Polymethacrylsauremethylestern, deren Molekulargewichte bei ungefahr 35 000, 500 000 und 8 000 000 lagen, wurden durch fortgesetzte Fraktionierung Praparate von sehr verschiedener Einheitlichkeit hergestellt. Das Molekulargewicht der einzelnen Fraktionen wurde in der Ultrazentrifuge gemessen, sowie die zugehorige Viskositatszahl in Benzol bestimmt. Es zeigt sich, das der Einflus der Einheitlichkeit fur die Beziehung zwischen Polymerisationsgrades und Viskositatszahl gering ist, falls man den Gewichtsdurchschnitt des Molekulargewichtes mist. Die bei diesen Versuchen gewonnenen Sedimentations- und Diffusionskurven werden im Hinblick auf die aus ihnen zu berechnenden Verteilungskurven…

Separation Efficiency of Two SEC Packings: Comparison of Chromatographic, Thermodynamic, and Fractal Parameters

2004

Abstract The size‐exclusion chromatographic (SEC), thermodynamic, and fractal behavior of two organic packings, named TSK‐Gel HHR and TSK‐Gel HXL, has been compared in order to assess their separation efficiency. The different experimental elution trends of five solvent/polymer systems have been evidenced through the universal calibration curves, and the existence of secondary mechanisms (such as adsorption) has been quantified by the chromatographic partition coefficient K p. From a thermodynamic point of view, the swelling and crosslinking degrees have been evaluated and compared in the two gels assayed. Moreover, the values of some fractal parameters (fractal dimension of the surface and…

MALDI-TOF characterization of macromonomers

1996

Methacryloyl endfunctionalized oligostyrene macromonomers were characterized by matrix assisted laser desorption ionization/time of flight (MALDI-TOF) spectroscopy and by isocratic and gradient high performance liquid chromatography (HPLC). The molar mass distribution derived by the different techniques coincide for the investigated oligomers. Mixing experiments revealed that the MALDI-TOF peak areas do not necessarily represent the mixing ratio of the components. Combination of gradient HPLC and MALDI-TOF has resolved the chemical composition of the coupling products formed by reaction of the living anion with oxygen.

Large scale fractionation of pullulan and dextran

2006

Abstract A recently developed large scale fractionation technique named continuous spin fractionation (CSF) was applied to fractionate pullulan and dextran. 450 g of pullulan with a broad molecular weight distribution were fractionated using water as solvent and acetone as precipitant. In this study, we have in five CSF runs prepared three fractions with apparent M ¯ w * values ranging from 17.6 to 413 kg mol−1. Seventy grams of dextran were fractionated with a mixed solvent of water plus methanol. Five fractionation steps resulted in four samples with M ¯ w values between 4.36 and 18.2 kg mol−1.

Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization. 1. Molecular weight distribution

1997

The molecular weight distribution (MWD) and its moments are calculated for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers (“inimers”) with the general structure AB*, where A is a vinyl group and B* is an initiating group. The calculated MWD is extremely broad, the polydispersity index (PDI) being equal to the number-average degree of polymerization:  Pw/Pn = Pn. It is twice as broad as that for the polycondensation of AB2 type monomers. If the fraction of unreacted monomer is not taken into account, the MWD becomes somewhat narrower, P‘w/P‘n ≈ 0.40P‘n. The kinetics of the polymerization process are first order with respect to the concentration of vi…

1981

The dynamical region of the measured calibration curves is investigated using the results of the theory published previously. The kinetic constants of the flow-equilibrium are calculated from the measurements according to two different models for a spontaneous polymer diffusion of the transported P-mer from sol into gel of the Phase Distribution Chromatography (PDC)-column. The corresponding lateral concentration profiles in the gel are found by analytical integration of Fick's second law under the corresponding boundaries. An energetic model of this flow-equilibrium is stated, giving the activation enthalpy and -entropy of the rediffusion of the polymer from gel into sol after some retarda…

Lensing of fast radio bursts: future constraints on primordial black hole density with an extended mass function and a new probe of exotic compact fe…

2018

The discovery of gravitational waves from binary black hole mergers has renewed interest in primordial black holes forming a part of the dark matter density of our Universe. Various tests have been proposed to test this hypothesis. One of the cleanest tests is the lensing of fast radio bursts. In this situation, the presence of a compact object near the line of sight produces two images of the radio burst. If the images are sufficiently separated in time, this technique can constrain the presence of primordial black holes. One can also try to detect the lensed image of the mini-bursts within the main burst. We show that this technique can produce the leading constraints over a wide range in…

Dispersion Polymerization of Vinylidene Fluoride in Supercritical Carbon Dioxide

2006

The dispersion polymerization of vinylidene fluoride in supercritical carbon dioxide is investigated using two ammonium carboxylate perfluoropolyether stabilizers of different molecular weights. Under suitable operating conditions a polymer made of well-dispersed spherical particles has been obtained up to relatively high conversion. The experimental data of polymerization rate and molecular weight distribution are in good agreement with the predictions of a model previously developed. Such an agreement supports the conclusion that the polymerization kinetics is dominated by the interphase transport of the active radicals between the continuous phase and the polymer particles.

Zur kinetik der anionischen polymerisation von methyl-methyacrylat in tetrahydrofuran bei −75°C

1973

Die anionische Polymerisation von Methylmethacrylat (MMA) in Tetrahydrofuran (THF) verlauft bei −75°C mit Cumylcasium bzw. oligomerem α-Methylstyrylcasium als Initiatoren ohne erkennbare Nebenreaktionen analog der anionischen Polymerisation von unpolaren Monomeren in atherischen Losungsmitteln. Als Beweis wird hauptsachlich die enge Molekulargewichtsverteilung der unter diesen Bedingungen hergestellten Polymethylmethacrylate angefuhrt. Bei −75°C betragen die Geschwindigkeitskonstanten fur die Monomeranlagerung an das Ionenpaar kw(±) = 80 dm3 mol−1 s−1 und an das freie Anion etwa kw(−) ≈ 6 · 104 dm3 mol−1 s−1. Leitfahigkeitsmessungen ergeben, das die Dissoziationskonstante des Polymethylmeth…