On the upper critical solution temperature of PNIPAAM in an ionic liquid: Effect of molecular weight, tacticity and water

The upper critical solution temperature (UCST) of 1.0 wt% Poly(N-isopropylacrylamide) (PNIPAAM) in the ionic liquid (IL) 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)amide ([EMIM][TFSI]) is strongly affected by the molecular weight and tacticity of the polymer and water content of the IL. UCSTs in IL/water mixtures are tuned in a wide range by modulating the abovementioned parameters: notably UCST spans from about −12 °C for atactic and low MW PNIPAAM in anhydrous IL up to 79 °C for the stereo-regular high MW one in presence of water. In all cases depicted above the transition always remains sharp, a convenient feature to consider in view of possible applications. The significant effect of water on the upward shift of UCSTs, which interestingly is opposite to that observed in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4], is related to the water organization in the IL, depending on the concentration therein. The above phenomena are discussed in terms of polymer-IL-water interactions balance. [Display omitted] •The UCST of PNIPAAM is strongly affected by the molecular weight and tacticity.•The effect of water depends on its organization in the IL.•The above phenomena are discussed in terms of polymer-IL-water interactions balance.