Peroxides, photosensitized decomposition

The measurement of bulk copolymerization of styrene (Mi) and methyl methaciylate (M2) at 30°C in a feed of 0.031 mole fraction styrene with initiation by photosensitized decomposition of benzoyl peroxide gave a value... 

Long-lived radicals could also be generated in solid polymers by the thermal decomposition of peroxides and by irradiation in the presence of photosensitizers at room temperature 46). 

Absorption of radiation by absorbers other than peroxide can be beneficial for treatment under the following conditions (1) M is the absorber and direct photolysis is applied and (2) the absorber causes M to decompose by some other process such as photosensitization. In general, the overall rate of decomposition of M can be given by Equation (7.66). 

R CHORj. Such radicals have been formed by hydrogen atom abstraction from the ether by radicals produced from thermal decomposition of peroxides (67, 75, 76). Similar radicals may be produced in photochemical processes, either by direct irradiation (29, 54), or by the use of a photosensitizer or a photoinitiator, such as acetone or benzophenone (21, 64, 66). The ether radicals once produced, participate in a variety of chemical reactions. It might be noted that resonance forms as illustrated... 

The altered NMR spectra characteristic of chemically induced dynamic polarization (CIDNP) (22) are observed during the photo-lytic decomposition of various peroxides in the presence of photosensitizers at ambient temperatures, as well as the thermal decomposition of these peroxides in the absence of light at temperatures where they have a short half-life. The reactions which are responsible for CIDNP are apparently similar in both cases. 

CL was determined in Fluoroskan Ascent FL (j he,rm.oLabsystems, Finland) at 25 °C and 37 °C in phosphate buffer pH 7.6. Chemiluminescent reaction was initiated by the injection of hydrogen peroxide in solution of CL compound in the presence of CUSO4 or HRP. The solution of NaOCl is quite unstable at room temperature. In order to minimize the effect of NaOCl decomposition, the stock solution was defrosted immediately before priming the automatic dispenser and solution was kept on ice. The photodynamic effect was initiated by the irradiation of the solution of photosensitizer by a semiconductor laser (Lasotronic pocket therapy laser, power 50 mW, wavelength 670 nm). All manipulations with chlorophyll a and /0-carotene were done in the dark room and the extracts were kept at -20 °C to minimize degradation processes. All measurements were performed in a volume of 2(X) pL. 

Neff, W.E., Frankel, E.N. and Weisleder, D. Photosensitized oxidation of methyl Unoleate monohydroperoxides Hydroperoxy cycUc peroxides, dihydroperoxides, keto esters and volatile thermal decomposition products. Lipids 18, 868-876 (1983). 

For example, the silver halides (Chapter 3), silver nitrate, hydrogen peroxide and nitric acid are all photosensitive and undergo partial decomposition (to form radicals, often in the form of reactive atoms) in the presence of sunlight. 

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