GRAFT-COPOLYMERS HAVING HYDROPHOBIC BACKBONE AND HYDROPHILIC BRANCHES.11. PREPARATION AND THERMOSENSITIVE PROPERTIES OF POLYSTYRENE MICROSPHERES HAVING POLY(N-ISOPROPYLACRYLAMIDE) BRANCHES ON THEIR SURFACES

Thermosensitive microspheres with 0.4-1.2 mu m diameter consiting of a polystyrene core and poly(N-isopropylacrylamide) (polyNIPAAm) branche s on their surfaces were prepared by the free radical polymerization o f a polyNIPAAm macromonomer and styrene in ethanol. Electron spectrosc opy for chemical analysis (ESCA) of the microsphere surface suggested that polyNIPAAm chains were favorably located on the surface of the mi crospheres. The morphology of the microspheres was observed by transmi ssion electron micrograph (TEM) and the particle size of was estimated by submicron particle analyzer. The molecular weight of the polyNIPAA m macromonomer, the ratio of the macromonomer and styrene, and the pol ymerization temperature affected the particle size. Thermosensitive pr operties of polyNIPAAm-coated polystyrene microspheres were evaluated by the turbidity of their dispersion solutions and the hydrodynamic si ze of the miocrospheres. The transmittance in dispersion solutions cha nged clearly, similar to oligoNIPAAm and polyNIPAAm macromonomers. In addition, the particle size of microspheres decreased with rising temp erature. These results were explained by the thermosensitivity of poly NIPAAm branches on the microsphere surface. (C) 1996 John Wiley & Sons , Inc.