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Poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL) block copolymers were synthesized as new biocompatible, thermosensitive, amphiphilic block polymers by a combination of ring-opening polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization, and their thermosensitive micellar behavior was examined. The PCL macro-chain-transfer agent was first synthesized by converting the end group of PCL-OH to O-ethyl xanthate, which was subsequently used for the RAFT polymerization of N-vinylcaprolactam. The critical micelle concentration of PCL-b-PVCL (M n,NMR 056,300 g/mol, polydispersity index01.18) was 0.026 mg/mL. The mean diameter of the PCL-b-PVCL micelles determined by transmission electron microscopy was 55±25 nm. The PCL-b-PVCL micelles exhibited repetitive aggregation and dispersion during reversible cooling and heating cycles between 20 and 40°C due to the thermosensitive behavior of the PVCL shell. Overall, the PCL-b-PVCL block copolymers have potential applications in thermosensitive drug delivery applications.

Well-defined amphiphilic poly(N-vinylpyrrolidone)-b-poly(ε-caprolactone) (PVP-b-PCL) block copolymers were synthesized at 30 °C using a hydroxylfunctionalized xanthate reversible addition−fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate, as a dual initiator for RAFT polymerization and ring-opening polymerization (ROP) in a one-pot procedure. Hydrophilic PCL blocks were first synthesized via the ROP of ε-caprolactone (CL) using diphenyl phosphate as a catalyst followed by the RAFT polymerization of Nvinylpyrrolidone (VP) by the addition of VP and 2,2′-azobis(4-methoxy-2,4dimethylvaleronitrile) (V-70) to the reaction mixture. VP quenched the ROP of CL, and V-70 initiated the RAFT polymerization of VP. The resulting PVP-b-PCL block copolymers showed very narrow molecular weight distributions, indicating that the ROP and RAFT polymerization proceeded independently in a controlled manner. To the best of our knowledge, this one-pot process is the most convenient method for the synthesis of PVP-b-PCL block copolymers. The PVP-b-PCL block copolymers could be labeled fluorescently through a reaction with rhodamine B isothiocyanate in the same pot.

A range of well-defined block copolymers were synthesized using 4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanylpentanol (CDP) as a dual initiator for reversible additionfragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) in a one-step process. Styrene, (meth)acrylate, and acrylamide monomers were polymerized in a controlled manner for one block composed of vinyl monomers, and d-valerolactone (VL), e-caprolactone (CL), trimethylene carbonate (TMC), and L-lactide (LA) were used for the other block composed of cyclic monomers. Diphenyl phosphate was used as a catalyst for the ROP of VL, CL, and TMC, and 4-dimethyamino pyridine for the ROP of LA. These catalysts did not interfere with RAFT polymerization and the synthesis of various block copolymers proceeded in a controlled manner. CDP was found to be a very useful dual initiator for a one-step synthesis of various block copolymers by a combination of RAFT polymerization and ROP. V C 2012 Wiley Periodicals, Inc. J.