Preparation of PS/CaC0₃ composite nanoparticles and PS hollow nano-spheres

Surface-grafted or cross-linked polystyrene(PS)/CaCO₃ composite nanoparticles with nanometer CaCO₃ as the core were synthesized by in situ emulsion polymerization. Subsequently, PS hollow nano-spheres were prepared by etching the core with dilute hydrochloric acid. The effects of the type and amount of emulsifier, the addition method of initiator and the feeding interval on emulsion stability, the yield and grafting efficiency were investigated. Composition and morphology of composite nanoparticles before and after etching were characterized by TGA, FT-IR and TEM. The results show that cationic emulsifier is in favor of the stability of emulsion system, and a higher yield and grafting efficiency can be achieved when using 3.7% - 5.5% cetyltrimethylammonium bromide ( CTAB ) as the emulsifier. With the amount of CTAB increased, the size of composite nanoparticles becomes smaller and the size distribution becomes broader. 2, 2'-azobisisobatyronitrile (AIBN), the initiator, should avoid ultrasonic treatment along with monomers and CaCO ₃ particles, which may induce irreversible agglomeration. With the feeding interval prolonged, the yield and grafting efficiency decrease, and one-pot method contributes to obtain composite nanoparticles with higher yield and grafting efficiency ( or cross-linked degree ) . Although hollow particles can be prepared from either surface-grafted or cross-linked PS/CaCO₃ composite particles by etching, the latter with cross-linked polymer shell have rather better size and shape stability and can retain their sphere shape after etching.