Estimation of molecular weight distribution of poly(vinylpyrrolidone) from diaphragm‐cell diffusion measurements

Abstract Viscometry, gel permeation chromatography (GPC) and diffusion measurements on three samples of poly(vinylpyrrolidone) (PVP) were made. The diffusion measurements were carried out by means of a Stokes cell. An equation with five parameters was derived, linking the difference in PVP amount between the two compartments of the cell to the time of the experiment: three parameters are related to the diffusional behavior of the macromolecules and the other two define the molecular weight distribution (the Tung expression has been chosen). A least‐squares procedure allowed us to obtain the five parameters and the calculated weight average molecular weights agree with the ones evaluated by viscometry and GPC. The ratio M w / M n (heterogeneity of the polymer) calculated from the parameter z of the Tung expression is very different from the one obtained from GPC.