Preparation and Properties of Self-healing Hydrogels with Schiff Base-Metal Complexes

Author:Tang Liu Yan

Supervisor:zuo jin qing


Degree Year:2019





Self-healing metallo-hydrogels,having the advantages of long life-time,low energy consumption and multi-stimuli responsive properies,show excellent adaptablitity to satisfy the requirement of different devices,and have great potential applications in the areas of electricity,optics,magnetism,catalysis and sensing.However,the current reports of self-healing metallo-hydrogels are still limited in few kinds of ligands and did not have good mechanical properties due to the high hydrophobicity of most ligands and the poor stability of metal-ligand coordination in aqueous environment.To overcome these drawbacks,in this thesis,we reported different gelation strategies.Using these strategies,we have successfully prepared self-healing metallo-hydrogels with hydrophobic Schiff-base ligands.These hydrogels,as containing Schiff-base ligands,have the advantage of dynamic structure,reversible response and optical sensing.(1)A novel strategy for the preparation of metallo-hydrogels based on amphiphilic polymers containing hydrophobic ligands has been designed and an amphiphilic polymer,P(DMA-co-BHMP),has been synthesized.Selected divalent metal ions(Cu2+,Co2+,Ca2+,Mn2+,Pb2+and Fe2+)were able to gelate P(DMA-co-BHMP).Hydrogel crosslinked by P(DMA-co-BHMP)and Cu2+(Cu-gel)formed repidly in 30 s.Cu-gel had shear-thinning behavior,indicating their injectability.The rapid self-healing process of Cu-gel was observed optically in 1 min.Besides,The designed ligand with a pH sensitive Schiff base structure(BHMP)contributed to the pH-responsive properties of the prepared hydrogels.The addition of competing ligands(EDTA and EDA)caused the degradation of Cu-gel.The hydrogel crosslinked by P(DMA-co-BHMP)and Fe2+(Fe-gel)showed reversible redox responsiveness.(2)A cooperation strategy combining metal coordination and hydrophobic interaction for hydrogel preparation was studied:utilizing metal-ligand coordination to synthesize amphiphilic metallopolymers with hydrophobic metal coordination units and promoting gelation by the enhancement of hydrophobic interaction after polymerization.A salicylaldehyde benzoyl hydrazone-terminal poly(ethylene glycol)(2SBH-PEG)was synthesized and formed hydrogel(Ni-PEGel)after coordinating with Ni2+.Ni-PEGel exhibited rapid self-healing ability,enabled to 100%heal itself in 1.5 min.Also,Ni-PEGel showed reversible multi-stimuli responsive properties and sensing ability towards biogenic amines.The change of pH would lead to its“gel-sol”transition;the existence of EDTA and pyridine would cause its degradation;and the change of temperature would change its transparency.In addition,Ni-PEGel showed colorimetric changes when exposed to biogenic amine vapor,indicating its ability to be an optical sensor of biogenic amine.As a sensor,Ni-PEGel could also use to detect the freshness of the real meat sample,exhibiting high potential in monitoring food spoilage.(3)Aiming at the problem that the reported smart optical metallo-hydrogels were limited and with poor mechanical properties,a novel smart optical metallo-hydrogel(Al-hydrogel)with excellent extension,self-healing ability,shape-memory property and controllable fluorescence intensity was prepared.As-prepared hydrogel was first prepared by one-pot micellar copolymerization of acrylic acid(AAc),acrylamide(AAm),and hydrophobic ligand,(E)-N-(4-(2-(2-Hydroxybenzylidene)-hydrazinecarbonyl)phenyl)methacrylamide(HHPMA).Transparent Al-hydrogel was obtained after the Al3+-HHPMA and Al3+-AAc coordination.Al-hydrogel showed excellent stretchability and could be extended up to 5000%its original length without fracture.Its fluorescence intensity was tunable by adding OH-or Zn2+.When the concentration of OH-or Zn2+in Al-hydrogel reached 0.1000 M,its fluorescence increased500%to its the original fluorescence intensity.The fluorescent change of Al-hydrogel was reversible,so its application in cleanable fluorescence printing material was also investigated.Al-hydrogel was able to partly heal itself after incubated at 60°C for 15 minutes.By the coordination and damage between polyacrylic acid and Fe3+,the shape of Al-hydrogel was memorized or recovered,proving the shape-memory ability of Al-hydrogel.This highly stretchable and multi-functional Al-hydrogel has potential applications in information transmission,flexible devices and flexible sensors.