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.

Microcapsules can encapsulate various chemical substances in their inner spaces, and it is thus possible to attain a controlled permeation of chemicals by using appropriate microcapsules. Because of their characteristics such as small size, huge total surface area, large inner volume, and stable membrane, microcapsules have found many applications in various fields from drug delivery through to the textile, petroleum, and pesticide industries. As the release rate from core-shell microcapsules is generally controlled by the rate of diffusion of the permeants across the thin microcapsule membrane, a faster response of the release rate to environmental stimuli may be expected as compared to crosslinked gels and microspheres. Therefore, core-shell microcapsules are suitable for stimuli-responsive controlled-release systems. Since the 1980s, environmental stimuli-responsive microcapsules have been investigated widely. These microcapsules control the release of their contents according to environmental stimuli. They are considered to be potentially useful as controlled-release systems, and especially so for drug delivery, because the target of a controlled drug delivery system is improved drug treatment (outcome) through rate- and time-programmed and site-specific drug delivery. [1] By encapsulation inside these microcapsules, chemicals or drugs can be released at a desired rate only when and/or where the release is needed. Modern environmental stimuli-responsive microcapsules have been reported to act in response to changes in temperature, [2-9] pH, [10-16] light, [17] external electric field, [18] redox conditions, [19] Ca2-ions, [20] and other stimuli, and these ™smartº capsules continue to gather increasing attention. In order to promote the applications of environmental stimuli-responsive microcapsules, development of microcapsules responsive to other signals remains essential. Herein, we report on the development of a molecular-recognition microcapsule for environmental stimuli- responsive controlled release: The release of the solute vitamin B12 (VB12) from the prepared microcapsules was significantly sensitive to the presence of Ba2+ ions in the environmental solution. In solution, the release of VB12 from the microcapsules was fast but slowed dramatically in the presence of BaCl2. The prepared microcapsules showed satisfactorily reversible and reproducible molecular-recognition stimuli-responsive release characteristics.

Experimental investigations on the Shirasu-porous-glass (SPG)-membrane emulsification processes for preparing monodisperse core-shell microcapsules with porous membranes were carried out systematically. The results showed that, to get monodisperse oil-in-water (O/W) emulsions by SPG membrane emulsification, it was more important to choose an anionic surfactant than to consider hydrophile-lipophile balance (HLB) matching. Increasing the viscosity of either the disperse phase or the continuous phase or decreasing the solubility of the disperse phase in the continuous phase could improve both the monodispersity and the stability of emulsions.With increasing monomer concentration inside the disperse phase, the monodispersity of emulsions became slightly worse and the mean diameter of emulsions gradually became smaller. Monodisperse monomer-containing emulsions were obtained when the SPG membrane pore size was larger than 1.0