Well-defined poly(sodium 2-(acrylamido)-2-methylpropanesulfonate-block-sodium 6-acrylamidohexanoate) (pNaAMPS-AaH) was synthesized by reversible addition−fragmentation chain transfer (RAFT) radical polymerization of sodium 6-acrylamidohexanoate (AaH) using the sodium 2-(acrylamido)-2-methylpropanesulfonate-based macrochain transfer agent. The “living” polymerization of AaH was evidenced by the fact that the number-average molecular weight increased linearly with monomer conversion while the molecular weight distribution remained narrow independent of the conversion. pH-induced association and dissociation behavior of the diblock copolymers was investigated by quasi-elastic light scattering (QELS), static light scattering (SLS), 1H NMR spin−spin relaxation time, and fluorescence probe techniques. At pH < 4, the diblock copolymers exhibited large values of the hydrodynamic radius and small values of the 1H NMR spin−spin relaxation time. These observations indicated that micellization occurred to form polymer micelles comprising hydrophobic protonated AaH cores and hydrophilic NaAMPS coronas at pH < 4. On the other hand, these diblock copolymers dissolved in aqueous solutions as a state of unimer under high-pH conditions. 8-Anilino-1-naphthalenesulfonic acid, ammonium salt hydrate (ANS), as a fluorescence probe could be incorporated into the protonated AaH core of diblock copolymer micelles at low pH and released upon dissociation of the micelles at high pH, which was completely reversible.

A water-soluble diblock copolymer was prepared from sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and N-isopropylacrylamide (NIPAM) via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. The RAFT "living" radical polymerization process of NIPAM using an NaAMPS-based macrochain transfer agent was confirmed by the fact that the numberaverage molecular weight increased linearly with monomer consumption while the molecular weight distribution remained to be narrow for the polymerization. The NIPAM block exhibited a lower critical solution temperature (LCST) in water. Both the NaAMPS and NIPAM blocks are soluble in water at room temperature. At temperatures above the LCST, the NIPAM blocks associated into a polymer aggregate. The polymer aggregate was assumed to be an elongated micelle or a multiple aggregate due to intermicellar association of the spherical core-corona micelles based on characterization data obtained from 1 H NMR, turbidity, light scattering, and fluorescence probe experiments. A hydrophobic compound such as 8-anilino-1-naphthalenesulfonic acid, ammonium salt hydrate (ANS), was incorporated into the hydrophobic aggregate of the NIPAM blocks above LCST and released from the aggregate when temperature was reduced below LCST. The capture and release of ANS triggered by temperature change were completely reversible.