Effect of p-toluensulfonic acid on oxidation of polyethylene and polyethylene-poly-p-methylstyrene blends

p-Toluensulfonic acid retards oxidation of polyethylene and, to a greater extent, of polyethylene-poly-p-methylstyrene blends. The real antioxidant is p-cresol, formed by p-toluensulfonic acid transformation in oxidizing polyethylene and, in blends, through peroxidation and subsequent acid-catalyzed decomposition of hydroperoxides of poly-p-methylstyrene.     

Thermal oxidation and photo- and biodestruction of the statistical copolymer of ethylene with carbon monoxide

Thermal and photooxidation of the statistical copolymer of ethylene containing 1.5% carbonyl units -C(O)- by molecular O₂ was studied at 160–200°C in the presence and absence of phenyl-β-naphthylamine (PNA) antioxidant. The incorporation of a small number of -C(O)- groups into the polyethylene chain insignificantly decreased the rate of thermal (dark) oxidation but substantially accelerated oxidation under the action of light. At the same time, the oxidation of the copolymer occurred at a lower rate than the oxidation of pure polyethylene (PE), which was evidence of an important role played by intramolecular oxidation chain propagation in PE, which is disturbed already at a comparatively low fraction of foreign units. Phenyl-β-naphthylamine noticeably decelerated oxidation. The rate of polymer biodestruction was much higher than the rate of PE biodestruction. The influence of biodestruction on the physicomechanical properties of samples was studied by ultrasonic microscopy. The velocity of sound propagation in PE was somewhat lower compared with the ethylene-carbon monoxide copolymer (ECO). Clearly, the introduction of a small amount of CO molecules into the polyethylene chain changed the microstructure of PE. The structure of ECO was more ordered and denser because of plasticization by metabolites.     

Mechanism of nitrosation of ascorbic acid by nitrite in neutral aqueous media

The main issues in nitrosation of ascorbic acid by the nitrite ion in aqueous media are discussed. Possible mechanisms of the reaction in aqueous media with different acidities are analyzed on the basis of available published data. The main kinetic characteristics of nitrosation of ascorbic acid in neutral Tris-HC1 and phosphate buffers were obtained, and they are interpreted with due regard for the possible active participation of buffer components in the reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2242–2247, October, 1991.     

Ultrasonic dispersers for sample preparation in the electron microscopy of polymers

The design features of UZDN-1 and UZDN-2T ultrasonic dispersers are described. The optimum conditions for dispersion using these apparatuses to prepare samples for the electron microscopy of polymers are determined.     

Solubility of low-molecular-mass compounds in copolymers

The solubility of some low-molecular-mass antioxidants in polyethylene-based copolymers was studied. It is shown that another copolymer has a complex effect on the solubility of low-molecular-mass compounds and the concentration of their saturated vapor over the copolymers.     

Nitrosation of ascorbic acid by nitrite ion in unbuffered neutral and moderately acidic aqueous solutions

The kinetics of nitrosation of ascorbic acid by nitrite in unbuffered aqueous solutions was measured in the pH range from 6.7 to 4.0 at 25°C. The reaction order with respect to the proton is reliably lower than 2, especially in a more acidic solution. This means that under the studied conditions unprotonated nitrous acid may be involved directly in nitrosation of ascorbic acid.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1540–1544, July, 1992.     

Specific Features of Thermal Degradation of Polypropylene in the Presence of Magnesium Hydroxide

Specific features of thermal oxidative degradation of polypropylene and its composite with Mg(OH)₂ were studied by pyrolytic gas chromatography-mass spectrometry and thermal gravimetric analysis.     

Application of an ultramicrotome in SEM and TEM studies of polymeric systems with metal-containing clusters

Design features of UMTP-6 and UMTP-7 ultramicrotomes are described. The instruments were tested on the following systems: (1) polyethylene and Nylon 6 fibers treated with AgNO₃ and (2) different photographic films based on cellulose triacetate and containing silver halides.