Mikhail A. Matsko

Study of the compositional heterogeneity of ethylene-1-hexene copolymers via thermal fractionation with the use of differential scanning calorimetry

The compositional heterogeneity of ethylene-1-hexene copolymers synthesized with various types of supported catalysts, namely, the titanium-magnesium catalyst TiCl4/MgCl2 and the zirconocene catalyst SiO2(MAO)/Me2Si(Ind)2ZrCl2, is studied via the method of successive self-nucleation-annealing (SSA) with the use of differential scanning calorimetry. On the basis of the data on the temperatures of individual peaks on SSA curves, the thickness of lamellas composed of macromolecules with a certain degree of short-chain branching is estimated. The copolymer synthesized with the zirconocene catalyst has a narrower range of fusion and does not contain large lamellas composed of molecules with a low degree of short-chain branching. With the use of the broadness index, it is shown that the copolymer synthesized with the zirconocene catalyst has a more uniform distribution of the comonomer than does the copolymer synthesized with the titanium-magnesium catalyst. For the copolymers synthesized with the titanium-magnesium catalyst, the compositional heterogeneity increases with an increase in the content of 1-hexene.

Titanium-magnesium catalysts for propylene polymerization: The effect of donors

The chain transfer reaction with hydrogen at propylene polymerization over Ti-Mg catalysts (TMCs) of composition TiCl4/D1/MgCl2-AlEt3/D2 is studied in a wide hydrogen concentration range. A two-step mechanism of this reaction is suggested. This mechanism accounts for the fractional order of the reaction with respect to hydrogen concentration. Constants of chain transfer reaction with hydrogen are determined for TMC with different donors: 1,3-diether or dibutyl phthalate as D1 and tetraethoxysilane or dicyclopentyldimethoxysilane as D2. In propylene polymerization over the TMCs, the length of the polymer chain is mainly determined by the ratio of the propylene and hydrogen concentrations because the propagation and chain transfer rate constants are comparable. The rate constant of chain transfer with hydrogen at ethylene polymerization is significantly (more than one order of magnitude) less, and higher hydrogen concentrations are required for attaining the same degree of polymerization. The results of this study might be helpful in simulation of industrial polymerization processes and in control of the polymer molar mass.

Analysis of the molecular structure of ethylene hexene-1 copolymers produced over highly active supported Ziegler-Natta catalysts

The mechanical and rheological properties of ethylene α-olefin copolymers are governed by a molecular and supramolecular structure that depends on its molecular weight characteristics, comonomer concentration, and the uniformity of branching distributions for polymer chains with different molecular weights (compositional heterogeneity). Using state-of-the-art methods, we study the parameters of molecular weight distribution, molecular structure, and compositional heterogeneity of ethylene hexene-1 copolymers with different compositions, produced over highly active supported Ti-Mg and V-Mg Ziegler-Natta catalysts, and show the possibility of controlling these parameters to improve the quality of the resulting polymers.