Natural Triterpenoid-based Supramolecular Polymer Assembly Regulated By Host-guest Interaction

With the development of supramolecular chemistry,many supramolecular polymer assemblies with diverse topological structures and unique physical and chemical properties have been constructed successfully.Among them,the host-guest recognition based on cyclodextrin has been widely used due to the strong binding force,good specificity and high versatility.However,it still remians great research potentials so far in the precise structure control,diversification of functions and practical applications of supramolecular polymer assemblies.Natural triterpenoids have the unique characteristics like abundant reaction sites,chiral centers,hydrophobic rigid skeleton and good biocompatibility.Abundant reaction sites facilitate its chemical modification and introduction into polymer backbone,while the hydrophobic rigid backbone provides a recognition site for host-guest complexation with cyclodextrin.Therefore,triterpenoids are considered as ideal building blocks for supramolecular polymer assemblies.At present,the research on host-guest inclusion complexation of triterpenoids and cyclodextrin mainly focuses on the improvement of solubility and biological activity of triterpenoids,while the study on triterpenoids-based supramolecular polymer system is still limited.In this thesis,glycyrrhetinic acid and glycyrrhizic acid,two of triterpenoids,are introduced into polymer backbones as the basic research units through different polymerization methods.Taking advantage of host-guest recognition between cyclodextrin and glycyrrhetinic acid/glycyrrhizic acid,we successfully constructed the novel cyclodextrin-based main-chain polyrotaxane and dynamic host-guest hydrogel,and studied their precise structure control and properties.Meanwhile,we also explored their potential applications in stimulus-responsive biomaterials.The main research results are as follows:1.A series of glycyrrhetinic acid-based main-chain cyclodextrin polyrotaxanes with alternating hydrophilic and hydrophobic fragments were prepared efficiently and simply by complex polymerization.The influence of hydrophilic fragments of different chain lengths on the structural rigidity and hydrophilic-hydrophobic balance of polyrotaxane was investigated in depth.The results showed that their self-assembly process and thermal phase transition behaviors can be effectively regulated by controlling the chain length of the hydrophilic fragments.This work provides an efficient and convenient strategy to construct bio-based thermosensitive polyrotaxane with precise and controllable properties,which is conducive to exploring the potential application of polyrotaxane in thermal stimulus responsive materials.2.Benifiting from the advantages of natural glycyrrhizic acid with multiple binding sites,a double dynamic hydrogel network was prepared via the polymerization reaction,which was mainly promoted by the synergistic effect of glycyrrhizic acid/cyclodextrin host-guest interaction and glycyrrhizic acid/phenylboronic acid dynamic covalent interaction.The formation of monomer and inclusion complex were characterized by 1D and 2D NMR.Moreover,the impact of the introduction of boronic ester bonds on the mechanical strength,self-healing,shape memory and other properties of the host-guest hydrogel network was expored thoroughly.This work provides a new idea for the construction of bio-based double dynamic hydrogels.