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Daniel J. Keddie - One of the best experts on this subject based on the ideXlab platform.

  • effect of scandium triflate on the raft Copolymerization of methyl acrylate and vinyl acetate controlled by an acid base switchable chain transfer agent
    Macromolecules, 2018
    Co-Authors: Ashton Tselepy, Simon Harrisson, Tara L. Schiller, Graeme Moad, Daniel J. Keddie, Carlos Guerrerosanchez
    Abstract:

    Modulation of the activity of an acid/base switchable dithiocarbamate RAFT agent, cyanomethyl (4-fluorophenyl)(pyridin-4-yl)carbamodithioate, with the Lewis acid scandium triflate (Sc(OTf)3) was investigated to examine the ability to deliver improved control over RAFT Copolymerizations involving both more-activated and less-activated monomers—specifically the Copolymerization of methyl acrylate (MA) and vinyl acetate (VAc). The introduction of either 0.5 or 1 mol equiv of Sc(OTf)3, with respect to RAFT agent, into a RAFT Copolymerization of MA and VAc provides substantially improved control resulting in significantly reduced molar mass dispersities (Đ) (∼1.1–1.3) than achieved in its absence (Đ ∼ 1.3–1.4). Furthermore, similar introduction of Sc(OTf)3 into MA homopolymerization mediated by the same RAFT agent also delivered polymers of very low Đ (∼1.15). Sc(OTf)3 was also found to lower the rate of polymerization and alter the Copolymerization reactivity ratios for MA and VAc. Increasing the Lewis acid c...

  • Effect of Scandium Triflate on the RAFT Copolymerization of Methyl Acrylate and Vinyl Acetate Controlled by an Acid/Base “Switchable” Chain Transfer Agent
    2018
    Co-Authors: Ashton Tselepy, Simon Harrisson, Tara L. Schiller, Carlos Guerrero-sanchez, Graeme Moad, Daniel J. Keddie
    Abstract:

    Modulation of the activity of an acid/base switchable dithiocarbamate RAFT agent, cyanomethyl (4-fluorophenyl)­(pyridin-4-yl)­carbamodithioate, with the Lewis acid scandium triflate (Sc­(OTf)3) was investigated to examine the ability to deliver improved control over RAFT Copolymerizations involving both more-activated and less-activated monomersspecifically the Copolymerization of methyl acrylate (MA) and vinyl acetate (VAc). The introduction of either 0.5 or 1 mol equiv of Sc­(OTf)3, with respect to RAFT agent, into a RAFT Copolymerization of MA and VAc provides substantially improved control resulting in significantly reduced molar mass dispersities (Đ) (∼1.1–1.3) than achieved in its absence (Đ ∼ 1.3–1.4). Furthermore, similar introduction of Sc­(OTf)3 into MA homopolymerization mediated by the same RAFT agent also delivered polymers of very low Đ (∼1.15). Sc­(OTf)3 was also found to lower the rate of polymerization and alter the Copolymerization reactivity ratios for MA and VAc. Increasing the Lewis acid concentration provides enhanced incorporation of the less active monomer, VAc, into the copolymers ([Sc­(OTf)3]/[RAFT] = 0, rMA = 4.04, rVAc = 0.032; [Sc­(OTf)3]/[RAFT] = 0.5, rMA = 3.08, rVAc = 0.17; [Sc­(OTf)3]/[RAFT] = 1, rMA = 2.68, rVAc = 0.62). Carbon nuclear magnetic resonance (13C NMR) and differential scanning calorimetry (DSC) analysis of preparative samples confirm the enhanced VAc incorporation with increased levels of Sc­(OTf)3. Importantly the inclusion of Sc­(OTf)3 does not deleteriously affect the thiocarbonylthio end-groups of the RAFT polymers, with high end-group fidelity being observed in all Copolymerizations

Changle Chen - One of the best experts on this subject based on the ideXlab platform.

  • palladium catalyzed direct synthesis of various branched carboxylic acid functionalized polyolefins characterization derivatization and properties
    Macromolecules, 2018
    Co-Authors: Shengyu Dai, Changle Chen
    Abstract:

    Ethylene-co-acrylic acid (E–AA) copolymers are typically produced via high-pressure free radical Copolymerization and have great industrial importance because of their many applications. The radical polymerization mechanism usually leads to highly branched products with poor mechanical properties. Transition-metal-catalyzed E–AA Copolymerization represents a direct and economical route to access these copolymers with potentially better control over their microstructures and material properties. However, this is highly challenging due to catalyst poisoning from both the oxygen and carboxylic acid moieties in the monomers. In this contribution, we demonstrate that a series of α-diimine-based palladium catalysts can mediate efficient Copolymerizations of ethylene with AA, allylacetic acid, and 10-undecenoic acid, leading to the formation of various branched, carboxylic acid-functionalized polyolefin materials. These comonomers exist as carboxylic acid-based dimeric species at ambient temperatures, which is p...

  • Palladium-Catalyzed Direct Synthesis of Various Branched, Carboxylic Acid-Functionalized Polyolefins: Characterization, Derivatization, and Properties
    2018
    Co-Authors: Shengyu Dai, Changle Chen
    Abstract:

    Ethylene-co-acrylic acid (E–AA) copolymers are typically produced via high-pressure free radical Copolymerization and have great industrial importance because of their many applications. The radical polymerization mechanism usually leads to highly branched products with poor mechanical properties. Transition-metal-catalyzed E–AA Copolymerization represents a direct and economical route to access these copolymers with potentially better control over their microstructures and material properties. However, this is highly challenging due to catalyst poisoning from both the oxygen and carboxylic acid moieties in the monomers. In this contribution, we demonstrate that a series of α-diimine-based palladium catalysts can mediate efficient Copolymerizations of ethylene with AA, allylacetic acid, and 10-undecenoic acid, leading to the formation of various branched, carboxylic acid-functionalized polyolefin materials. These comonomers exist as carboxylic acid-based dimeric species at ambient temperatures, which is proposed as the key reason for the successful Copolymerizations. These polar, functionalized polyolefins demonstrate greatly improved surface properties based on water contact angle measurements and dyeing experiments. Furthermore, these copolymers can be converted to sodium-, zinc-, and iron-based ionomers. The metal ions can act as physical cross-links and dramatically improve the mechanical properties of these copolymers

  • A Second-Coordination-Sphere Strategy to Modulate Nickel- and Palladium-Catalyzed Olefin Polymerization and Copolymerization.
    Angewandte Chemie (International ed. in English), 2017
    Co-Authors: Xingbao Wang, Yi Luo, Changle Chen
    Abstract:

    Transition-metal-catalyzed Copolymerization reactions of olefins with polar-functionalized comonomers are highly important and also highly challenging. A second-coordination-sphere strategy was developed to address some of the difficulties encountered in these Copolymerization reactions. A series of α-diimine ligands bearing nitrogen-containing second coordination spheres were prepared and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymerizations and Copolymerizations were investigated. In the nickel system, significant reduction in polymer branching density was observed, while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control experiments and computational results reveal the critical role of the metal-nitrogen interaction in these polymerization and Copolymerization reactions.

  • Accessing Multiple Catalytically Active States in Redox-Controlled Olefin Polymerization
    2017
    Co-Authors: Minhui Zhao, Changle Chen
    Abstract:

    The majority of work in the field of olefin polymerization catalysis has been focused on ligand modifications. In this work, we describe an alternative strategy for the modulation of olefin polymerization and Copolymerization processes. The two ferrocenyl units in an α-diimine palladium catalyst can be oxidized in a stepwise fashion. This stepwise redox control can be used to modulate the catalyst properties during the homopolymerization of ethylene and 1-hexene, as well as the Copolymerizations of ethylene with norbornene, methyl acrylate, and 5-norbornene-2-yl acetate. Moreover, polymer microstructure and polydispersity can be controlled during these stepwise oxidation processes

Takeshi Endo - One of the best experts on this subject based on the ideXlab platform.

  • anionic alternating Copolymerization behavior of bifunctional six membered lactone and glycidyl phenyl ether
    Journal of Polymer Science Part A, 2009
    Co-Authors: Kazuya Uenishi, Atsushi Sudo, Takeshi Endo
    Abstract:

    A Copolymerization of 10-methyl-2H,8H-benzo-[1,2-b:5,4-b′]bipyran-2,8-dione (1) and glycidyl phenyl ether (GPE) was studied. 1 was a bislactone designed as a bifunctional analogue of 3,4-dihydrocoumarin (DHCM), of which anionic 1:1 alternating Copolymerization with GPE has been reported by us, previously. This alternating nature was inherited by the present Copolymerization of 1 and GPE, leading to an intriguing Copolymerization behavior in contrast to the ordinary statistical Copolymerizations of monofunctional monomers and bifunctional monomers usually controlled by the proportional dependence of the crosslinking density on the monomer feed ratio: (1) When the feed ratio [GPE]0/[1]0 was 1, the two monomers underwent the 1:1 alternating Copolymerization. In this case, 1 behaved as a monofunctional monomer, that is, only one of the two lactones in 1 participated in the Copolymerization allowing the other lactone moiety to be introduced into the side chain almost quantitatively. (2) Increasing the feed ratio [GPE]0/[1]0 to larger than 4 allowed almost all of the lactone moieties to participate in the Copolymerization system to give the corresponding networked polymers efficiently. The compositions of the copolymers [GPE unit]/[1-derived acyclic ester unit] were always biased to smaller values than the feed ratios [GPE]0/[lactone moiety in 1]0 by the intrinsic 1:1 alternating nature of the Copolymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3662–3668, 2009

  • anionic alternating Copolymerization of 3 4 dihydrocoumarin and glycidyl ethers a new approach to polyester synthesis
    Journal of Polymer Science Part A, 2008
    Co-Authors: Kazuya Uenishi, Atsushi Sudo, Takeshi Endo
    Abstract:

    Anionic Copolymerizations of 3,4-dihydrocoumarin (DHCM) and a series of glycidyl ethers (n-butyl glycidyl ether, tert-butyl glycidyl ether, and allyl glycidyl ether) with 2-ethyl-4-methylimidazole as an initiator proceeded in a 1:1 alternating manner to give the corresponding polyesters, whose structures were confirmed by spectroscopic analyses and reductive scission of the ester bonds in the main chain with lithium aluminum hydride, followed by detailed analyses of the resulting fragments. The polyester obtained by the Copolymerization of DHCM and allyl glycidyl ether inherited the allyl groups in the side chain, whose applicability to chemical modifications of the polyester was successfully demonstrated by a platinum-catalyzed hydrosilylation reaction.

  • cationic Copolymerization behavior of a bicyclic orthoester having hydroxy group with glycidyl phenyl ether and volume change on their Copolymerization
    Journal of Applied Polymer Science, 2006
    Co-Authors: Makoto Kume, Takeshi Endo
    Abstract:

    This article describes cationic ring-opening Copolymerization of a bicyclic orthoester having hydroxy group (BOE-OH) and glycidyl phenyl ether (GPE), and the volume shrinkage behavior during the Copolymerization. THF soluble polyethers [poly(BOE-OH-co-GPE)] were obtained by the Copolymerizations at 80–180°C, while crosslinked poly(BOE-OH-co-GPE) was obtained by the Copolymerizations at 220–250°C. This crosslinking reaction may originate from the dehydration of methylol groups in the side chain of poly(BOE-OH-co-GPE). The volume shrinkage during the cationic Copolymerization reduced as the increase of the BOE-OH feed ratio. By contrast, the volume shrinkage on the crosslinking polymerization was almost independent on the BOE-OH feed ratio. Poly(BOE-OH-co-GPE)s with higher BOE-OH composition showed lower thermal weight loss temperature owing to the release of H2O by dehydration of methylol groups. The BOE-OH component in the THF soluble poly(BOE-OH-co-GPE)s lowered the glass transition temperature (Tg), while that in the crosslinked poly(BOE-OH-co-GPE) increased the Tg probably because of the higher crosslinking density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1356–1361, 2006

  • anionic ring opening Copolymerization of bicyclic bis gamma lactone s with mono and bifunctional epoxides via double ring opening isomerization of the bis gamma lactone s and volume change during Copolymerization
    Macromolecules, 1995
    Co-Authors: Keunwo Chung, Toshikazu Takata, Takeshi Endo
    Abstract:

    The first anionic polymerization with small volume shrinkage is described. Volume change in anionic Copolymerization of bicyclic bis(γ-lactone) 1c and glycidyl phenyl ether (2) with tBuOK (4 mol %) at 120°C was nearly zero (small expansion, +0.25±0.15%). The anionic Copolymerization of aromatic substituent-containing bicyclic bis(γ-lactone)s (1e-g) with 2 was carried out at 120°C in THF and in bulk for 72 h in the presence of tBuOK (4 mol %). The 1 H NMR, 13 C NMR, and IR spectra of the methanol-insoluble parts clearly suggested the proposed alternating copolymer structures consisting of two successive units derived from 1e-g and 2. The anionic Copolymerizations of bicyclic bis(γ-lactone)s (1a-g) with equimolar amounts of bifunctional epoxides (5a,b) in bulk were carried out at 120-160°C in the presence of tBuOK (4 mol%) to afford the corresponding dichloromethane-insoluble copolymers (6aa-gb) in quantitative yields. The copolymer composition was ca. 1:0.5 in any case, as estimated from the 1 H NMR spectra of the dichloromethane-soluble parts. Yield of the copolymers decreased when the monomer feed ratio was deviated from 1:0.5. The IR spectral analysis of 6aa-gb strongly suggested the occurrence of the efficient alternating Copolymerization. Small shrinkages or expansions in volume (-2.5±0.15% to +2.4±0.15%) were observed during the Copolymerizations of 1 and 5, definitely indicating the possibility of 1 as expanding monomers. Thermal properties such as glass transition and 10% weight loss temperatures of the obtained copolymers were evaluated by DSC and TGA

Christopher Barner-kowollik - One of the best experts on this subject based on the ideXlab platform.

  • Reversible addition fragmentation chain transfer Copolymerization: influence of the RAFT process on the copolymer composition
    Polymer, 2004
    Co-Authors: Achim Feldermann, Andrew Ah Toy, Hong Phan, Martina H. Stenzel, Thomas P. Davis, Christopher Barner-kowollik
    Abstract:

    Abstract Reversible addition fragmentation chain transfer (RAFT) mediated and conventional Copolymerizations at low monomer conversions have been carried out for the systems methyl methacrylate (MMA)-styrene, methyl acrylate (MA)-styrene and methyl methacrylate-butyl acrylate (BA). The polymer samples have been analyzed via 1H-NMR spectroscopy to obtain the copolymer composition and the terminal model reactivity ratios. In the RAFT mediated Copolymerizations, the polymer mole fraction of the monomer with the larger reactivity ratio is increased compared to the conventional Copolymerization. Simulations have been carried out using the program package PREDICI® to examine possible explanations for the experimental findings. The simulations demonstrate that the RAFT process itself may alter the macroradical populations and the copolymer composition by offering additional reaction pathways. Further, the rate coefficients for the initiation reaction and the pre-equilibrium play an important role in determining the copolymer composition. The rate coefficients governing the main equilibrium of the RAFT process have only a minor impact on the copolymer composition.

  • Reversible addition fragmentation chain transfer Copolymerization: Influence of the RAFT process on the copolymer composition
    2004
    Co-Authors: Achim Feldermann, Andrew Ah Toy, Hong Phan, Martina H. Stenzel, Thomas P. Davis, Christopher Barner-kowollik
    Abstract:

    Reversible addition fragmentation chain transfer (RAFT) mediated and conventional Copolymerizations at low monomer conversions have been carried out for the systems methyl methacrylate (MMA)-styrene, methyl acrylate (MA)-styrene and methyl methacrylate-butyl acrylate (BA). The polymer samples have been analyzed via 1H-NMR spectroscopy to obtain the copolymer composition and the terminal model reactivity ratios. In the RAFT mediated Copolymerizations, the polymer mole fraction of the monomer with the larger reactivity ratio is increased compared to the conventional Copolymerization. Simulations have been carried out using the program package PREDICI ® to examine possible explanations for the experimental findings. The simulations demonstrate that the RAFT process itself may alter the macroradical populations and the copolymer composition by offering additional reaction pathways. Further, the rate coefficients for the initiation reaction and the pre-equilibrium play an important role in determining the copolymer composition. The rate coefficients governing the main equilibrium of the RAFT process have only a minor impact on the copolymer composition. © 2004 Elsevier Ltd. All rights reserved.

D J Hourston - One of the best experts on this subject based on the ideXlab platform.

  • radical Copolymerization of maleic anhydride and substituted styrenes by reversible addition fragmentation chain transfer raft polymerization
    Polymer, 2005
    Co-Authors: Mark C Davies, John V Dawkins, D J Hourston
    Abstract:

    Abstract Reversible addition fragmentation transfer (RAFT) Copolymerization with benzyl dithiobenzoate (BDTB) as chain transfer agent was used to copolymerize maleic anhydride (MA) with styrene (St) and with the substituted styrenes p -chlorostyrene ( p ClSt), p -methoxystyrene ( p MeOSt) and p -methylstyrene ( p MeSt). Kinetic studies indicated that radical Copolymerizations proceeded with apparent ‘living’ character, deduced from experiments demonstrating an increase in molar mass with monomer conversion, narrow molar mass distribution and chain extension to form block copolymer. All copolymers were alternating in chain structure as confirmed by determinations of monomer reactivity ratios. The degree of control in the RAFT mechanism and the establishment of the fragmentation equilibrium incorporating MA are discussed for styrene and for p -substituted styrenes, in relation to experimental Copolymerizations producing molar masses somewhat higher than expected. For Copolymerizations of MA with α-methylstyrene (αMeSt), conventional rather than controlled behaviour was observed, suggesting that the fragmentation equilibrium could be shifted towards the αMeSt propagating radical.