K. S. Minsker

Active Sites Structure and Mechanism of Stereospecific Polymerization of α-Olefins and Dienes Employing Ziegler-Natta Catalysts

Abstract Stereospecific polymerization of α-olefin and diene hydrocarbons in the presence of catalysts of a new type proposed by Ziegler and Natta is a significant discovery of the twentieth century in the chemistry of macromolecular compounds. Heterogeneous Ziegler-Natta catalysts involving Ti and V trichlorides in combination with organoaluminum compounds have been widely used for nearly 30 years in commercial stereospecific polymerization of a number of o-olefins (propylene, hexene-l,4-methyl-pentene-1, etc.) and dienes (butadiene, isoprene, etc.). However, despite the great success achieved in practical implementation of the processes there is no common point of view so far and broad discussions are still under way as to the mechanism of polymerization and stereoregulation in the presence of the above catalysts.

The stabilizing action of β-dicarbonyl compounds in the thermal decomposition of poly(vinyl chloride)

Abstract The stabilizing effect of β-dicarbonyl compounds on the thermal degradation of PVC is shown to be related to their ability to exhibit protondonating properties and consists of the destruction of primary active sites for polymer decomposition, namely carbonylallyl groups.

Stabilization of poly(vinyl chloride) by β-dicarbonyl compounds

Abstract The possibilities of using β-dicarbonyl compounds as thermal stabilizers of vinyl chloride polymers have been studied. The stabilizing properties are connected with the strongly marked CH-acidity shown by these compounds. Ideas on the mechanism of their interaction are presented.

Solvation stabilization of vinyl chloride polymers to degradation in solution

The rates of thermal degradation of vinyl chloride (VC) polymers in organic solvents and in the solid phase are significantly different. The kinetics of the process in the liquid phase is determined by the effects of specific and non-specific solvation interaction between the solvent and the polymer molecules. In the process of polymer degradation, solvation has different effects on the rate of random elimination of HCl from PVC with the formation of isolated CC bonds and on the formation of poly-conjugated systems of double bonds. The rates of liquid-phase degradation of VC polymers in different classes of organic solvents are mainly determined by specific polymer-solvent solvation interaction; the overall dehydrochlorination rates of VC polymers in solution increase linearly with the basicity B (donor number DN) of a solvent: In addition to specific solvation, the rate of the liquid phase degradation of VC polymers in solvents is also affected by polymer-solvent non-specific interaction. The loosening of solvation interactions between polymer and solvent, resulting from addition of a non-polar hydrocarbon to the system, induces stabilization in solutions of VC polymers.

Structural-physical effects at thermal degradation of PVC in complex polymer objects

The influence of structure formation on thermodegradation of poly(vinyl chloride) (PVC) in complex polymer objects is considered in the article. It was shown that structural–physical states of polymer mixtures depend on the method of obtaining a composite and affinity of the polymers. Composites of the same composition may be obtained, which possess rather different dehydrochlorination rates for PVC.

Peculiarities of the thermal degradation of chlorosulphonated polyethylenes

Abstract A kinetic study is made of the thermal degradation of chlorosulphonated polyethylenes containing 3–40 wt% of Cl and 1·4-2·2 wt% of sulphur. It is concluded that the instability of these polymers is principally due to activation of the CHCl structures in the β-position to the CH 2 SO 2 Cl groups.

The reason for the low stability of poly (vinyl chloride) ― a review

Abstract The experimental evidence relating to the role of carbonylallyl groups as the principal labile structures which cause instability in poly(vinyl chloride) is discussed.

The Macroscopic Kinetics of Rapid Processes of Polymerization in Turbulent Flows

Abstract The peculiarities of the macrokinetics of rapid polymerization processes in turbulent flows (when the times of the chemical reaction are less than or compatible with those of the reagent mixing) have been discussed. The characteristic specific phenomena have been elucidated, namely: dependence of the molecular characteristics output (MW and MWD) of the polymer formed on the geometry of the reaction volume and on the parameters of the processes of mixing and heat transfer (flow rates, turbulization, boiling, etc.). Such reactions require special methods of investigation and control including those in industries with principally new material-, resource-, and power-saving technology, in particular, for the production of the isobutylene polymers. It is expedient to distinguish the rapid processes of polymerization as a separate class.

Thermal degradation of vinyl chloride homo- and copolymers in solution

Abstract The results of investigations on the thermal degradation of vinyl chloride (VC) homo- and copolymers in dilute and concentrated solutions are presented. Depending upon the nature of the solvent, the thermal degradation of VC polymers in solvents which do not react with the macromolecules may be accelerated or retarded compared with degradation in the solid phase. The effects are explained from the standpoint of the influence of solvation effects, i.e. specific (donor-acceptor) and non-specific (Van der Walls) interactions between macrochains and solvent molecules. Specific interactions between the solvent and the abnormal structures present in the macrochains of VC polymers bring about either a reduced or an increased rate of polymer dehydrochlorination, depending upon the basicity of the solvent, whilst non-specific solvation always tends to intensify the degradation of polymeric molecules due to the increased small-scale dynamics of macromolecules.

Calculation and simulation of the polymerization of isobutylene as a fast reaction

A mathematical analysis of the kinetics of the rapid polymerization of isobutylene has been made; this has been done with a continuous scheme in which the special features of the properties of the reaction medium and the technological parameters of the reaction behaviour are taken into account. It has been shown that rapid reaction with local introduction of the catalyst occur in separate zones as a “flame” with different temperatures and kinetic parameters: this is accompanied by the formation of a polymer with enhanced molecular non-uniformity. The calculated data have been compared with experimental data and they have been found to agree.