Radicals produced by Irradiation

Fig. 3. Polymerization initiation and propagation by radiation-generated free radicals. A is the initiating radical produced by irradiating the Hquid coating. (1) represents the Hquid monomer—unsaturated polymer reactive coating system. R is functional. (2) is the growing polymer chain (free radical). The cured...

The total yield of radicals produced by irradiation of alkyl sulfones at 77 K was estimated65 by comparison of the areas of the absorption peaks with that of a known amount of diphenylpicrylhydrazine to be G(radicals) 2.0. 

The radicals produced by irradiation will react with NO and SO2, which are well-known good radical scavengers. These radical reactions related to NO and SO , removals are very... 

In the 1940 8 and early 1950 8, H atoms were believed to be the only reducing radicals produced by irradiation (47, 54). 

The reaction with swollen starch produced the greatest amount of grafted polymer and the largest conversion of monomer. This was probably due to the high viscosity of the medium, which caused reduction in the termination rate by immobilization of the polymeric free radicals produced by irradiation. 

In contrast to other poly (olefin sulfone) s, little isomerization of the olefin occurs during cationic depropagation. The degradation of PMPS is extremely rapid and it is possible that the lifetime of the cationic intermediates may be too short for appreciable isomerization to occur. However, isomerization of the 2-methyl-l-pentene product to 2-methyl-2-pentene did occur during the postexposure period. The isomerization proceeded both in solution and in the solid state. It seems unlikely that the reactive intermediates (e.g. cations and free radicals) produced by irradiation catalyse the isomerization reaction since they would be expected to be destroyed during dissolution. However sulfur dioxide is well known to form charge transfer complexes (CTC) with olefins (1) and we propose that the isomerization occurs via such an intermediate ... 

Oxygen reacted with the metal radicals produced by irradiation ... 

B-1) Assignment of unstable free radicals produced by irradiation of polymers with ionizing radiation and ultraviolet light, mechanical fracture, and deterioration of polymers and polymerization. 

Free Radicals Produced by Irradiation of Polymers with Ionizing Radiation... 

The effect of gamma irradiation on the physical properties of PTFE film are shown in Table 52.10. The faUoff in physical properties is dramatic, even after irradiation in vacuo followed by exposure to air. The radicals produced by irradiation have been shown to have a long lifetime even after heating to 300 °C [103], By looking at the electron spin resonance spectrum, radical I is detected for irradiation in vacuo and peroxy radical II is detected after exposure to air [ 105]. 

Essentially, the process as developed by the Esso Company was the passing of sulfur dioxide and oxygen through various straight chain hydrocarbons in the presence of a source of y radiation. Alkyl radicals produced by irradiation of the hydrocarbon add sulfur dioxide, forming an alkyl sulfonyl radical ... 

In the early stages of ESR application to polymer research, many studies on the identification of free radicals produced by irradiation with ionizing radiation, x-ray, and ultraviolet light were made. Some of the irradiation effects in polymeric materials were considered to originate from the radical processes and, therefore, clear identification of the radicals trapped in irradiated polymers was one of the most important problems at that stage. In this meaning, ESR application was considered to be a very convenient technique for this purpose, because detection and identification of the free radicals bearing unpaired electrons in principle can be done easily by the ESR method without any chemical modification of the materials. 

Oxidizing and nonoxidizing conditions play a very important part in surface modification. When oxygen is present it reacts very rapidly with radicals produced by irradiation. As a result, the free-radical reaction pathways and the molecular reaction products are dominated by oxidation chemistry and these differences are reflected in the physical property changes. 

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