Fabrication And Stimuli-Responsive Behaviors Of Hydrogels Based On β-Cyclodextrin Dimer

In recent years,supramolecular gels based on host-guest interaction ofβ-cyclodextrin(β-CD)and its derivatives have aroused intense interest in control release,molecular switches,micro-actuators,color-changing and luminescent materials.β-CD grafted polymer,β-CD dimer orβ-CD oligomer can be used to construct supramolecular gels.β-CD dimer is widely used in the design of gelators due to the advantages of clear chemical structures and simple gelation mechanism.However,the reported synthesis routes forβ-CD dimer often include sulfonylation,ammonification and amidation.The post-treatment for each step is complicated and the yield is low.To solve these problems,β-CD dimer has been synthesized through one-step ring opening and substitution reaction betweenβ-CD and epichlorohydrin in this thesis.With the low-molecular-weight crosslinker ofβ-CD dimer,a series of stimuli responsive supramolecular gels based on the host-guest interactions between methoxy azobenzene(mAzo),ferrocene andβ-CD have been constructed.The control release behaviors of rhodamine B in the gels have also been investigated.Firstly,since most photoresponsive gels based onβ-CD and azobenzene are corresponded to ultraviolet light,which is harmful to organisms and the environment,the fabrication of visible light responsive gels is of great significance.On the other hand,in comparison with polymeric gelators,low-molecular-weight gelators are more sensitive to external stimuli and can be synthesized more accurately,which is more suitable to construct stimuli responsive gels.In this thesis,β-CD and mAzo dimer are used as low molecular weight gelators to construct gel in the mixed solution of dimethyl sulfoxide and water.The critical gel concentration is 6 wt%.The gel is visible light responsive.Upon the irradiation of 550 nmgreen light,the gel transforms into sol,while the sol forms gel again upon 450 nmblue light irradiation.When the concentration of binary gelators is greater than 7 wt%,the storage modulus of gel is higher than 10~4 Pa,indicative of a good self-supporting ability.The gel can be used as the carrier of small model molecule rhodamine B,and the control release of rhodamine B can be achieved by adjusting the intensity and irradiation time of green light.Secondly,in this thesis,mAzo group is grafted to polyacrylic acid(PAA)via esterification reaction.Then,the hydrogel can be constructed with the addition ofβ-CD dimer in water.The hydrogel has both wholly visible light and p H responses.The main driving forces for the formation of hydrogel include the host-guest interaction betweenβ-CD and mAzo groups,as well as the electrostatic repulsion interaction between the carboxylate anions of PAA.With shear strain increasing,loss modulus displays overshoot effect,while the hydrogel also has the characteristics of thixotropy.Under the high shear force,the gel changes into sol,while the sol quickly returns to the gel state under the lower shear force.The hydrogel can be used as a carrier for the control release of Rhodamine B upon the irradiation of green light or in the acidic media.Thirdly,ferrocene group is grafted to the PAA chain(PAA-Fc)through esterification reaction in this thesis.The binary gelators of PAA-Fc andβ-CD dimer can be used to construct hydrogel.The hydrogel is dually responsive to redox and p H.With the dynamic crosslinking network of hydrogel,the control release of rhodamine B can be achieved by loading oxidant or acid media.Finally,due to the complexity of design,synthesis and post-treatment,the fabrication of multi-responsive gels meets a great challenge.In this thesis,mAzo and ferrocene groups are both grafted to PAA chain through simple esterification reaction.With the help ofβ-CD dimer,the hydrogel with the properties of visible light,redox and p H responses,can be fabricated successfully.The control release of rhodamine B can be achieved with the irradiation of green light,the addition of oxidant or in acidic medium.Moreover,the combined stimuli of green light and acidic mediumcan greatly improve the rate and amount of rhodamine B release.