Chromatography Forum

How big can be the difference in retention times between same molecular mass poly(acrylic acid) and poly(methacrylic acid). (under same circumstances)?

Any approximate ideas and suggestions are welcome

If you are doing gel filtration chromatography? (gfc in subject) then your molecules should be separated by
size rather than functionality. The porosity range of a good GPC column is around 0.4 to 0.8 extrastitial
to total porosity respectively so you would expect an elution time of between 5 and 11 minutes at a mL/min
on 7.8 x 300 mm column.

If you are doing gel filtration chromatography? (gfc in subject) then your molecules should be separated by
size rather than functionality. The porosity range of a good GPC column is around 0.4 to 0.8 extrastitial
to total porosity respectively so you would expect an elution time of between 5 and 11 minutes at a mL/min
on 7.8 x 300 mm column.

What I mean is:
under same circumstances the size and shape of macromolecule would depend on their chemical structure; and since there is one hydrophobic (methyl) group per each unit, how significantly would it effect the overal size (hydrodynamic radius) and therefor elution time.

If they have the same MW they may have a different size and shape.
I think it is not possible to predict though you could make some arguments depending upon
which solvent you picked. Do you mean PMMA?

You could run GPC vs PMMA MW standards and confirm MW via MALLS.

Only asking here because somebody might have come accross similar comparison in their practice.
I know the experiment is the best way to find out