Synthesis and characterization of poly (N-isopropylacrylamide)-coated polystyrene microspheres with silver nanoparticles on their surfaces

Dispersion copolymerization of styrene and a poly(N-isopropylacrylamide) macromonomer in ethanol water media has been successfully carried out in the presence of AgNO3. Nearly monodisperse polystyrene microspheres with diameters ranging from 530 to 1250 nm were obtained. Nanoscopic silver particles were generated on their surfaces via in situ reduction of Ag+ by radicals generated from the initiator, 2,2'-azobisisobutyronitrile (AIBN). The particle sizes of both polystyrene microspheres and silver nanoparticles were affected by the initial AIBN, AgNO3, and macromonomer concentrations. The diameters of the silvered microspheres and silver nanoparticles followed the relationships D(n)proportional to[AIBN](0)(-0.107)[AgNO3](0)(0.083)[macromonomer](0)(-0.533) and d(n)proportional to[AIBN](0)(0.027)[AgNO3](0)(0.173)[macromonomer](0)(-0.137), respectively. Over 95.8% of the silver ions are converted into zerovalent metal and immobilized on the microspheres, according to atomic absorption spectroscopy measurements. The silvered microspheres were characterized by transmission electron microscopy, atomic force microscopy, and FTIR, UV-visible, and X-ray photoelectron spectroscopy. The surface-grafted PNIPAAm chains were found not only to serve as steric stabilizers to prevent the flocculation of the polystyrene particles but also to adsorb the Ag nanoparticles onto the surface of the microspheres. A mechanism for the formation of silvered polystyrene microspheres in dispersion copolymerization was presented.