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09/2011: pages 643 - 672; , ISBN: 9783527631421
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ABSTRACT: The photopolymerization process of acrylate coatings initiated by visible light (λ > 380 nm) and performed in air was studied in the presence of zirconium complexes. Depth profiling experiments were performed using confocal Raman microscopy showing that the conversion, which is low at the surface of the sample, increases with increasing depth and reaches a full conversion close to the substrate. RT-FTIR spectroscopy corroborates Raman results in evidencing the efficiency of some zirconium compounds to reduce oxygen inhibition. Finally, laser flash photolysis experiments revealed that the beneficial effect in air is attributable to the reaction of the zirconium complex on the peroxyl radicals formed from the reaction of oxygen with radicals. Therefore, the oxygen present in the medium is depleted, allowing a better efficiency of the photopolymerization process.
Journal of Polymer Science Part A: Polymer Chemistry. 01/2011; DOI: 10.1002/pola.24984.
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03/2010: pages 351 - 419; , ISBN: 9780470594179
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ABSTRACT: The ability of a bis(germyl)ketone Ph(3) GeCOGePh(3) to act as a photoinitiator of free radical polymerization under visible light is investigated. The results suggest that this compound could be the starting point of a new high performance class of photoinitiators. The excited state processes, as well as the generation and the reactivity of the germyl radicals, are studied by laser flash photolysis, ESR spin trapping experiments, and molecular orbital calculations; they are compared to the results obtained on a mono- (germyl)ketone CH(3) COGePh(3) . Time dependent density functional theory calculations allow discussion of the strongly red-shifted ground state absorption of Ph(3) GeCOGePh(3) .
Macromolecular Rapid Communications 03/2010; 31(5):473-8. · 4.60 Impact Factor
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Macromolecular Materials and Engineering 02/2010; 295(4):351 - 354. · 1.99 Impact Factor
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ABSTRACT: A set of multivalent atom-containing amines (e.g., tetrakis(dimethylamido)silane, tetrakis(dimethylamido)tin(IV), tetrakis(diethylamido)titanium(IV), tetrakis(dimethylamido)zirconium(IV), and 1,3,5-triaza-7-phosphaadamantane) are proposed as new coinitiators in Type II photoinitiating systems (based, for example, on benzophenone) and additives for Type I photoinitiators (such as phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone) for free radical photopolymerization under air. The polymerization rates (Rp’s) were determined under experimental conditions where a strong detrimental oxygen effect is expected, that is, both under low light intensity and in thin low viscosity monomer samples. The remarkable performance achieved under air (up to a 100- and a 5-fold increase in Rp and final conversion (%), respectively) lies on the presence of a bimolecular homolytic substitution (SH2) reaction that allows us to convert peroxyls into new initiating radicals efficiently. The mechanisms are investigated by laser flash photolysis (LFP) and electron spin resonance (ESR) experiments.
02/2010;
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ABSTRACT: The role of silanes, germanes, and stannanes R3XH as co-initiators and additives to overcome the oxygen inhibition usually encountered in photopolymerization reactions in aerated media is demonstrated in experimental conditions where both a low light intensity and thin and low-viscosity samples are used. These results concerned with silanes as co-initiators are compared to data previously obtained in more viscous media where a lower effect of oxygen is expected. The striking role of R3XH here is their use as additives in both type I and II photoinitiating systems. It allows to dramatically increase the polymerization rates and the final monomer conversions in the above-selected conditions. The mechanisms investigated by laser flash photolysis (LFP) and electron spin resonance (ESR) experiments are discussed.
11/2009;
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ABSTRACT: Photochemical properties of 4-coumarinylmethyl derivatives (CM-X, X = Br, Cl, OH, OPh, SH, and SPh) in solution were studied by laser flash photolysis and DFT calculations. It was found that CM-Br and CM-SPh undergo photoinduced bond dissociation in the lowest excited singlet state, yielding the 4-coumarinylmethyl radical (CMR) and the corresponding radical with quantum yields of approximately 0.25. Laser flash photolysis of CM-Cl, OH, OPh, and SH provided no or very little transient absorption of the corresponding triplet state. Upon triplet sensitization of CM-X using benzophenone (BP) as a triplet sensitizer, efficient formation of triplet CM-OH and -OPh was seen, whereas CM-SH and -SPh underwent the C-S bond cleavage in the lowest triplet (T(1)) state, resulting in production of CMR and the corresponding radicals with efficiencies (alpha(rad)) of >or=0.66. CM-Br and -Cl efficiently quenched triplet BP without formation of appreciable intermediates. On the basis of the results of laser flash photolysis and DFT calculations, photochemical features of triplet CM-X were discussed in detail.
The Journal of Physical Chemistry A 05/2009; 113(20):5815-22. · 2.95 Impact Factor
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Journal of Physical Organic Chemistry 04/2009; 22(10):986 - 993. · 1.96 Impact Factor
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Macromolecular Chemistry and Physics 01/2009; 210(5):311 - 319. · 2.36 Impact Factor
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ABSTRACT: We design a new photoinitiating system where the two-photon absorption of a 2,7 bisaminofluorene moiety leads to the photoactivation of a camphorquinone subunit through a Förster-type intramolecular energy transfer: the application to a two-photon polymerization reaction is demonstrated.
Chemical Communications 01/2009; · 6.17 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 10/2008; 46(22):7369 - 7375. · 3.92 Impact Factor
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ABSTRACT: Seven alpha-aminoalkylperoxyl radicals have been generated by 355 nm laser flash photolysis (LFP) of oxygen-saturated di-tert-butyl peroxide containing mono-, di-, and trialkylamines and a dialkylarylamine. All these peroxyls possess absorptions in the near-UV (strongest for the trialkylamine-derived peroxyls) which permits direct monitoring of the kinetics of their reactions with many substrates. The measured rate constants for hydrogen atom abstraction from some phenols and oxygen atom transfer to triphenylphosphine demonstrated that all seven alpha-aminoalkylperoxyls have similar reactivities toward each specific substrate. More importantly, a comparison with literature data for alkylperoxyls shows that alpha-aminoalkylperoxyls and these alkylperoxyls have essentially the same reactivities. The combination of LFP and alkylamines provides a quick, reliable method for determining absolute rate constants for alkylperoxyl radical reactions, an otherwise laborious task.
The Journal of Organic Chemistry 10/2008; 73(17):6489-96. · 4.45 Impact Factor
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Macromolecular Chemistry and Physics 09/2008; 209(21):2223 - 2231. · 2.36 Impact Factor
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ABSTRACT: A set of selected acetophenone derivatives was investigated using absorption and emission spectroscopy, laser flash photolysis and DFT calculations. The triplet state lifetimes and the activation energy of the cleavage reaction were measured. Computed triplet-triplet absorption spectra were found in very good agreement with the experimental ones. Bond dissociation energies, activation energies, partial charges, ground state geometries were calculated. The transition state theory TST was successfully used to calculate the cleavage rate constants: a very good correlation was found between the experimental and the calculated values. It is found that the entropy change influences the preexponential factor. This study also points out the role of the partial charges in the transition state, although this effect alone does not account for the reaction rate constants.
Photochemical and Photobiological Sciences 06/2008; 7(5):558-65. · 2.58 Impact Factor
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ABSTRACT: The photophysical properties of a series of 1,8-naphthalimide photoacid generators were studied by steady state fluorescence and phosphorescence spectroscopy. Emission and excitation anisotropies, triplet quantum yields in polar and nonpolar solvent and photoacid generation were evaluated. The singlet excited state exhibits a low polarity and is strongly deactivated by an efficient intersystem crossing process. In protic solvent, a homolytic singlet cleavage of the N-O bond occurs and leads to the acid production. The existence of a triplet state close to the singlet state was clearly evidenced. The presence of close singlet excited states is supported by fluorescence anisotropy and picosecond laser spectroscopy experiments. Results of DFT calculations well confirm the experimental contentions and yield important information about the cleavage process involved in such compounds.
The Journal of Physical Chemistry A 06/2008; 112(17):3879-85. · 2.95 Impact Factor
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Macromolecular Rapid Communications 04/2008; 29(10):804 - 808. · 4.60 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 03/2008; 46(9):3042 - 3047. · 3.92 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 02/2008; 46(6):2008 - 2014. · 3.92 Impact Factor
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ABSTRACT: The reactivity of the tris(trimethylsilyl)silane (TTMSS)-derived radical is studied through an approach combining laser flash photolysis and quantum mechanical calculations. The results obtained for TTMSS are compared both to a classical silyl radical derived from triethylsilane and to a previously studied carbon-centered structure. Different worthwhile results are obtained: (i) the addition and hydrogen abstraction rate constants are directly measured, (ii) the high reactivity and the low selectivity of TTMSS toward the addition to alkenes are perfectly explained by antagonist polar and enthalpy effects, (iii) efficient hydrogen abstraction reactions from antioxidants such as vitamin E are observed, and (iv) TTMSS is seen to also act as an efficient initiator for the polymerization of an acrylate monomer.
The Journal of Organic Chemistry 09/2007; 72(17):6434-9. · 4.45 Impact Factor
