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

Author : Fumin Ma
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Page : 7 pages
File Size : 15,10 MB
Release : 2011
Category : Ionic Liquid
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Three brønsted acidic ionic liquids, 1-methylimidazolium acetate ([Hmim][CH3COO]), 1-methylimidazolium propionate ([Hmim][CH3CH2COO]) and 1-methylimidazolium butyrate ([Hmim][CH3CH2CH2COO]) were used as reaction medium for atom transfer radical polymerization of methyl methacrylate with ethyl 2-bromoisobutyrate (EBiB)/CuBr as the initiating system. Kinetic studies, chain extension and block copolymerization confirmed the well-controlled manner of these polymerizations in three brønsted acidic ionic liquids. The reactions were fast and the polydispersities of the polymers were quite narrow (1.10

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Page : pages
File Size : 40,29 MB
Release : 2004
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In this work, methylmethacrylate, MMA was polymerized by ATRP method to obtain low molecular weight living polymers. The initiator was p-toluenesulfonylchloride and catalyst ligand complex system were CuCl-4,4’ dimethyl 2,2’bipyridine. Polymers with controlled molecular weight were obtained. The polymer chains were shown by NMR investigation to be mostly syndiotactic. The molecular weight and molecular weight distribution of some polymer samples were measured by GPC method. The K and a constants in [h]=K Ma equation were measured as 9.13x10-5 and 0.74, respectively. FT-IR and X-Ray results showed regularity in polymer chains. The molecular weight-Tg relations were verified from results of molecular weight-DSC results.

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Page : 5 pages
File Size : 38,74 MB
Release : 1996
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Kinetic aspects of Atom Transfer Radical Polymerization of methyl acrylate MA were studied. The results showed the characteristic features of living polymerization up to Mn (80,000, e.g. constant concentration of propagating species, a linear relation between conversion and molecular weight and narrow polydispersities (Mw/Mn (1.2). As an initiation system, 2- bromomethyl propionate and CuBr complexed by 4,4'-Di-tert-butyl-2,2'-bipyridine DThipy or 4,4'-di-(5-nonyl)-2,2'-bipyridine DNbipy were employed. Kinetic studies showed that the propagation rate is first order in relation to the monomer and initiator. For the homogeneous catalyst system (copper(I)/dNbipy), the propagation rate is first order with respect to the initial concentration of catalyst and inverse first order with respect to the initial concentration of Cu(II)Br2. The propagation rate in non-homogeneous system (copper(I)/dTbipy) less depends on the on the initial concentration of catalyst and Cu(II)Br2. These results can be explained by the reversible formation of growing polyacrylate radicals by the reaction of dormant bromo-terminated chains with copper halide.

Author : Lapporn Vayachuta
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Page : 191 pages
File Size : 29,48 MB
Release : 2009
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Atom Transfer Radical Polymerization (ATRP) technique was applied for synthesis of natural rubber-grafted-poly(methyl methacrylate) (NR-g-PMMA). Active sites on macromolecular chains of NR were created by fixation of bromoalkyl groups via a two-step chemical modification: partial epoxidation on unsaturated carbon-carbon bonds, followed by nucleophilic addition of a bromoalkyl-functionalized carboxylic acid on the oxirane rings of the epoxidized natural rubber (ENR) obtained. The resulting bromoalkyl-functionalized rubber was then used as macroinitiator to initiate the ATRP of methyl methacrylate (MMA) from NR chains by varying reaction conditions. The study was successively envisaged with 4-methyloct-4-ene (a model molecule of NR repeating unit), a synthetic cis-1,4-polyisoprene, and natural rubber. In the first part, the feasibility of the grafting reaction is verified by studying the ATRP of MMA from model molecules of bromoalkyl-functionalized 1,4-polyisoprene units. The model of the 1,4-polysisoprene unit, 4-methyloct-4-ene, is transformed in various models of bromoalkyl-functionalized 1,4-polyisoprene units via a chemical modification procedure carried out in two-steps: epoxidation performed with m-chloroperbenzoic acid (CPBA) followed by the addition of the bromoalkyl-functionalized carboxylic acid (2-bromopropionic acid, A1, or 2-bromo-2-methylpropionic acid, A2) on the oxirane ring formed. The addition of the acid occurs according to an SN2 mechanism with fixation of the acid group on the less substituted carbon of the oxirane ring and is competed with a secondary reaction of rearrangement of oxirane ring, leading to the formation of two allyl alcohols. The yield of the addition depends on the acidity of the carboxylic acid used. Afterwards, resulting O-(2-hydroxy-2-methyl-1-(n-propyl)pentyl)-2-bromopropionate and O-(2-hydroxy-2-methyl-1-(n-propyl)pentyl)-2-bromoisobutyrate, were used to initiate the ATRP of MMA at 90°C in toluene using Cu(I)Br complexed with a polyamine ligand. Several ligands were tested: N-(n-octyl)-2-pyridylmethanimine (NOPMI), N-(n-octadecyl)-2-pyridylmethanimine (NODPMI), and 1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA). A good control of molecular weights (SECn,M) and polydispersity indexes (PDI) were obtained with O-(2-hydroxy-2-methyl-1-(n-propyl)pentyl)-2-bromoisobutyrate as the initiator in presence of CuBr/NOPMI as catalytic system. In the second part, the synthetic cis-1,4-polyisoprene (PI) is transformed into a bromoalkyl-functionalized polyisoprene (PI-Br) macroinitiator using a two-step chemical modification procedure similar to that used for synthesis of the model. PI was partially epoxidized using CPBA in dichloromethane, and then the epoxidized PI (EPI) obtained was reacted with A2. The addition of the acid occurs according to an SN2 mechanism with fixation of the acid group on the less substituted carbon of the oxirane ring ([beta]-addition) and is competed with rearrangement reactions of oxirane rings, leading to external allyl alcohol. SECn,M and PDI of PMMA grafts were determined by Size Exclusion Chromatography after separation from the PI backbone by hydrolysis of the ester bond using trifluoroacetic acid. An internal first order kinetic plot with respect to monomer and an increase of SECn,M with MMA conversion were observed using Cu(I)Br complexed with bidentate (NOPMI and NODPMI) and tridentate (PMDETA) ligands, as catalytic systems. With bidentate ligands, the PDI of grafts is better controlled. Moreover, the control of SECn,M and PDI of PMMA grafts was affected by increasing the degree of initiating units in PI-Br. In the last part, NR is used as a starting material. It was partially epoxidized in ENR in latex medium by reaction with performic acid generated in-situ from formic acid and hydrogen peroxide, and then ENR was transformed in bromoalkyl-functionalized NR (NR-Br) by nucleophilic addition of A2 on the oxirane rings. The addition of the acid is similar to that observed during the studies performed with 4-methyloct-4-ene and PI. Resulting NR-Br was then used to initiate the graft polymerization of MMA from NR chains using normal ATRP in toluene solution and in aqueous dispersed medium, respectively. AGET-ATRP was also considered in aqueous dispersed medium to study the effect of water for further ATRP graft copolymerization studies with NR latices. By normal ATRP in toluene solution, the termination reactions by recombination decreased as MMA concentration deceased, from 30 wt% to 10 wt%. PDIs of PMMA grafts vary in range from 1.7 (at 8.1 % MMA conversion) to 2.0 (at 52.0 % MMA conversion). A better control of the SECn,M and PDI of PMMA grafts was obtained by using normal ATRP in aqueous dispersed medium, more especially when CuBr was complexed with NODPMI. In these conditions, PDIs of PMMA grafts were low (closed to 1.5 at low MMA conversion). In AGET-ATRP performed in aqueous dispersed medium, it was shown that the efficiency of graft copolymerization is affected by the concentration in ascorbic acid used as reducing agent. The chemical structures obtained were characterized by FT-IR, and by 1H and 13C NMR. The thermal properties of the graft copolymers synthesized were studied by Differential Scanning Calorimetry (DSC). The presence of two Tgs, at about -14°C and 99°C respectively, on the DSC curves when the amounts of PMMA in NR-g-PMMAs are higher than 65 wt%, shows that these materials adopt a biphasic morphology.

Author : Mary Nguyen
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Page : pages
File Size : 21,68 MB
Release : 2017
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Atom transfer radical polymerizations (ATRP) of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St) were conducted by continuous feeding of Cu(I)X/Ligand activators. Typically, the monomer, the initiator, and a certain amount of deactivator, Cu(II)X2/Ligand, were placed in a Schlenk flask deoxygenized by bubbling with N2. The activator, Cu(I)X/Ligand, was placed in a gas-tight syringe and was added at a constant rate to the Schlenk flask using a syringe pump. In ATRP, the Cu(I) catalyst would undergo many oxidation/reduction cycles when the propagation of polymer chains is taking place. However, some of the Cu(I) would finally be oxidized to Cu(II) irreversibly. According to the principle of halogen conservation, the end-group loss equals the amount of Cu(I) that is permanently oxidized to Cu(II). Thus, by reducing the amount of Cu(I) added to the reaction, ATRP by continuous feeding of activators sets an upper limit of the potential end-group loss. The end-group fidelity information is readily known at the beginning of the reaction.