Synthesis And Properties Of Supramolecular Hydrogels Based On Terpyridine-metal Coordination

Supramolecular hydrogels based on terpyridine-metal coordination interactions have a wide range of applications in stimulus response materials,self-healing materials,and optical detection.In this thesis,two linear polymers with pendant moiety of terpyridine derivatives were constructed,one with maleic anhydride-acrylic acid copolymer as the main chain,and the other with poly(aspartic acid)as the main chain.Different supramolecular hydrogels were prepared via the coordination interaction between terpyridine and metal ions.The morphological,optical,and mechanical properties of these supramolecular hydrogels were studied.1.Supramolecular hydrogels based on terpyridine modified acrylic acid-maleic anhydride copolymers.A terpyridine derivative with terminal amino group(NH₂-Tpy)and a hydrophilic copolymer(PAAMA)of maleic anhydride(MA)and acrylic acid(AA)were synthesized.The terpyridine unit was successfully introduced onto the copolymer through the reaction of the terminal amino group in NH₂-Tpy with the anhydride group of the maleic anhydride unit,and a series of target polymers P1,P2and P3 with different terpyridine content were obtained by changing the molar ratio of PAAMA with NH₂-Tpy.Supramolecular hydrogels H1,H2 and H3 with different cross-linking degree were prepared by the coordination of Ni²⁺with terpyridine ligands.The UV spectra of polymers P1-P3 had an absorption peak at 290 nm caused by the?-?*transition of the terpyridine moiety,while there was a new peak at about335 nm leaded by the metal-to-ligands charge transfer(MLCT)when coordinated with Ni²⁺ions.The hydrogels showed gel-like characteristics when the terpyridine content of the hydrogels exceeded 10%,while the hydrogels showed liquid-like characteristics when the terpyridine content of the hydrogels was less than 7%.The storage modulus(G')and loss modulus(G'')of supramolecular hydrogels increased with increasing frequency,while G'decreased with increasing strain and G''showed a maximum value with increasing strain.When the water content of the supramolecular hydrogels was 90%,the gel-sol transition temperature of H1,H2 and H3 were 55°C,60°C and 75°C,respectively,and when the water content of H3 was 85%,90%,91%,the gel-sol transition temperatures were 70°C,75°C and 93°C,respectively,and the transition of the hydrogel was reversible.2.Supramolecular hydrogels based on terpyridine modified poly(aspartic)acid.Polysuccinimide was synthesized by polycondensation.The reaction of amino group and polysuccinimide was adopted to introduce terpyridine moiety onto molecular chain of polysuccinimide,and the intermediates with different terpyridine content were obtained by changing the molar ratio of PSI and NH₂-Tpy.The target polymers P1,P2,P3 were obtained after hydrolysis of the intermediates.Different supramolecular hydrogels H1-M,H2-M and H3-M(M=Ni,Zn,Cd,Eu,Tb)were prepared via the coordination interaction between terpyridine and different metal ions.The UV spectrum of P1 in aqueous solution presented an absorption peak at 290 nm caused by the?-?*transition of the terpyridine moiety,while there was a new peak at335 nm attributed to the metal-ligand charge transfer(MLCT)after coordination with Ni²⁺.The characterized peaks at 335 nm and 331 nm after coordinated with Zn²⁺and Cd²⁺were assigned to the intramolecular charge transfer(ILCT).New absorption peaks at 328 nm were ascribed to the electronic influence from the complexation of the lanthanide metal with terpyridine after Eu³⁺and Tb³⁺were added.Different metal ions possessed different effects on the fluorescence properties of hydrogels.The introduction of Ni²⁺led to fluorescence quenching of hydrogels,while Zn²⁺and Cd²⁺showed fluorescence enhancement by reducing the energy loss.The introduction of Eu³⁺and Tb³⁺resulted in bathochromic shift of the emission peaks of 200 and 100 nm,because of the energy transfer from terpyridine to Eu³⁺and Tb³⁺.H1-Zn had the characteristic of humidity responsiveness.When the water content of the H1-Zn film was 0%,30%,50%,80%,and 100%,the H1-Zn exhibited blue,light blue,blue-green,green and yellow-green emission under UV irradiation at 365 nm,respectively.