Critically evaluated termination rate coefficients for free-radical polymerization: Experimental methods

Barner‐Kowollik, Christopher; Buback, Michael; Egorov, Mark; Fukuda, Takeshi; Goto, Atsushi; Olaj, Oskar Friedrich; Russell, Gregory T.; Vana, Philipp; Yamada, Bunichiro; Zetterlund, Per B.

doi:10.1016/j.progpolymsci.2005.02.001

“…1, where 〈k t 〉 is the chain-length averaged termination rate coefficient and 〈k p 〉 is the chainlength averaged propagation rate coefficient for the given system. The use of a systemdependent 〈k t 〉 instead of an (incorrect) single chain-length independent value of k t in this equation seems to be generally accepted now, [1,2] but as we have shown previously and will elaborate upon in this paper, in certain cases the use of 〈k p 〉 instead of the long-chain k p value is also required. [3][4][5] [M] [I] …”

Section: Introductionmentioning

confidence: 91%

The Importance of Chain‐Length Dependent Kinetics in Free‐Radical Polymerization: A Preliminary Guide

Heuts¹,

Russell²,

Smith³

et al. 2007

Macromolecular Symposia

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Summary:The effect of chain-length dependent propagation at short chain lengths on the observed kinetics in low-conversion free-radical polymerization (frp) is investigated. It is shown that although the values of individual propagation rate coefficients quickly converge to the high chain length value (at chain lengths, i, of about 10), its effect on the average propagation rate coefficients, 〈k p 〉, in conventional frp may be noticeable in systems with an average degree of polymerization (DP n ) of up to 100. Furthermore it is shown that, unless the system is significantly retarded, the chain-length dependence of the average termination rate coefficient, 〈k t 〉, is not affected by the presence of chain-length dependent propagation and that there exists a simple (fairly general) scaling law between 〈k t 〉 and DP n . This latter scaling law is a good reflection of the dependence of the termination rate coefficient between two imeric radicals, k t i,i , on i. Although simple expressions seem to exist to describe the dependence of 〈k p 〉 on DP n , the limited data available to date does not allow the generalization of these expressions.

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“…The reason for this is not just the greater difficulty of measuring termination rate coefficients, [17] but even more so is the sheer complexity of these systems compared with those in which backbiting does not occur. To wit, in acrylate polymerizations there are three different termination reactions contributing to the overall termination rate: SPR homotermination, rate coefficient k t s,s ; MCR homotermination, k t t,t ; and SPR-MCR cross-termination, k t s,t…”

Section: Introductionmentioning

confidence: 99%

“…There is the general consideration that this method is held to be the best available method for probing CLDT, [17] because it directly measures radical concentration, as opposed to doing so indirectly via conversion-time measurements. It also has specific advantages over the RAFTbased methods, namely: SP PLP EPR does not rely on increasing conversion to effect change in chain length, but instead can deliver k t i,i at a constant conversion; and in SP PLP EPR there is not the complicating possibility of a contribution to the overall rate of termination in cases where cross-termination between the RAFT intermediate and propagating radicals occurs.…”

Section: Introductionmentioning

confidence: 99%

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Barth

¹

,

Buback

²

,

Russell

³

et al. 2011

Macro Chemistry & Physics

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SUMMARY:The technique of SP PLP EPR, which is single-pulse pulsed-laser polymerization (SP PLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy, is used to carry out a detailed investigation of secondary (chain-end) radical termination of acrylates. Measurements are performed on methyl acrylate, n-butyl acrylate and dodecyl acrylate in bulk and in toluene solution at -40 °C. The reason for the low temperature is to avoid formation of mid-chain radicals, a complicating factor that has imparted ambiguity to the results of previous studies of this nature. Consistent with these previous studies, composite-model behavior for chain-length-dependent termination rate, is found in this work. However, lower and more reasonable values of α s , the exponent for variation of k t i,i at short chain lengths, are found in the present study.

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“…1, where 〈k t 〉 is the chain-length averaged termination rate coefficient and 〈k p 〉 is the chainlength averaged propagation rate coefficient for the given system. The use of a systemdependent 〈k t 〉 instead of an (incorrect) single chain-length independent value of k t in this equation seems to be generally accepted now, [1,2] but as we have shown previously and will elaborate upon in this paper, in certain cases the use of 〈k p 〉 instead of the long-chain k p value is also required. [3][4][5] [M]…”

Section: Introductionmentioning

confidence: 91%

The Importance of Chain‐Length Dependent Kinetics in Free‐Radical Polymerization: A Preliminary Guide

Heuts¹,

Russell²,

Smith³

et al. 2007

Radical Polymerization

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Summary:The effect of chain-length dependent propagation at short chain lengths on the observed kinetics in low-conversion free-radical polymerization (frp) is investigated. It is shown that although the values of individual propagation rate coefficients quickly converge to the high chain length value (at chain lengths, i, of about 10), its effect on the average propagation rate coefficients, 〈k p 〉, in conventional frp may be noticeable in systems with an average degree of polymerization (DP n ) of up to 100. Furthermore it is shown that, unless the system is significantly retarded, the chain-length dependence of the average termination rate coefficient, 〈k t 〉, is not affected by the presence of chain-length dependent propagation and that there exists a simple (fairly general) scaling law between 〈k t 〉 and DP n . This latter scaling law is a good reflection of the dependence of the termination rate coefficient between two imeric radicals, k t i,i , on i. Although simple expressions seem to exist to describe the dependence of 〈k p 〉 on DP n , the limited data available to date does not allow the generalization of these expressions.

show abstract

Critically evaluated termination rate coefficients for free-radical polymerization: Experimental methods

Cited by 136 publications

References 104 publications

The Importance of Chain‐Length Dependent Kinetics in Free‐Radical Polymerization: A Preliminary Guide

The Importance of Chain‐Length Dependent Kinetics in Free‐Radical Polymerization: A Preliminary Guide

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

The Importance of Chain‐Length Dependent Kinetics in Free‐Radical Polymerization: A Preliminary Guide

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