Free Radical Production upon Photoinduced Electron Transfer Reactions in the Presence of Vinyl Monomers. Effect of Water Addition*

Abstract

Free radical fragments produced in the photoinduced electron transfer from triethylamine (TEA) to excited pyrenebutyltrimethylammonium (*PyBu+) lead to l-vinyl-2-pyrrolidinone (VP) and 2-hydroxyethyl methacrylate (HEMA) polymerization. Experiments carried out in waterlacetonitrile solvent mixtures showed that the polymerization rate of VP increases upon increasing the water content, whereas the polymerization rate of HEMA follows the opposite trend. These results are interpreted in terms of the strong dependence on the solvent properties of the photochemical behavior of PyBu' in the presence of the amine or monomers. Thus, the *PyBu+ quenching by VP is almost negligible in both solvents (water and acetonitrile). Whereas, the *PyBu+ quenching rate constant by HEMA in water is 4 x lo9 M-l s-l and decreases four orders of magnitude in acetonitrile. The quenching of *PyBu+ by TEA in aqueous solutions is controlled by hydrogen-bonding interactions between water molecules and the amine. Quantum yields of the pyrene radical anion (ap,-) also strongly depend on the water content, decreasing from 0.28 to 0.015 upon going from acetonitrile to water.

Chemical and spectroscopic characterization of a vegetable oil used as dielectric coolant in distribution transformers

“…Figure 15 shows the relative diminishing of the intensity of the 1 H NMR signals at the vinylic and allylic regions (i.e., 5.0-5.5 ppm and 1.5-2.8 ppm respectively) for the same concentrations. Similarly, the relative intensities of the same 13 C NMR signals also diminished with respect to sample (I) (see Figure S10). The NMR spectra of the aged oil samples B and C, also exhibited diminishing in the intensities of their signals, but to lesser degree than sample A, (see Figures S11, S12 for NMR spectra of samples B and C).…”

“…Pursuing the further development of a spectroscopybased methodology for monitoring the life-time and performance of vegetable dielectric oils as coolant for distribution transformers, several studies were performed in this work. A complete UV-Vis, IR, 1 H NMR, 13 C NMR and DEPT spectroscopic analysis was carried out to an unused vegetable FR3 ® dielectric coolant oil sample (I) in order to establish its structural properties. The same spectroscopic analysis was performed for three used FR3 ® oil samples (i.e., 4 months old (II), 8 months old (III) and 7 years old (IV)), obtained from several operating distribution transformers.…”

“…For the oil sample (I) the 1 H NMR, 13 C NMR and DETP-135 spectra were obtained ( Figures 3 and 4 respectively). Although a vegetable oil is constituted by a complex mixture of triacylglycerols, surprisingly the FR3 ® oil showed relatively well defined NMR spectra.…”

“…the others B and C samples, Figure 14, (see Figure S9 for IR spectra of samples B and C). The main differences between the 1 H NMR, 13 C NMR and DEPT-135 spectra of the original oil sample (I) and those of the accelerated aged samples were found for the sample A. Figure 15 shows the relative diminishing of the intensity of the 1 H NMR signals at the vinylic and allylic regions (i.e., 5.0-5.5 ppm and 1.5-2.8 ppm respectively) for the same concentrations.…”

“…Because this mechanism is mediated by oxygen-and carbon-based free radicals, the presence of water in the media (samples B and C), should decrease the speed of formation of those species. 13 For that reason processes B and C proceeded slower than process A, where no water was present. Apparently the presence or absence of Kraft paper in the media did not affect significantly the aging rate of the oil samples.…”