Amphiphilic Diblock Copolymers Bearing A Cysteine Junction Group:Synthesis And Encapsulation Of Inorganic Nanoparticles

Amphiphilic block copolymers with highly asymmetric structures can self-assemble in selective solvents a wide range of morphologies,such as spherical micelles,rods,bicontinuous cubics,and vesicles.Recently,plenties of studies have focused on the co-assembly of nanoparticles and block copolymers,which can construct various hybrid aggregates.These hybrid nanostructures not only combine the inherent properties of block copolymers and nanoparticles,but also show more complex structures and properties,which provide the aggregates with an optimistic outlook in the field of biomedicine,optoelectronics,catalysis,etc.It is of great importance to accurately control the location and distribution of nanoparticles in different morphologies of BCP aggregates,which may critically affect the resulting properties and potential applications of the hybrid nanomaterials.Among the accessible morphologies,amphiphilic block copolymer vesicles are of great interest to scientists.So far,a lot of attempts focused on embedding nanoparticles into the vesicular structures have been reported,while the encapsulation of nanoparticles into the hydrophilic/hydrophobic interface is still a challenging work.The traditional strategy is to use amphiphilic triblock copolymers as self-assembly precursors,which possess two outer blocks for building the walls and coronas of vesicles,and one middle block for binding nanoparticles to locate at the internal or external interface of vesicles.In this thesis,we design and synthesize an amphiphilic diblock copolymer,PEG-SH-b-PS bearing a cysteine junction.Through the free pendant thiol group at the centre point between the hydrophilic poly(ethylene glycol)block and the hydrophobic polystyrene block,two kinds of nanoparticles(gold NPs and copper sulfide NPs)are modified with the designed copolymers.Then,the amphiphilicity-driven self-assembly in aqueous solution of the pure linear diblock copolymers PEG-SH-b-PS and the corresponding composites of copolymers and nanoparticles are examined.In order to further explore the potential of PEG-SH-b-PS polymers encapsulating inorganic NPs for future applications,the near-infrared-responsive experiments of the functional vesicles with embedded CuS NPs are conducted under illumination of a 980 nm laser to study the near infrared photoresponsive properties of the newly formed hybrid nanomaterials.The main research contents can be divided into the following three parts:1.A series of amphiphilic diblock copolymers PEG114-SH-b-PSn with different polystyrene(PS)length are designed and synthesized by using the atom transfer radical polymerization(ATRP)procedure.Meanwhile,there is a pendant thiol group at the centre group between the hydrophilic poly(ethylene glycol)block and the hydrophobic polystyrene block for interacting with the nanoparticles.Consequently,the average molecular weight and the weight ratio of the hydrophilic block and the hydrophobic block are determined by 1H NMR and GPC analysis.2.The small molecules on the surface of nanoparticles(GNPs and CuS NPs)are then replaced by the selected amphiphilic diblock copolymers through interfacial ligand exchange.The formations of GNPs(or CuS NPs)coated with the corresponding copolymers are confirmed by FT-IR and UV-Vis spectroscopy as well as thermogravimetric analysis(TGA)measurements.Assuming that the synthesized nanoparticles are spherical,the grafting densities of the generated nanocomposites are further estimated through the results of TGA and 1H NMR analysis.3.From TEM observations of the self-assembled samples containing the conjugated nanoparticles,it can be concluded that most of the nanoparticles are dispersed at the interfaces of the formed vesicles.In addition,the PEG-SH-b-PS vesicles containing copper monosulfide nanoparticles are conducted near-infrared photoresponsive experiments.It is found that the hollow spherical structures of PEG-SH-b-PS/CuSNPs vesicles can disassemble due to the rise of temperature under NIR illumination of 980 nm.Thus,the hybrid nanomaterials have the potential in biomedical applications,such as molecular imaging and photothermal therapy.