I can measure the length chains from the rheological test through testing of viscosity ,but this give me approximate result, therefore i look for any exact way for that test.
Dear Nizar
In my opinion, the best way to determine the molecular weight of a polymer is GPC (gel permeation chromatography). In most cases, you use polystyrene standards to do a calibration curve (elution time vs. molecular weight (or, more precisely, "molecular size"). For that reason, you won´t have a real value of molecular weight but with respect to polystyrene. Some GPCs now, apart from the refractive index detector, have other detectors (light scattering, viscosimeter, etc.). In these cases, you can elucidate the real molecular weight of your polymer.
I hope it helps,
Aitor
Dear Nizar
In my opinion, the best way to determine the molecular weight of a polymer is GPC (gel permeation chromatography). In most cases, you use polystyrene standards to do a calibration curve (elution time vs. molecular weight (or, more precisely, "molecular size"). For that reason, you won´t have a real value of molecular weight but with respect to polystyrene. Some GPCs now, apart from the refractive index detector, have other detectors (light scattering, viscosimeter, etc.). In these cases, you can elucidate the real molecular weight of your polymer.
I hope it helps,
Aitor
Light scattering would be another technique
Take a look at the textbook by Hiemenz: Principles of Colloid and Surface Chemistry
I think that is GPC / SEC is the best method because it is the only technique that measures Mn, Mw, Mz and Mz+1 at the same time by
measuring the entire distribution of the polymer. SEC also allows another average
molecular weight to be calculated, the peak molecular weight Mp, defined as:
Mp = molecular weight of the highest peak
Therefore, Mp is the mode of the molecular weight distribution. Mp is quoted for very
narrowly distributed polymers, such as polymer standards used in calibrations.
in addition to the expense of viscosity to calculat Molecular weight can be calculated by measuring the scattering of light and Another technique is through osmotic pressure accounted
Dr,
You can measure the molecular weight of polymer by using Gpc,scattering of light ,scattering of light .....
There are different methods used for measuring MW are:
End group analysis
Membrane osmometry
Viscometry
Light scattering
although you can see
http://www.azom.com/article.aspx?ArticleID=12255
in addition to the expense of viscosity to calculat Molecular weight can be calculated by measuring the scattering of light and Another technique is through osmotic pressure accounted
There are a variety of analytical techniques used to characterize molecular weight in polymers, each providing useful information about the influence of molecular weight on the measured properties. CPG offers molecular weight analysis using GPC, Dilute Solution or Intrinsic Viscometry (IV) and Melt Flow Index (MFI).
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