Abstract
This investigation is concerned with molecular weight determination on ligninsulfonate fractions of lower molecular weight, where determinations useful for macromolecules—e.g., osmometry, light scattering, etc.—are not yet fully applicable. In the present paper, application of the Gross' method
(molecular weight determination on non-charged lignins, i. e., cryoscopic method in ethylene carbonate) to ligninsulfonates with ionizable groups were examined.
In order to loss the charge of ligninsulfonate molecules, the solutions of fractionated ligninsulfonic acids were neutralized by higher amines with less polarity and these amine salts were used for cryoscopic determination.
Molecular weight determinations on dicyclohexylamine salts of ligninsulfonic acids were made in ethylene carbonate by cryoscopy. Molecular weights of these amine salts in this solvent were reproducible. Association was apparently not a problem with this method, for the values were practically concentration-independent.
On basis of the above-obtained molecular weight value of dicyclohexylamine salts, thereafter, the molecular weight of the original ligninsulfonic acids or salts was calculated by applying the observed nitrogen content of their amine salts.
This method can be used for molecular weight determinations on ligninsulfonates in the range below about four thousand.
