S. Ya. Khaikin

Determination of the concentration of active centres and the propagation reaction rate constants of the macrochain on polymerization of ethylene on highly active catalysts

A number of variants of use of the kinetic method of determining the concentration of active centres and the propagation constant of the process of polymerization of ethylene on the catalytic system titanium-magnesium catalyst—Al(i-Bu)2H are considered. The best results were obtained when the MWD of polyethylene was examined in the early period of polymerization. The catalytic system investigated is characterized by the presence of two types of active centres with values of the propagation constant 1500 and 10,000 1./mole·sec, respectively.

Features of post-radiation oxidation of trapped radicals in high and low density polyethylene

Abstract The post-radiation oxidation of trapped allyl radicals in HDPE and LDPE films has been studied by ESR. The radical oxidation rate in the crystalline regions of LDPE is two orders higher than that in HDPE, due to the greater oxygen diffusion rate, owing to the lower density of the crystalline regions of the LDPE. In LDPE, peroxide radicals were formed whereas oxide ones formed in HDPE.

Link between the structure of amorphous-crystalline polymers and the features of oxidation of polymer radicals formed by gamma irradiation☆

Abstract The ESR method has been used to study the oxidation of the primary radicals formed by γ-irradiation in polyvinylidene fluoride and polyethlene. It has been established that in them only some of the primary alkyl radicals may be oxidized with formation of peroxide radicals. In polyvinylidene fluoride radicals of three types are found: stable non-oxidizable fluoroalkyl, stable peroxide and unstable peroxide. It is assumed that they are localized respectively within the crystallites, on the surface and in the amorphous regions of the polymer, the concentration ratio of the stable peroxide to alkyl radicals being a measure of the specific surface of the crystallites. It is shown that this ratio for polyvinylidene fluoride is constant in time and depends on the structure of the sample changing on orientation drawing, thermal treatment and impact loading of the polymer. It has been established that high and low density polyethylene samples are characterized by different values of this ratio.

Sensitization of radiation-chemical crosslinking of polyvinylidene fluoride by N,N′-m-phenylene dimaleimide

Abstract The authors have studied the sensitizing action of N,N′- m -phenylene dimaleimide on the process of radiation-chemical crosslinking of PVDF. The sensitizing action of N,N′- m -phenylene dimaleimide may be explained by the interaction of the vinylene groups of the diimide with PVDF with formation of transverse bonds. In presence of N,N′- m -phenylene dimaleimide the ratio of the radiation-chemical yields of degradation and crosslinking falls as result of rise in the radiation-chemical yield of crosslinking.

Model for volumetric rupture of non-oriented polymers☆

A phenomenological model is proposed describing the kinetics of accumulation of damage recorded by the method of IR spectroscopy from the rise in the concentration of terminal carboxyl groups in non-oriented high density PE. The approach adopted makes it possible to describe the influence of temperature and load on the form of the kinetic curve, in particular, the duration of the induction period. A very simple evaluation of the effectiveness of the action of chemical stabilizers is also presented.

Buildup of failures in polymers on micro- and macrolevels

The buildup of damage in polymers has been studied by mechanical and structural—analytical methods. A method of programmed loading has been developed which makes it possible to make an estimate of damage buildup in macroscopic experiments. A comparison has been performed of kinetic curves of failure buildup on molecular and macroscopic levels. It is shown that the kinetic equations where the rate of failure is basically initiated by true stress qualitatively follow the experimental curves for failure buildup on micro- and macrolevels.