1-heptene, 3-heptenes and cumene as model compounds of SBS block copolymers. Study of their photoreactions in the presence of photoinitiators of polymerization

Bosch, Paula; Mateo, J. L.; Serrano, J.

doi:10.1016/s1010-6030(96)04510-8

Cited by 12 publications

(10 citation statements)

References 8 publications

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“…This phenomenon was first explained in 1934 by Franck and Rabinowitch, who described the solvent cage as a hole in the solvent that temporarily traps two reactive molecules together until random motion allows their separation (Scheme ). − The “radical cage effect” successfully explains many aspects of radical chemistry, including magnetic isotope effects, , radical polymerization kinetics, − cobalamin reactivity, product distributions in photochemistry, stereochemistry of rearrangements, , the reactivity of halogenase analogues, and chemically induced dynamic nuclear polarization effects (CIDNP). , In addition to the solution phase, the cage effect has been observed to occur in solid state films, , inside micelles, as well as in compressed and supercritical gases . New reports of the radical cage effect appear frequently in the literature. − …”

Section: Introductionmentioning

confidence: 99%

Radical Cage Effects: The Prediction of Radical Cage Pair Recombination Efficiencies Using Microviscosity Across a Range of Solvent Types

2017

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This study reports a method for correlating the radical recombination efficiencies (F cP ) of geminate radical cage pairs to the properties of the solvent. Although bulk viscosity (macroviscosity) is typically used to predict or interpret radical recombination efficiencies, the work reported here shows that microviscosity is a much better parameter. The use of microviscosity is valid over a range of different solvent system types, including nonpolar, aromatic, polar, and hydrogen bonding solvents. In addition, the relationship of F cP to microviscosity holds for solvent systems containing mixtures of these solvent types. The microviscosities of the solvent systems were straightforwardly determined by measuring the diffusion coefficient of an appropriate probe by NMR DOSY spectroscopy. By using solvent mixtures, selective solvation was shown to not affect the correlation between F cP and microviscosity. In addition, neither solvent polarity nor radical rotation affects the correlation between F cP and the microviscosity.

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Section: Introductionmentioning

confidence: 99%

Radical Cage Effects: The Prediction of Radical Cage Pair Recombination Efficiencies Using Microviscosity Across a Range of Solvent Types

2017

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“… , Radical cage effects have an enormous impact on chemical reactivity in solution. , In particular, they are necessary to explain a host of kinetic observations and fundamental reaction phenomena. For example, cage effects are necessary to explain magnetic isotope , and CIDNP , effects, rate-viscosity correlations, variations in products and yields as a function of medium, , variations in quantum yields as a function of medium, and regio- and stereochemical control. − Examples of important reactions where cage effects are necessary to explain the kinetics include the initiation, propagation, and termination steps of radical polymerization reactions, − the reactions of coenzyme B 12 and its model complexes, ,− the reactions of hemes with O 2 , and various electron transfer reactions. − New observations of cage effects and their impact on reactivity are reported regularly. − …”

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confidence: 99%

Radical Cage Effects: Comparison of Solvent Bulk Viscosity and Microviscosity in Predicting the Recombination Efficiencies of Radical Cage Pairs

2016

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This study reports the results of experiments that probed how solvents affect the recombination efficiency (FcP) of geminate radical cage pairs. The macroviscosity of solvents has traditionally been used to make quantitative predictions about FcP, but experiments reported here show that FcP varies dramatically for solvent systems with identical macroviscosities. Experiments show that FcP correlates with the solvent microviscosity: five different solvent systems (consisting of a solvent and a structurally similar viscogen) were examined, and FcP was the same for all five solvent systems at any particular microviscosity. The translational diffusion coefficient of the radicals (measured by DOSY) in the solvent system was used to define the microviscosity of the solvent system.

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“…On the other hand, phenomena of electronic energy transfer [16,17] have been indicated to be highly efficient under UV ablation and may be partly responsible for the change in the photochemistry. Alternatively, because the integrity of the substrate is significantly affected in the ablation regime, the rapid deactivation and/or cage effects [18,19] that limit the fragmentation efficiency of the chromophores at lower fluences may be less stringent under ablation conditions. Not only is there a change in the photolysis yield, but also different products are observed above and below the ablation threshold.…”

Section: Resultsmentioning

confidence: 99%

Photochemical effects in the UV laser ablation of polymers: Implications for laser restoration of painted artworks

Lassithiotaki¹,

Athanassiou²,

Anglos³

et al. 1999

Applied Physics A: Materials Science & Processing

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The photochemical modifications induced in the UV ablation of molecular substrates are examined in model systems of polymer films (PMMA) doped with a highly photosensitive organic pigment (1-iodonaphthalene). Ablation by nanosecond laser pulses at 248 nm is shown to result in an increase of photolysis yields and in the efficient formation of new products. In sharp contrast, photoproduct formation in the corresponding ablation with 500 fs pulses is well defined and limited. Thus, besides its well-acknowledged thermal advantage, fs ablation is shown to provide a high degree of control over the induced photochemical modifications. The results of the study are correlated with the specific procedures that have been defined for the efficient restoration of painted surfaces with minimal photochemical modification to the substrate. PACS: 42.60; 82.65 UV laser ablation constitutes the basis of a number of diverse techniques aiming at the analysis and material processing of molecular substrates [1][2][3]. In a rather unconventional extension of these implementations, we have demonstrated [4,5] the potential of excimer laser ablation for the restoration of painted artworks. This approach has been shown to overcome the limitations of conventional restoration methods and to enable successful treatment of demanding problems that are otherwise difficult or even not amenable to the traditional techniques.The restoration of painted artworks focuses largely, though not exclusively, on the removal of degraded superficial varnish layers that cover the painting's surface [6]. Varnish is a mixture of cyclic organic substances [7] and is applied to paintings for aesthetic (enhancing the painting's colour appearance) and protective (preventing direct exposure of the painted surface to the environment) purposes. With time, it polymerizes and undergoes photooxidation at its outer layers, with detrimental effects on the artwork's appearance and even for its long-term integrity. This necessitates removal of the degraded varnish layers without, of course, compromising the integrity and the authenticity of the original painted surface.Varnish absorbs strongly in the UV [9], which suggests its efficient etching by excimer laser irradiation with minimal light penetration to the sublayers. Indeed, initial studies [4,8] demonstrated that degraded surface layers 20-100 µm thick can be etched by ablation at 248 nm with a resolution of 0.1-1 µm/pulse. Thus, the excimer-laser-based procedure meets the restoration needs by effecting removal of the degraded varnish in a controlled, highly selective and welldefined manner. A further advantage for the laser-based approach accrues from the possibility of on-line control of the procedure through interfacing with a variety of in-situ laserbased analytical techniques [5].Although the potential of the procedure has been established, it is critical to assess the short-and long-term effects on the integrity of the substrate. In particular, the fact that conditions of relatively strong irradiation are employed f...

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1-heptene, 3-heptenes and cumene as model compounds of SBS block copolymers. Study of their photoreactions in the presence of photoinitiators of polymerization

Cited by 12 publications

References 8 publications

Radical Cage Effects: The Prediction of Radical Cage Pair Recombination Efficiencies Using Microviscosity Across a Range of Solvent Types

Radical Cage Effects: The Prediction of Radical Cage Pair Recombination Efficiencies Using Microviscosity Across a Range of Solvent Types

Radical Cage Effects: Comparison of Solvent Bulk Viscosity and Microviscosity in Predicting the Recombination Efficiencies of Radical Cage Pairs

Photochemical effects in the UV laser ablation of polymers: Implications for laser restoration of painted artworks

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