| In the past few decades, polymer/inorganic nanocomposites have been widely concerned due to its combinative properties of both polymers and inorganic materials. However, poor compatibility between inorganic and organic materials has negative influence on the comprehensive properties of composite materials, so the surface modification of inorganic nanoparticles becomes very important. Among the surface modification methods, polymer brushes grafting on particle surface is one of most commonly used method. In this method, the morphology and properties of these brushes play the key factor influencing the properties of the nanocomposites. So it’s critical to understand the properties of polymer brushes and their manipulation.First, in this study, surface-initiated atom transfer radical polymerization (ATRP) method was used to prepare poly(methyl methacrylate)(PMMA) brushes on silica wafer and SiO2nanoparticles.And various characterization tests were carried out to study their morphology and properties such as their molecular weight and its distribution, and glass transition temperature,especially the glass transition temperatures.The effects of curvature on above properties of the grafted polymer bushes has been studied.Finally, nanocomposites were prepared by mixing bulk PMMA with SiO2particles grafted with polymer brushes, then make a preliminary study on the relationship between the properties of the grafted polymer bushes and the nanocomposites.The surface morphology, thickness and Tg of the polymer layer for Si-PMMA brush were characterized by contact angle measurement, atomic force microscopy (AFM), and ellipsometry. The results based on contact angle measurements show that the hydrophilicity of Si-PMMA brush decreased. AFM showed that the surface roughness is lower, meaning that a denser graft polymer brushes were formed. The results of ellipsometry showed that the thickness of grafting polymer brush, in a certain time range, increased with increasing polymerization time. The Tg of Si-PMMA was found much higher than that of bulk PMMA, and with the increase of the thickness of the polymer brush, Tg decreased.Transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), thermogravimetry (TGA), differential scanning calorimetry surface (DSC) were applied to study the propeties of SiO2-PMMA brush. The results of TEM, FT-IR, TGA showed that PMMA was successfully chemically grafted on the silica partical surfaces.TEM showed that, within a certain time range, the thickness of graft polymer is proportional to the polymerization time, and inversely proportional to the curvature of SiO2. The Tg of grafted polymer was characterized by DSC analysis, which showed that the Tg of SiO2-PMMA brush is nearly20℃higher than bulk PMMA. The curvature of SiO2and the thickness of graft polymer had little effect on Tg of the brushes.The molecular weight and Polydispersity index(PDI) for free polymer in solution and grafted polymer were characterized by gel permeation chromatography (GPC), it was found that within a certain period of time, the molecular weight of polymer had been well controlled and the PDI of the polymer was low. In addition, when the polymerization time increased, it was showed a slight decrease in the molecular weight and the PDI become higher.The composites were characterized by TEM, TGA, DSC and dynamic mechanical thermal analysis (DMA).The results showed that SiO2-PMMA brush not only could effectively improve nanoparticle dispersion in the composite but also could improve the thermal stability of composite, but the different amount of nanoparticles addition had little effect on the Tg. |
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