[PDF] Silica Gel Supported Atom Transfer Radical Polymerization Of Styrene In The Presence Of Oxygen And Sodium Phenoxide eBook

Author : Richard Oluwarotimi Ademola Osibanjo
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Page : pages
File Size : 20,74 MB
Release : 2013
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ISBN : 9781303792458

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The big picture for this work is the development of a biosensor that will determine contaminants in aqueous systems via surface-bound thin films. In order to make this a reality, it is important to have an understanding of the initial stages during polymerization. Details of the mechanisms and structures created in the earliest stages of surface-bound polymer films affect the nature and structure of the films in profound ways. The two major methods on tethering polymers onto various substrates are the "grating from" and the "grafting to" methods. This study used the grafting from approach owing to its ability to produce denser grafting densities and thus produce thicker films. This study investigates the stability, structure, kinetics and density of initiator binding to Au surfaces and formulation of polymers via atom transfer radical polymerization (ATRP) on Au surfaces at low temperatures (25 -50 °C). Though restricted by the lability of thiol-gold at 50 °C, advantages of lower temperatures includes; absence of side reactions, chain transfer reactions, thermal crosslinking and increased quality of the produced polymer film. Time-dependent molecular information is obtained in situ from deposition of thiol-based initiator on the substrate, addition of monomer and catalyst during surface initiated ATRP on a Au substrate.Surface initiated atom transfer radical polymerization (SI-ATRP) is accompanied by tethering an initiator molecule such as 11-Mercaptobromoisobutyrate bromides onto a gold surface via formation of a Au-S bond. As a monolayer of the compound binds to the surface, the chains line up to form a quasi-crystalline self-assembled monolayer. The bromine can be abstracted with a catalyst, such as CuBr/CuBr2 or photochemically to produce a radical which then takes part in polymerization. ATR-FTIR is the method of choice because it is a surface specific technique and information regarding the nature of the adsorbed initiator molecule and details concerning polymer orientation desorption, mechanisms and kinetics can be obtained. These studies will contribute to further understanding the implementation of overlayer enhancement for IR spectroscopy at interfaces and understanding of the structure and dynamics of supported polymer films. It will also help provide an in depth look into the reactions of thin films and the development of thin film sensor technologies. Research into newer catalysts may be required for Cu-SI-ATRP owing to findings showing that Cu catalysts aide the desorption of thiol based initiator molecules which result in extensive termination reactions and production of thin films.

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Page : 5 pages
File Size : 11,38 MB
Release : 1996
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Controlled/'Living' radical polymerization allows for the preparation of complex polymer architectures, end functional polymers and block copolymers. Recently, we reported atom transfer radical polymerization (ATRP), a novel route to the controlled - 'Living' - radical polymerization in which polymers with predetermined molecular weight up to Mn =100,000 and polydispersity as narrow as 1.05 have been obtained. In this paper, the kinetic scheme of atom transfer radical polymerization of styrene under homogeneous conditions is described. The polymerization was determined to be first order with respect to the concentration of monomer, initiator and Cu(I) halide. From the effect of the ratio of ligand to Cu(I) halide, possible active copper complex was proposed.

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Page : 19 pages
File Size : 20,37 MB
Release : 1996
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The role of exchange reactions in controlled/living radical polymerizations is analyzed. Styrene polymerization in the presence TEMPO and atom transfer radical polymerization (ATRP) catalyzed by transition metals (Cu(II)X2/2Bipy complex) are compared. ATRP proceeds approximately one order of magnitude faster than TEMPO-moderated polymerization due to a higher stationary concentration of radicals and an equilibrium more shifted to the side of radicals. ATRP can provide better defined polymers with polydispersities down to Mw/Mn approx.= l.05. This fact can he ascribed to a faster deactivation process and a smaller contribution of side reactions. The polydispersities in both systems are defined by the relative rates of the deactivation and propagation processes. The rate constant of deactivation of growing polystyryl radicals by TEMPO is in the range of kd=10(exp 8) L/mol/s, which is substantially higher than the previously reported value.

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Page : 5 pages
File Size : 20,86 MB
Release : 1996
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Polymerization of styrene in the presence of a stable radical TEMPO has been simulated using a Predici simulations package. Based on the experimental data, a kinetic model for the TEMPO-moderated polymerization of styrene has been proposed. It was shown that in order to properly simulate the experimental data, in addition to the reversible cleavage of the TEMPO-polymeric radical adduct, it is necessary to include thermal self-initiation, transfer and irreversible decomposition of intermediate alkoxyamines in the polymerization model. This model, combined with the experimental data and literature values of the rate constants of propagation (kp), termination (kt), transfer (ktrm), and alkoxyamines decomposition (kdecomp), was then employed to estimate kinetic and thermodynamic parameters of the exchange between dormant and active species. The equilibrium constant K was estimated to be around 1.10(exp -10) mol/L, the deactivation rate constant kd - 3.10(exp 7) mol-1Ls-1 and the activation rate constant ka= 3.10(exp -3)mol-1Ls-1 for bulk styrene polymerization at 120 deg C.

Author : Gang Fan
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Page : 372 pages
File Size : 17,79 MB
Release : 2019
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Atom transfer radical polymerization (ATRP) has emerged as a robust tool to synthesize soft materials with defined structures for bioengineering and nanocomposites. In the past decade, numerous efforts were devoted to developing a novel polymerization method, electrochemically controlled radical polymerization (eATRP), which requiring less catalysts. However, due to restriction of special design, susceptible to oxygen and less control in aqueous buffers, challenges still remain. To address these difficulties, we hypothesized extracellular electron transfer from micro-oganisms could be utilized to control the performance of an exogenous oxidation-reduction (redox) reaction. We show that the electroactive bacterium Shewanella oneidensis can control the activity of a copper catalyst in ATRP. Precise control over the molecular weight and polydispersity of synthetic polymer could be achieved by mixing the bacterial suspension into the reaction medium. We also found that catalyst performance could be augmented by specific electron transport proteins and bacterial metabolism, offering potential targets for future applications. Performing ATRP under air is almost impossible because oxygen will quench the polymerization. We show that S. oneidensis can control metal-catalyzed living radical polymerizations under aerobic conditions by first consuming dissolved oxygen via aerobic respiration, then directing extracellular electron flux to the polymerization catalysts. In both open and closed containers, S. oneidensis enabled living radical polymerizations without requiring the pre-removal of oxygen. Polymerization activity was effective for wide ranges of monomers using low concentrations of biocompatible metal catalysts including Fe and Co. Moreover, polymerizations could be initiated using lyophilized or spent (recycled) cells. Finally, in order to understand the surface chemistry of metal organic frameworks (MOFs), we develop a surface functionalization method for water-stable MOFs by phage display. Specific frameworks binding peptides were identified, and their thermodynamic binding affinities and specificities were measured. Microscopy, X-ray diffraction, and gas adsorption analysis confirmed that the peptide functionalized frameworks retained similar characteristics. Microcopy imaging technique showed that peptide was localized on the surface of the frameworks, without blocking pore of MOFs. Last but not least, we measured the pH-dependent release of fluorescein from peptide-functionalized frameworks and discovered that peptide-binding can attenuate fluorescein release by improving framework stability under low pH conditions