Novel amphiphilic diblock copolymers bearing acid-labile oxazolidine moieties: Synthesis, self-assembly and responsive behavior in aqueous solution

A novel oxazolidine based acid-labile monomer N-acryloyl-2,2-dimethyl-1,3-oxazolidine (ADMO) was synthesized and polymerized by reversible addition fragmentation chain transfer (RAFT) polymerization using poly(ethylene glycol) based chain transfer agent (PEG-CTA). The diblock copolymers PEG-b-PADMO were composed of hydrophilic PEG with fixed length and hydrophobic PADMO with different lengths, which formed core-shell micelles in water. Morphologies and sizes of micelles were obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS), which showed that the shapes of polymeric aggregates developed from small spherical micelles, worm-like micelles to larger size of vesicles, as the length of PADMO increased. The hydrolysis kinetics of the micelles was studied using 1H NMR, DLS and release of loaded Nile Red dye, whose rate strongly depended on pH and micellar structure. It led to the disruption of polymeric micelles and concomitant release of the guest molecules, due to the transformation of hydrophobic PADMO into hydrophilic poly(2-hydroxyethyl acrylamide) (PHEAM).