Preparation And Thermo-Sensitive Characteristics Of Positive Type And Negative Type Hydrogel Microspheres

As a part of intellectual material, thermo-sensitive hydrogel microspheres are getting more and more attentions. Because of their small diameters and high sensitivity to temperature, thermo-sensitive hydrogel microspheres can be traced to their potential applications in numerous fields, including drug delivery, chemical separation, chemical sensors, and catalysis, which continue to attract more attention of scientific researchers. Although a lot of achievements have been made on the thermo-sensitive hydrogel microspheres, there are still many problems that need to be solved. For example, in the targeting drug delivery system (TDDS), some cases require small diameter and good monodispersity of microsphere drug carrier. In some fields, positive thermo-sensitive microspheres are preferred to negative ones. That is to say, with increasing environmental temperature, the microspheres volume should become larger. In this study, investigations were systematically carried out on preparation and thermo-sensitive characteristics of positive type and negative type hydrogel microspheres, and some exciting results have been gotten.Poly(A-isopropylacrylamide)(PNIPAM) is a preferable material for the preparation of negative thermo-sensitive hydrogel microspheres, because its lower critical solution temperature(LCST) is low and the responsiveness is fast. Thermo-responsive poly(jV-isopropylacrylamide-co-styrene) (P(NIPAM-co-St)) microspheres were prepared by surfactant-free emulsion polymerization methods in this paper. The prepared microspheres have spherical outer surface, small diameter, and good monodispersity. Effects of initiator dosage, stirring rate, phase ratio and polymerization time on the particle sizes and monodispersity were investigated systematically. Then, microspheres was prepared under optimum conditions. Theresults showed that, with increasing the initiator dosage, the mean diameter of particles increased slightly up 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 the stirring rate, the particle diameter decreased while the monodispersity became worse. When the amount of phase ratio 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 decreased firstly and then increased, and the monodispersity became better gradually. In the reaction, NIPAM rapidly homopolymerized, then St entered into precursor particles and polymerized, finally microspheres with hydrophobic core and hydrophilic shell are obtained. Particle size and monodispersity of the microspheres prepared under the optimum conditions were satisfied. On the base of soap-free emulsion, core-shell microspheres prepared by means of seed polymerization are thermo-sensitive. Effects of NIPAM and St dosage on the particle size and monodispersity were investigated. When increasing NIPAM dosage of the second step, the mean diameter became larger simply, whereas the monodispersity became better, and the thermo-sensitive swelling ratio became larger. When St dosage increased in the first step, the particle size also became larger, whereas the monodispersity became worse firstly and then became better again, and St dosage hardly changed the thermo-sensitive swelling ratio of the microspheres.The preparation and the thermo-sensitive characteristics of positive thermo-sensitive microspheres. or so-called thermo-swelling microspheres, were studied for the first time, and the results were satisfied. By adopting the structure and mechanism of interpenetrating polymer network (IPN), Poly (AAM-co-St-co-BMA) /PAAC IPN microspheres are prepared. Effects of some factors on the particle size, monodispersity and thermo-sensitive characteristics are investigated in processes of two-step reaction. Phase transition of these positive microspheres is based on the hydrogen bond between PAAC chains and...