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Surface-initiated Atom Transfer Radical Polymerization Based on Nano Titanium Dioxide

Author: CaoHengMing
Tutor: WangWenPing
School: Hefei University of Technology
Course: Applied Chemistry
Keywords: controlled/living radical polymerization (CRP) atom transfer radical polymerization(ATRP) nano titanium dioxide nanocomposites polystyrene thermal properties poly(glycidyl methacrylate) click reaction molecular design
CLC: TB383.1
Type: Master's thesis
Year: 2010
Downloads: 164
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Abstract

For the preparation of organic/inorganic hybrid materials consisting of an organic polymer and inorganic nanoparticles, different chemical methods have been proposed to attach a polymer to a surface. The first method is known as grafting to: polymers with suitable end-functional groups react with appropriate surface sites on the inorganic nanoparticles. The second method is known as grafting from: chains grow in situ from initiator molecules that have been pregrafted onto the surface of the nanoparticles. This technique, combined with controlled/living radical polymerization (CRP), has been used to build up highly dense polymer brushes on planar surfaces and recently has also been extended to nanoparticles to functionalize them.CRP combine the virtues of living ionic polymerization with the versatility and convenience of free-radical polymerization. One of the most common CRPs used to create polymer brushes is atom transfer radical polymerization (ATRP). ATRP has attracted much attention for its controlled/living character, tolerance of functional groups, and mild experimental requirements. A variety of nanoparticle-polymer core-shell systems with different kinds of cores, such as SiO2, Au, and Fe3O4 have been synthesized successfully with ATRP.Titanium oxide (TiO2) as an n-type semiconductor material with special photoresponse has been a key material of interest for many years. It has been widely used in dye-sensitized solar cells, photocatalysts, electrochemical sensors, selfcleaning coating, and water-splitting catalysts for hydrogen generation. Unfortunately, TiO2 cores intend to aggregate into larger clusters, losing the specific properties associated with their nanometer dimensions. A shell of coating materials, especially organic polymers, is often needed to cover the TiO2 cores to prevent such a core agglomeration. So, in this paper, we graft polymers on TiO2 nanoparticles via surface-initiated ATRP. The main investigations are as follows:(1) A core-shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (TiO2) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface-initiated atom transfer radical polymerization (ATRP) at 90°C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, 1H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core-shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO2-PS nanocomposites exhibited higher glass transition temperature (Tg) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface-attached polymers, were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2).(2) We demonstrate the first use of 3,4-dihydroxybenzoic acid inspired by catechol to introduce carboxylic groups onto the surfaces of titanium dioxide (TiO2) nanoparticles. The modified TiO2 was reacted subsequently with thionyl chloride and 2-hydroxylethyl-2’-bromoisobutyrate, producing TiO2-supported macroinitiators. Surface-initiated atom transfer radical polymerization (ATRP) of glycidyl methacrylate (GMA) was conducted well in anisole at ca. 50°C using CuBr/PMDETA as the catalytic system in the presence of sacrificial initiator. The plentiful epoxy groups of the TiO2-PGMA brushes were used for the direct coupling of 4-amino-1,2,4-triazole (NH2-trz) to give rise to the TiO2-PGMA-trz hybrids material with higher loading capacities for metal ions, such as Ag+, Cu2+ and Pd2+. We use FTIR, 1H NMR, XPS, TGA and XRD to characterize the synthesis of macromolecule initiator as well as the functionalized polymer, and the morphology of hybrid materials was characterized via HRTEM and SEM equipped with an EDS analyzer. The synthesis, derivatization, and metal loading of functionalized TiO2 suggest a new route for rational molecular design and augur well for future applications of functionalized nanomaterials, including device fabrication.(3)The epoxy groups of the grafted PGMA brushes were used for the direct coupling of sodium azide with the concomitant formation of hydroxyl groups to give rise to the TiO2-(PGMA-N3-OH) hybrid nanocomposites, and the resulting products were reacted subsequently with 2-bromoisobutyryl bromide for the subsequent surface-initiated ATRP. We combined the grafting from and grafting to methods ingeniously via ATRP and Click reaction successively.

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