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A method to promote upper critical solution temperature (UCST) type of behavior for polycations is introduced. This relies on in situ introduction of a hydrophobic anion to an aqueous solution of a polycation in the presence of sufficient ionic strength. This was studied using two polycations: poly(2-methacryloyloxyethyltrimethylammonium iodide) and poly(3-methyl-1-(4-vinylbenzyl)imidazolium chloride). The solution behavior of the polymers was investigated in the presence of bis(trifluoromethane)sulfonamide (NTf2) and trifluoromethanesulfonate (OTf), adjusting the ionic strength with sodium chloride. All the four studied cation–anion pairs undergo an UCST type phase separation. The phase separation was reversible and only very weakly dependent on polymer concentration in the studied range.
Karjalainen et al. (Tue,) studied this question.