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Well-defined amphiphilic poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) (PCL-b-PNVP) block copolymers were successfully prepared via the combination of ring-opening polymerization (ROP) and xanthate-mediated reversible addition−fragmentation chain transfer (RAFT) polymerization. Well-defined poly(ε-caprolactone) (PCL−OH) was synthesized by ROP in bulk at 110 °C using benzyl alcohol as initiator and stannous octate [Sn(Oct)2] as catalyst . The −OH end group was then converted into its corresponding xanthate (PCL−X) via the conversion to its corresponding bromide (PCL−Br). These are verified by 1H NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 °C using PCL−X as macro-chain transfer agent and characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL63-b-PNVP90forms spherical micelles of ∼34 nm diameter in water as shown by transmission electron microscopy (TEM), supported by 1H NMR spectroscopy, and light scattering. The critical micellar concentrations were determined by fluorescence spectroscopy using pyrene as probe. The critical micelle concentration (cmc) value of the block copolymers increases with the increase in the chain length of PNVP block. The overall hydrodynamic radius (Rh) of the micelles remains almost constant over the concentration range above the cmc value and over the angles of scattering measurement. [ABSTRACT FROM AUTHOR]

A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn= 7.0 × 104to 10.2× 104g mol–1, PDI = 1.23–1.35) having different isotacticity [meso diad (m) = 47–88%]] was successfully synthesized using the reversible addition–fragmentation chain transfer (RAFT) polymerization method in the presence of different concentrations of Y(OTf)3Lewis acid. Measurement of the glass transition temperature (Tg) of this high molecular weight isotactic PNIPAM series and the low molecular weight PNIPAM series (Mn= 3.5 × 104to 4.0 × 104g mol–1, PDI = 1.2–1.3) having different isotacticity [meso diad (m) = 45–72%)] reported earlier by us (Rayet al. Polym. J.2005, 37, 234) showed that Tgof PNIPAM decreases with increase in its meso diad content (m%) and decrease in its molecular weight. [ABSTRACT FROM AUTHOR]