Thermoresponsive Gelation of Amphiphilic Random Copolymer Micelles in Water

Herein, we developed thermoresponsive gelation systems of amphiphilic random copolymer micelles in water. To establish the design of micelle nanodomains for the physical gels, we synthesized random copolymers comprising hydrophilic poly(ethylene glycol) (average number of oxyethylene units = 4.5 or 8.5) and hydrophobic butyl or dodecyl groups. In water, the copolymers induced self-folding or intermolecular self-assembly to form unimer or multichain micelles, depending on their pendant structures and composition, and exhibited lower critical solution temperature-type solubility. When concentrated aqueous solutions of multichain aggregates were heated above their cloud points, they gelled entirely or induced macroscopic phase separation followed by gelation of their lower polymer-rich layers. Presumably, this gelation is due to physical association of the micelle domains above the overlap concentration of micelles. In contrast, solutions of unimer micelles became turbid only upon heating. Thus, it was found that controlled self-assembly of random copolymers into multichain micelles is a key factor in thermoresponsive gelation. These systems will open up a new way in designing thermoresponsive gels composed of micelle nanodomains with on-demand sol-gel transition properties by using common random copolymer micelles.

Automated summary

The study developed a thermoresponsive gelation system using amphiphilic random copolymer micelles in water. Controlled self-assembly of random copolymers into multichain micelles was found to be a key factor in thermoresponsive gelation.