Poly(2-ureidoethyl methacrylate) (PUEM) was prepared via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization and a post-modification reaction. PUEM shows upper critical solution temperature (UCST) behavior in aqueous solution. Although PUEM can dissolve in water above the UCST, it cannot dissolve in water below the UCST. Diblock copolymers (MmUn) composed of a biocompatible hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) block and a PUEM block with different compositions were prepared via RAFT radical polymerization and a post-modification reaction. "M" and "U" represent PMPC and PUEM blocks, respectively, and the subscripts represent the degree of polymerization of each block. M95U149 and M20U163 formed polymer micelles comprising a PUEM core and a PMPC shell below the critical aggregation temperature (Tc) in aqueous solution. Polymer micelles were formed from M20U163 below 32 °C, which can incorporate guest molecules into the core.

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Poly(2-ureidoethylmethacrylate) (PUEM n ) was synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization and following polymer reaction. We prepared two PUEM n samples with different degrees of polymerization (n 5 100 and 49). The polymers exhibited upper critical solution temperature (UCST) in phosphate-buffered saline (PBS) solution. The phase separation temperature (T p ) in PBS can be controlled ranging from 17 to 55 8C by changing molecular weight of the polymer, polymer concentration, and adding NaCl concentration. The polymers in PBS formed coacervate drops by liquid-liquid phase separations below T p . Results of the dielectric relaxation measurement, the hydration number per monomeric unit was 5 above T p . Based on a fluorescence study, the polymer formed slightly hydrophobic environments below T p . The liquid-liquid phase separation was occurred presumably because of weak hydrophobic interactions and intermolecularly hydrogen bonding interactions between the pendant ureido groups.

Biomimetic block copolymer-protected gold nanoparticles (AuNPs) were prepared by autoreduction. Excellent colloidal stability of the AuNPs was observed at a high salt concentration and over a wide pH range. Functional AuNPs are useful for label-free detection of an inflammation biomarker, C-reactive protein (CRP).

When a bioactive molecule is taken into cells by endocytosis, it is sometimes unable to escape from the lysosomes, resulting in inefficient drug release. We prepared pH-responsive polyion complex (PIC) vesicles that collapse under acidic conditions such as those inside a lysosome. Furthermore, under acidic conditions, cationic polymer was released from the PIC vesicles to break the lysosome membranes. Diblock copolymers (PM and PA) consisting of water-soluble zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) block and cationic or anionic blocks were synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Poly(3-(methacrylamidopropyl) trimethylammonium chloride) (PMAPTAC) and poly(sodium 6-acrylamidohexanoate) (PAaH) were used as the cationic and anionic blocks, respectively. The pendant hexanoate groups in the PAaH block are ionized in basic water and in phosphate buffered saline (PBS), while the hexanoate groups are protonated in acidic water. In basic water, PIC vesicles were formed from a charge neutralized mixture of oppositely charged diblock copolymers. At the interface of PIC vesicle and water exists biocompatible PMPC shells. Under acidic conditions, the PIC vesicles collapsed, because the charge balance shifted due to protonation of the PAaH block. After collapse of the PIC vesicles, PA formed micelles composed of protonated PAaH core and PMPC shells, while PM was released as unimers. PIC vesicles can encapsulate hydrophilic nonionic guest molecules into their hollow core. Under acidic conditions, the PIC vesicles can release the guest molecules and PM. The cationic PM can break the lysosome membrane to efficiently release the guest molecules from the lysosomes to the cytoplasm.