Polyoxometalate-Based Organic-Inorganic Composite Hydrogels:Design,Synthesis,and Performance Studies

Organic-inorganic composite hydrogels have been widely studied and used as a member of the hydrogels.With the introduce of inorganic materials,the mechanical properties and the water contents of hydrogels could be highly improved.Meanwhile,optic,electrical and magnetic properties could be introduced into the hydrogel system by using different kinds of inorganic materials.In the thesis,by grafting functional organic groups onto Anderson-type polyoxometalates(POMs)covalently or non-covalently,we obtained two kinds of new organic-inorganic hybrid materials,which were further used as cross-linkers for the construction of POM-based organic-inorganic composite hydrogels.(1)Acryloyl-Anderson cross-linkers were obtained by covalently grafting polymerizable acryloyl groups onto the both sides of Anderson cluster.The structure and composition of Acryloyl-Anderson were fully investigated by a various of techniques such as Fourier transform infrared spectroscopy(FT-IR),nuclear magnetic resonance spectroscopy(NMR),electrospray ionization mass spectra(ESI-MS)and single-crystal X-ray diffraction.Cation exchange process was also introduced in order to improve the water solubility of Acryloyl-Anderson.Then a new kind of thermo-sensitive POM-based composite hydrogel was prepared by free radical polymerization in DMSO/H20 mixture under elevated temperature.The structure and morphology of the resulting hydrogels were analyzed,and the thermo-sensitive,mechanical and rheological properties of the hydrogels were also investigated.Moreover,the cross-linking density and the average molecular weight between cross-linkers were calculated in order to elaborate the structure-function correlation.To put it simply,an ultrafast thermo-sensitive hydrogel was obtained in DMSO:H2O =1:1 solvent system,and the responsive time of our hydrogels only?1 min with the characteristic dimension of 20mm x 20mm.The existence of POMs could induce the monomer self-assembly into an algae-liked hyper-branched polymer structure and improve the water content and mechanical property of the hydrogels.With the quantitative test,we find that our hydrogels could stretch to more than 600%and retain more than 98%of water.(2)Photo-sensitive POM hybrid materials were obtained by covalently grafting azobenzene moieties on to the skeleton of Anderson clusters through pre-modification methods.The photo-responsiveness and the host-guest interaction between the Anderson-Azobenzene and ?-cyclodextrin(?-CD)were systematically investigated.As such,a new kind of organic-inorganic composite hydrogels was prepared by using the supramolecular inclusion complexes of Anderson-Azobenzene and ?-CD as non-covalent cross-linkers.