12. SEC & Polymer Analysis Flashcards
How can you isolate a high MW polymer from a plastic?
By dissolving it in a good solvent and then pouring it into a poor solvent/non-solvent, thereby only precipitating the high MW polymer.
What can you use for additive analysis?
Mostly HPLC-MS and GC-MS.
What is SEC?
Size Exclusion Chromatography. You can separate a sample by size. You have no interactions with the column.
What is GPC?
Gel Permeation Chromatography.
What is GFC?
Gel Filtration Chromatography.
How does the SEC profile look?
The bigger molecules first, the smaller last.
How is the SEC system constructed?
- Pump
- Injection valve
- SEC columns
- Detector
What does the K parameter tell you (elution equation)?
Where are you in the window that is available for analysis for this specific system.
What is the K parameters for large and small molecules?
Large molecules: K_av = 1 (V_r = V_0)
Small molecules: K_av = 0 (V_r = V_m)
Describe the elution profile
The polymers with the same volume cannot be separated and will elute at the same time. The profile will display the molecules large to small (as opposed to other analysis methods).
How can light scattering be used to determine MW?
The excess scattering (scattering from sample) is proportional to the MW of the sample. You need a high MW though.
Why use viscometry to determine MW?
Because it is possible to create a universally true calibration curve, so that the measured MW is fairly accurate.
Which compound would elute first in SEC?
An apolar high MW polymer. Polarity should not matter, but since an apolar molecule is less likely to interact with anything (i.e. column material), this would elute first.
What is the governing factor for separation in SEC?
Hydrodynamic volume (size of polymer in a given solvent).
What is the advantage of a standard calibrated SEC system?
It is independent of concentration of the sample.
But it can only determine MW of a specific polymer (i.e PE), MW of other polymer will be relative to the standard.
