Test No. 119: Determination of the Low Molecular Weight Content of a Polymer Using Gel Permeation Chromatography

         This Test guideline describes the Gel Permeation Chromatography (GPC). This method permits to determine the molecular weight distribution and the average molecular weights (Mn, Mw). GPC is a special type of liquid chromatography in which the sample is separated according to the hydrodynamic volumes of the individual constituents. Low molecular weight is arbitrarily defined as a molecular weight below 1000 dalton.According to their size, the eluted molecules can or not penetrate in the porous material (typically an organic gel) of which the columns are filled. Thus, the smallest molecules are retained whereas largest elute more quickly. At exit of column, detectors (generally by differential refractometry) provide the refractive index or UV-absorption and yield a simple distribution curve. However, to attribute actual molecular weight values to the curve, it is necessary to calibrate the column by passing down polymers of known molecular weight and, ideally, of broadly similar structure, e.g. various polystyrene standards. For each sample analyzed, two independent experiments must be undertaken. 