PREPARATION OF PSt/TiO2 CORE-SHELL COMPOSITE MICROSPHERES VIA SURFACE MODIFICATION OF PSt SEED LATEX PARTICLES

A negatively charged monodisperse PSt seed emulsion was first synthesized via batch emulsifier-free emulsion polymerization, and then polyethyleneimine (PEI) was added to modify the particle surface at 25 degrees C to prepare the positively charged PSt seed particles. Finally, the core-shell PSt/TiO2 composite microspheres were obtained by adding the diluted modified PSt seed emulsion into the medium of ethanol with certain amount of tetrabutyl titanate (TBT) under neutral condition. Influence of PEI amount on zeta potential of PSt seed emulsion, and influences of reaction time,addition models and EtOH/H2O mass ratio on the morphology of PSt/TiO2 composite microspheres were investigated. Results showed that zeta potential of PSt seed emulsion increased with the increase of PEI amount,and reached its optimum value of 38. 3 mV from -40. 3 mV when the amount of PEI was increased to 15 wt% of PSt seed weight. In the preparation of core-shell PSt/TiO2 composite microspheres, the encapsulation ratio of TiO2 onto the modified PSt particles increased with the increasing reaction time, and a maximum value of 90. 2% achieved when the reaction time prolonged to 7 h. With the decrease of EtOH/H2O, the number of TiO2 nanoparticles absorbed onto the composite microspheres decreased, and the uniform core-shell PSt/TiO2, composite microspheres with the shell thickness of about 29 nm were obtained in the medium with EtOH/H2O mass ratio of 100/6. 0.