Design And Preparation Of PH-responsive Polyvinylamine Self-assembled Film And Hydrogel

With the development of polymer science,the preparation of stimulus-responsive materials,especially pH-responsive materials,has attracted more and more attention.The pH-responsive material exhibits the ability to change reversibly under the change of environmental pH conditions,and at the same time has the simplicity and biological relevance,making it have great application potential in many fields such as biomedicine,separation catalysis,smart sensing,and chemical industry.The primary amine group of PVAm is highly reactive,and the primary amine group can be easily coupled with small molecules and oligomers or covalently coupled to the surface of high molecular polymers,thereby changing the properties of polyvinylamine and preparing a Series of functional polyvinylamine materials.In this paper,polyvinylamine is the main body,two pH-responsive materials are prepared and their pH-responsive mechanisms are respectively explored in detail.First,the experiment uses water-soluble EDC/NHS as coupling agent to prepare modified polyvinylamine PVAm-DOPA with cis 1,2-diol structure and PVAm-PBA with phenylboronic acid structure through amidation reaction.The properties of the grafted product were characterized.The zeta potential of the PS microspheres of PVAm-DOPA and PVAm-PBA showed a decreasing trend with the increase of pH value,and the isoelectric points of PVAm-DOPA and PVAm-PBA solutions were pH=10.5 and pH=9.2,respectively.In addition,the maximum ultraviolet absorption wavelength of the PVAm-DOPA solution increases with the increase of pH,and the color of PVAm-DOPA solution also showed a pH response change from colorless to dark brown.A pair of modified polyvinylamine films containing glycol structure PVAm-DOPA and modified polyvinylamine PVAm-PBA containing phenylboronic acid structure are assembled on the surface of the silicon plate through layer-by-layer self-assembly.Based on the interaction mechanism of boric acid polyols,the controlled self-assembly of modified polyvinylamine ultra-thin films was realized by changing the pH of the reaction.Experiments show that the thickness of the PVAm-PBA and PVAm-DOPA monolayer films on the silicon plate decreases with the increase of the pH value within the range of pH=2.0～12.0.The thickness of a pair of self-assembled films formed by PVAm-DOPA and PVAm-PBA on the silicon plate gradually increases to be stable with the increase of pH.At the same time,the influence of the modified polyvinylamine self-assembled ultra-thin film on the hydrophilic and hydrophobic properties of the surface of the silicon plate can also be effectively controlled by the change of the pH value.Subsequently,the amino group of polyvinylamine（PVAm）and the epoxy group on the ethylene glycol dimethyl glyceryl ether（EDGE）undergo a ring-opening reaction to form chemical crosslinks to increase the rigidity of the hydrogel,and coordinate the coordination of zinc ions to make the system tough,Successfully prepared a series of ultra-tough single-network hydrogel Gel-PVAm-EDGE.Zn（II）with good network uniformity and excellent mechanical properties with pH response performance.The experiment explored the influence of the molar ratio between the amino group of PVAm and the epoxy group of EDGE and the influence of zinc ion concentration on the properties of hydrogels such as stretching,rheology and adhesion,and focused on the pH responsiveness of hydrogels.Experiments show that in the hydrogel system,the molar ratio of amino group to epoxy has a greater impact on the tensile strength of the gel.The tensile strength first increases and then decreases with the increase in the amount of epoxy added.The toughness increases with the concentration of zinc ions.Increase gradually.When the molar ratio of amino group to epoxy is 1:0.5 and the concentration of zinc ion is 3wt%,the gel has high toughness while maintaining good mechanical properties.The adhesion strength and interfacial toughness of Gel-PVAm-EDGE-Zn（II）hydrogel gradually increase with the increase of zinc ion concentration,but the adhesion strength and change law of gel are different on different materials.When the zinc ion concentration is less than 3%,the gel can be easily separated from the surface of the substrate,but when the zinc ion concentration is greater than 3%,the adhesion performance of the gel is greater than its own tensile performance,and it is closer to colloid.Separated from the surface of the substrate.Through the analysis of the rheological properties of Gel-PVAm-EDGE-Zn（II）with different zinc ion concentrations,it can be seen that the viscosity and shear stress of the gel show a shear thinning trend,and the modulus and loss factor of the gel Both increase with the increase of Zn²⁺concentration.Due to the combined effect of the protonation of the amino group of polyvinylamine at low pH and the deprotonation at high pH,as well as the metal-ligand coordination bond,Gel-PVAm-EDGE-Zn（II）hydrogel has a reversible pH Responsiveness.As the pH value increases,the swelling degree of the hydrogel gradually decreases,and the compression modulus gradually increases.