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 ?C using (1-bromoethyl) benzene as an initiator. The Br- end group was then converted to xanthate as verified by 1H NMR spectroscopy, elemental analysis, and UV-spectroscopy. PS-b-PNVP copolymers were produced by MADIX of NVP in bulk at 60 ?C using PS-xanthate as a macro-chain transfer agent and the kinetics of polymerization were investigated. The structures of PS-6-PNVP were characterized using GPC and 1H NMR. Amphiphilic PS-b-PNVP could form spherical micelles with PS cores and PNVP shells in aqueous solution as confirmed by 1H 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 ?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.