Synthesis And Application Of Polymers Containing Disulfide Dynamic Covalent Bond

Dynamic covalent bond refers to the covalent chemical bond with the ability to form and break reversibly under certain environmental conditions?such as temperature,light,pH value,REDOX,electric field,etc.?.Common dynamic covalent bonds include dynamic oxime bond,dynamic disulfide bond,dynamic acyl hydrazone bond,dynamic boric acid ester bond and dynamic imine bond,etc.The introduction of such dynamic interactions into polymer materials transforms the intrinsic kinetic properties of dynamic covalent bonds at the molecular level into the macroscopic properties of the polymer,thus endowing the polymer materials with various dynamic properties.Based on this,two kinds of copolymers containing dynamic disulfide bond were synthesized in this paper,and their applications for the fabrication hollow SiO₂microspheres with rich thiols on their surfaces and the preparation of multi-responsive hydrogels were demonstrated,respectively.The main contents of this thesis were summarized as follows:?1?Templated preparation of hollow SiO₂ microspheres with rich thiols on their surfaces and its application as adsorbents for the toxic metal ions.In this study,templated fabrication of hollow SiO₂ microspheres with thiol-rich surfaces and their application as adsorbents for toxic metal ions were demonstrated.?Cyclohexane+TEOS?-in-water Pickering emulsion was first prepared employing detachable polyurethane-g-poly?N,N-dimethyl acrylamide??PU-g-PDMA?copolymer micelles as emulsifiers.The subsequent Pickering emulsion interface directing sol-gel reaction of TEOS led to the formation of SiO₂ microspheres.Hydrophobic PU cores of PU-g-PDMA copolymer emulsifier micelles were in-situ entrapped in formed SiO₂ layers,while hydrophilic PDMA shells were exposed on the surfaces of the formed SiO₂ shells,forming polymer brush-like structure.The subsequtent removal of PDMA shells through the cleavage of the reversible disulfide linkages between PU core and PDMA shells left a large number of thiol groups on the surfaces of hollow SiO₂ microspheres.The resulting hollow SiO₂ microspheres with thiol-rich surfaces,described as SiO₂@SH in the text,demonstrated a promising recyclable adsorption for toxic metal ions.?88%of adsorption capacity for Pb²⁺has been maintained after four adsorption/desorption cycles.The structure of hollow SiO₂@SH microspheres was carefully characterized with scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared spectroscopy?FT-IR?and Raman spectroscopy,respectively.?2?Preparation and application of injectable multiresponsive polymer hydrogels.Injectable multi-responsive hydrogels with gel networks dominated both by reversible covalent bonds and noncovalent interactions were demonstrated in this study.The gels were gained by the mixing of poly?N,N-dimethylacrylamide?-stat-poly?2-acrylamidophenylboronic acid??PDMA-stat-P?2APBA??copolymers with poly?N,N-dimethylacrylamide?-b-poly?N-isopropylacrylamide???OH?₂-PDMA-b-PNIPAM?in PBS?p H7.4?at the temperature above the low critical solubility temperature?LCST?of?OH?₂-PDMA-b-PNIPAM copolymers,i.e 37 ?,in which?OH?₂-PDMA-b-PNIPAM exhibited a diol group in one end of polymer chain and a disulfide linkage in the chain.At 37 ?,?OH?₂-PDMA-b-PNIPAM firstly self-assembled core-shell structure polymeric micelles with numerous diol groups on their hydrophilic shells,followed by the formation of the reversible boronic ester crosslinking networks as the result of the complexation interaction of PBA groups with diol groups.?OH?₂-PDMA-b-PNIPAM polymeric micelles acted as the cross-linkers in gel matrixes.Due to the integration of a library of stimulus factors including dynamic borate and disulfide covalent bonds together with thermal-driven coil-globule transition within the same system,the as-constructed hydrogels indicated injectibility and multi-responsive sol-gel transitions in response to p H,temperature,and glucose as well as redox.This work demonstrated a new strategy to construct multi-responsive hydrogels at physiological conditions?temperature and p H?.Such merits endowed the constructed hydrogels promising applications in biological systems.