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℃ 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.