Study On The Poly(Ethylene Glycol)and Cyclodextrin Based Supramolecular High-Strength Smart Hydrogel With Regular Network Structure

Most of traditional polymer hydrogels are deficient in mechanical strength,which limits their applications.In the last fifteen years,the emergence of a series of high-strength polymer hydrogels with peculiar or regular network structures improved this situation largely.Among these high-strength hydrogels,tetrahedron-like poly(ethylene glycol)hydrogel(Tetra-PEG hydrogel)and topological gel are classic.On the other hand,it is inevitable to endow it with function to apply a polymer hydrogel in high-tech field.However,there are few reports about functionalization of the above high-strength hydrogels,especially for tetra-PEG hydrogel and topological gel.Accordingly the work reported in this thesis is devoted to development of efficient methods to functionalize the Tetra-PEG hydrogel and topological gel.On one hand,hydroxypropyl cyclodextrins(Hy-CDs)were introduced into the network of Tetra-PEG hydrogel through supramolecular host-guest interaction to afford two types of high-strength supramolecular polymer hydrogels with homogeneous network structures——αSSS andβSSS hydrogels.The Hy-CDs in the networks of the hydrogels acted as potential functionalization sites for they carried many reactive hydroxyl groups on their molecules.Functional units of anthracenes were introduced into the network of theαSSS hydrogel through chemical bonding to the potential functionalization sites to afford a high-strength supramolecular smart polymer hydrogel with homogeneous network structure——anthracene functionalized high-strength supramolecular polymer hydrogel with homogeneous network structure(An-αSSS hydrogel).On the other hand,α-cyclodextrin(α-CD)in PEG/α-CD based polyrotaxane(PR)was used as functionalization site to introduce anthracene unit into the PR.The synthesized 2-anthracenecarbamyl-polyrotaxane(An-PR)could be cross-linked to form a UV/thermal responsive topological gel through dimerization of anthracene units on different An-PRs.The relationships between structure and property/functionality of the above two types of SSS hydrogels,the An-αSSS hydrogel and the topological gel were investigated in detail.The contents of each part are listed as follows:(1).Tetra-Azido-Terminated PEG(TAPEG)and Tetra-Propargyl-Terminated(TPPEG)weresynthesizedthroughterminalmodificationof Tetrahydroxyl-Terminated PEG.Clickable Tetra-PEG hydrogel was prepared through click-cross-end-coupling of the two symmetrical terminal modified tetra-PEG macronomoners in water.(2-Hydroxypropyl)-α-CD(Hy-α-CD)was introduced into the network of the Clickable Tetra-PEG hydrogel through supramolecular host-guest interaction to afford theαSSS hydrogel.Two stages were involved in theαSSS hydrogel preparation.In the stage of complexation,poly-pseudo-rotaxane consisting of tetra-PEG macromonomer and Hy-α-CD formed in pre-gel solution.The dynamic complexation process and the structure of the poly-pseudo-rotaxane were investigated by NMR experiment.In the stage of gelation,some cross-linking reactions were completed through click chemistry.The chemical composition,the network structure,the swelling and the mechanical properties of the resultant hydrogel were characterized by ATR-FTIR,XPS,SEM,swelling and compression test in detail.The number of Hy-α-CD introduced into the hydrogel is related closely to the structure of the poly-pseudo-rotaxane and can be controlled easily by tuning the feed ratio.In addition,theαSSS hydrogel showed good mechanical property and high equilibrium water content(EWC).(2).(2-Hydroxypropyl)-β-CD(Hy-β-CD)was introduced into the network of the Clickable Tetra-PEG hydrogel through supramolecular host-guest interaction to afford theβSSS hydrogel.Chemical and physical properties of theβSSS hydrogel were investigated through many characterization methods.The networks of theβSSS and theαSSS hydrogel can be considered as the Hy-CD/tetra-PEG based three-dimensional modified polyrotaxane(3D modified PR).The comparison between the Hy-β-CD/tetra-PEG based 3D modified PR system and the Hy-α-CD/tetra-PEG based one point by point provided us plenty of information from macroscopic material view to microscopic molecular view.From the macroscopic view,it was found that theβSSS hydrogel is superior to theαSSS one in threading ratio(SR)of Hy-CD,compressive strength and EWC with median values of the feed ratio.The two hydrogels are also different in properties,including the internal morphology,thermal behaviors and the critical gelation concentration(CGC).More importantly,from the microscopic view,through the comparisons of the above properties of the two hydrogels,in combination with the investigation of the complexation between Hy-CD and tetra-PEG by NMR experiments,what were revealed are that the threading mechanism of Hy-CD/tetra-PEG based poly-pseudo-rotaxane,and the conformation of Hy-CD and the segment dynamics of PEO chain within Hy-CD’s cavity in Hy-CD/tetra-PEG based 3D modified PRs.These deductions can not be clarified through the investigation of any single system.(3).Anthracene unit was chemically linked to the potential functionalization site of Hy-α-CD to afford the 2-anthracenecarbamyl-(2-hydroxypropyl)-α-cyclodextrin(An-Hy-α-CD)through the reaction between 2-anthraceneisocyanate and Hy-α-CD.The An-Hy-α-CD was introduced into the network of the Clickable Tetra-PEG hydrogel through supramolecular host-guest interaction to afford the An-αSSS hydrogel.Chemical and physical properties of the An-αSSS hydrogel were investigated through many characterization methods.The compression strength of the An-αSSS hydrogel is higher than the correspondingαSSS hydrogel and the compression strength of the An-αSSS hydrogel increases with the increase of the amount of introduced An-Hy-α-CD.The An-αSSS hydrogel possesses fluorescence property and the property is chemical and UV responsive.When the hydrogel was immersed in the aqueous solution ofβ-CD,the fluorescence intensity of it increases;when the hydrogel was immersed in the aqueous solution ofγ-CD,the fluorescence intensity of it decreases;when the hydrogel was immersed in the aqueous solution ofα-CD,the fluorescence intensity of it was constant.There are host-guest interactions between anthracene unit in the hydrogel network andβ-andγ-CDs.Thus the chemical environment surrounding the anthracene unit and the relative conformations of anthracene units on two adjacent An-Hy-α-CDs threaded on the PEO chain changed after the cyclodextrins were added.These led to the fluorescence intensity changes of the hydrogel.The responsiveness of the fluorescence property of the An-αSSS hydrogel on the stimuli of different cyclodextrin is exclusive feature of this hydrogel with slide-ring structure.When the An-αSSS hydrogel complexed withβ-CD was immersed in the aqueous solutions of salts of cholic acid,ibuprofen and1-adamantanamine,the fluorescence intensity of the hydrogel decreased quickly.This may be the result of competition complexation ofβ-CD by the compounds above from the anthracene unit.With this property,the hydrogel may be used as soft fluorescence sensor in biomedical field.In addition,the fluorescence,the swelling and the mechanical properties of the An-αSSS hydrogel are UV stimulus responsiveness.The fluorescence intensity of the hydrogel decreased gradually with the increase of the irradiation time under UV light with wavelengths>360 nm.And the swelling and the mechanical properties of the hydrogel changed largely after it was irradiated by the UV light.The successful introduction of the function of anthracene unit into theαSSS hydrogel as well as the multi-stimuli responsiveness of the resulted An-αSSS hydrogel demonstrate the validity of the functionalization method of the Tetra-PEG hydrogel through hydroxypropyl cyclodextrin based supramolecular way.(4).2-Anthracenecarbamyl-polyrotaxane(2-An-PR),was synthesized through an efficient reaction between 2-anthraceneisocyanate and PEG/α-CD based PR.The DMSO solution of the resultant 2-An-PR can form a topological gel under UV irradiation(λ>360 nm)at room temperature.And the gel undergoes gel-sol transition to return to the liquid state after thermal treatment at 70 ~0C.The mechanism of this sol-gel-sol transition was demonstrated by ~1H-NMR and UV-Vis spectroscopy.Anthracene units on 2-An-PRs dimerize under the UV-irradiation and cross-link2-An-PRs to cause the gelation of the solution.Under the thermal treatment,the dimer dissociates and causes the topological gel break up.This novel smart topological gel has a very important application value in many high-tech fields,such as soft actuators,sensors and polymer cells.