By Golden on Thursday, July 24, 2003 - 06:03 pm:
I have a project to quantitatively test an unreacted monomer in a polymerization reaction using HPLC. The organic polymer is soluble in water and methanol and methanol/water will be used as the mobile phase.
I like to know what filter pore size should be used to filter the reaction mixture. And I do not quite understand what will happen to the polymers, which are smaller than the filter pore size, in the HPLC column. Will they be able to be flushed out after the test? What kind of mobile phase, more water or more methanol, should be used?
By bill tindall on Friday, July 25, 2003 - 07:40 pm:
This sounds like it might be a latex polymerization. A significant amount of monomer may be dissolved in the polymer. If the polymer is soluble in THF it can be used to wash polymer from the column, if that becomes a problem.
Headspace GC is a way of doing the analysis you are trying to do.
By Chris Pohl on Monday, July 28, 2003 - 09:38 am:
Golden,
Assuming that the polymer being formed contains no cross-linking agent, since, as you say, the polymer is soluble in the mobile phase the chromatographic behavior of the polymer will depend upon two factors: how close the polymer is in size to the pore size of the stationary phase and the chromatographic properties of the monomer in the mobile phase. Regarding the first point, the closer the polymer is to the pore size of your stationary phase, the worse the mass transport will be. In some cases, it can take hours to clear from the column if the size is too close to that of the stationary phase pores. Regarding the second point, you can expect all oligomeric species to elute after the monomer. Typically, low molecular weight oligomers can be baseline resolved from one another but if the molecular weight is high enough the peaks will merge together to form a "hump". Of course, as mentioned above, if the molecular weight is high enough that some oligomers are a "tight fit" with the stationary phase pore size, then you will likely see a long tail to the hump.
By Anonymous on Tuesday, July 29, 2003 - 05:15 am:
When we analyse monomer content by GC or HPLC typically we try to remove any polymeric components off-line by precipitation of polymer in a non-solvent and filtration. It does usually mean you have to use an internal standard to allow for the volume errors.