Poly(vinyl acetate)/silver nanocomposite microspheres prepared by suspension polymerization at low temperature

High molecular weight (HMW) poly(vinyl acetate)/silver nanocomposite microspheres (PVAc/Ag), which are promising precursors of embolic materials with radiopacity, were prepared via a suspension polymerization approach in the presence of silver nanoparticles. It was found that a high yield and high molecular weight PVAc/Ag could be concurrently obtained even using a low-temperature initiator 2,2′-azobis(2,4-dimethylvaleronitrile) (≈30 °C). In the case of presence of silver nanoparticles, the rate of polymerization was slightly slower than that without Ag. The suspension polymerization approach introduced could produce PVAc/Ag composite with conversion and viscosity-average molecular weight (M̄_v) up to 95% and 1 300 000, respectively, in spite of the low polymerization temperature (≈30 °C), in sharp contrast with an only ≈30% conversion of VAc under bulk polymerization. Morphology studies revealed that except normal suspension microspheres with a smooth surface, a golf ball-like appearance of the microspheres was observed, due to the migration and aggregating of the hydrophilic Ag nanoparticles at the sublayer beneath the microsphere's surface.