How this works
Most GPC/SEC systems are calibrated with narrow polystyrene (or PMMA) standards, so the molecular weight your software reports is a "PS equivalent" value, the molecular weight a polystyrene chain would need to elute at the same retention time. Your actual polymer almost never has the same relationship between chain length and hydrodynamic size as polystyrene, so that number is only a true molecular weight if your sample happens to be polystyrene too.
The universal calibration principle says two polymers that elute at the same retention volume have the same hydrodynamic volume, which is proportional to [η]·M. Since intrinsic viscosity follows the Mark Houwink equation [η] = K·Mα, you can convert between the calibration standard's apparent molecular weight and your polymer's true molecular weight if you know both polymers' K and α values in the same solvent.
Conversion calculator
Reference Mark Houwink parameters
Representative literature values, typically THF near room temperature unless noted. Polystyrene's constants are very well established; the others vary more across sources depending on tacticity, microstructure, and exact conditions. Always use your own column supplier's or a primary literature source's values for quantitative work.
| Polymer | Solvent | K (×10⁻⁴ dL/g) | α |
|---|
This conversion assumes the universal calibration principle holds and that the GPC was calibrated with narrow, well characterized standards spanning the relevant molecular weight range. It does not account for branching, which changes a polymer's hydrodynamic volume independent of its true molecular weight, so branched samples will still read inaccurately even after this correction.