Absolute rate constants for the self-termination of the isopropyl radical and for the decarbonylation of the 2-methylpropanoyl radical

Lipscher, Juraj; Fischer, Hanns

doi:10.1021/j150656a025

Cited by 35 publications

(19 citation statements)

References 7 publications

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“…The same experiment in DMSO under otherwise identical conditions resulted in k t =7.8×10 8 L mol −1 s −1 (Figure b) , indicating that the termination in more viscous DMSO was 7.4 times slower than that in less viscous benzene. The k t values are in good agreement with those reported in previous kinetic studies on benzyl and cumyl radicals, and the observed viscosity effect is also consistent with previous reports on the termination reaction using small radicals …”

Section: Resultssupporting

confidence: 92%

Control of the Termination Mechanism in Radical Polymerization by Viscosity: Selective Disproportionation in Viscous Media

Nakamura

Ogihara

Hatano

et al. 2016

Chemistry A European J

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The termination mechanism of radical polymerization, that is, disproportionation (Disp) versus combination (Comb), determines the chain length and end-group structure of the resulting polymer as well as polymer properties, and yet factors governing the mechanism are still unclear. Furthermore, no attempts have been made to control the mechanism. Here, the effects of temperature and viscosity on the termination of methyl methacrylate (MMA) and styrene (St) polymerization were elucidated by using small molecular model-radicals and the corresponding polymer radicals in various solvents. The results showed that Disp was preferred over Comb if the temperature was decreased and the viscosity of the media was increased for all the radicals examined. Although the temperature effect on the Disp/Comb selectivity is counterintuitive because Disp should be favored entropically over Comb considering the decrease in the number of polymer chains in Comb, the results clearly showed that the observed inverse temperature effect was a result of the viscosity effect. Disp was favored over Comb at lower temperatures and in more viscous solvents because the transition state leading to Disp is more flexible than that for Comb. Because of the significant viscosity effect, Disp selectively occurred in highly viscous solvents; the Disp/Comb selectivity was 97/3 in both MMA and St termination. For the first time, the termination mechanism was intentionally controlled and such a high Disp selectivity was observed. In particular, the termination mechanism in St is described as Comb in textbooks, but nearly complete inversion of the selectivity from Comb to Disp is realized by simply changing the viscosity of the media.

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Section: Resultssupporting

confidence: 92%

Control of the Termination Mechanism in Radical Polymerization by Viscosity: Selective Disproportionation in Viscous Media

Nakamura

Ogihara

Hatano

et al. 2016

Chemistry A European J

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“…But one may envision an activation of the product by photochemical excitation or by another reaction with Ar*. This consideration leads us again to the mechanism used for the above-presented simulations, formulated in Equations (20). 4 3.2 | Peculiarities of atmospheric-pressure plasma polymerization compared with processes at low pressure In the past, the mechanistic interpretation of low-pressure plasma-polymerization experiments has been dominated by the concept of the parameter "W/F" (power divided by monomer flow rate, corresponding to p/Φ in our nomenclature) introduced by Yasuda et al (see reference [34] and earlier papers cited there) and by an equation introduced by Park and Kim in 1990, relating the "Yasuda parameter" (or "reaction parameter") to the deposition rate of pp-HMDSO as the prototype plasma polymer.…”

Section: Improved Growth Model Including Recombination Of Radical Pmentioning

confidence: 98%

DBD‐based plasma polymerization from monomer‐argon mixtures: Analytical model of monomer reactions with excited argon species

Klages

Czerny

Philipp

et al. 2017

Plasma Processes & Polymers

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Experimental studies of DBD‐based atmospheric‐pressure plasma polymerization from mixtures of hexamethyldisiloxane (HMDSO) with argon are presented and interpreted using an analytical model of the plasma‐chemical kinetics. Gradient films are obtained using a special DBD‐PACVD reactor. Growth‐rate profiles and their monomer fraction dependence show that long‐living excited Ar species play a major role in the deposition mechanism. Reactions of HMDSO with metastable and resonance argon atoms as well as argon excimers are considered within the presented model which may be simplified by introducing a lumped excited argon species Ar*. Model predictions are compared with experimental results. Recombination reactions must be included in order to reproduce characteristic features of the measured growth‐rate curves.

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“…Self-and cross-termination rate constants often obey the cross-termination Ansatz (24) k: = 2(k: * k8)"z at least approximately [5,18]. We have tested this relation for t-butyl and t-butoxicarbonyl radicals by time-resolved experiments employing photolysis of t-butylpivalate in butene-l-oxide at the low temperature of 209 K. Under these conditions decarboxylation is unsignificant and good fits of Eqs.…”

Section: (23)mentioning

confidence: 99%

“…The ratio of rate constants was found to be 2 k ; : k ; : 2 k t = 1.65:1.00:0.63 which gives k ; / 2 ( k t * tZ:)1'2 = 0.98 in accord with Eq. (24). Assuming that Eq.…”

Section: (23)mentioning

confidence: 99%

Rate constants for the decarboxylation of the t‐butoxicarbonyl radical and concurring radical terminations directly obtained by kinetic ESR

Rüegge

Fischer

1986

Int J of Chemical Kinetics

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Rate constants of various simultaneous reactions of t-butoxicarbonyl and t-butyl radicals generated by photolysis of t-butylpivalate in n-heptane are directly determined by kinetic electron spin resonance. The temperature dependence of the decarboxylation reaction t-BuOCO + t-Bu + CO, obeys log(k/s-') = 13.8-49.0/8 where 8 = 2.303 RT/ kJ . mol-'. The self-and cross-termination of the radicals are diffusion limited.

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Absolute rate constants for the self-termination of the isopropyl radical and for the decarbonylation of the 2-methylpropanoyl radical

Cited by 35 publications

References 7 publications

Control of the Termination Mechanism in Radical Polymerization by Viscosity: Selective Disproportionation in Viscous Media

Control of the Termination Mechanism in Radical Polymerization by Viscosity: Selective Disproportionation in Viscous Media

DBD‐based plasma polymerization from monomer‐argon mixtures: Analytical model of monomer reactions with excited argon species

Rate constants for the decarboxylation of the t‐butoxicarbonyl radical and concurring radical terminations directly obtained by kinetic ESR

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