Radiation-induced chlorination

H. Hopff and N. Balint developed a copolymerization process for tetrachloroethylene with ethylene. Radiation-induced chlorination of polyisobutylene is the subject of the chapter of C. Schneider and P. Lopour. M. Litt, V. T. Stannett, and E. Vanzo show that the polymerization of vinyl caproate follows the kinetics of styrene. 

Radiation-induced chlorination of polyisobutene in carbon tetrachloride was studied at various temperatures. The process is a chain reaction with a G value of about 10 to 105, depending on the reaction conditions. At very low dose rates (0.1 to 0.2 rad I sec), the chlorination rate is directly proportional to the dose rate. At higher dose rates, the rate approaches a square-root dependence on the dose rate. The termination reaction and the influence of oxygen are discussed. The reaction is first order with respect to chlorine concentration. An activitation energy of about 4 kcal/mole was obtained. In connection with the chlorination reaction, degradation of the polyisobutene takes place. This degradation was followed by osmometric measurements. The structure of the chlorinated product was briefly investigated by IR spectroscopy. 

Chlorination is one of the most interesting processes for polymer modification, and is usually carried out by means of catalysts or by UV irradiation. Since 1960, radiation-induced chlorination of polyethylene and polypropylene has been studied, especially by Soviet workers (1-3). As the polymers used in that work are insoluble in the usual solvents at normal temperature, chlorination was done in the heterogeneous phase— for example, by leading continuously a stream of chlorine over the finely ground polymer or through an aqueous suspension of the polyolefin. It is, therefore, difficult to compare the results obtained under the different conditions used. 

In radiation-induced chlorination, additional degradation of PIB by direct interaction with the C-C chain bond occurs (5). From a comparison with our results with literature data, we suggest that in our case, degradation takes place mainly by the more effective chlorination process. 

Radiation-induced cross-linking of chlorinated and chlorosulfonated high-density PE has been reported by Korolev et al. [262]. It has been observed that the extent of cross-linking is strongly dependent on the chlorine content in the sample, chlorosulfonated PE is cross-linked more readily than the chlorinated sample in air and inert atmosphere. 

The time-conversion curves do not pass through the origin in spite of all precautions taken, there was always a small dark reaction. This dark reaction is obviously caused by traces of light penetrating into the ampule during the preparation and is not caused by a thermal reaction. The conversion of the dark reaction in experimental times is always so small that it does not have any implications for the size of the radiation-induced reaction. Irradiation of a solution of polyisobutene in carbon tetrachloride in the absence of chlorine showed that only negligible amounts of chlorine (about 2 weight %) were taken up from the solvent. 

In analogy to classical chlorination reactions, the mechanism of the radiation induced process is presumed to be ... 

Czapski G, Goldstein S, Andorn N, Aronovitch J (1992) Radiation induced generation of chlorine derivatives in N20-saturated phosphate buffered saline toxic effects on Escherichia coli cells. Free Radical Biol Med 12 353-364... 

Getoff N, Solar S. Radiation induced decomposition of chlorinated phenols in water. Radiat Phys Chem 1988 31 121-130. 

K. Friese and F. Tannert, Radiation-induced grafting of chlorinated PVC for preparation of plastic foams. Radiat. Phys. Chem., 55 (1), 47-54 (1999). 

Confinement to the reactor is no problem if the reaction is radiation-induced. Examples are gas-phase chlorination of alkanes or alkyl side chains initiated by ultraviolet light. The reactor, usually a differential one, then is a cell in which the fluid passes through a beam of light. 

In equation (29) the symbol hv denotes the energy of a quantum of light of frequency v. The notation signifies that when the H2-CI2 mixture is irradiated by light of an appropriate frequency, light quanta are absorbed by chlorine molecules, causing them to dissociate. Any process of this kind, where radiation induces a reaction in an otherwise metastable system, is termed photosensitization. There are also many examples of processes in which reaction intermediaries or products are formed in excited states and deactivate by emitting nonthermal radiation this phenomenon is called... 

With the objective of oxidizing the fullerene core, radiolysis of any chlorinated hydrocarbon solvent provides the means of forming strongly oxidizing radical species [71]. For example, the radiation-induced ionization of dichloroethane (DCE) yields the short-lived and highly reactive solvent radical cation. In general, the electron affinity of [DCE] + is sufficient to initiate one-electron oxidation of the fullerene moiety (Eq. 6) [72-76]. 

It has been reported (II, 21) that the presence of mono- and dichloro-ethylene carbonate decreases the yield and molecular weight of PVCA. This can be confirmed for the radiation-induced polymerization when these compounds are present at levels above 1 %. However, as inhibition experiments demonstrated, the inhibition effectiveness of mono- and dichloroethylene carbonate was too small to account for the induction period observed. Furthermore, even after careful separation of these two substances, an unpolymerizable monomer with a chlorine content of about 0.1% was obtained. It should be noted that radiation-initiated polymerization of VCA is especially sensitive to inhibiting impurities, and that the induction period can be easily overrun by using conventional initiators. 

To test our assumption, we conducted polymerization experiments with small amounts of dichlorovinylene carbonate added to VCA. The inhibition effect was marked addition of even less than 0.5% dichlorovinylene carbonate completely suppressed radiation-induced polymerization of VCA under the given conditions. Although this may not be considered convincing proof, it is supported by the effect of reaction conditions on monomer quality the amount of trichloroethylene carbonate increases with more drastic chlorination condi-... 

Reduction Typical fullerene solvents are organics of low or medium polarity, such as toluene, benzonitrile, chlorinated hydrocarbons and CS2. In contrast, fullerenes are poorly soluble in polar solvents, including various alcohols. In polar solvents a spontaneous and irreversible cluster formation is noticed, yielding aggregates of various sizes. In aqueous solutions, [60]fullerene and its higher homologous, are practicable insoluble. It should be noted that most of the listed solvents cannot per se be employed for radiation-induced reduction studies. 

Uzun, C., Ilgm, R, Giiven, O., Radiation induced in-situ generation of conductivity in the blends of polyaniUne-base with chlorinated-pol5dsoprene. Radiation Physics and Chemistry 2010, 79,343-346. 

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