Construction And Properties Research Of Metallacycle-linked Supramolecular Star Polymers

Star polymer,as a kind of polymer with special morphological structure,have evolved to be one of the most attractive topics within polymer science due to their special mechanical,magnetic and optoelectronic properties in recent years.With the development of supramolecular chemistry,supramolecular star polymer constructed by different types of non-covalent interactions has become a crucial branch of star polymer.In addition,supramolecular star polymers have proven to not only be privileged candidates for the construction of dynamic supramolecular materials,but also show diverse potential applications in catalysis,drug and gene delivery etc.Among various non-covalent binding tools to design supramolecular star polymers,metal-coordination has turned out to be one of the most successful and versatile methods because of the organised manner in which the coordination assemblies can be arranged while simultaneously allowing precise control over the size,shape and functionality.In order to further extend and enrich the supramolecular star polymers system,and based on our previous research work on coordination-driven self-assembly,we presented the construction and properties research of different types of metallacycle-linked supramolecular star polymers through post-assembly polymerization in this dissertation.There are seven parts in this dissertation:Chapter one,we reviewed the recent research progress of star polymer,supramolecular star polymer and supramolecular materials based on discrete metal-coordination self-assemblies.At the end of this chapter,we put forward our projects in this dissertation.Chapter two,we first combined coordination-driven self-assembly and postassemblyreversibleaddition-fragmentationchain-transfer（RAFT）polymerization to produce a new family of star supramolecular polymers containing well-defined metallacycles as cores,which featured typical lower critical solution temperature（LCST）behavior in water because of the existence of poly（N-isopropylacrylamide）（PNIPAM）moieties.Moreover,the obtained star polymers could further form supramolecular hydrogels cross-linked by discrete hexagonal metallacycles at room temperature.Interestingly,the resultant polymeric hydrogels exhibited stimuli-responsive behavior toward temperature and bromide anion as well as self-healing property.We demonstrated that the dynamic nature of Pt-N bonds in the hexagonal metallacycles played an important role in determining the stimuli-responsive and self-healing property of the final soft matters.Chapter three,we present the successful preparation of CO₂ stimuli-responsive,injectable block copolymer hydrogels cross-linked by discrete organoplatinum（II）metallacycles.Through the combination of coordination-driven self-assembly and stepwise post-assembly polymerization,star block copolymers containing well-defined hexagonal metallacycles as cores were successfully prepared,which featured CO₂ stimuli-responsive properties including CO₂-triggered morphology transition and CO₂-induced thermoresponsive behavior.Interestingly,the resultant SBCPs were capable of forming supramolecular hydrogels with organoplatinum（II）metallacycles as junctions near physiological temperature,which allowed the realization of a reversible gel-to-sol transformation through the removal and addition of CO₂.More importantly,the resultant supramolecular hydrogels presented good cytocompatibility in vitro.Chapter four,we report the preparation of a new family of discrete,TPE-based supramolecular star polymer decorated with three PNIPAM arms through combination of an exo-functionalization strategy and post-assembly polymerization.The obtained supramolecular star polymer could spontaneously self-assemble into fluorescent nanoparticles in water.The AIE property of supramolecular star polymer was then evaluated in a mixed THF/water solvent system.Moreover,by taking advantages of both AIE property and good biocompatibility of the obtained TPE-based supramolecular star polymer,its potential application in cell imaging was investigated.Chapter five,in this study,through the combination of coordination-driven self-assembly and postassembly ring-opening polymerization,a six-armed star polymer linked by well-defined hexagonal metallacycle as core was successfully prepared.At the same time,the trans-platinum acetylide moieties as transformation sites were anchored onto the discrete metallacycle scaffold.Subsequently,the simple phosphine ligand-exchange reaction induced the conversions of platinum acetylide building blocks with the varied binding angles,which thus resulted in the successive hexagon-rhomboid-hexagon transformations of metallacyclic scaffold,therefore allowing for the corresponding supramolecular transformation of metallacycle-linked star polymers.More importantly,accompanied by such transformation process,property modulation of the resultant polymers has been successfully realized.In a word,by taking advantage of dynamic nature of metal-ligand coordination bonds and simple phosphine ligand-exchange reactions,facile architecture transformation of a star polymer to a linear polymer and back to a star polymer was successfully realized.