Chain-length-dependent termination in radical polymerization: Subtle revolution in tackling a long-standing challenge

Barner‐Kowollik, Christopher; Russell, Gregory T.

doi:10.1016/j.progpolymsci.2009.07.002

Cited by 191 publications

(321 citation statements)

References 186 publications

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“…[23] This prediction of the composite model has been born out for polymerizations with negligible backbiting: as already mentioned, α s is found to be between 0.50 and 0.65 for methacrylates and styrene, with remarkably good agreement between the values from different experimental techniques. [18] Further, these values of α s are consistent with the power-law exponents found in measurements of D i as a function of i for oligomers. [31,32] Given all this it seems reasonable to say that chain-length-dependent termination at low conversion may now be regarded as well understood for methacrylates and styrene polymerization.…”

Section: Introductionsupporting

confidence: 86%

“…For radicals larger in size than a certain crossover chain length i c of around 50, the dependency becomes much weaker, with observed values of α l mostly falling in the range 0.15-0.30. [18] Such values are convincingly in accord with O'Shaughnessy's prediction of α l = 0.16 for control of (longchain) termination by segmental diffusion in a good solvent. [24] The parameter that stimulated the proposal of the composite model is k t 1,1 , the rate coefficient for termination between two monomeric radicals.…”

Section: Introductionsupporting

confidence: 81%

“…On the other hand, the error margin in k t 1,1 , which is essentially given by the quality of calibrating radical concentration, has been conservatively estimated to be 30 % on the basis of the above limitations. While this may seem disappointing, it has to be seen in the context of k t 1,1 being difficult to measure at all: [18] in fact the present values are highly accurate and precise by historical standards.…”

Section: Data Analysis and Resultsmentioning

confidence: 95%

“…In fact matters are even more complicated than this, because one should additionally allow for these individual termination rate coefficients to depend on the chain lengths of the radical species involved [18] and, just as importantly, the conversion of monomer into polymer.…”

Section: Introductionmentioning

confidence: 99%

“…[18] It is that the so-called composite model for termination, Equation (1), [23] seems to be obeyed for all monomers:…”

Section: Introductionmentioning

confidence: 99%

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Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Barth

Buback

Russell

et al. 2011

Macro Chemistry & Physics

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147

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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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Section: Introductionsupporting

confidence: 86%

Section: Introductionsupporting

confidence: 81%

Section: Data Analysis and Resultsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

“…[18] It is that the so-called composite model for termination, Equation (1), [23] seems to be obeyed for all monomers:…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Barth

Buback

Russell

et al. 2011

Macro Chemistry & Physics

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147

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Kinetics of Radical Polymerization

Russell¹

2010

Encyclopedia of Polymer Science and Technology

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This contribution expounds the principles of radical polymerization (RP) kinetics. It emphasizes the defining population‐balance equations and shows how everything springs from them. As far as possible, an equation‐ rather than modeling‐based approach is advocated, because this provides much greater understanding of kinetics. Numerous examples in support of this philosophy are presented. The treatment covers both steady‐state and nonsteady‐state polymerization and also presents some of the extra considerations involved in acrylate polymerization, copolymerization, and emulsion polymerization. Methods for measuring the values of rate coefficients are naturally elucidated in the wider context of RP kinetics in general. The strengths and limitations of equations and methods are made clear. It is argued that very little defies explanation when proper attention is given to the necessary fundamentals.

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Kinetics of Polymerizations

Buback

Russell

2012

Encyclopedia of Radicals in Chemistry, Biology and Materials

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First of all, the machinery for treating radical polymerization (RP) kinetics is presented. On the one hand, this involves kinetic descriptions that may be implemented without undue difficulty and that account for subtle but pivotal phenomena such as chain‐length‐dependent termination and penultimate‐unit effects in copolymerization. At the same time, this machinery also includes reliable, probing experimental methods for measuring rate coefficients. It is then shown how these tools have been used to develop mechanistic understanding of the fundamental RP reactions, which are initiation, propagation, termination, and chain transfer. In the case of propagation, there is a particular emphasis on entropic effects arising from hindered rotations, while with termination the composite model for chain‐length dependence is stressed, as is variation of overall termination rate coefficient with conversion. Finally, it is shown that chain transfer to polymer and β‐scission are recurring and important motifs in many RP systems. All in all, a pleasing picture of a scientifically maturing field is revealed as taking shape.

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Chain-length-dependent termination in radical polymerization: Subtle revolution in tackling a long-standing challenge

Cited by 191 publications

References 186 publications

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Kinetics of Radical Polymerization

Kinetics of Polymerizations

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