Polymeric/Inorganic Hybrid Nanocomposite With Polymer Brushes

Polymeric/inorganic hybrid nanocomposite, which combined the advantages of inorganic materials, polymer materials and nancomposite materials, is not only a kind of novel materials with high strength, high hardness, high stability, high flexibility and processability, but also materials with special optical, electricity, magnetic, thermal and other properties. So the study of polymeric/inorganic hybrid material is the hot focus in materials science field in this decade. In the preparation of polymeric/inorganic hybrid material, the two most important issues are dispersion and compatibility of the nanoparticles. Polymer brush is a type of polymer with special structure. Polymer brushes produced on the material surfaces provide an effective route to modify properties of the surfaces. In recent years, it has become an important tool in surface modification. In this thesis, we will report the use of polymer brushes to solve the two basic problems mentioned above and prepare some new polymeric/inorganic hybrid nanocomposite with polymer brushes.Clay layers, Au nanoparticles and silica microspheres are the most widely used materials in the field of composite materials. In this research, we modified the inorganic materials with functional polymer brushes to prepare the following five functional polymeric/inorganic hybrid nanocomposites. The preparation methods, structural characteristics and potential applications of the materials were also studied. The main researches were summarized as followings.1. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) mixed polymer brushes on the surface of clay layers were prepared by using in situ free radical polymerization. Free radical initiator molecules with two quaternary ammonium groups at both ends were intercalated into the interlayer spacing of clay layers. The kinetics of the grafting of the monomers was studied, so the amount of polymer brushes grafted on the surface of clay layers can be controlled by controlling the polymerization time. Thermogravimetric analysis (TG), X-ray diffraction (XRD), and high-resolution transmission electron microscope (TEM) results indicated successful preparation of the mixed polymer brushes on the surface of clay layers. The mixed polymer brushes on the surface of clay layers were used as compatibilizers in blends of PS and PMMA. In the blends, the intercalated clay particles tend to locate at the interface of two phases reducing the interfacial tension. In the meanwhile, PMMA homopolymer chains tend to intercalate into clay layers. The driving force for the intercalation is the compatibility between homo-PMMA chains and PMMA brushes on the surface of clay layers.2. Poly[2-(dimethylamino) ethyl methacrylate] (PDMAEMA) brushes on the surfaces of clay layers were prepared by in situ free-radical polymerization. PMMA colloid particles stabilized and initiated by clay layers with PDMAEMA polymer brushes were prepared by Pickering emulsion polymerization. TEM was used to characterize the structure and morphology of the colloid particles. The XRD results indicated that the intercalated structures of the clay layers were almost destroyed in Pickering emulsion polymerization, and clay layers with exfoliated structures were created. The surface of the colloid particles was analyzed by using X-ray photoelectron spectroscopy (XPS) and Zeta potential. The results provided direct evidence that the clay layers with PDMAEMA chains covered the PMMA colloid particles.3. Amphiphilic gold nanoparticles with hydrophobic PS and hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) mixed polymer brushes were prepared. Different morphologies of the nanoparticles could be observed in chloroform (a common solvent for both of the polymers) and water (a precipitant for PS and a good solvent for PPEGMA). The nanoparticles could be used as surfactants in Pickering suspension polymerization. Upon addition of nanoparticles to a mixture of oil and water, the nanoparticles located at the interface and the size of the oil droplets got smaller. After polymerization of styrene oil droplets, PS colloid particles with gold nanoparticles on the surface could be obtained.4. Amphiphilic Janus silica particles with hydrophobic PS and hydrophilic poly(sodium methacrylate) (PSMA) brushes on two hemispheres were prepared at the liquid-liquid interface by surface-initiated polymerization. After introduction of free-radical initiator modified silica particles into a mixture of styrene and water, the silica particles were adsorbed at the liquid-liquid interface. One hemisphere of a silica particle is immersed in aqueous phase, and the other one is in styrene phase. After initiation at an elevated temperature, PSMA chains grow on one hemisphere and PS chains grow on the other one. After removal of free PS and PSMA chains, the Janus silica particles were obtained. TG and infrared spectra (FT-IR) results confirmed the grafting of polymer brushes on the surfaces. TEM was used to characterize the asymmetric surface structure of the Janus particles.5. Janus silica particles decorated with biotin molecules and poly(ethylene oxide) PEO chains on two hemispheres were prepared by two-step click reactions. PS particles coated with azide modified silica particles were used as templates. The alkynated biotin molecules were grafted onto the exposed side of the silica particle by click reaction. After removal of PS, the embedded part of the silica particle was released, and alkynated PEO chains were grafted to the particle by click reaction. FT-IR, TG, and TEM were employed to characterize the Janus particles. The Janus particles show strong interaction with avidin.