Solutions of Carboxymethylcellulose with Organic Counterions (I): The Influence of Counterion Properties on the Polymer Structure and Solubility

Polyelectrolytes often display good solubility in water but not in organic solvents, a feature that limits their applications in nonaqueous media such as hand sanitizers. Here, we show that this limitation can be overcome by tuning the counterion-solvent affinity. To this end, the solubility and chain conformation of carboxymethylcellulose (CMC) salts with different organic counterions in a variety of solvents were studied by employing the Hansen solubility parameter (HSP) framework and small-angle X-ray scattering (SAXS), respectively. The solubility phase mapping demonstrates an increase in the soluble region in HSP space for the polyelectrolyte to encompass more solvents as the counterion side arm length increases or if the side arm is substituted with a large functional group, while substituting the central atom does not change the solubility, suggesting that the solubility is mainly influenced by the interaction between the peripheral atoms and the solvents. Scattering measurements revealed that for a given solvent, the nature of the counterion does not influence the conformation of chains in solution, as seen by the independence of the stretching parameter <i>B</i> on counterion type.