Synthesis of temperature responsive polymer brushes from polystyrene latex particles functionalized with ATRP initiator

Thermally responsive poly(N-isopropylacrylamide) (PNIPAAM) brushes were grafted from polystyrene particles synthesized with surfactant free emulsion polymerization and functionalized with a thin shell of ATRP initiator on the surface. The ATRP initiator was present in the shell either alone or along with copolymerized styrene and also a crosslinker. The grafted brushes were characterized with transmission electron microscopy before and after negative staining with uranyl acetate. Cryo-scanning electron microscopy confirmed the growth of extremely long PNIPAAM layers from the surface, which otherwise looked shrunken in the transmission electron microscope owing to dehydration and possibly the effect of staining agent. The amount of grafted polymer also increases proportionally to the increase of the monomer concentration in the initial reaction system. The change in character from hydrophilic to hydrophobic with temperature and salt was found to be reversible and fast. The adsorption of protein complexes (tobacco mosaic virus) could be readily achieved at higher temperatures indicating the potential of the grafted particles to be used as stationary phases in temperature regulated chromatographic separations.