Radiation induced ionic processes

Tn recent years the investigation of ionic processes has become one of the main efforts in radiation chemistry. The existence of the blue electrons predicted by Platzmans theory (17) has been confirmed in different irradiated materials, and their properties and reactions have been extensively studied. This progress in our knowledge about the radiation-induced ionic processes arises mainly from the use of pulse radiolysis, flash photolysis, and matrix isolation techniques. 

Yoshida, H. and Hayashi, K. Initiation Process of Radiation-induced Ionic Polymerization as Studied by Electron Spin Resonance. Vol. 6, pp. 401—420. 

In 1957 Davison, Pinner, and Worrall (8) published data on the radiation polymerization of isobutene, which could best be explained as an ionic process. These initial findings were further confirmed by subsequent investigations (7, 9, 26, 27), Needless to say, these disclosures prompted reinvestigation of the question of radiation-induced ionic polymerizations in other systems. 

So far as vinyl monomers are concerned, ionic propagation proceeds with carbonium ions (cationic polymerization) or carbanions (anionic polymerization) at the chain ends. The study of the initiation process of radiation-induced ionic polymerization seeks to elucidate how these ions are formed from the primary ionic intermediates. Possible reactions... 

Initiation Process of Radiation-induced Ionic Polymerization as Studied byESR 403... 

The present review paper is concerned mainly with the ESR studies of irradiated organic glass matrices containing vinyl monomers made by the present authors to study the initiation process of radiation-induced ionic polymerization. In the following chapter, the study of the pure... 

It seems to the present authors that the above-mentioned scheme of the initiation process in the glass matrices can be extended, at least, to the radiation-induced ionic polymerizations in liquid solutions at higher temperatures. This will be verified by rapid techniques of measurement, such as the pulse radiolysis method. 

The formation of ion radicals from monomers by charge transfer from the matrices is clearly evidenced by the observed spectra nitroethylene anion radicals in 2-methyltetrahydrofuran, n-butylvinylether cation radicals in 3-methylpentane and styrene anion radicals and cation radicals in 2-methyltetrahydrofuran and n-butylchloride, respectively. Such a nature of monomers agrees well with their behavior in radiation-induced ionic polymerization, anionic or cationic. These observations suggest that the ion radicals of monomers play an important role in the initiation process of radiation-induced ionic polymerization, being precursors of the propagating carbanion or carbonium ion. On the basis of the above electron spin resonance studies, the initiation process is discussed briefly. 

In many processes (e.g. polymerizations, catalytic reactions) even trace amounts (< 50 ppm) of water can cause problems and the only practical solution for dehydration of these liquids is the use of an appropriate zeolite. For example, Stannet et al. (4 ) report on the use of molecular sieves to dehydrate liquid vinyl monomers prior to radiation-induced ionic polymerization. ... 

Yamazaki, N. Electrolytically Initiated Polymerization. Vol. 6, pp. 377-400. Yoshida, H. and Hayashi, KInitiation Process of Radiation-induced Ionic Polymerization as Studied by Electron Spin Resonance. Vol. 6, pp. 401-420. Zachmann, H. G. Das Kristallisations- und Schmelzverhalten hochpolymerer Stoffe. Vol. 3, pp. 581-687. 

Sufficient experimental data from several laboratories now exist to describe the conditions under which the radiation-induced ionic propagation of many pure liquid vinyl monomers can be observed. The kinetic data and electrical conductivity measurements establish the ionic nature of the reaction scavenger studies appear to establish the preponderant role played by the carbonium ion in propagating the polymerization. On the basis of a single propagating species, it is possible to write a simple mechanism to describe the process. Limiting values of several of the kinetic rate constants can be estimated, notably the rate constant for reaction between a bare carbonium ion and a vinyl double bond. These rate constants are compared with similar constants arrived at in chemically initiated free radical, carbonium ion and carbanion polymerization. Several shortcomings of the present scheme are discussed. 

A singular contribution that a detailed study of radiation-induced ionic polymerization can make to fundamental processes, then, is that the rate constants for the family of reactions typified by... 

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