Anomalous behaviour in the diffusion of polyethylene oxide through dialysis membrane

Dialysis is a common technique adopted in biochemistry to purify biopharmaceutical drugs. This methodology is also of interest in macromolecular chemistry and pharmaceutical nanotechnology in order to purify synthetic macromolecules and nanodrug carriers designed for drug delivery purposes. However, based on their original applications, the diffusion characteristic of the dialysis membrane is given in respect to the diffusion rate of globular proteins. So the diffusion capacity is function of molecular weight cut-off, i.e. corresponding to the maximum molecular weight of a globular macromolecule to be able to cross the membrane.

The diffusion kinetics of synthetic macromolecules is expected to differ significantly from globular proteins due to at least the following differences :
Specific relationship between hydrodynamic diameter and molecular weight,
Flexibility
Ionic density
Solubility/miscibility/adsorption behaviour with the dialysis membrane
Polymer chain entanglement above a critical concentration.

In view to validate the application of this technique to purify synthetic macromolecules, we have compared the diffusion ability of neutral polyethyetylene oxide (PEO) standards or poly(dimethyl-aminoethyl-methacrylate) (PMADAM) to protein standards (human insulin and ovalbumin).