Synthesis and self-assembly of poly(styrene)-b-poly (N-vinylpyrrolidone) amphiphilic diblock copolymers made via a combined ATRP and MADIX approach

Amphiphilic diblock copolymers of polystyrene (PS) and poly(N-vinylpyrrolidone) (PNVP) were prepared by a combination of ATRP and MADIX. Well-defined PS with bromine end group was synthesized by ATRP in bulk at 110 degrees C using (1-bromoethyl) benzene as an initiator. The Br- end group was then converted to xanthate as verified by H-1 NMR spectroscopy, elemental analysis, and UV-spectroscopy. PS-b-PNVP copolymers were produced by MADIX of NVP in bulk at 60 degrees C using PS-xanthate as a macro-chain transfer agent and the kinetics of polymerization were investigated. The structures of PS-b-PNVP were characterized using GPC and H-1 NMR. Amphiphilic PS-b-PNVP could form spherical micelles with PS cores and PNVP shells in aqueous solution as confirmed by H-1 NMR and laser light scattering (LLS). The values of critical micelle concentration of PS-b-PNVP and the average aggregation number of PS-b-PNVP in the micelles were measured using pyrene as a probe and static LLS, respectively. The aggregation number increases concomitantly with temperature (10-50 degrees C), but the hydrodynamic radius of the micelles remains almost constant over the same temperature range, which may indicate shell dehydration at a higher temperature. (C) 2008 Wiley Periodicals, Inc.