Influence of Hydrophobic Anion on Solution Properties of PDMAEMA

The effect of bis(trifluoromethane)sulfonimide, NTf2, anion on solution properties of the thermoresponsive poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, has been studied. Nonstoichiometric amounts of LiNTf2 were added to aqueous solutions of PDMAEMA, with or without a buffer in the pH range 6-10. Since PDMAEMA is a weak polybase, the interaction between PDMAEMA and NTf2 can be manipulated by the concentration of the anion and also by varying the degree of charging of PDMAEMA with pH. PDMAEMA has a well-known LCST behavior which can be modulated by the counterion. It was observed that the hydrophobic NTf2 anion not only decreases the cloud point of PDMAEMA but also triggers an upper critical solution temperature (UCST) type behavior in acidic pH. In a higher pH regime, NTf2 makes the cloud point increase because the anion turns PDMAEMA to a stronger base, presumably by effectively shielding the charges.