Coil-Globule Transition and/or Coacervation of Temperature and pH Dual-Responsive Carboxylated Poly(N-isopropylacrylamide)

We now report the stimuli-responsive behavior of an ionic poly(N-isopropylacrylamide)-based functional polymer, poly(NIPAAm-co-2-carboxyisopropylacrylamide) (poly(NIPAAm-co-CIPAAm)), which has carboxyl groups on the isopropyl side chains. The poly(NIPAAm-co-CIPAAm) exhibits a sensitive dehydration involving a coil-globule transition in acidic media above the lower critical solution temperature, while it induces an incomplete dehydration and shows coacervate formation when the carboxylic groups of the CIPAAm units are deprotonated. Therefore, by using the poly(NIPAAm-co-CIPAAm), we can first demonstrate that the dynamically tunable switching system between the coilglobule transition and the coacervation of thermoresponsive polymers can be successfully achieved by controlling the external stimuli, such as the pH change.