Temperature Driven Self-Assembly of a Zwitterionic Block Copolymer That Exhibits Triple Thermoresponsivity and pH Sensitivity

We report a zwitterionic block copolymer composed of N -isopropylacrylamide and N, N -dimethyl- N -(3-(methacrylamido)propyl)ammoniopropanesulfonate monomers which self-assembles into different structures depending on the solution temperature. As the temperature is increased from 20 to 70 °C, the solubility of the polymer switches direction from insoluble to soluble to insoluble to soluble. During this process, the polymer self-assembly changes from polymersomes to micelles. These extraordinary transitions are possible because of the hydrophilic–hydrophobic ratio of the polymer blocks and the presence of a carboxyl end group attached to the end of the poly( N -isopropylacrylamide) chain. Additionally, one of these transitions can be controlled by the pH of the solution thanks to the protonation–deprotonation of the carbonyl and the charge neutralization of the ammonium moieties. The present work opens the possibility of designing polymers with temperature driven self-assembly properties that could be used for biomedical applications.