We report the synthesis and characterization of monodispersed thermoresponsive hydrogel microspheres with a volume phase transition driven by hydrogen bonding. The prepared microspheres, composed of poly (acrylamide-co-styrene) (poly (AAM-co-St)) cores and poly (acrylamide)/poly (acrylic acid) PAAM/PAAC) based interpenetrating polymer network (IPN) shells, were featured with high monodispersity and positively thermoresponsive volume phase transition characteristics with tunable swelling kinetics, i.e. the particle swelling was induced by an increase rather than a decrease in temperature. The monodisperse poly (AAM-co-St) seeds were prepared by emulsifier-free emulsion polymerization, the PAAM or poly (acrylamide-co-butyl methacrylate) (poly (AAM-co-BMA)) shells were fabricated on the seeds by free radical polymerization, and the core-shell microspheres with PAAM/PAAC based IPN shells were finished by a method of sequential IPN synthesis. The microsphere size increased with increasing both AAM and BMA dosages. The increase of hydrophilic monomer AAM dosage resulted in a better monodispersity, but the increase of hydrophobic monomer BMA dosageled to a worse monodispersity. With increasing the crosslinker methylenebisacrylamide (MBA) dosage, the mean diameter of the microspheres decreased and the monodispersity became better. An equimolar composition of AAC and AAM in the IPN shells of the microspheres resulted in a more complete shrinkage for the microspheres at temperatures lower than the upper critical solution temperature. Both BMA and MBA additions depressed the swelling ratio of the hydrodynamic diameter of the microspheres.

A thermo-responsive core-shell microcapsule with a porous membrane and poly (N-isopropylacrylamide) (PNIPAM) gates was prepared using interfacial polymerization to prepare polyamide core-shell microcapsules, and plasma-graft pore-filling polymerization to graft PNIPAMinto the pores in the microcapsule wall. The proposed thermo-responsive microcapsule could be a positive thermo-response controlled-release one or a negative thermo-response one by changing the PNIPAM graft yield. When the graft yield is low, the release rate from the microcapsules is higher at temperatures above the lower critical solution temperature (LCST) than that below the LCST, due to the opened/closed pores in the microcapsule membranes controlled by the PNIPAM gates. In contrast, when the graft yield is high, the release rate is lower at temperatures above the LCST than that below the LCST, due to the hydrophilic/hydrophobic phase transition of the PNIPAM gates.

In this paper, we report on a novel family of monodisperse thermo-sensitive core-shell hydrogel microspheres that is featured with high monodispersity and positively thermo-responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabri-cated in a three-step process. In the first step, monodisperse poly(acrylamide-co-styrene) seeds were prepared by emulsifier-free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide-co-(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core-shell microspheres with poly-(acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core-shell microspheres provide a new mode of the phase transition behavior for thermo-sensitive "smart" or "intelligent" monodisperse micro-actuators that is highly attractive for targeting drug delivery sys-tems, chemical separations, sensors, and so on.