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 B on counterion type.