Concentration Dependence of the Termination Rate Constant During the Initial Stages of Free Radical Polymerization

Mahabadi, H. K.; O’Driscoll, K. F.

doi:10.1021/ma60055a009

Cited by 90 publications

(39 citation statements)

References 2 publications

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“…[22] These changes may result from an interplay of thermodynamic and transport properties, as has been discussed by Mahabadi and O'Driscoll. [35,36] Also of appreciable interest are studies into the chainlength dependence of the termination rate coefficient carried out within extended ranges of pressure, temperature, and monomer conversion.…”

Section: Resultsmentioning

confidence: 99%

Termination Kinetics of Methyl Acrylate and Dodecyl Acrylate Free-Radical Homopolymerizations up to High Pressure

Buback

Kuelpmann

Kurz

2002

Macromol. Chem. Phys.

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Section: Resultsmentioning

confidence: 99%

Termination Kinetics of Methyl Acrylate and Dodecyl Acrylate Free-Radical Homopolymerizations up to High Pressure

Buback

Kuelpmann

Kurz

2002

Macromol. Chem. Phys.

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“…[23] This only reinforces the important point that one should always expect k t to vary with (monomer) conversion, x, and one should speak of k t (x). It is this potential variation right from the beginning of polymerization which distinguishes k t from k p and initiator decomposition rate coefficients, k d , both of which are generally chemically controlled and so are usually constant in value throughout most of the conversion range, and thus are much more easily described for modeling purposes.…”

Section: Conversion Dependencementioning

confidence: 90%

Critically Evaluated Termination Rate Coefficients for Free‐Radical Polymerization, 1. The Current Situation

Buback

Egorov

Gilbert

et al. 2002

Macro Chemistry & Physics

184

213

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This is the first publication of an IUPAC‐sponsored Task Group on “Critically evaluated termination rate coefficients for free‐radical polymerization.” The paper summarizes the current situation with regard to the reliability of values of termination rate coefficients kt. It begins by illustrating the stark reality that there is large and unacceptable scatter in literature values of kt, and it is pointed out that some reasons for this are relatively easily remedied. However, the major reason for this situation is the inherent complexity of the phenomenon of termination in free‐radical polymerization. It is our impression that this complexity is only incompletely grasped by many workers in the field, and a consequence of this tendency to oversimplify is that misunderstanding of and disagreement about termination are rampant. Therefore this paper presents a full discussion of the intricacies of kt: sections deal with diffusion control, conversion dependence, chain‐length dependence, steady state and non‐steady state measurements, activation energies and activation volumes, combination and disproportionation, and theories. All the presented concepts are developed from first principles, and only rigorous, fully‐documented experimental results and theoretical investigations are cited as evidence. For this reason it can be said that this paper summarizes all that we, as a cross‐section of workers in the field, agree on about termination in free‐radical polymerization. Our discussion naturally leads to a series of recommendations regarding measurement of kt and reaching a more satisfactory understanding of this very important rate coefficient. Variation of termination rate coefficient kt with inverse absolute temperature T−1 for bulk polymerization of methyl methacrylate at ambient pressure.[6] The plot contains all tabulated values[6] (including those categorized as “recalculated”) except ones from polymerizations noted as involving solvent or above‐ambient pressures.magnified imageVariation of termination rate coefficient kt with inverse absolute temperature T−1 for bulk polymerization of methyl methacrylate at ambient pressure.[6] The plot contains all tabulated values[6] (including those categorized as “recalculated”) except ones from polymerizations noted as involving solvent or above‐ambient pressures.

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“…While k t is relatively constant over such low-conversion intervals for monomers like MMA and STY, in fact, for thermodynamic reasons, a slight increase in k t takes place as polymer is formed, typically by about 20%. [58] Further, the longer the chains, the stronger this effect. Thus at low c I this effect will be strongest, while at high c I it will be weakest.…”

Section: Variation Of K T With Initiator Concentrationmentioning

confidence: 99%

Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

Taylor

Berkel

Alghamdi

et al. 2010

Macro Chemistry & Physics

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A comprehensive and systematic study of overall termination rate coefficients, k t , in low-conversion radical (homo)polymerization of methyl methacrylate and styrene is presented. Values of k t were determined by gravimetric analysis of steady-state experiments, employing 2,2'-azoisobutyronitrile as initiator. The values delivered by this simple method were found to be in qualitative and quantitative agreement with those from more modern and sophisticated techniques for measuring k t . Accordingly, correlations for bulk, low-conversion k t as a function of temperature are given for each monomer. The effects of initiator concentration, c I , and temperature on bulk k t were studied in a controlled way for both monomers. Additionally, ethyl benzene was used as solvent in order to investigate rigorously the effect of monomer concentration, c M , on styrene k t . The trends found by these systematic studies were considered in the light of what is known about the chain-length dependence of 2 termination. Styrene's behavior was always found to be qualitatively in accord with expectation, although the variations of k t with c I and c M were not as strong as should be the case. However its activation energy, 15 kJ·mol -1 , is shown to be almost perfectly in agreement with theory. Methyl methacrylate, on the other hand, is recalcitrant in that its overall k t does not make manifest the chain-length dependent termination that has been directly measured by other techniques. Possible reasons for these discrepancies are discussed, as are reasons for the difference in values between k t for the two monomers. On the latter topic it is concluded likely that the chain-length dependence of termination at short chain lengths is primarily responsible for styrene having k t that is higher by a factor of about 3, with there also being a contribution that arises from styrene's slower propagation.

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Concentration Dependence of the Termination Rate Constant During the Initial Stages of Free Radical Polymerization

Cited by 90 publications

References 2 publications

Termination Kinetics of Methyl Acrylate and Dodecyl Acrylate Free-Radical Homopolymerizations up to High Pressure

Termination Kinetics of Methyl Acrylate and Dodecyl Acrylate Free-Radical Homopolymerizations up to High Pressure

Critically Evaluated Termination Rate Coefficients for Free‐Radical Polymerization, 1. The Current Situation

Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

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