pH-responsive micelles and vesicles formed from a water-soluble schizophrenic diblock copolymer

• A well-controlled and structured pH-responsive double hydrophilic diblock copolymer was prepared via reversible addition–fragmentation chain transfer (RAFT) controlled/living radical polymerization.
• In aqueous solution the block copolymer self-assembles to a schizophrenic micelle under acidic and basic conditions.
• In pure water the block copolymer forms vesicles that can incorporate guest water-soluble polymers into the interior water phase.

A pH-responsive diblock polymer (pDEA-b-pAaH) composed of poly(N,N-diethylaminoethyl methacrylate) (pDEA) and poly(6-acrylamidohexanoic acid) (pAaH) was synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled/living radical polymerization and characterized by NMR. pDEA-b-pAaH in water and salt solution self-assembled to schizophrenic micelles in acidic and basic conditions. NMR, light scattering, TEM, and fluorescence measurements provided clear evidence of core–shell micelles and inverted micelles under acidic and basic pH conditions. The micelle size was determined by dynamic light scattering (DLS) measurement at different pH values. pDEA-b-pAaH does not dissolve in water at around pH 6, because the anionic pAaH and cationic pDEA blocks were subject to electrostatic interactions; however, the precipitate formed in pure water at pH 6 dissolved in 1.1 M NaCl because the electrostatic interactions were screened by the large excess of NaCl. When pDEA-b-pAaH in 1.1 M NaCl aqueous solution was dialyzed against pure water to remove NaCl, the polymer formed a vesicle structure that could incorporate water-soluble polymer guest molecules into the interior water phase.