Problems in the Determination of Molecular Weight Distributions by Sedimentation Transport

Meyerhoff, Guenther

doi:10.1016/b978-1-4831-4497-9.50010-1

Cited by 7 publications

(2 citation statements)

References 24 publications

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“…Then, we found that the partial specific volume of branched polystyrene in cyclohexane at 35°C was 0.934 ml/g, which was equal to that of the linear one observed in this work and reported also by Meyerhoff 16 and Kurata, et al 9 Therefore, use of our method is justified, at least in principle, for determination of the molecular weight distribution and the branching parameter of branched polymers.…”

Section: Viscositysupporting

confidence: 50%

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Characterization and Solution Properties of Randomly Branched Polymers

Matsuda

Yamada

Okabe

et al. 1977

Polym J

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ABSTRACT:The characterization method of branched polymers recently proposed by the present authors was tested experimentally by using three samples of randomly branched polystyrene. The distribution curve of the molecular weight and the correlation between branching parameter and molecular weight were determined from the sedimentation velocity and diffusion patterns of each polymer sample in a theta solvent, cyclohexane at 35°C, and it was ascertained that the average molecular weights derived from the distribution curve were in good agreement with the results of osmotic pressure and light scattering measurements. The molecular weight distribution curve thus established was utilized for converting the sedimentation pattern into the sedimentation constant vs. molecular weight relationship of each polymer, from which an average density of branch points was evaluated with the aid of the Kurata-Fukatsu theory. This estimate of the average branch-point density was of reasonable magnitude.

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Section: Viscositysupporting

confidence: 50%

“…The results are shown in Figure 2 ( 1-vp0), where p0 is the density of the solvent. 16 The observed value of v were 0.934 ml/g for both the linear and the branched polystyrenes. This value is in good agreement with 0.934 ml/g reported by Meyerhoff 16 and 0.933 ml/g by Kurata, et al 9 for linear polystyrenes.…”

Section: Sedimentation Velocity1°mentioning

confidence: 99%

Characterization and Solution Properties of Randomly Branched Polymers

Matsuda

Yamada

Okabe

et al. 1977

Polym J

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Untersuchungen über das Reibungsverhalten von Polymethacrylsäuremethylestern in verschiedenen Lösungsmitteln

Lütje

Meyerhoff

1963

Makromol. Chem.

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An drei Polymethacrylsiiuremethylester-Fraktionen wurden Sedimentationskoeffizienten, Diffusionskoeffizienten und Viskositltszahlen im O-Losungsmittel n-Butylchlorid und in den guten Losungsmitteln Aceton und Dioxan gemessen. Die Reibungszahl [f] = kT/Dq,, ist der Ausdehnung des Knauels proportional. Mit dem Tragheitsradius R gilt [f] = Y. R, worin der Faktor Y von der Giite des Losungsmittels abhangt. Experimentell wurde am O-Punkt Yo = 15,5 gefunden. Hydrodynamische Rechnungen verschiedener Autoren ergeben dagegen Y o = 12,5. I n den beiden guten Losungsmitteln fanden wir Y M 13. Fiir alle Losungsmittel 1aBt sich Y als Funktion des Exponenten a der Viskositats-Molekulargewichtsbeziehung [q] = K,.Ma angeben zu [f] -15,5 [l-1/3 (za-l)] R Diese empirische Gleichung unterscheidet sich in den Koeffizienten betrachtlich von einer analogen von PTITSYN-EJZNER theoretisch ermittelten Beziehung. SUMMARY:The sedimentation coefficients, diffusion coefficients and intrinsic viscosities t,;] of three fractionated' samples of polymethylmethacrylate were determined in three different solvents. A @-solvent n-butylchloride, and two good solvents, acetone and dioxane, were tested.The friction number [f] = kT/Dq, is proportional to the dimension of the molecule. Combining the radius of gyration R with [f], we have [f] = Y.R with Y as a function of the solvent. Experiments at the @-temperature yield Y o = 15.5 in contrast to the value Y, = 12.5 as predicted by various hydrodynamic theories. I n the good solvents we observed Y M 13. We found the empirical relationship [f] = 15.5 [l-1/3 (2a-1)] R between the radius of gyration, the exponent a of the viscosity molecular weight relationship [?] = %.Ma and [f]. This equation differs appreciably from an analogous relation predicted theoretically by PTITSYN and EJZNER.

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On the pressure and concentration dependence of the sedimentation coefficient

1965

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Tn the ultracentrifugation of solutions in organic solvents the sedimentation coefficient has to be corrected for two effects: the increasing dilution of the solution due to the sector shape of the centrifuge cell and the increasing density and viscosity of the solvent caused by the effective field of gravity. The corrections can amount to 10-30% of the measured value. A new graphical method of correcting for both effects without the need for any additional data is described. This technique in combination with established procedure also allows calculation of an average molecular weight of the solute. ZUSAMMENFASSUNG:Bei der Untersuchung von Polymerlosungen in organischen Losungsmitteln mit der Ultrazentrifuge mu8 der Sedimentationskoeffizient fur zwei Eidiisse korrigiert werden: fiir die zunehmende Verdunnung der Losung auf Grund der Sektorform der Zentrifugenzelle und fur die wachsende Dichte und Viskositat des Losungsmittels durch das effektive Schwerefeld. Diese Korrekturen konnen 10-30 yo des MeBwertes betragen. Eine graphische Methode wird vorgeschlagen, die beide Korrekturen ohne zusatzliche Informationen ermoglicht. I n Verbindung mit einem in der Literatur beschriebenen Verfahren ist die gleichzeitige Bestimmung eines Mittelwertes des Molekulargewichts des gelosten Polymeren moglich.

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Problems in the Determination of Molecular Weight Distributions by Sedimentation Transport

Cited by 7 publications

References 24 publications

Characterization and Solution Properties of Randomly Branched Polymers

Characterization and Solution Properties of Randomly Branched Polymers

Untersuchungen über das Reibungsverhalten von Polymethacrylsäuremethylestern in verschiedenen Lösungsmitteln

On the pressure and concentration dependence of the sedimentation coefficient

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