Influence of Hydrophobic Anion on Solution Properties of PDMAEMA

The effect of bis(trifluoromethane)sulfonimide, NTf 2, anion on solution properties of the thermoresponsive poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, has been studied. Nonstoichiometric amounts of LiNTf 2 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 NTf 2 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 NTf 2 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, NTf 2 makes the cloud point increase because the anion turns PDMAEMA to a stronger base, presumably by effectively shielding the charges.