Hindered diffusion of flexible polymers through polyimide ultrafiltration membranes

The hindered diffusion of polystyrene in dilute solutions of ethyl acetate through polyimide ultrafiltration membranes has been investigated. The pres ent system did not show specific membrane-solute interactions; furthermore, polystyrene can be considered as a flexible polymer coil. It is shown that the hindered diffusive permeability for monodisperse dilute solutions for a series of molecular weights can be compared well with the diffusive perme ability curve of one polydisperse dilute polystyrene solution. In the case of very dilute solutions, the polymer coils have no interaction with each o ther, and the whole range of molecular-weight-dependent permeabilities can be determined from only one measurement. The diffusion behavior of polydisp erse solutions through various polyimide membranes has been investigated as well. It was found that the diffusive permeability curve is strongly depen dent on the type of membrane, that is, on the pore size distribution. It wa s not possible to calculate a pore size distribution from diffusion experim ents due to mathematical limitations. Nevertheless, it was shown that hinde red diffusion measurements are useful to estimate a maximum pore size for e ach membrane. (C) 2000 John Wiley & Sons, Inc.