The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Krzysztof Matyjaszewski - One of the best experts on this subject based on the ideXlab platform.
-
radical generation and termination in sara atrp of methyl acrylate effect of solvent ligand and chain length
Macromolecules, 2016Co-Authors: Pawel Krys, Krzysztof Matyjaszewski, Yu Wang, Simon HarrissonAbstract:Supplemental activator and reducing agent (SARA) ATRP is an efficient way to diminish the amount of Cu catalyst. A kinetic study of radical generation and termination in SARA ATRP was conducted to better understand and improve the “livingness” of the process. Monomer conversions and CuII/L concentrations were concurrently determined by UV–vis–NIR spectroscopy during polymerization of methyl acrylate in dimethyl sulfoxide (DMSO) or in acetonitrile (MeCN) with tris[2-(dimethylamino)ethyl]amine (Me6TREN) or tris(2-pyridylmethyl)amine (TPMA) as ligands. The polymerization was well controlled in DMSO with either Me6TREN or TPMA and in MeCN with Me6TREN. However, when TPMA was used in MeCN, the rate of polymerization and the generation of CuII/L accelerated exponentially even using small surface area of Cu0, rendering control over polymerization under such conditions difficult, plausibly due to excessive comproportionation. The study revealed that the rates of both activation of (macro)Alkyl Halide by Cu0 and C...
-
model studies of Alkyl Halide activation and comproportionation relevant to rdrp in the presence of cu0
Macromolecules, 2015Co-Authors: Thomas G Ribelli, Pawel Krys, Yidan Cong, Krzysztof MatyjaszewskiAbstract:Model studies of Alkyl Halide activation by Cu0 and comproportionation between CuII/L and Cu0 in the presence of tris[2-(dimethylamino)methyl]amine (Me6TREN), tris(2-pyridylmethyl)amine (TPMA) and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as ligands were conducted and quantified in dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN). When more active Alkyl Halides such as ethyl α-bromophenylacetate (EBPA) were used, the rate coefficients of activation by Cu0, ka0app, were the same as the rate coefficients of comproportionation, kcompapp indicating that desorption of the newly formed CuI species from the Cu0 surface could be a rate-determining step. When less active Alkyl Halides, such as methyl 2-bromopropionate (MBrP) were used, the activation was 2.5 orders of magnitude slower than for EBPA and slower than comproportionation. This indicates that atom transfer between Alkyl Halide and Cu0 is slower than desorption of CuI from the surface. Under the same conditions (solven...
-
aqueous rdrp in the presence of cu0 the exceptional activity of cui confirms the sara atrp mechanism
Macromolecules, 2014Co-Authors: Dominik Konkolewicz, Pawel Krys, Joana R Gois, Patricia V Mendonca, Mingjiang Zhong, Yu Wang, Armando Gennaro, Abdirisak Ahmed Isse, Marco Fantin, Krzysztof MatyjaszewskiAbstract:Polymerizations and mechanistic studies have been performed to understand the kinetic pathways for the polymerization of the monomer oligo(ethylene oxide) monomethyl ether acrylate (OEOA) in aqueous media. Typically, the medium consisted of 18 wt % OEOA in water, in the presence of Cu catalysts coordinated by tris[2-(dimethylamino)ethyl]amine (Me6TREN). Well-controlled polymerization of OEOA can be achieved in the presence of Halide anions and Cu wire with ≲600 ppm of soluble CuII species, rather than previously reported ca. 10 000 ppm of CuII and Cu0 particles formed by predisproportionation of CuI prior to monomer and initiator addition. The mechanistic studies conclude that even though disproportionation is thermodynamically favored in aqueous media, the SARA ATRP, not SET-LRP, mechanism holds in these reactions. This is because Alkyl Halides are much more rapidly activated by CuI than by Cu0 (contribution of Cu0 to activation is <1%). Because of the high activity of CuI species toward Alkyl Halide act...
Martina Roeselová - One of the best experts on this subject based on the ideXlab platform.
-
Partial hydration of n-Alkyl Halides at the water–vapor interface: a molecular simulation study with atmospheric implications
Theoretical Chemistry Accounts, 2014Co-Authors: Alena Habartová, Anthony Obisesan, Babak Minofar, Martina RoeselováAbstract:Classical molecular dynamics simulations with a polarizable force field were used to study adsorption of gas-phase Alkyl Halides to the surface of liquid water and their hydration properties in the interfacial environment. A systematic investigation has been performed for a set of monosubstituted Alkyl chlorides, bromides and iodides of the Alkyl chain length from one to five carbon atoms (C_ n H_2 n +1X, n = 1–5, X = Cl, Br, or I). All Alkyl Halides readily adsorb to the water surface and exhibit a strong preference for interfacial (partial) hydration. When adsorbed, the Alkyl Halide molecules reside primarily in the outermost region of the water–vapor interface. The (incomplete) hydration shell of the surface-adsorbed methyl Halide species is centered on the methyl end of the molecule, with the halogen atom largely exposed and facing away from water into the gas phase. The maximum hydration of the longer-chain Alkyl Halides is localized around the α-CH_2 group next to the halogen. With an increasing chain length, the Alkyl Halide molecules align more parallel to the surface. However, ethyl and propyl Halides still have the halogen atom rather exposed, pointing almost freely into the gas phase. The behavior of butyl and pentyl Halides on the water surface resembles that of alcohols, with the polar region of the CH_2X group interacting with water and the rest of the increasingly nonpolar hydrocarbon chain pointing on average away from water. Consequently, the halogen atom becomes more, albeit not fully, hydrated. The propensity of Alkyl Halides for the water–vapor interface along with the specific character of the partial hydration of the surface-adsorbed Alkyl Halides and their preferred interfacial orientation is likely to be of importance for heterogeneous chemical processes, involving Alkyl Halides adsorbed on the surface of aqueous aerosol droplets or ice particles in the atmosphere.
-
Partial hydration of n-Alkyl Halides at the water-vapor interface: a molecular simulation study with atmospheric implications
Theoretical Chemistry Accounts, 2014Co-Authors: Alena Habartová, Anthony Obisesan, Babak Minofar, Martina RoeselováAbstract:Classical molecular dynamics simulations with a polarizable force field were used to study adsorption of gas-phase Alkyl Halides to the surface of liquid water and their hydration properties in the interfacial environment. A systematic investigation has been performed for a set of monosubstituted Alkyl chlorides, bromides and iodides of the Alkyl chain length from one to five carbon atoms (C n H2n+1X, n = 1–5, X = Cl, Br, or I). All Alkyl Halides readily adsorb to the water surface and exhibit a strong preference for interfacial (partial) hydration. When adsorbed, the Alkyl Halide molecules reside primarily in the outermost region of the water–vapor interface. The (incomplete) hydration shell of the surface-adsorbed methyl Halide species is centered on the methyl end of the molecule, with the halogen atom largely exposed and facing away from water into the gas phase. The maximum hydration of the longer-chain Alkyl Halides is localized around the α-CH2 group next to the halogen. With an increasing chain length, the Alkyl Halide molecules align more parallel to the surface. However, ethyl and propyl Halides still have the halogen atom rather exposed, pointing almost freely into the gas phase. The behavior of butyl and pentyl Halides on the water surface resembles that of alcohols, with the polar region of the CH2X group interacting with water and the rest of the increasingly nonpolar hydrocarbon chain pointing on average away from water. Consequently, the halogen atom becomes more, albeit not fully, hydrated. The propensity of Alkyl Halides for the water–vapor interface along with the specific character of the partial hydration of the surface-adsorbed Alkyl Halides and their preferred interfacial orientation is likely to be of importance for heterogeneous chemical processes, involving Alkyl Halides adsorbed on the surface of aqueous aerosol droplets or ice particles in the atmosphere.
Pawel Krys - One of the best experts on this subject based on the ideXlab platform.
-
radical generation and termination in sara atrp of methyl acrylate effect of solvent ligand and chain length
Macromolecules, 2016Co-Authors: Pawel Krys, Krzysztof Matyjaszewski, Yu Wang, Simon HarrissonAbstract:Supplemental activator and reducing agent (SARA) ATRP is an efficient way to diminish the amount of Cu catalyst. A kinetic study of radical generation and termination in SARA ATRP was conducted to better understand and improve the “livingness” of the process. Monomer conversions and CuII/L concentrations were concurrently determined by UV–vis–NIR spectroscopy during polymerization of methyl acrylate in dimethyl sulfoxide (DMSO) or in acetonitrile (MeCN) with tris[2-(dimethylamino)ethyl]amine (Me6TREN) or tris(2-pyridylmethyl)amine (TPMA) as ligands. The polymerization was well controlled in DMSO with either Me6TREN or TPMA and in MeCN with Me6TREN. However, when TPMA was used in MeCN, the rate of polymerization and the generation of CuII/L accelerated exponentially even using small surface area of Cu0, rendering control over polymerization under such conditions difficult, plausibly due to excessive comproportionation. The study revealed that the rates of both activation of (macro)Alkyl Halide by Cu0 and C...
-
model studies of Alkyl Halide activation and comproportionation relevant to rdrp in the presence of cu0
Macromolecules, 2015Co-Authors: Thomas G Ribelli, Pawel Krys, Yidan Cong, Krzysztof MatyjaszewskiAbstract:Model studies of Alkyl Halide activation by Cu0 and comproportionation between CuII/L and Cu0 in the presence of tris[2-(dimethylamino)methyl]amine (Me6TREN), tris(2-pyridylmethyl)amine (TPMA) and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as ligands were conducted and quantified in dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN). When more active Alkyl Halides such as ethyl α-bromophenylacetate (EBPA) were used, the rate coefficients of activation by Cu0, ka0app, were the same as the rate coefficients of comproportionation, kcompapp indicating that desorption of the newly formed CuI species from the Cu0 surface could be a rate-determining step. When less active Alkyl Halides, such as methyl 2-bromopropionate (MBrP) were used, the activation was 2.5 orders of magnitude slower than for EBPA and slower than comproportionation. This indicates that atom transfer between Alkyl Halide and Cu0 is slower than desorption of CuI from the surface. Under the same conditions (solven...
-
aqueous rdrp in the presence of cu0 the exceptional activity of cui confirms the sara atrp mechanism
Macromolecules, 2014Co-Authors: Dominik Konkolewicz, Pawel Krys, Joana R Gois, Patricia V Mendonca, Mingjiang Zhong, Yu Wang, Armando Gennaro, Abdirisak Ahmed Isse, Marco Fantin, Krzysztof MatyjaszewskiAbstract:Polymerizations and mechanistic studies have been performed to understand the kinetic pathways for the polymerization of the monomer oligo(ethylene oxide) monomethyl ether acrylate (OEOA) in aqueous media. Typically, the medium consisted of 18 wt % OEOA in water, in the presence of Cu catalysts coordinated by tris[2-(dimethylamino)ethyl]amine (Me6TREN). Well-controlled polymerization of OEOA can be achieved in the presence of Halide anions and Cu wire with ≲600 ppm of soluble CuII species, rather than previously reported ca. 10 000 ppm of CuII and Cu0 particles formed by predisproportionation of CuI prior to monomer and initiator addition. The mechanistic studies conclude that even though disproportionation is thermodynamically favored in aqueous media, the SARA ATRP, not SET-LRP, mechanism holds in these reactions. This is because Alkyl Halides are much more rapidly activated by CuI than by Cu0 (contribution of Cu0 to activation is <1%). Because of the high activity of CuI species toward Alkyl Halide act...
Zhenping Cheng - One of the best experts on this subject based on the ideXlab platform.
-
thermoregulated phase transfer catalysis in aqueous organic biphasic system facile and highly efficient atrp catalyst separation and recycling in situ using typical Alkyl Halide as initiator
Polymer Chemistry, 2015Co-Authors: Xiaowu Jiang, Zhen Li, Lifen Zhang, Zhenping ChengAbstract:Developing a highly efficient and facile method for catalyst separation and recycling from an ATRP system facilitates wide application of atom transfer radical polymerization (ATRP). In this work, an important development of thermoregulated phase transfer catalysis (TRPTC)-based initiators for continuous activator regeneration (ICAR) ATRP for transition metal catalyst separation and recycling in a water/p-xylene biphasic system was achieved using Alkyl Halide (ethyl-2-bromo-2-phenyl acetate, EBPA) as the initiator for the first time. Herein, poly(poly(ethylene glycol) methyl ether methacrylate)-supported dipicolylamine (PPEGMA-BPMA) was designed as the thermoregulated ligand, CuBr2 as the catalyst, 1,1′-azobis(cyclohexanecarbonitrile) (ACHN) as the azo-initiator and methyl methacrylate (MMA) as the model monomer, respectively. The polymerization kinetics was investigated in detail, and the “living” feature of this novel polymerization system was confirmed by chain-end analysis and chain extension experiments for the resultant PMMA. It is noted that the catalyst complex (PPEGMA-BPMA/CuBr2) existed only in an aqueous phase at room temperature, and it transferred to an organic phase and subsequently catalyzed the ICAR ATRP of MMA when the temperature increased to 90 °C. After polymerization the catalyst complex successfully transferred to the aqueous phase almost completely from the organic phase again while the resultant PMMA existed in the p-xylene phase once the temperature cooled down to room temperature. Therefore, the process described above combined the advantages of homogeneous catalysis in the organic phase and heterogeneous catalyst separation in situ in the aqueous/organic biphasic phase system by just changing the reaction temperature. Importantly, the catalyst complex in the aqueous phase could be recycled easily, and the catalyst retained high catalytic activity even after eight recycling times.
Alena Habartová - One of the best experts on this subject based on the ideXlab platform.
-
Partial hydration of n-Alkyl Halides at the water–vapor interface: a molecular simulation study with atmospheric implications
Theoretical Chemistry Accounts, 2014Co-Authors: Alena Habartová, Anthony Obisesan, Babak Minofar, Martina RoeselováAbstract:Classical molecular dynamics simulations with a polarizable force field were used to study adsorption of gas-phase Alkyl Halides to the surface of liquid water and their hydration properties in the interfacial environment. A systematic investigation has been performed for a set of monosubstituted Alkyl chlorides, bromides and iodides of the Alkyl chain length from one to five carbon atoms (C_ n H_2 n +1X, n = 1–5, X = Cl, Br, or I). All Alkyl Halides readily adsorb to the water surface and exhibit a strong preference for interfacial (partial) hydration. When adsorbed, the Alkyl Halide molecules reside primarily in the outermost region of the water–vapor interface. The (incomplete) hydration shell of the surface-adsorbed methyl Halide species is centered on the methyl end of the molecule, with the halogen atom largely exposed and facing away from water into the gas phase. The maximum hydration of the longer-chain Alkyl Halides is localized around the α-CH_2 group next to the halogen. With an increasing chain length, the Alkyl Halide molecules align more parallel to the surface. However, ethyl and propyl Halides still have the halogen atom rather exposed, pointing almost freely into the gas phase. The behavior of butyl and pentyl Halides on the water surface resembles that of alcohols, with the polar region of the CH_2X group interacting with water and the rest of the increasingly nonpolar hydrocarbon chain pointing on average away from water. Consequently, the halogen atom becomes more, albeit not fully, hydrated. The propensity of Alkyl Halides for the water–vapor interface along with the specific character of the partial hydration of the surface-adsorbed Alkyl Halides and their preferred interfacial orientation is likely to be of importance for heterogeneous chemical processes, involving Alkyl Halides adsorbed on the surface of aqueous aerosol droplets or ice particles in the atmosphere.
-
Partial hydration of n-Alkyl Halides at the water-vapor interface: a molecular simulation study with atmospheric implications
Theoretical Chemistry Accounts, 2014Co-Authors: Alena Habartová, Anthony Obisesan, Babak Minofar, Martina RoeselováAbstract:Classical molecular dynamics simulations with a polarizable force field were used to study adsorption of gas-phase Alkyl Halides to the surface of liquid water and their hydration properties in the interfacial environment. A systematic investigation has been performed for a set of monosubstituted Alkyl chlorides, bromides and iodides of the Alkyl chain length from one to five carbon atoms (C n H2n+1X, n = 1–5, X = Cl, Br, or I). All Alkyl Halides readily adsorb to the water surface and exhibit a strong preference for interfacial (partial) hydration. When adsorbed, the Alkyl Halide molecules reside primarily in the outermost region of the water–vapor interface. The (incomplete) hydration shell of the surface-adsorbed methyl Halide species is centered on the methyl end of the molecule, with the halogen atom largely exposed and facing away from water into the gas phase. The maximum hydration of the longer-chain Alkyl Halides is localized around the α-CH2 group next to the halogen. With an increasing chain length, the Alkyl Halide molecules align more parallel to the surface. However, ethyl and propyl Halides still have the halogen atom rather exposed, pointing almost freely into the gas phase. The behavior of butyl and pentyl Halides on the water surface resembles that of alcohols, with the polar region of the CH2X group interacting with water and the rest of the increasingly nonpolar hydrocarbon chain pointing on average away from water. Consequently, the halogen atom becomes more, albeit not fully, hydrated. The propensity of Alkyl Halides for the water–vapor interface along with the specific character of the partial hydration of the surface-adsorbed Alkyl Halides and their preferred interfacial orientation is likely to be of importance for heterogeneous chemical processes, involving Alkyl Halides adsorbed on the surface of aqueous aerosol droplets or ice particles in the atmosphere.
