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Macromolecular Chemistry and Physics 02/2011; 212(7):699 - 707. · 2.36 Impact Factor
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Macromolecular Reaction Engineering 12/2010; 4(11‐12):691 - 706. · 1.85 Impact Factor
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ABSTRACT: A penultimate model of acrylate polymerization has been proposed to account for reduced reactivity of radicals formed by monomer addition to midchain radicals. New expressions derived for polymerization rate, number-average degree of polymerization and branching level are used for a comparative analysis of the penultimate and terminal models. The penultimate model has been also implemented into the simulation program PREDICI to conduct a comparative analysis of time dependencies of conversion, cumulative number-degree of polymerization and cumulative branching levels calculated for the different models. The calculations show that, depending on radical reactivity ratio s(i) and monomer concentrations, the predictions from the penultimate model significantly deviate from those of the terminal model.
Macromolecular Rapid Communications 12/2009; 30(23):1981-8. · 4.60 Impact Factor
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ABSTRACT: n-Butyl acrylate (BA) starved-feed solution semibatch experiments with varying final polymer content and monomer feed times were carried out at 138 °C. A full mechanistic model of the system implemented in Predici includes intermolecular chain transfer to polymer and macromonomer propagation as well as backbiting, chain scission, and midchain radical propagation and termination. The importance of macromonomer propagation under these conditions of industrial interest is illustrated by experiment and simulation, with the macromonomer reaction responsible for the significant increase in polymer weight-average molecular weight ($\overline M _{\rm w}$) with time. Rate coefficients for macromonomer propagation (k(mac) ) and β-scission (k(β) ) of k(mac) /k(p) = 0.55 and k(β) = 12 s(-1) (with k(p) the rate coefficient for BA chain-end propagation) provide a good representation of experimental $\overline M _{\rm w}$ and macromonomer end group data at 138 °C.
Macromolecular Rapid Communications 12/2009; 30(23):2022-7. · 4.60 Impact Factor
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ABSTRACT: A novel method to extract individual free-radical polymerization rate coefficients for butyl acrylate intramolecular chain transfer (backbiting), kbb, and for monomer addition to the resulting midchain radical, , is presented. The approach for measuring kbb does not require knowledge of any other rate coefficient. Only the dispersion parameter of SEC broadening has to be determined by fitting measured MWDs or should be available from separate experiments. The method is based upon analysis of the shift in the position of the inflection point of polymer molecular weight distributions produced by a series of pulsed-laser polymerization (PLP) experiments with varying laser pulse repetition rate. The coefficient kbb is determined from the onset of the sharp decrease of the apparent propagation rate coefficient ( ) with decreasing repetition rate, an approach verified by simulation. With experiments performed between −10 and +30 °C, the estimated values are fitted well by an Arrhenius relation with pre-exponential factor A(kbb) = (4.84 ± 0.29) × 107 s-1 and activation energy Ea(kbb) = (31.7 ± 2.5) kJ·mol-1. At low pulse repetition rates, the experimental values are related to an averaged propagation rate coefficient, , that is dependent on the relative population of chain-end and midchain radicals. Evaluated by comparing simulated and experimental molecular weight distributions, provides an estimate for . The Arrhenius parameters are: A( ) = (1.52 ± 0.14) × 106 L·mol-1·s-1 and Ea( ) = (28.9 ± 3.2) kJ·mol-1.
11/2007;
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Macromolecular Theory and Simulations 01/2007; 16(1):29 - 42. · 1.71 Impact Factor
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ABSTRACT: New expressions that account for the formation of acrylate midchain radicals by intramolecular transfer and their subsequent propagation, termination, and transfer events have been derived for polymerization rate, average chain-length, and chain-length distribution under stationary conditions. The nonidealities observed in previous kinetic studies are captured in a single lumped rate coefficient, θ, that controls the apparent order of rate on monomer concentration. Applied to rate data from the literature, the treatment yields consistent estimates for θ and kp/kt0.5 for butyl acrylate polymerization at 50 °C. Combining these ratios with chain-end propagation values determined by pulsed-laser polymerization, intramolecular transfer rate coefficients estimated from 13C NMR data, and/or radical concentrations measured by ESR provides a new means to estimate the individual rate coefficients for acrylate polymerization systems. It is also shown that estimates for butyl acrylate transfer to monomer rate coefficients obtained from chain-length distributions are valid even in the presence of acrylate backbiting events.
01/2005;
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José M. Asua,
Sabine Beuermann,
Michael Buback,
Patrice Castignolles,
Bernadette Charleux,
Robert G. Gilbert,
Robin A. Hutchinson,
José R. Leiza, Anatoly N. Nikitin,
Jean-Pierre Vairon,
Alex M. van Herk
Macromolecular Chemistry and Physics 10/2004; 205(16):2151 - 2160. · 2.36 Impact Factor
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Macromolecular Theory and Simulations 12/2002; 11(9):961 - 968. · 1.71 Impact Factor
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ABSTRACT: A new approach for the simulation of PLP (pulsed laser polymerization) is presented. This approach allows one to obtain new analytical solutions for different polymerization schemes, including either chain transfer to the monomer or intramolecular chain transfer to the polymer. The first results of the simulation of PLP experiments on n-butyl acrylate at 20 °C and ambient pressure are presented.
