Two-step phase transition via in situ hydrolysis of thermosensitive polymeric micelles with acid-labile core

This communication reports thermoresponsive diblock copolymer micelles composed of a hydrophilic poly(ethylene glycol) (PEG) shell with temperature-responsive functionality and an acid-labile, hydrophobic poly(N-acryloyl-2,2-dimethyl-1,3-oxazolidine) (PADMO) core. Because of the partial in situ hydrolysis of these micelles, an interesting two-step phase transition occurs, exhibiting two separate cloud points. This can be attributed to the dual characters displayed by poly(2-hydroxyethyl acrylamide) (PHEAM), the hydrolysis product of PADMO in an acid medium. The formation of hydrogen bonding between PEG and PHEAM enhances the hydrophobicity of PEG chains and promotes the phase transition that takes place at a lower temperature than before. On the other hand, generation of water-soluble PHEAM increases the hydrophilicity of the whole micelles and requires higher temperature that induces dehydration of these micelles. This finding could help us better understand the relationship between micellar microstructure and thermosensitive behaviors.