In-situ formation of nanoparticals in polyurethane microspheres

Linear or cross-linked aqueous polyurethane dispersions with carboxyl Ag sa lt were prepared. TEM photos show that Ag+ was homogeneously distributed in the microspheres, The Ag+ was reduced in-situ by photochemical method. For linear polyurethane particles, as the extent of the reduction reaction of silver ions increased, the silver particles grew larger, but the number of the silver particles kept almost constant. In crosslinked polymer system, t he number of silver particles increased, but the size of silver particles r emained almost the same. We concluded that nucleation and growth of the sil ver particle are the result of the silver atom movement in the polymer matr ix. In the linear polymer system, the movement of silver atom and aggregati on of silver particles result in the formation and growth of several silver particles; in the cross-linked polymer system, the polymer chain prevents the movement of silver particles, resulting in a number increase of silver particles.