The Experts below are selected from a list of 100014 Experts worldwide ranked by ideXlab platform

Sébastien Perrier - One of the best experts on this subject based on the ideXlab platform.

Ezio Rizzardo - One of the best experts on this subject based on the ideXlab platform.

  • ambient temperature reversible addition fragmentation Chain Transfer polymerisation
    Chemical Communications, 2001
    Co-Authors: John F Quinn, Ezio Rizzardo, Thomas P Davis
    Abstract:

    Reversible addition fragmentation Chain Transfer was performed at ambient temperature for the first time.

  • living radical polymerization with reversible addition fragmentation Chain Transfer raft polymerization using dithiocarbamates as Chain Transfer agents
    Macromolecules, 1999
    Co-Authors: Roshan T. A. Mayadunne, Y K Chong, John Chiefari, Ezio Rizzardo, Graeme Moad, San H Thang
    Abstract:

    Living radical polymerization with reversible addition−fragmentation Chain Transfer (RAFT polymerization) can be achieved with the use of dithiocarbamate derivatives that have the nonbonded electron pair of the nitrogen included as part of an aromatic system. These compounds have been shown to be highly effective in RAFT polymerization of styrene and (meth)acrylate esters to produce polymers of predetermined molecular weight and narrow polydispersity (usually <1.2). By contrast, simple N,N-dialkyl dithiocarbamates (those compounds previously described as “photoiniferters”) are ineffective as RAFT agents. The reasons for the different behavior are discussed.

  • Chain Transfer to Polymer: A Convenient Route to Macromonomers
    Macromolecules, 1999
    Co-Authors: John Chiefari, Roshan T. A. Mayadunne, Ezio Rizzardo, Graeme Moad, Justine Leigh Jeffery, San H. Thang
    Abstract:

    Two effective and well-known methods for the preparation of macromonomers are the use of radical addition-fragmentation Chain Transfer agents (e.g., allyl sulfides)6 and catalytic Chain Transfer (CCT) with cobalt complexes.7-10 Recently, the scope of the CCT process has been expanded by demonstrating how cobalt complexes can be used to prepare macromonomers based on, among others, acrylates and styrene by copolymerizing these monomers in the presence of R-methylsubstituted comonomers, such as R-methylstyrene and methyl methacrylate.11 We now wish to report on a new process leading to macromonomers of structure 2 and 3 based on monosubstituted monomers which does not require the use of an added Chain Transfer agent or an R-methyl-substituted vinyl monomer as comonomer.12 In this communication, we describe the preparation of polyacrylate and polystyrene macromonomers using this process.

  • Control of polymer structure by Chain Transfer processes
    Macromolecular Symposia, 1996
    Co-Authors: Ezio Rizzardo, Y K Chong, Richard A. Evans, Graeme Moad And And, San H. Thang
    Abstract:

    Chain Transfer can be performed effectively by a mechanism of addition-fragmentation with appropriately substituted allylic compounds, vinyl ethers and thionoesters. Selection of substituents allows the optimization of Chain Transfer activity and the preparation of macromonomers and other end-functional polymers from acrylates, methacrylates, styrene and vinyl acetate. The addition-fragmentation concept has been extended to the free radical ring-opening polymerization of cyclic allylic sulfides.

  • New Chain Transfer agents for free radical polymerizations
    Polymer International, 1991
    Co-Authors: Gordon Francis Meijs, Ezio Rizzardo
    Abstract:

    The palmitoyl ester of N-hydroxypyridine-2-thione displayed useful Chain Transfer properties in free radical polymerizations of methyl methacrylate and styrene. Retardation, however, accompanied the lowering of molecular weight in methyl acrylate and vinyl acetate polymerizations. 4-Methyl-3-palmitoyloxythiazol-2(3H)-thione had good Chain Transfer activity with methyl methacrylate, styrene and methyl acrylate. Although benzyl thionobenzoate exhibited virtually ‘ideal’ behaviour (Chain Transfer constant Cx ∼1) in styrene and methyl acrylate polymerizations, it was ineffective in lowering molecular weight of poly(methyl methacrylate). Severe retardation was observed with vinyl acetate. Addition-fragmentation pathways are postulated for Chain Transfer.

Thomas P Davis - One of the best experts on this subject based on the ideXlab platform.

  • ambient temperature reversible addition fragmentation Chain Transfer polymerisation
    Chemical Communications, 2001
    Co-Authors: John F Quinn, Ezio Rizzardo, Thomas P Davis
    Abstract:

    Reversible addition fragmentation Chain Transfer was performed at ambient temperature for the first time.

  • The role of monomer in the Chain Transfer reaction in cobaloxime‐mediated free‐radical polymerization
    Macromolecular Rapid Communications, 1999
    Co-Authors: Johan P. A. Heuts, Darren J. Forster, Thomas P Davis
    Abstract:

    The role of monomer in catalytic Chain Transfer polymerization was studied by determination of the Chain Transfer constants of the tetraphenyl derivative of cobaloxime boron fluoride (COPhBF) in methyl methacrylate at 60 degrees C varying the monomer concentration instead of the COPhBF concentration as is common practice. Toluene and tert-butyl acetate were used as diluents in these studies and it was found that the Chain Transfer constants obtained in the present studies were not significantly different from those observed in conventional experiments. These results suggest the absence of a direct participation of monomer molecules in the hydrogen abstraction step in catalytic Chain Transfer.

  • The Effects of Ester Chain Length and Temperature on the Catalytic Chain Transfer Polymerization of Methacrylates
    Macromolecules, 1999
    Co-Authors: Johan P. A. Heuts, Darren J. Forster, Thomas P Davis
    Abstract:

    The catalytic Chain Transfer polymerizations of methyl, ethyl, and butyl methacrylates were studied over the temperature range 40−70 °C with cobaloxime boron fluoride (COBF) and its tetraphenyl derivative (COPhBF). It was found that for both catalytic Chain Transfer agents the Chain Transfer constant decreases in going from methyl to butyl methacrylate, and that there is no significant temperature effect on the observed Chain Transfer constants. The results are consistent with a diffusion-controlled rate coefficient for the Chain Transfer reaction.

  • Copolymerization of styrene and α-methylstyrene in the presence of a catalytic Chain Transfer agent
    Macromolecules, 1998
    Co-Authors: Dax Kukulj, Johan P. A. Heuts, Thomas P Davis
    Abstract:

    Copolymerizations of styrene (STY) and α-methylstyrene (AMS) have been performed at different monomer feed compositions and temperatures (40−70 °C) in the presence of the catalytic Chain Transfer agent bis(boron difluorodimethylglyoximate)cobaltate(II) (COBF). The average Chain Transfer constant, 〈CS〉, was found to increase approximately 3 orders of magnitude upon going from pure STY to pure AMS. The addition of only 10% AMS increased the 〈CS〉 by 1 order of magnitude. This behavior can be predicted from the relative fractions of growing radical end groups, which results in the majority of polymer Chains being formed with an unsaturated AMS end group. No significant penultimate unit effects in the Chain Transfer reaction were observed. The addition of 10−20% AMS results in the majority of the growing radicals having AMS end groups, and hence AMS dominates the catalytic Chain Transfer reaction. The 〈CS〉 values continue to increase as the AMS content is increased beyond 20%; however, this can be mostly attri...

  • Copolymerization of Styrene and Methyl Methacrylate in the Presence of a Catalytic Chain Transfer Agent
    Macromolecules, 1998
    Co-Authors: Johan P. A. Heuts, Darren J. Forster, Dax Kukulj, Thomas P Davis
    Abstract:

    Copolymerizations of styrene and methyl methacrylate have been performed using different monomer feed compositions in the presence of a catalytic Chain Transfer agent at 40 C. Average Chain Transfer constants as a function of monomer feed composition were determined with the conventional Mayo procedure using both number (Mn) and weight (Mw) average molecular weights, and with the Chain length distribution procedure using both high (H) and peak (P) molecular weight slopes. It is found that the average Chain Transfer constants determined from Mw and P are generally very similar, with those obtained from Mn and H being larger and smaller, respectively. The average Chain Transfer constants obtained from Mw and P are compared with model predictions based upon both the terminal and penultimate unit models of free-radical copolymerization and are in satisfactory agreement. These two models are used to predict the fraction of propagating radicals with a terminal styrene unit, and it is found, similar to earlier s...

San H Thang - One of the best experts on this subject based on the ideXlab platform.

Youliang Zhao - One of the best experts on this subject based on the ideXlab platform.

  • reversible addition fragmentation Chain Transfer graft polymerization mediated by fumed silica supported Chain Transfer agents
    Macromolecules, 2007
    Co-Authors: Youliang Zhao, Sébastien Perrier
    Abstract:

    In this study, the Z supported reversible addition−fragmentation Chain Transfer (RAFT) graft polymerization to prepare silica-polymer hybrids was investigated. Two Chain Transfer agents (CTAs), S-benzyl S‘-trimethoxysilylpropyltrithiocarbonate and S-methoxycarbonylphenylmethyl S‘-trimethoxysilylpropyltrithiocarbonate, were synthesized and covalently attached to the surface of fumed silica. The resultant silica supported CTAs were used to mediate RAFT polymerization of vinyl monomers such as methyl acrylate, butyl acrylate, N,N-dimethylacrylamide, N-isopropylacrylamide, methyl methacrylate, and styrene in the presence of a free CTA to synthesize polymer grafted silica particles. Effects of CTA loadings on solid supports, types of free CTAs, and reaction media on graft polymerization were investigated in detail. Under optimal conditions such as using 2-(2-cyanopropyl)dithiobenzoate as a free CTA and controlling the polymerization at a low conversion (typically less than 40%), well-defined polymeric Chains w...

  • Reversible Addition−Fragmentation Chain Transfer Graft Polymerization Mediated by Fumed Silica Supported Chain Transfer Agents
    Macromolecules, 2007
    Co-Authors: Youliang Zhao, Sébastien Perrier
    Abstract:

    In this study, the Z supported reversible addition−fragmentation Chain Transfer (RAFT) graft polymerization to prepare silica-polymer hybrids was investigated. Two Chain Transfer agents (CTAs), S-benzyl S‘-trimethoxysilylpropyltrithiocarbonate and S-methoxycarbonylphenylmethyl S‘-trimethoxysilylpropyltrithiocarbonate, were synthesized and covalently attached to the surface of fumed silica. The resultant silica supported CTAs were used to mediate RAFT polymerization of vinyl monomers such as methyl acrylate, butyl acrylate, N,N-dimethylacrylamide, N-isopropylacrylamide, methyl methacrylate, and styrene in the presence of a free CTA to synthesize polymer grafted silica particles. Effects of CTA loadings on solid supports, types of free CTAs, and reaction media on graft polymerization were investigated in detail. Under optimal conditions such as using 2-(2-cyanopropyl)dithiobenzoate as a free CTA and controlling the polymerization at a low conversion (typically less than 40%), well-defined polymeric Chains w...