In the case of polymers which have ionic functional groups, the ionic functional groups repel each other and/or aggregation take place, and therefore, the apparent molecular size of the polymers become large. When analyzing such polymers by a organic SEC (GPC) column (GPC KD-806M) with DMF as the eluent, elution time may be very fast and/or abnormal peak shape may be obtained. To prevent such ionic dissociation, the addition of salts such as LiBr is know to be effective. Although the optimal concentration of LiBr is considered to be around 10mM, no systematic study on this point has been performed. Here, the result of the study to determine the optimal concentration range of LiBr in DMF is shown for cellulose acetate. It is confirmed that the concentration of 10mM which has been used traditionaly is in the range of optimal concentration range. In the figure, chromatograms show the output from RI detector and “x” marks show the output from MALS (multi angle light scattering) detector.
From the result, we can say that apparent large molecular weight components exist when LiBr is not added.
Please refer to the case of Poly(vinylpyrrolidone).
Sample : 0.1% Cellulose acetate, 100μL
Column : Shodex GPC KD-806M (8.0mmI.D. x 300mm) Eluent : LiBr in DMF Flow rate : 1.0mL/min Detector : Shodex RI, MALS Column temp. : 40°C