Synthesis and characterization of amphiphilic poly(N‐vinyl pyrrolidone)‐b‐poly(ε‐caprolactone) copolymers by a combination of cobalt‐mediated radical polymerization and ring‐opening polymerization

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 ( M n = 11,400, M w / M n = 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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 ( M n = 18,000, M w / M n = 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.