T.V. Monakhova

Specific features of formation and properties of hydroperoxides of polyolefins

Abstract Oxidized polyolefins may contain hydroperoxide groups but hydroxyl, carbonyl and other oxygen-containing groups also may be distributed in the polymer. The distribution of these groups and their proportions depend on oxygen pressure and other reaction conditions. Properties of hydroperoxides are functions of the conditions prevailing during the oxidation of the polyolefin. The mechanism of hydroperoxide formation during oxidation of polyolefins is discussed.

Effect of polydimethylsiloxane on oxidation of isotactic polypropylene

Addition of liquid polydimethylsiloxane to isotactic polypropylene retards its non-inhibited and inhibited oxidation by molecular oxygen. We propose that the reasons for this retardation are the migration of mobile free radicals and the reversible transition of antioxidant into inclusions of liquid siloxane in the polymer matrix.

The role of topological disorder in the inhibited oxidation of polypropylene melt

Abstract The parameters of the inhibited oxidation of polypropylene in the melt depend on the conditions of the sample preparation. These parameters for samples prepared by polymer precipitation from chlorobenzene and from decane are markedly different, although they only differ slightly in crystallinity and density. The authors believe that these differences are associated with differences in the character of topological disorder, which is stable even in a polymer melt.

Uninhibited and inhibited oxidation of poly-4-methylpentene-1

Abstract The oxidation of poly-4-methylpentene-1, in the form of either quenched or slowly cooled films, has been studied at 130–180°C. The oxidation rate depends on the conditions under which the specimens are prepared; the yield of hydroperoxide per mole of oxygen absorbed amounts to 0·3–0·36 and an inhibitor slows down oxidation in different ways in the quenched and annealed specimens.

Thermooxidative destruction of polypropylene-graphite composites☆

Abstract Thermooxidation of composites prepared by polymerization filling of polypropylene (PP) with natural and synthetic graphite was studied. Graphite retards PP oxidation; the dependence of the oxidation rate on the form and dispersity of graphite and on the composition of the composites was determined. Chain termination at the graphite surface appears as the chief retarding mechanism.

The noninhibited and inhibited oxidation of polyamides

Abstract Oxidation of polyamide-6,6 has been investigated at 150–230° at various oxygen pressures. The oxidation reaction involves only a small fraction of the polymeric material containing 0·6% methylene groups at 155°, and 1·4% at 200°, percentages that are not a function of the O 2 pressure. The PA-6, 6 hydroperoxide contains not less than two fractions that are quite dissimilar as to their stability. Features of oxidation of the polymer are in good agreement with a zone model of the process. According to this model the oxidation process primarily involves zones of disruption of short-range order existing in the polymer.

Solubility of additives in polyethylene and aliphatic polyamides. The effect of oxidation

Abstract The solubility of diphenylamine, phenyl benzoate and diphenyl methane in high-density polyethylene and various polyamides has been studied as a function of oxidation and of sample annealing. Oxidative destruction of topological structures forming the non-polar sorption centers and accumulation of new-formed polar groups, participating in sorption of polar compounds, result in complicated dependencies of solubility upon oxidation, in some cases showing minima.

Application of inhibitor methods to the study of oxidation of polyolefins

Abstract A study was made of the theory of using inhibitors for determining kinetic parameters of oxidation and of specific problems arising on using these methods for investigating oxidation of polyolefins. Special attention was given to latest modifications of the inhibitor method. An investigation was made in the experimental part of the use of three different inhibitors during non-initiated and initiated oxidation of atactic polypropylene and it was shown that inhibitors, which behave the same way under conditions of initiated oxidation, are utilized at different rates without initiators. It was shown that a stable iminoxyl radical reacts with different functional groups present in the polypropylene oxidized.

The initiating properties of polypropylene hydroperoxide as a function of oxygen pressure

Abstract The dependence of the rate of oxidation of isotactic polypropylene initiated by polypropylene hydroperoxide (PPHP) prepared by mild oxidation of thin polypropylene films under standard conditions, or by dicumyl peroxide, was studied at variuos oxygen pressures. We believe that the yield of radicals from dicumyl peroxide decomposition is independent of oxygen pressure. The dependence of the radical yield on pressure was calculated in the case of hydroperoxides.

Critical Concentrations of Some Phenolic Antioxidants in Butyl Rubber

Abstract Induction period of oxidation of butyl rubber non-linearly increases with concentrations of antioxidants: slowly below a certain threshold or “critical” concentration, and rapidly above that concentration. Three industrial antioxidants have been studied, the most effective from those appeared to be Agidol 2: 2,2′-methylene-bis(4-methyl-6-tert.butyl-phenol) otherwise known as “Antioxidant 22–46”. The theory of the effect is considered.