Photoresponsive Polyoxometalate-based Organic-inorganic Supramolecular Hydrogel:Design,synthesis And Performance Studies

Polyoxometalates(POMs),possessing abundant structural compositions and unique physical and chemical properties,are widely used in fields such as catalysis,materials,energy,and medicine.Introducing inorganic POMs into hydrogel network is promising to augment its mechanical and responsive properties,and extends the application scope of POM materials in smart devices.Currently,most reported POM-based hydrogels are constructed by simply encapsulating POMs into polymer network through electrostatic interactions,which inevitably causes a heterogeneous structure and therefore leads to poor mechanical properties.Covalently integrating POMs into hydrogel can well disperse POMs into polymer matrices and finely control the interactions between the organic and inorganic components,which enhances the uniformity of the hydrogel structure and long-term stability.In this thesis,?-cyclodextrin(CD)was grafted onto the both sides of Mn-Anderson type POM to obtain POM-CD hybrid,which could form an inclusion complex with Azo moiety in aqueous solution by host and guest recognition.Then hydrogel was constructed by the copolymerization of the host-guest inclusion complex with acrylamide(AAm)monomer,opening a new opportunity to combine the POMs and hydrogel smart materials.The specific research contents of the thesis are listed as follows:(1)The polyoxometelates-cyclodextrin(POM-CD)hybrid was synthesized and assembled with water-soluble Azo monomer Azo-PEG-Acryl,and then copolymerized with acrylamide(AAm)to obtain a POM-based hydrogel.By adjusting the content of POM-CD in the hydrogel,the effect of POM on the tensile and swelling properties of the hydrogel was systematically studied.The results show that the fracture strain and fracture stress of POM-based hydrogels have been greatly improved when comparing to cyclodextrin-azobenzene hydrogel and azobenzene hydrogel.The swelling ratio of hydrogel also increases as POM contents increases The results of successive cyclic stretching indicate that the introduction of POM enhances the fatigue resistance of the hydrogel.By drying in confined condition,the internal network of POM gel oriented along the extended direction,enhancing ultraviolet responsive ability and showing good ultraviolet-visible response cycling ability.(2)On the basis of the previous work,the host-guest inclusion complex of POM-CD and Azo-PEG-Azo served as the first network of hydrogel,then the cationic monomer methacryloyloxyethyl trioxide methyl ammonium chloride(DMC)was added,copolymerized with acrylamide to obtain a POM-based double network hydrogel.With the content of POM-CD/Azo-PEG-Azo in the first network increases.the fracture strain of the POM-based hydrogel increases,the corresponding fracture strength gradually decreases,the swelling rate of the hydrogel also gradually increases and the UV response ability was also gradually enhanced.Comparing with last chapter,the synergistic effect of electrostatic interaction and host-guest interaction enhanced the fracture stress of the double network hydrogel,which can reach 18 times,nearly doubled than that in last chapter.Also,the swelling rate can reach 480 times,which is 8 times more than that in last chapter.After being treated by drying in confined condition,the internal network ordered along the stretch direction,and its UV light response ability augmented.DN POM gel could recover under visible light irradiation,possessing a good ultraviolet-visible response cycle ability.