N. N. Kolesnikova

Interaction kinetics of peroxides and organic sulphides in atactic polypropylene

Abstract Kinetics of the reactions between benzoyl peroxide and sulphides (dilaurylthyodipropionate and dibenzyl sulphide), of the reaction between diphenylethyl hydroperoxide and dibenzylsulphide in atactic polypropylene and of the reaction of benzoyl peroxide with dibenzyl sulphide in polyisobutylene have been studied. The stoichiometry of the reactions was determined and the dependence of the rate constants on the initial concentration of reactant was established. At low reactant concentrations, the rate constants decrease and at high concentration increase with increasing concentration. In model low-molecular-weight hydrocarbon, the reaction rate constants do not change with reactant concentrations. The reaction mechanism is discussed. It is based on specific features of the dissolution of low-molecular additives in polymer.

Physical chemistry of topological disorder in polymers: Reconstruction of sorption centers and antioxidant effectivity in isotactic polypropylene

Formation and transformation of additive sorption centers in isotactic polypropylene was studied. According to a two-component model of a polymeric substance, these centers are formed around the elements or units of disorder (UODs) which are knots, folds, and other interlacements of long polymer chains. These elements are formed at the precipitation of the polymer and are stable even in the polymer melt because of the great lengths of the polymer chains. In some cases, the elements unable to sorb the given compound may be transformed into the sorption centers for it. When present in the sorption center, antioxidant molecules cannot move and react with macroradicals participating in the polymer oxidation, which results in the dependence of the so-called critical antioxidant concentration on that of the sorption centers. The theory of the formation and reconstruction of UOD-based sorption centers is discussed. Formation of a polymeric substance may be divided into two stages: polymerization or polycondensation of low-molecular compounds and self-assembling of macromolecules into polymeric material. Opposite to numerous investigations of the first step of this process and of the properties of the end products, the stage of transition of the macromolecules into the polymeric material and possibilities of regulating its properties in this stage are usually neglected.

Evaluation of antioxidant effectiveness in polyolefins

Abstract Antioxidants added to a polymer take part not only in reactions leading to retardation of the polymer oxidation, but also in many other stages of the oxidation process, including direct interaction with oxygen. Their effectiveness in polyolefins can be evaluated by analysing the dependence of oxygen consumption rate on initial antioxidant concentration.

Physical Chemistry of Topological Disorder in Polymeric Substance: Rearrangement of Additive Sorption Centers

Abstract Low-molecular compounds present in the melt of isotactic polypropylene in concentrations exceeding a certain limit, transform some elements of disordered domains into additional sorption centers for the same compounds. These centers can persist after the removal of the low-molecular compound leading to a post-plasticizing effect. This effect slowly disappears at elevated temperatures (80-100°C). The theory of sorption centers rearrangement is discussed.

The sorption of low molecular weight substances by atactic polypropylene

The sorption by atactic polypropylene (PP) of phenyl benzoate, diphenylamine and of other low mol.wt. substances has been studied. The sorption isotherms have been found to be described by the equation [A]p = a · [A]s(1+b[A]s)−1. The concentration of the sorption centres accessible to the low mol.wt. substances is independent of temperature in the 75–100°C range. The sorption of binary mixtures of such substances in the absence of a specific reaction in the polymer of one of the components will cause its linear decrease when the concentration of the other component increases. A model is suggested for describing the macromolecular packing processes producing greater kinetic stability.

Kinetics of the reaction between benzoyl peroxide and dibenzyl sulphide in atactic polypropylene

Abstract The theory of bimolecular reactions between low molecular substances dissolved in a polymer is discussed, on the basis of the assumption that most of a substance dissolved in a polymer exists in the form of immobile complexes of the substance with defects in the packing arrangement of the macromolecules. A considerable proportion of such reactions occurs in ternary complexes containing molecules of two reacting substances. The theory is illustrated by experimental evidence in which the kinetics of the reaction between benzoyl peroxide and dibenzyl sulphide and iso-octane and atactic PP are compared.

The concentrational dependence of the diffusion coefficients of low molecular weight substances in atactic polypropylene

Abstract The concentrational dependence of the diffusion coefficients of diphenylamine, phenyl benzoate and dibenzyl sulphide in atactic polypropylene (APP) at 313°K have been studied. The dependence observed is described by an expression based on concepts of the sorption of a significant fraction of the solute molecules in stable, disordered zones of close ordering in the disposition of the macromolecular segments and the non-equivalence of these zones in respect of sorptional properties. The values of effective activation energies have been obtained and the effect of an inert substance on the diffusion rate has been examined.

Kinetics of the reaction between benzoyl peroxide and dilauryl thiodipropionate

Abstract A study of the reaction between benzoyl peroxide and dilauryl thiodipropionate, proceeding in atactic polypropylene or in isooctane as its low-molar-mass model, revealed that at 50°C the compounds react in the ratio 1:1 and the reaction obeys the second-order kinetics. The rate constant of the reaction proceeding in isooctane is independent of concentration whereas in polypropylene the rate constant decreases with increasing concentration of dilauryl thiodipropionate and goes through a minimum when plotted against the peroxide concentration. The reaction mechanism is characterized by two parallel reaction routes.