• amphiphilic block copolymers;
  • block copolymer;
  • cobalt-mediated radical polymerization (CMRP);
  • micelles;
  • poly(ε-caprolactone) (PCL);
  • poly(N-vinyl pyrrolidone) (PVP);
  • ring-opening polymerization (ROP)


An amphiphilic block copolymer of poly(N-vinyl pyrrolidone)-b-poly(ε-caprolactone) (PVP-b-PCL) was synthesized by a combination of cobalt-mediated radical polymerization (CMRP) and ring-opening polymerization (ROP). The micellar characteristics of this copolymer were subsequently investigated. PVP (Mn = 11,400, Mw/Mn = 1.32) was synthesized at 20 °C via CMRP using a molar ratio of [VP]0/[V-70]0/[Co]0 = 150/8/1. The PVP was then reacted with 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (VA-086) to modify its cobalt complex chain end to a hydroxyl group. The cobalt (Co) content in the resulting PVP-OH was 1.2 ppm, indicating that all of the covalent Co[BOND]C bonds were cleaved and reacted with VA-086, and that the separated cobalt complexes were successfully removed. The ROP of CL was subsequently carried out using the produced PVP-OH as a macroinitiator at 110 °C. The GPC trace of PVP-b-PCL was monomodal without any tailing caused by the residual PVP-OH, indicating that the initiation efficiency was very high. The critical micelle concentration (CMC) of PVP-b-PCL (Mn = 18,000, Mw/Mn = 1.35) was 0.015 mg/mL. The PVP-b-PCL micelles were spherical in shape with an average diameter of 105 nm. The nanosized PVP-b-PCL micelles show promise as novel drug carriers in biomedical and pharmaceutical applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3078–3085, 2009