Preparation And Properties Of Multifunctional Self-healing Schiff Base Polymeric Hydrogel

Schiff base polymeric hydrogel with multiple responsiveness,low energy consumption and long life cycle,has broad application prospects in the fields of biochemistry,biomedicine,sensor recognition and electronic devices.At present,most of Schiff base compounds have hydrophobicity and poor stability,making the development of Schiff base self-healing smart hydrogels more difficult,which limits its application promotion.In view of this,this paper successfully prepared two novel salicylaldehyde-based Schiff base polymeric hydrogels.The advantages of the dynamic covalent bond structure,reversible response,metal coordination and sensor recognition of salicylaldehyde Schiff base were combined into the hydrogel system,which enriches the types of Schiff base self-healing hydrogels and expands its application fields.?1?In order to solve the problem of poor water solubility of salicylaldehyde-based Schiff base compounds,it was grafted on both ends of water-soluble polyethylene glycol imidazole salt to prepare salicylaldehyde-terminated polyethylene glycol imidazole salt?2MIS-PEG?,which was used as a gel factor to crosslink polyethyleneimine?PEI?to prepare a new self-healing intelligent hydrogel?PEI-PEG Gel?.PEI-PEG Gel had a self-healing rate of up to95%in 1 minute,and had excellent mechanical strength,of which storage modulus?G'?is as high as 2×10⁴Pa.PEI-PEG Gel had p H responsiveness and bio-amine recognition ability.The PEI-PEG Gel system was in a sol state when p H<5,and re-formed a gel when p H>5.In particular,as the p H of the hydrogel increases?5?13?,the color of the hydrogel changed from pale yellow to orange-red.Since the amine vapor?solution?produced by food spoilage is alkaline,it was applied for the freshness detection of pork.As a good metal ligand,salicylaldehyde-based Schiff base was able to complex with a variety of ions.As the color and fluorescence intensity of the hydrogel after complexation is different,it had ion recognition ability.The complexing of PEI-PEG Gel and Zn²⁺produced strong blue-green fluorescence,which was used for fluorescent writing and rewriting,realizing the transmission of confidential information.?2?This work firstly synthesized salicylaldehyde-based Schiff base monomer?APIMP?,and then one-pot polymerization with NIPAM and AAM to prepare a new type of intelligent hydrogel namely P?AAm-NIPAM-APIMP?hydrogel,which has excellent stretchability,temperature responsiveness,self-healing ability,and tunable fluorescence.P?AAm-NIPAM-APIMP?hydrogel was able to stretch to 2000%of its original length without fracture,and its fluorescence intensity was controlled by the concentration of Zn²⁺.When the concentration of Zn²⁺is 0.1M,the fluorescence intensity increased to 660%,indicating that the hydrogel is a kind of circulating fluorescent printing material.The phase transition temperature of the hydrogel system was adjusted by changing the content of NIPAM.When the AAm:NIPAM is 150:50,the DSC showed that the maximum exothermic temperature was46.4^°C,but the transparency of the hydrogel was changed at 40^°C obviously.P?AAm-NIPAM-APIMP?hydrogel is applied for temperature-sensitive materials potentially,such as temperature-controlled curtains.P?AAm-NIPAM-APIMP?hydrogel also had self-healing capability,and it can partially repaired its skeleton after being placed at 50^°C for30 minutes.With excellent stretchability and multifunction,P?AAm-NIPAM-APIMP?hydrogel has potential applications in temperature sensitive materials,information transmission,and soft sensors.