No abstract

No abstract

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.

This study was performed to investigate the convective heat transfer coefficient of nanofluids made of several alumina nanoparticles and transformer oil which flow through a double pipe heat exchanger system in the laminar flow regime. The nanofluids exhibited a considerable increase of heat transfer coefficients. Although the thermal conductivity of alumina is not high, it is much higher than that of the base fluids. The nanofluids tested displayed good thermal properties. One of the possible reasons for the enhancement on heat transfer of nanofluids can be explained by the high concentration of nanoparticles in the thermal boundary layer at the wall side through the migration of nanoparticles. To understand the enhancement of heat transfer of nanofluid, an experimental correlation was proposed for an alumina-transformer oil nanofluid system.

No abstract

No abstract