Thermo-responsive poly(N-isopropylacrylamide-co-styrene)［P(NIPAM-co-St)］ hydrogel microspheres were prepared by surfactant-free emulsion polymerization. The effects of initiator dosage

stirring rate

phase ratio and polymerization time on particle size and monodispersity were investigated.The results showed that

with increasing initiator dosage

mean diameter increased slightly to a maximum

and then decreased drastically; meanwhile

the monodispersity of the particles became a little better at first

and then became worse significantly. With increasing stirring rate

particle diameter decreased while the monodispersity became worse. When the amount of phase rate increased

the mean diameter became larger simply

whereas the monodispersity became worse firstly and then became better again. As the polymerization proceeded

the mean diameter of the particles hardly changed

and the monodispersity became better gradually. The microspheres prepared under the optimum experimental conditions showed satisfactory particle size and monodispersity.