Polymerisation radiochimique de l'acetaldehyde en phase solide

The radiation induced solid-state polymerization and post-polymerization of crystalline acetaldehyde were studied in a diathermic calorimeter by measuring the heat evolution during polymerization. The heat of melting of crystalline acetaldehyde was found to be 1,4 ± 0,07 kcal mol^?1 and the heat of polymerization 2,5 ± 0,5 kcal mol^?1 at 80–150°K. Under isothermal conditions the rate of the solid state polymerization of acetaldehyde increased with irradiation time up to a maximum and thereafter it decreased. This phenomenon is connected with an increase of the concentration of active centres during irradiation. The propagation rate constant is $\text{k}{}_{\mathrm{p}}\text{? 5 × 10}{}^{\mathrm{?4}}\text{exp(?11,000/RT) cm}{}^3\text{sec}{}^{\mathrm{?1}}$ at 130–140°K and the average time of addition of one monomer unit is 10^?1–10^?2 sec.     

Formation of N-vinylpyrrolidone homopolymer and its grafting during radiation-induced copolymerization with triethylene glycol dimethacrylate

The kinetics of radiation-induced copolymerization of N-vinylpyrrolidone with triethylene glycol dimethacrylate was studied. It was shown that the formation of a water-soluble N-vinylpyrrolidone homopolymer and its subsequent grafting onto the copolymer takes place in the system during the process. Copolymers containing up to 90 mol % N-vinylpyrrolidone in the macromolecular chain to provide their high sorption power were obtained.     

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H₂C=N and HC=NH radicals, respectively (the molar absorption coefficients are k ₂₇₀ 2.7 × 10²l mol^–1cm^–1and k ₂₉₀ 1.5 × 10²l mol^–1cm^–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with 300 nm, can belong to the cyanide ions (CN^–) and H₂C=N⁺cations (the molar absorption coefficients of the ions are k _ion= (0.4–1.0) × 10²l mol^–1cm^–1). In the photobleaching of -irradiated HCN ( = 236–280 nm), H₂C=N⁺radicals were additionally formed by the photoinduced reaction of electron transfer from the CN^–anion to the H₂C=N⁺cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.     

Radiation chemistry of polymers

Results of basic and applied research in radiation chemistry of polymers in Russia and Belarus for the last 5–10 years are presented.     

Radiation-induced cryocopolymerization of hydrogen cyanide and epichlorohydrin: Copolymerization traveling waves initiated by mechanical fracture at 77 K

Low-temperature (77–150 K) radiation-induced copolymerization of hydrogen cyanide (HCN) and epichlorohydrin (ECH) has been studied. Copolymers have been obtained in two modes of running the reaction, the thermally activated postpolymerization at slow heating of the preliminarily γ-irradiated system and the traveling wave of copolymerization initiated by local brittle fracture of solid samples at 77 K. The threshold values of parameters (a dose of preliminary irradiation, comonomer ratio in the initial mixture) necessary for the realization of the self-sustained wave mode of copolymerization have been determined. An increase in the HCN concentration in the initial comonomer mixture suppresses the copolymerization, and the yield of the copolymer decreases. Epichlorohydrin-soluble copolymers with the content of HCN units up to 5.7 mol % have been obtained as the result of the process.     

Intrinsic charge transport on the surface of organic semiconductors

The air-gap field-effect technique enabled realization of the intrinsic (not limited by static disorder) polaronic transport on the surface of rubrene (C42H28) crystals over a wide temperature range. The signatures of this intrinsic transport are the anisotropy of the carrier mobility, mu, and the growth of mu with cooling. Anisotropy of mu vanishes in the activation regime at low temperatures, where the transport is dominated by shallow traps. The deep traps, introduced by x-ray radiation, increase the field-effect threshold without affecting mu, an indication that the filled traps do not scatter polarons.     

Syntheses relating to anabasine base

Chlorination of anabasine and piperidine with chlorine at 220–230° leads to dehydrogenation and formation of respectively, 5-chloro-2, 3-dipyridyl and 3-chloropyridine.For Part XIX see [8].     

Low-temperature radiation-induced copolymerization of N-vinylpyrrolidone with divinyl sulfone

The low-temperature copolymerization of N-vinylpyrrolidone with divinyl sulfone was studied in vitrifying dimethylformamide solutions. It was shown that the copolymerization proceeds efficiently in a viscous supercooled liquid after devitrification of the system. The mechanism and conditions are determined for the formation of random and alternating copolymers.