Low-temperature Radiolysis Research Articles

On the mechanism of radiation-induced crosslinking of poly(vinyl chloride) in the presence of some polyfunctional monomers

Some features of low-temperature radiolysis of poly (vinyl chloride) and the effect of added polyfunctional monomers such as triallyl cyanurate have been studied using the technique of infrared spectrophotometry. It has been found that the radiation yield of HCl formed in the radiolysis of poly(vinyl chloride) alone at 100°K is equal to 2.5. Additives form a complex with radiolytically produced HCl. The structure of this complex corresponds to on oxonium compound. The radiation yield of the complex reaches 50–80 per 100 eV of energy absorbed by additives. At the same time, the addition of triallyl cyanurate in poly (vinyl chloride) decreases the radiation yield of HCl associated with polymeric matrix by 2–3 times. The reaction of the allyl groups of the additive with the polymer free radicals already occurs at low temperatures. On heating, the irraditated at low temperature samples, the complex of additive with HCl decomposes, the remaining allyl groups disappear, and triazine rings are partly transformed to the isocyanurate form. These results are interpreted in terms of a mechanism which postulates the localization of the dehydrochlorination process of poly(vinyl chloride) in the vicinity of the additive molecules and the promotion of crosslinking efficiency by the formation of complex of additive with HCl.

Low-temperature radiolysis of aqueous solutions of deoxyribonucleic acid

1. The products of the radiolysis of water which participate in the decomposition of deoxyribonucleic acid and the biopolymer radicals which form as a result of these reactions were identified from EPR spectra. 2. At 77°K, DNA reacts with the reducing component of water radiolysis. 3. The radiation-chemical yields of radicals in solutions of DNA and glucose irradiated at 77°K were determined.

Study of the mechanism of structuration of solid rubbers by radiation

THE radiolysis of polymers is known to produce a variety of structural conversions [1], some of them being very intensive, such as crosslinking and degradation, which cause a qualitative change of the polymer properties. Where condensed systems are subjected to radiolysis, especially during their transition to the glass-like state, the probability of chemical bond fracture in the main chain is smaller and the fragments will be larger. The recovery of the latter from the reaction zone is made difficult by the so-called cell effect [2]. The primary bond fracture in condensed hydrocarbon systems will involve a C H bond and give rise to free H atoms, which easily escape from the cell [3]. The latter will be the preferred process during low-temperature radiolysis, although the bond energy (D) DC_H>Dc_ c. The free valencies produced by this fracture (free polymer radicals R') are stable under low temperature conditions. Release of mobility in the system can result in the recombination of two from different molecules, and the formation of an intermoleeular erosslinkage: R'q-R --> R R . (1) This is not the only process leading to chemical bond formation. Earlier studies [4-6] dealt with the reactions of R and R + ions after thermal and photochemical initiation [7]; these are produced when the radicals t rap the charges: t R + R + -> R R (2) R + R --> R R + e (3) R + + R -> R--R+ (4) I t was established in other investigations [6, 9] that photo-sensitive paramagnetic centres of two types are produced and stabilized when fluorine-containing elastomers are subjected to low-temperature radiolysis; these centres are regarded as molecular R F anions. They will accumulate rapidly and probably

On the mechanism of low temperature radiolysis of crystalline ice

Abstract The free radicals from γ-radiolysis of crystalline ice with additions of alcohols and alkali hydroxides at 77 °K have been studied by EPR and optical spectroscopy methods. It has been found that trapped electrons are formed in these systems. In the case of alcohol additions it has been shown by optical spectroscopy that the electrons are stabilized in traps consisting of molecules of impurities. The yield of radicals is increased with the growth of concentration of additions and is dependent on sample structure. The mechanism of radiation chemical processes in crystalline ice is discussed.

Effect of Temperature on Decay of Radicals Formed during Radiolysis of Solid Rubbers

Abstract Temperature-time curves for radical decay, when radicals formed in rubbers by low-temperature radiolysis (−196° C) are heated, have been studied by the EPR method. Analysis of results shows that radical decay processes begin much below Tg, with simple increase in the amplitude of thermal vibrations. Extent of decay is greater the lower the steric hindrance in the monomer unit, the order of this effect being SKD > SKS > KHK > SKI, NR, SKEP. On the other hand, contribution of the sudden change in the region of Tg in the processes of unfreezing of motion and decay of radicals is greater in rubbers with side chains. Results obtained permit determination of a number of important energy characteristics of the polymers, in particular molecular energy barriers, UT, activation energies for radical decay, ET and energies of thermal motion at which radical decay begins. These results show that the radical decay process at low temperatures begins before movement of macromolecules relative to one another and is dependent on a migration mechanism with very low energy of activation. This process consists in migration of “secondary” ions formed by capture of charges by free radicals. Schemes of radical decay processes involving a combination of reactions between radicals and “secondary” ions of radical origin are suggested.

Radical formation in low-temperature radiolysis of benzoyl peroxide

Radical formation in low-temperature radiolysis of benzoyl peroxide

A study of radicals arising in the low-temperature radiolysis of thiophene and some of its derivatives

EPR was used to investigate the radicals formed by radiolysis of furan, thiophene, and some of their substitution products having the general formula C4H3RS, where R = Cl, Br, COOH, C(CH3)3, and of di-tert-butylthiophene. By analyzing the EPR spectra it is shown that radicals formed by radiolysis of furan, thiophene, their alkyl substitution products, and 2-thiophene carboxylic acid arise in primary radiation-chemical events with splitting of the C-H bond in both ring and side chain. Characteristic of the radiolysis of these compounds is formation of secondary radicals by addition of hydrogen atoms at the double bond of the heteroaromatic ring. The values of the hyperfine splittings in the spectra of the secondary radicals are, for protons of methylene group 32 e [positions 2(5)] or 40 e [positions 3(4)], and 13 e for protons of the thiophene ring. In radiolysis of 2-chlorothiophene and 3-bromothiophene the main products are radicals with the unpaired electron localized on the sulfur atom.

Investigation of low temperature radiolysis of simple aromatic compounds with the aid of EPR and mass spectrometric methods

Investigation of low temperature radiolysis of simple aromatic compounds with the aid of EPR and mass spectrometric methods

Formation of radicals in low temperature radiolysis of toluene

Formation of radicals in low temperature radiolysis of toluene

The production of hydrogen in the low-temperature radiolysis of polyethylene

1. The kinetics of the production of H2 and D2 in the radiolysis of high pressure polyethylene and deuteropoly-ethylene, respectively, has been investigated at temperatures of ∼20°C and ∼90°K. 2. The radiation yields G(H2) and G(D2) decrease in the course of radiolysis. 3. The decrease in G(H2) and G(D2) at a temperature of ∼90°K is not associated with a reaction of the type H+R → RH, where H is a hydrogen atom and R is a stabilized radical.