Amphiphilic Random-Block Copolymer Micelles in Water: Precise and Dynamic Self-Assembly Controlled by Random Copolymer Association

Amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) chains and hydrophobic butyl groups induce precise and dynamic self-assembly in water to form small micelles with a controlled size and aggregation number, chain exchange behavior, and thermoresponsive properties. Focusing on the characteristics, we newly designed random-block copolymers comprising the amphiphilic random copolymers as association segments and hydrophilic PEG chains and developed controlled self-assembly systems of the random-block copolymers into micelles in water. Owing to the random copolymer segments partly containing hydrophilic units, the random-block copolymers easily dissolved in water to form micelles (similar to 20 nm) smaller than the corresponding block copolymer micelles. Importantly, the size and aggregation number of random-block copolymer micelles were controlled precisely by the composition and degree of polymerization of the random copolymer association units, respectively. The random-block copolymers, as well as core-forming random copolymers, afforded dynamic chain exchange between micelles, while the exchange rate was suppressed by the hydrophilic polymer chains. Additionally, the thermoresponsive properties and cloud-point temperatures of the random-block copolymer micelles in water could be controlled by the aggregation number since the volume fraction of hydrophilic polymer chains is varied. Thus, we revealed that random copolymers were effective as association units to create dynamic core-shell micelles with a controlled size and aggregation number and thermoresponsive properties in water.