文摘
Well-defined amphiphilic poly(蔚-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鈭抐ragmentation chain transfer (RAFT) polymerization. Well-defined poly(蔚-caprolactone) (PCL鈭扥H) was synthesized by ROP in bulk at 110 掳C using benzyl alcohol as initiator and stannous octate [Sn(Oct)2] as catalyst . The 鈭扥H end group was then converted into its corresponding xanthate (PCL鈭扻) via the conversion to its corresponding bromide (PCL鈭払r). These are verified by 1H NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 掳C using PCL鈭扻 as macro-chain transfer agent and characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL63-b-PNVP90 forms 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.