Journal Article•
Reactions of Triplet Decafluorobenzophenone with Alkenes. A Laser-Flash Photolysis Study
TL;DR: In this paper, the rate constants for triplet decafluorobenzophenone (3DFB) with 30 alkenes have been measured, with values in the range 107−109 L mol-1 s-1.
Abstract: Rate constants for the reactions of triplet decafluorobenzophenone (3DFB) with 30 alkenes have been measured, with values in the range 107−109 L mol-1 s-1. The rate constant increases upon substitu...
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TL;DR: The placement of the hydrogen species most susceptible to abstraction by triplet benzophenone is found to greatly influence gelation efficiency, since radical generation on the polymer backbone typically increases the probability of dislinking events, while hydrogen abstraction pendent to the copolymer backbone tends to enhance cross-linking.
Abstract: A series of copolymers containing covalently attached benzophenone (BP) photo-cross-linkers were synthesized, and their UV-induced gelation was monitored as a function of the extent of BP conversion. For poly(methyl methacrylate) copolymers, the recombination yield between BP- and aliphatic-centered radicals was estimated and compared to that for dimerization of each species, directly confirming that the high gelation efficiencies observed for these copolymers arise due to the additional cross-linking pathways provided by covalently incorporated BP, as compared to doping with a small-molecule cross-linker. The placement of the hydrogen species most susceptible to abstraction by triplet benzophenone is found to greatly influence gelation efficiency, since radical generation on the polymer backbone typically increases the probability of dislinking events, while hydrogen abstraction pendent to the copolymer backbone tends to enhance cross-linking. Finally, the presence of atmospheric oxygen during photo-cros...
94 citations
TL;DR: In this article, the rate constants of quenching of triplet excited ketones by several monomers were determined through time-resolved laser spectroscopy or culled from the literature.
Abstract: Rate constants of quenching of triplet excited ketones by several monomers were determined through time-resolved laser spectroscopy or culled from the literature. The semi-empirical calculation method PM3 allows the quenching mechanisms to be refined and can be used to predict the reactivity of aromatic ketones toward monomers. It is apparent from both experimental results and theoretical calculations that the rate constant (kq ) measured for the bimolecular quenching between the triplet state of a given aromatic ketone and both electron-rich as well as electron-poor monomers, depends linearly on the free enthalpy of formation of the regioselectively favored 1,4-biradical, which is the primary reaction step of the ketone/monomer interaction. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1785–1794, 2000
14 citations
TL;DR: In this article, a versatile approach for building dynamic covalent networks for polymers containing C-H bonds was proposed, inspired by the abstraction of hydrogen and the iniferter polymerization of benzophenone (BP).
Abstract: Despite many efforts, there is no versatile way to realize reversible cross-linking for most polymers. Inspired by the abstraction of hydrogen and the iniferter polymerization of benzophenone (BP), we report a versatile approach for building dynamic covalent networks for polymers containing C–H bonds. Under ultraviolet irradiation, BP can effectively abstract the hydrogen from polymers to form dormant diarylsemipinacol (DASP) groups on the polymer chains. Then, the dormant DASP-based linkages can be homolytically cleaved upon heating, after which they generate carbon-centered aliphatic radicals and DASP-based radicals. Therefore, the cross-linked polymer network can rearrange its topology through the dissociation and association of DASP-based linkages, which endow polymer networks with remodeling and self-healing abilities. Given that most commercially available polymers contain aliphatic C–H bonds, this provides a general method for forming thermal reversible cross-linked networks.
13 citations
TL;DR: A nanosecond time-resolved resonance Raman (ns-TR3) spectroscopic investigation of the photoreduction reactions and ability of several chloro-substituted benzophenone (Cl-BP) triplets is described in this paper.
Abstract: A nanosecond time-resolved resonance Raman (ns-TR3) spectroscopic investigation of the photoreduction reactions and ability of several chloro-substituted benzophenone (Cl-BP) triplets is described. The TR3 results show that the 3-chlorobenzophenone (3-Cl-BP), 4-chlorobenzophenone (4-Cl-BP) and 4,4′-dichlorobenzophenone (4,4′-dichloro-BP) triplets exhibit similar hydrogen abstraction ability with the parent BP triplet. In 2-propanol, the 3-Cl-, 4-Cl- and 4,4′-dichloro-diphenylketyl (DPK) radicals were observed and they appear to react with dimethylketyl radicals at the para-position to form a light absorption transient species. These transient species were characterized with TR3 spectra, and identified with the help of results from density functional theory calculations. In an acetontitrile/water (MeCN:H2O) 1:1 mixed solvent, these DPK radicals were also observed but with slower formation rates. However, the 2-Cl-DPK radical was observed to form with a lower yield and a significantly slower formation rate than the other chloro-substituted benzophenones examined here in 2-propanol under the same experimental conditions. These results reveal that the 2-chloro substituent reduces the hydrogen abstraction ability of the substituted BP triplet, which was not as expected based on the assumption that the electron-withdrawing group could increase its photoreduction ability. This unusual ortho effect of the chlorine substitution is briefly discussed. Copyright © 2011 John Wiley & Sons, Ltd.
7 citations