Temperature-sensitive hairy particles prepared by living radical graft polymerization.

Four types of temperature-sensitive hairy particles were prepared by living radical graft polymerization using a photoiniferter. The hairs were poly(N-isopropylacrylamide) (N), poly(N-isopropylacrylamide)ran-poly(acrylic acid) (NA), and diblock copolymers composed of N and NA. The block copolymer was attached to the particle in different modes, that is, one has a N-block inner and a NA-block outer but the other has the inverse arrangement. The acrylic acid content in NA was adjusted to be only 1%, but NA had a higher transition temperature by 5 degrees C than N in a neutral aqueous solution. The sequence of blocks attached onto the particle was the key factor to control the temperature responsiveness of the particle. The hairy particles exhibited a two-step transition with increasing temperature under certain conditions. The hairy particle also responded to the pH and ionic strength. Some unique behaviors of the hairy particles were studied in detail in terms of electrophoretic mobility and adsorption of dye molecules as well as swelling/deswelling.