Dispersion of polystyrene inside polystyrene‐b‐poly(N‐isopropylacrylamide) micelles in water

The addition of mixture of polystyrene-b-poly(N-isopro- pylacrylamide) (PS-b-PNIPAM) and polystyrene homopolymer (h- PS) in tetrahydrofuran dropwise into water leads to nanoparticles with a PS core and a thermally sensitive PNIPAM shell. The effects of the ratio of the homopolymer to copolymer and temperature on the formation and stabilization of the dispersion were investigated by using a combination of static and dynamic laser light scattering. PNIPAM shell continuously collapses as temperature increases in the range 20-40 � C. Such formed particles are stable even at tem- peratures much higher than lower critical solution temperature (LCST � 32 � C) of PNIPAM. Our results reveal that the area occu- pied per hydrophilic PNIPAM chain on the hydrophobic PS core remains nearly a constant regardless of the amount of h-PS in the polymer mixture. This clearly indicates that the surface area occu- pied per hydrophilic group is a critical parameter for stabilizing par- ticles dispersed in water. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 749-755, 2010

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