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Photolysis Experiments (photolysi + experiment)

Distribution by Scientific Domains

Polymers and Materials Science	60%

Selected Abstracts

1,5-Diphenyl-1,4-diyn-3-one: A highly efficient photoinitiator

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2005
Robert Liska
Abstract In a continuation of our research on new chromophores for photoinitiators (PIs), we investigated a triple-bond-containing benzophenone derivative. 1,5-Diphenyl-1,4-pentadiyn-3-one (2) was prepared from phenylacetylene and ethyl formate by a one-pot reaction. Differential scanning photocalorimetry experiments in lauryl acrylate of 2 showed surprisingly high activity for the double-bond conversion and rate of polymerization at the lowest PI concentrations and even without any coinitiator. By the application of monomers with abstractable hydrogens, significant improvement in the photoreactivity was observed. Ultraviolet,visible spectroscopy revealed strong absorption up to 350 nm. Steady-state photolysis experiments proved that the photochemistry of this compound was faster than that of benzophenone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 101,111, 2005 [source]

Polymerization of acrylamide photoinitiated by tris(2,2,-bipyridine)ruthenium(II),amine in aqueous solution: Effect of the amine structure

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2001
Claudia R. Rivarola
Abstract The photopolymerization of acrylamide (AA) initiated by the metallic complex tris(2,2,-bipyridine)ruthenium(II) [Ru(bpy)3+2] in the presence of aliphatic and aromatic amines as co-initiators was investigated in aqueous solution. Aromatic amines, which are good quenchers of the emission of the metal-to-ligand-charge-transfer excited state of the complex, are more effective co-initiators than those that do not quench the luminescence of Ru(bpy)3+2, such as aliphatic amines and aniline. Laser-flash photolysis experiments show the presence of the reduced form of the complex, Ru(bpy)3+1, for all the amines investigated. For aliphatic amines, the yield of Ru(bpy)3+1 increases with temperature, and on the basis of these experiments, a metal-centered excited state is proposed as the reactive intermediate in the reaction with these amines. The decay of the transient Ru(bpy)3+1 is faster in the presence of AA. This may be understood by an electron-transfer process from Ru(bpy)3+1 to AA, regenerating Ru(bpy)3+2 and producing the radical anion of AA. It is proposed that this radical anion protonates in a fast process to give the neutral AA radical, initiating in this way the polymerization chain. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4265,4273, 2001 [source]

Reinvestigation of the Mechanism of the Free Radical Polymerization Photoinitiation Process by Camphorquinone,Coinitiator Systems: New Results

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2004
Ilona Pyszka
Abstract Summary: Comparative studies of photoinitiation processes using camphorquinone (CQ) and benzophenone (BP) as light absorbers were performed. The experimental results show that after the transformation of (phenylthio)acetic acid (PTAA) into its tetrabutylammonium salt (PTAA AS), a substantial decrease of the polymerization photoinitiation ability for the CQ,PTAA AS pair in comparison to the CQ,PTAA pair is observed. The mechanism of the photoinitiated polymerization for the tested photoredox pair was clarified based on laser flash photolysis experiments obtained using benzophenone as an electron acceptor and (phenylthio)acetic acid and its tetrabutylammonium salt as electron donors in solution in MeCN. It is documented and deduced that the photoreduction of benzophenone in the presence of (phenylthio)acetic acid and its tetrabutylammonium salt occurs by a photoinduced electron transfer process, while for CQ as initiator, the free radicals are formed by hydrogen atom abstraction by the triplet state of camphorquinone. Schematic of the transients formed after an electron-transfer process for benzophenone,PTAA and benzophenone,PTAA AS pairs. [source]

Mass spectrometry of the photolysis of sulfonylurea herbicides in prairie waters

MASS SPECTROMETRY REVIEWS, Issue 4 2010
John V. Headley
Abstract This review of mass spectrometry of sulfonylurea herbicides includes a focus on studies relevant to Canadian Prairie waters. Emphasis is given to data gaps in the literature for the rates of photolysis of selected sulfonylurea herbicides in different water matrices. Specifically, results are evaluated for positive ion electrospray tandem mass spectrometry with liquid chromatography separation for the study of the photolysis of chlorsulfuron, tribenuron-methyl, thifensulfuron-methyl, metsulfuron-methyl, and ethametsulfuron-methyl. LC,MS/MS is shown to be the method of choice for the quantification of sulfonylurea herbicides with instrumental detection limits ranging from 1.3 to 7.2,pg (on-column). Tandem mass spectrometry coupled with the use of authentic standards likewise has proven to be well suited for the identification of transformation products. To date, however, the power of time-of-flight MS and ultrahigh resolution MS has not been exploited fully for the identification of unknown photolysis products. Dissipation of the herbicides under natural sunlight fit pseudo-first-order kinetics with half-life values ranging from 4.4 to 99 days. For simulated sunlight, radiation wavelengths shorter than 400,nm are required to induce significant photolytic reactions. The correlation between field dissipation studies and laboratory photolysis experiments suggests that photolysis is a major pathway for the dissipation of some sulfonylurea herbicides in natural Prairie waters. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:593,605, 2010 [source]

Reactions of Cl,/Cl2,, Radicals with the Nanoparticle Silica Surface and with Humic Acids: Model Reactions for the Aqueous Phase Chemistry of the Atmosphere

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007
Paula Caregnato
ABSTRACT Reactions of chlorine radicals might play a role in aqueous aerosols where a core of inorganic components containing insulators such as SiO2 and dissolved HUmic-LIke Substances (HULIS) are present. Herein, we report conventional flash photolysis experiments performed to investigate the aqueous phase reactions of silica nanoparticles (NP) and humic acid (HA) with chlorine atoms, Cl,, and dichloride radical anions, Cl2,,. Silica NP and HA may be taken as rough models for the inorganic core and HULIS contained in atmospheric particles, respectively. Both Cl, and Cl2,, were observed to react with the deprotonated silanols on the NP surface with reaction rate constants, k ± ,, of (9 ± 6) × 107 M,1 s,1 and (7 ± 4) × 105 M,1 s,1, respectively. The reaction of Cl, with the surface deprotonated silanols leads to the formation of SiO, defects. HA are also observed to react with Cl, and Cl2,, radicals, with reaction rate constants at pH 4 of (3 ± 2) × 1010 M,1 s,1 and (1.2 ± 0.3) × 109 M,1 s,1, respectively. The high values observed for these constants were discussed in terms of the multifunctional heterogeneous mixture of organic molecules conforming HA. [source]