Synthesis of temperature sensitive PNIPAAm cryogels in organic solvent with improved properties

We have demonstrated a new strategy for preparing poly(N-isopropylacrylamide) (PNIPAAm) gel with significantly improved properties by polymerization–crosslinking in organic solvent (dimethyl sulfoxide, DMSO) and at low temperatures (0.5 and −20 °C, below the melting point of DMSO). The effects of different synthesis conditions, including monomer concentration and polymerization temperature, on the formation of the PNIPAAm gels in DMSO were investigated. The properties of the resulting cryo-PNIPAAm gels were characterized by scanning electron microscopy (SEM) to reveal their interior morphology as well as the temperature dependence of the equilibrium swelling ratio, shrinking and swelling kinetics in water and their oscillatory shrinking–swelling kinetics over 3 min temperature cycles between 26 and 37 °C. The SEM micrographs reveal that the interior microstructures of the cryo-PNIPAAm gels are very different from conventional PNIPAAm gels, and are much more regular and oriented than the conventional gels. This unique interior morphology of the cryo-PNIPAAm gels is believed to be responsible for the improved swelling and deswelling kinetics and excellent dynamic response without loss of water retention upon temperature cycling.