Yu.A. Shlyapnikov

Diffusion-controlled polymer oxidation

Abstract Some features of diffusion-controlled polymer oxidation are discussed. The difficulty of oxygen transport results in a decrease in the observed oxidation rate of thick polymer samples. Formulae have been derived for the dependence of oxidation rate on the flat sample thickness.

Antagonism between phenolic antioxidants and an organic acid

Abstract The role of stearic acid in the kinetics of polypropylene oxidation in the presence of 2,21-methylene-bis(4-methyl-6-tert-butyl-phenol) and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid diethyleneglycol ester has been studied. It has been demonstrated that this acid increases the critical concentration of the antioxidant with little effect on the rate constant of its consumption. The role of esterification reactions between antioxidant and acid is negligible. It is presumed that oxidant effectiveness is reduced by formation of complexes of antioxidant and acid.

Antioxidant action in polymers: The role of ‘inert’ compounds in inhibited oxidation

Abstract Low-molecular-weight compounds which take no part in polymer oxidation can change the reactivities of other compounds dissolved in the polymer, including antioxidants, by redistributing the antioxidant molecules among the elements of the polymer structure. The effects may be comparable with chemical synergism between antioxidants of different types.

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.

Loss of additives from polyethylene under natural conditions

The loss of antioxidants phenyl-β-naphthylamine and 2,6-di-tert-butyl-4-methylphenol from polyethylene in the open air, in soil and in a water reservoir has been studied. The rates of loss of the antioxidant correspond to the first-order law (−d[A]pdt = k[A]p, where [A]p is the current antioxidant concentration). The role of the environment is discussed.

Inhibited oxidation of polyethylene: anatomy of induction period☆

Abstract Oxidation of high-density polyethylene containing the strong phenolic antioxidant 2,2′-methylene-bis(4-methyl-6-tertbutylphenol) has been studied. During the induction period the antioxidant is consumed according to first-order kinetics, the rate constant depending on the initial antioxidant concentration; during the induction period about three moles of O 2 are consumed per mole of antioxidant. Formation of hydrogen peroxide in the induction period of oxidation has been established. The mechanism of inhibited oxidation is discussed. Antioxidants are more reactive compounds than polymers as such and, on being added to a polymer, they participate in many processes proceeding in it. Although the most important of these processes is chain termination, the major part of the antioxidant is usually consumed in direct reaction with oxygen and in termination of secondary chains initiated by its oxidation. In this work we studied some regularities of consumption of a strong antioxidant 2,2′- methylene-bis(4-methyl-6-tert,butylphenol) (MBP) in oxidation of high-density polyethylene.

Interaction of a phenolic antioxidant dissolved in polycarbonate with molecular oxygen

Abstract The reaction of the antioxidant 2,2′-methylene-bis(4-methyl-6-tertbutylphenol), dissolved in polycarbonate, with O 2 has been studied at 200 °C and oxygen pressure 300 mm Hg. The reaction follows first-order kinetics related to antioxidant concentration; its rate is directly proportional to oxygen pressure. The apparent rate constant is 1.1 × 10 −4 s −1 , or 3.7 × 10 −7 s −1 mm Hg −1 . The process is complicated with oxidation of the intermediate product, presumably monophenol X. The rate constant of its oxidation is about 1.6 × 10 −4 s −1 or 5.5 × 10 −7 s −1 mm Hg −1 . Peroxides were found among the volatile oxidation products.

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.

Solubility of antioxidants in poly(vinyl butyral)

Abstract The solubility of phenolic and phosphorus antioxidants in plasticized poly(vinyl butyral) (PVB) and in pure plasticizers at 20–60°C was studied. It was shown that the solubility of the antioxidant in PVB is not a linear function of the plasticizer concentration in the polymer. A turbidity of PVB containing antioxidants at low temperatures was observed.

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.