Synthesis and micellization of star-shaped poly(ethylene glycol)-block-poly(ε-caprolactone)

The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3-arm star-shaped and 4-arm star-shaped block copolymers based on poly(ethylene glycol) and poly(epsilon-caprolactone) were synthesized. Micelles of star-shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady-state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di-, 3-arm star-shaped and 4-arm star-shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4-arm star-shaped block copolymers than for di- and 3-arm star-shaped block copolymers, which qualitatively agrees with the experiments.