Because the density of water is approximately the same as the aqueous PVA solutions since they are so diluted , the density terms in equation 9 cancels. All these methods except the last are, in principle, able to calculate absolute molecular weight. Absolute molecular weight means a molecular weight which can be calculated without a reference to calibration by another method. Dilute solution viscosity, however, is not a direct measure of molecular weight. Its value lies in the simplicity of the technique and the fact that it can be related empirically to molecular weight for many systems.
Intrinsic viscosity is determined by plotting vs. c and on the same graph paper plot vs. c.
There are two precautions which are to be taken very seriously. First, the solutions of PVA should not stand for many days for the air-borne bacteria will degrade the polymer. This will change the concentration and will make particles which will plug the viscometer. Second, every piece of glassware used in this experiment which touches the PVA solution, must be rinsed thoroughly with water and acetone to prevent a plastic-coating on the glassware. 2.0011 g of PVA was weighed and dissolved in a beaker with at least 200 mL hot water with a magnetic string bar.