Remark on the paper by R. L. Herbst, Jr., and R. E. Martin, entitled “relative reactivities of polymer radicals in vinyl polymerizations” (original) (raw)
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Molecular Aspects of Radical Polymerizations-The Propagation Frequency
Macromolecular Rapid Communications, 2010
The product of the propagation rate constant and monomer concentration is a central issue of radical polymerization. Both quantities are strongly interrelated as the determination of a reliable value of the propagation rate constant requires exact knowledge of the monomer concentration. Even for homogeneous polymerization conditions, exact knowledge of the monomer concentration at the reaction site from the molecular perspective is not trivial. For emulsion polymerizations the situation is additionally complicated by mass transfer events and colloidchemical effects. Molecular modeling appears as an attractive alternative or complement to the deterministic kinetic description of radical polymerizations.
Critically Evaluated Rate Coefficients for Free-Radical Polymerization, 4
Macromolecular Chemistry and Physics, 2003
Pulsed-laser polymerization (PLP) in conjugation with molecular weight distribution (MWD) measurement has emerged as the method of choice for determining the propagation rate coefficient k, in free-radical polymerizations. Detailed guidelines for using this technique (including essential internal consistency checks) and reporting the results therefrom are given by the authors, members of the IUPAC Working Party on Modeling of kinetics and processes of polymerization. The results for PLP-MWD k, measurements from many laboratories for bulk free-radical polymerization of styrene at low conversions and ambient pressure are collated, and are in excellent agreement. They are therefore recommended as constituting a benchmark data set, one that is best fitted by (the confidence ellipsoid for the Arrhenius parameters is also given). These benchmark data are also used to evaluate the merits of several other methods for determining k,; it is found that appropriately calibrated electron paramagnetic resonance spectroscopy appears to yield reliable values of k, for styrene. 0 1995, Hiithig &
Critically Evaluated Rate Coefficients for Free-Radical Polymerization, 5
Macromolecular Chemistry and Physics, 2004
Pulsed-laser polymerization (PLP) in conjugation with molecular weight distribution (MWD) measurement has emerged as the method of choice for determining the propagation rate coefficient k, in free-radical polymerizations. Detailed guidelines for using this technique (including essential internal consistency checks) and reporting the results therefrom are given by the authors, members of the IUPAC Working Party on Modeling of kinetics and processes of polymerization. The results for PLP-MWD k, measurements from many laboratories for bulk free-radical polymerization of styrene at low conversions and ambient pressure are collated, and are in excellent agreement. They are therefore recommended as constituting a benchmark data set, one that is best fitted by (the confidence ellipsoid for the Arrhenius parameters is also given). These benchmark data are also used to evaluate the merits of several other methods for determining k,; it is found that appropriately calibrated electron paramagnetic resonance spectroscopy appears to yield reliable values of k, for styrene. 0 1995, Hiithig &
Polymer, 1975
The reactivity ratios for the free radical copolymerization of styrene and methyl methacrylate at 50°C have been evaluated in dioxane, acetone and dimethylformamide solutions. In all these systems there is a marked solvent effect on both r 1 and r 2, which can be correlated to the variation in the dielectric constant of the solvent. The role of solvents in enhancing the polarization of growing chains and the alternation tendency is discussed.
Vinyl pivalate Propagation Kinetics in Radical Polymerization
Macromolecular Chemistry and Physics, 2016
Radical propagation kinetics of the bulk homopolymerizations of vinyl pivalate (VPi) and vinyl benzoate (VBz) have been studied using pulsed-laser polymerization (PLP) combined with size exclusion chromatography (SEC). As part of the study, the Mark-Houwink parameters of poly(VPi) and poly(VBz) in tetrahydrofuran were determined using a triple detector SEC. The observed significant increase (by approximately 20%) of the bulk VPi propagation rate coefficient (kp) as pulse repetition rate is increased from 200 to 500 Hz is similar to that reported for vinyl acetate (VAc). Data collected in the temperature range of 25 to 85 °C for VPi is well fit by the Arrhenius relation ln(kp/Lꞏmol1ꞏs1)= 15.73 2093(T/K). The activation energy is similar to that found for vinyl acetate (VAc), with kp values higher by ~50%. PLP studies in ethyl acetate and in heptane found no substantial solvent effect on VPi or VAc kp values. Attempts to measure the propagation kinetics of VBz by PLP were not succ...
Kinetics, thermodynamics, and monomer reactivities in radical polymerization of α-acetoxystyrene
Macromolecules, 1990
The radical polymerization behavior of a-acetoxystyrene (ACOST) was investigated in toluene, using a,a'-azobis(isobutyronitri1e) (AIBN) as the initiator. The polymerization of ACOST is an equilibrium process with a ceiling temperature (T,) of 47 "C at 1 mol/L of monomer due to the steric hindrance. The rate of polymerization (R,) can be expressed by R, = k[AIBN]o.46([M]-[M]J1.O, considering the depolymerization process with an equilibrium monomer concentration of [MIe. The overall activation energy has been determined to be 116 kJ/mol. The enthalpy of polymerization and entropy of polymerization obtained from a linear relationship between In [MIe and 1/Tare-26.5 kJ/mol and-82.6 J/(K.mol), respectively. The T, is low because of the low AHp but high enough to allow radical homopolymerization owing to the low AS,, which is significantly lower than the typical values (-100 to-125 J/(K.mol)) for vinyl monomers. Monomer reactivity ratios of bulk copolymerization of ACOST (M2) with methyl methacrylate (MMA, MI) are rl = 0.644 and r2 = 0.754, respectively, at 60 O C. The temperature dependence (50-80 "C) of the reactivity ratios has revealed that the copolymerization mechanism can be adequately described by the Mayo-Lewis model; a depolymerization process does not have to be taken into consideration in copolymerization. Q and e values of ACOST can be calculated as 0.82 and-0.45 from the reactivity ratios. Although the values seem to be reasonable, the serious steric effect makes their meaning obscure.
Polymer Chemistry, 2013
Propagation rate coefficient (k p ) data for radical polymerization of methyl acrylate (MA) in the bulk are critically evaluated and a benchmark dataset is put forward by a task-group of the IUPAC Subcommittee on Modeling of Polymerization Kinetics and Processes. This dataset comprises previously published results from three laboratories as well as new data from a fourth laboratory. Not only do all these values of k p fulfill the recommended consistency checks for reliability, they are also all in excellent agreement with each other. Data have been obtained employing the technique of pulsed-laser polymerization (PLP) coupled with molar-mass determination by size-exclusion chromatography (SEC), where PLP has been carried out at pulse-repetition rates of up to 500 Hz, enabling reliable k p to be obtained through to 60 C. The best-fitand therefore recommended -Arrhenius parameters are activation energy E A ¼ 17.3 kJ mol À1 and pre-exponential (frequency) factor A ¼ 1.41 Â 10 7 L mol À1 s À1 . These hold for secondary-radical propagation of MA, and may be used to calculate effective propagation rate coefficients for MA in situations where there is a significant population of mid-chain radicals resulting from backbiting, as will be the case at technically relevant temperatures. The benchmark dataset reveals that k p values for MA obtained using PLP in conjunction with MALDI-ToF mass spectrometry are accurate. They also confirm, through comparison with previously obtained benchmark k p values for n-butyl acrylate, methyl methacrylate and n-butyl methacrylate, that there seems to be identical familytype behavior in n-alkyl acrylates as in n-alkyl methacrylates. Specifically, k p for the n-butyl member of each family is about 20% higher than for the corresponding methyl member, an effect that appears to be entropic in origin. Furthermore, each family is characterized by an approximately constant E A , where the value is 5 kJ mol À1 lower for acrylates.