The hyperfine structure of the components of the doublet EPR spectrum of atomic hydrogen in silicon dioxide (silica gel, quartz, or molybdenum glass) γ-irradiated at 77 K is due to the overlap of two doublets with α = 50.5 and 50.4 mT, a standard singlet and a resolved multiplet, responsible for the accumulation and stabilization of two types of surface and bulk atomic hydrogen. Surface hydrogen atoms formed upon the dissociation of surface OH groups and water molecules are stabilized in dry traps, and they have a standard doublet with α = 50.5 mT in the EPR spectra. Bulk hydrogen atoms are formed (upon radiolysis) and stabilized in internal water clusters of SiO 2 . In the water medium of clusters, bulk hydrogen atoms are affected by the protons of the water environment and, interacting with protons, they exhibit a multiplet doublet with α = 50.4 mT in the EPR spectra. The contribution of the multiplet doublet to the total spectrum depends on the type of SiO 2 and the radiation dose. The fraction of a multiplet doublet in macroporous glass at a dose of 120 kGy was 40%. When water was completely removed from a SiO 2 matrix, bulk hydrogen atoms disappeared, and a standard doublet of atomic hydrogen was recorded in the EPR spectra after an irradiation dose of 40 kGy or higher.

The photolysis of dry benzoyl peroxide (BP) at 77 K in the 480–236 nm range of wavelengths and an ethanol solution is studied via EPR. It is determined that the main photochemical process in irradiating BP at λ = 480–365 nm is the direct photodissociation of the O–O peroxide bonds and C–H bonds of benzene rings to form benzoyloxy radicals and atomic hydrogen, which likely forms via a two-quantum mechanism. The quantum yield of primary intermediates is φ ≈ 2.7 × 10−5. Upon subsequent irradiation of a sample using light with λ = 300–236 nm, benzoyloxy radicals release carbon dioxide and transform into phenyl radicals with a quantum yield of φ ≈ 3 × 10−4. At 120–145 K, phenyl radicals react with double bonds of aromatic rings of PB to form phenyl-substituted cyclohexadienyl radicals vanishing at 273 K. Quantum chemical calculations of the radical structures of photolyzed peroxide are made with the density functional approach (B3LYP/6-311g), and good agreement between the experimental and theoretical parameters is noted. Calculations show that in the structure of benzoyloxy radicals, the spin density is distributed almost equally between the two oxygen atoms of the radical, due to the conjugation of the unpaired electron to the lone p electron pair on the oxygen atom of the C=O group. In the photolysis of BP solutions in ethanol at λ ≥ 365 nm, solvent radicals form via sensitized photolysis through the reaction between primary benzoyloxy radicals and solvent molecules.

Using EPR spectroscopy, it has been established that monomers affect the decomposition rate of their polymerization initiators by forming complexes with them. Several structures of the complexes have been optimized, and their decomposition mechanisms, the activation energies of the chain initiation and propagation reactions, and the heat of polymerization have been determined by means of quantum chemistry methods. In the absence of radical inhibitors (evacuation), the polymerization proceeds with high efficiency (98%) at room temperature without stimulation of the system with external energy.

The kinetics of radiation telomerization of tetrafluoroethylene (TFE) in trifluoroethanol and hexafluoropropan-2-ol (HFIP) has been investigated by method of kinetic calorimetry. The nature of active centers initiating the process of telomerization of tetrafluoroethylene in hexafluoroisopropanol in the temperature range of 77—300 K was investigated by ESR spectroscopy. The molecular structure and properties of the obtained telomeres were studied by IR spectroscopy and TGA.

Molecular mobility of a nitroxyl radical (as a paramagnetic probe) in methylcyclohexane (MCH) solutions of chiral biomimetic gelators—trifluoroacetylated amino alcohols (synthetic analogues of biological molecules)—has been studied by monitoring thermally induced changes in EPR spectra. The phase state of the systems has been examined by the low-temperature scanning calorimetry method. There has been found an unusual concentration and temperature dependence of probe species mobility in diluted solutions (10–2–10–3 M) of trifluoroacetylated amino alcohols with a molecular weight of no more than 200. From the temperature-induced changes in EPR spectra of the paramagnetic probe in the temperature range 170–290 K, the rotation activation energies of probe species in biomimetic solutions and in the neat solvent. The minimum radical rotation activation energy (2.1 kcal/mol) is observed in the most concentrated gelator solution, whereas in neat MCH, this energy is 3.7 kcal/mol.

The radical telomerization of tetrafluoroethylene initiated by benzoyl peroxide (BP) photolysis at λ ≥ 365 nm is studied in acetone, dichloromethane, carbon tetrachloride, and Freon 114B2 at 25°C. The products of synthesis are a mixture of telomers of different molar masses, segregated into soluble and insoluble fractions. To characterize the radicals initiating telomerization, crystalline BP and its solution in ethanol are subjected to low-temperature (77 K) photolysis, with the liquid system serving as a model for BP behavior in solutions of telogens. It is established that radicals are not only initiators but also participate in chain termination reactions, lowering the telomers’ molar mass and thus raising the proportion of the soluble fraction. Telomerization initiated by an initiator compound versus initiation by gamma radiation are compared and discussed.

The molecular mobility of nanocellulose hydrogels isolated from microcrystalline cellulose is evaluated using the spin probe method, from the correlation time τ (s) and rotational frequency ν = 1/τ(s–1) of stable nitroxyl radicals introduced into the medium under study. In an aqueous gel medium, the EPR spectrum of the probe features an anisotropic triplet of frozen particles over a temperature range of 77 to 265 K. In an aqueous–ethanolic gel solution, the temperature of onset of rotation of the radical is 85 K lower. The rotational correlation time is determined from the parameters of the EPR spectrum recorded in the temperature range of 180–290 K. The resulting Arrhenius temperature dependence logν = f(1/T) is used to evaluate the activation energy of rotation E of the radical and the preexponential factor ν0(s–1), the frequency of rotational vibrations of the particle around the equilibrium position. For the aqueous medium, E = 11.2 kcal/mol; in the presence of ethanol, E = 5.2 kcal/mol; the preexponential factors for the aqueous and aqueous–ethanolic media are ν0 = 7 × 1018 and 6 × 1014 s–1, respectively. The parameters E and ν0 measured in the pure solvents and in the samples containing nanocellulose differ little, which is indicative of a high hydrophobicity of the probe molecule (and hydrogel particles) and of their weak interaction with the environment. The high value (~1018 s–1) of the preexponential factor is explained in terms of the compensation effect of water.

Kinetic calorimetry was used to study the kinetics of low-temperature post-radiation telomerization of tetrafluoroethylene in ethanol and hexafluoroisopropanol. The temperature range in which the reaction occurs and its efficiency depend on the phase state of the reaction mixture at low-temperatures and on the chemical nature of the solvent. The nature of active centers initiating the telomerization process of tetrafluoroethylene in hexafluoroisopropanol and their accumulation kinetics were examined by EPR spectroscopy. The molecular structure and properties of the resulting telomers were examined by IR spectroscopy and thermogravimetric analysis.

Kinetics of radiation-induced cotelomerization of tetrafluoroethylene with methyl acrylate and terafluoroethylene with acrylamide in solutions of methylene chloride was studied. The synthesis process occurs under the conditions of kinetic chain transfer to the telogen, which involves only the radical with a terminal fragment of tetrafluoroethylene, whereas methyl acrylate or acrylamide molecules are added to the growing telomer chain. The composition of the telomer and its properties depend on the relative reactivities of the monomers in the chain-growth reaction. The incorporation of methyl acrylate into the telomer chain results in that the molecular mass and the fraction of the soluble fraction of the cotelomer become larger. It was found that the adhesion properties of fluorine-containing coatings formed on the basis of cotelomers of tetrafluoroethylene and methyl acrylate are improved.

The kinetics of radiation-induced telomerization of tetrafluoroethylene in chlorinated solvents was studied. In the presence of an additionally introduced chain-transfer agent, 1-decanethiol, the soluble telomers are formed more efficiently, and their yield increases. At the ratio tetrafluoroethylene: 1-decanethiol ≤ 2: 1, the completely soluble telomer is formed in the system. By varying the reaction mixture composition, it is possible to control the process and obtain a fully or partially soluble product in a high yield.

A range of issues related to free-radical processes in polymer-monomer systems is considered. Spectral (EPR, IRS) and other physicochemical methods (calorimetry, chromatography, viscometry) are used to demonstrate that the low-temperature treatment of polymers and monomers with halogens (fluorine, chlorine) is accompanied by the spontaneous formation of free radicals. At F2 and Cl2 pressures below 100 Torr, the concentration of radicals reaches 1017–1019 spin/g, which can be reproduced in the case of radiolysis only by using doses of several hundred (or thousand) kGy. The formation of radicals through the cleavage of chemical bonds (without external energy impact on the system) is discussed in the framework of the model of low-temperature reactions in polymolecular complexes, involving the simultaneous occurrence of endothermic and exothermic steps in one elementary event with an overall exothermic effect. It is shown that the radicals formed can be used to initiate the polymerization of vinyl and acetylene monomers.

Методами ЭПР-, ИК-спектроскопии и сканирующей калориметрии исследован механизм низкотемпературной радиационной теломеризации тетрафторэтилена (ТФЭ) в гексафторизопропаноле (ГФИП). Установлено, что низкотемпературная теломеризация ТФЭ в ГФИП протекает по ион-радикальному механизму, процесс инициируют анион-радикалы (CF3)2C. O-, образующиеся при депротонировании ОН-групп первичных гидроксирадикалов (CF3)2C. O, обладающих сильными кислотными свойствами. Предложена интерпретация выделенных при 230–240К спектров ЭПР облученного ГФИП с учетом анизотропии на -атомах фтора и оценки углов между соответствующими С–F-связями и осью орбитали неспаренного электрона.

ESR and IR spectroscopy and scanning calorimetry are used to investigate the mechanism of low-temperature radiation telomerization of tetrafluoroethylene (TFE) in hexafluoroisopropanol (HFIP). It is found that the low-temperature telomerization of TFE in HFIP proceeds via an ion-radical mechanism. This process is initiated by the radical anions (CF3)2C·-O− formed during the deprotonation of OH groups of primary hydroxyl radicals (CF3)2C·-OH exhibiting strong acidic properties. An interpretation of ESR spectra of irradiated HFIP recorded at 230–240 K is proposed with regard to the anisotropy on β-fluorine atoms and estimates of the angles between the corresponding C-F bonds and the axis of the unpaired electron orbital.

Radiolysis of plant biomass with doses of 200–300 kGy prior to dispersing by chemimechanical methods increases the yield of nanocellulose from cellulosic feedstock by more than a factor of two. Another advantage of radiation pretreatment of initial samples is the effect of radiation sterilization of isolated nanocellulose hydrogels, whereas the hydrogel obtained without preliminary irradiation rapidly suffers from the attack of molds during storage in the laboratory. Photolysis of plant raw material at a wavelength of 253.7 nm has almost no effect on the yield of nanocellulose. The molecular and supramolecular structure of nanoparticles with a size of 200–300 nm remains unchanged on passing to the nanoscale and corresponds to the macromolecular structure of cellulose. Industrial testing of the hydrogel as an additive (2.5%) for an adhesive composite used in the manufacture of wood laminates (plywood) showed an enhancement of the strength characteristics of the products by 15–20%. The increase in strength is mainly due to an increase in the contact area of cohesive bonding through small coiled molecular entities composed of 10–16 Kuhn segments including up to 28 monomer units each.