Synthesis of novel amphiphilic star-shaped poly(ε-caprolactone)-block-poly(N-(2-hydroxypropyl)methacrylamide) by combination of ring-opening and chain transfer polymerization

Novel amphiphilic star-shaped block copolymer, star-poly(ε-caprolactone)-block-poly(N-(2-hydroxypropyl)methacrylamide), was synthesized and characterized. Star-block copolymers with varying feed ratios were prepared by free radical polymerization of N-(2-hydroxypropyl)methacrylamide in the presence of a novel biodegradable, macromolecular chain-transferring agent star-poly(ε-caprolactone)-tetrakis-thiol. All star-block copolymers self-assembled in aqueous solutions to form unimodal micelles of 100–150 nm size. Micelle size was independent of polymer concentration. The critical aggregation concentrations of the polymers were in the range of 1–2.5 mg/l. The partition equilibrium constant of pyrene in the hydrophobic core of micelles was comprised between 5 and 8×105. The star-block copolymer micelles were loaded by a dialysis procedure with 5–12% (w/w) of a model poorly water-soluble drug (indomethacin). These star-block copolymers could prove useful as nanocarriers for the solubilization and transport of hydrophobic drugs. Star-shaped macromolecular chain-transferring agent reported in this work can also find application in the synthesis of a variety of novel biodegradable star-block copolymers.