Polyoxometalate Based Supramolecular Hydrogels:Synthesis And Performance Studies

Polyoxometalates(POMs)are a kind of anionic metal-oxo cluster composed of early transition metals(such as Mo,W,V,Nb,etc.).POMs have excellent thermal stability,redox characteristics and Br(?)nsted acidity.POMs could also be modified by covalent and non-covalent means,making POMs an ideal choice for building multifunctional materials.Hydrogel is a kind of hydrophilic 3D polymeric network with excellent deformation performance and biocompatibility.Hydrogel has been widely used in the field of biomedicine.The high electronegative,photochromic and fluorescence characteristics of POMs may endow hydrogel new properties by introducing POMs into hydrogel.However,the interaction between POMs and polymer is mainly electrostatic interaction which is monotonous,leading to poor mechanical properties and instable state of hydrogel.It needs further research and exploration.Therefore,we constructed a new type of POM-cyclodextrin hybrid compound through covalent modifications,and on this basis,we prapared two new kinds of POM-based hydrogel systems.Our results showed that the introduction of POMs effectively reduced the crosslinking density of hydrogels and improved the mechanical properties of hydrogel.The host-guest interaction based on cyclodextrin endowed the hydrogel self-healing performance.The main results of the research are listed as follows:1.POM-cyclodextrin was obtained by covalent modification,and its structure was analyzed by IR,NMR,ESI-MS,etc.Then,adamantane POM-based hydrogel was prepared by free radical polymerization and its mechanical properties,rheological properties were studied.The results showed that the optimal adamantane POM-based hydrogel had good mechanical properties.Moreover,the host-guest interaction and the introduction of POMs improved the mechanical properties and swelling ratio.The optimal adamantane POM-based hydrogel can be stretched to more than 16 times of the original length,with a stress of 147.9±6.7 kPa,a toughness of 1104.4±117.6 kJ·m-3,and a swelling ratio of up to 71.7±4.9.2.By free radical polymerization,ferrocene POM-based hydrogel was prepared,the mechanical properties of the hydrogel and redox property was studied.Ferrocene POM-based hydrogel had good tensile properties(1581.6±2.6%)and toughness(1489.8±41.2 kJ·m-3).In addition,the redox of the hydrogel also had been proved.In 0.1 M ammonium persulfate solution,the ferrocene POM-based hydrogel was oxidized and decomposed.