Effects of reaction temperature and reaction time on positive thermosensitivity of microspheres with poly(acrylamide)/poly(acrylic acid) IPN shells

We have successfully prepared monodispersed positively thermoresponsive core-shell hydrogel microspheres with poly(acrylamide-co-styrene) [P(AAM-co-St)] cores and IPN(interpenetrating polymer network)-based shells composed of poly(acrylamide)/poly(acrylic acid). The submicron-sized monodispersed P(AAM-co-St) core seeds were prepared by using a surfactant-free emulsion polymerization method, and the IPN-based shell layers were fabricated onto the core seeds by using a method of sequential IPN synthesis. Effects of reaction time and reaction temperature during preparation of IPN on the particle size, monodispersity, and thermoresponsive characteristics of microspheres were investigated. The results show that the sizes of particles with IPN shell layer are smaller than that of seeds, and the change of monodispersity among them is not obvious and the monodispersity of particles prepared under higher reaction temperature is higher than that of seeds and those particles prepared under lower reaction temperature. With increasing reaction time, thermoresponsive characteristics of microspheres increases. While thermoresponsive characteristics of microspheres decreases sharply with increasing reaction temperature. The results display preparation of IPN-structured microspheres is so careful to need longer reaction time and lower reaction temperature.