Radiation-induced ionic polymerization

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. 

An obvious question then arose is this a phenomenon common to all vinyl monomers In other words is this exclusion of water sufficient to promote radiation-induced ionic polymerizations even in media of very low dielectric constant and at room temperature We believe that the answer to both forms of the question is yes, although it may be difficult to achieve the proper conditions in some systems. 

The most important feature of ionizing radiations is, as the term implies, ionization to give ionic intermediates in irradiated systems. Though radiation-induced radical polymerization had long been studied, it is only a decade since radiation-induced ionic polymerization was first found. In 1957, Davison et al. obtained polymer from isobutene, which is known not to be polymerized by radical catalysts, by irradiating at low temperature with y-rays (7). Before long, the radiation-induced polymerization of styrene was proved to proceed as an ionic mechanism in suitable solvents (2,3,4). Since these pioneering researches, the study of the chemical kinetics of radiation-induced ionic polymerization has been extended to several vinyl, diene and cyclic monomers. 

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... 

InitiationProcess of Radiation-induced Ionic Polymerization asStudied by ESR 409... 

According to the studies of monomers in the organic glass matrices mentioned so far, the ion radicals formed from solute monomers relate their radiation-induced ionic polymerization to the primary effect of ionizing radiations on matter. It is concievable that the initiating species in the anionic polymerization (caxbanions) are formed by the addition of the monomer molecules to the anion radicals which result from electron transfer from the matrices to the solute monomer. The formation of the cation radicals is necessary also to initiate the cationic polymerization. 

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. ... 

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