Kinetic Features of Hexene-1 Polymerization over Titanium-Magnesium Catalysts
This study focuses on polymerization of hexene-1 over high-activity stereospecific titanium–magnesium catalyst. The data on the effect of cocatalyst composition and polymerization conditions (temperature, concentrations of cocatalyst, monomer and hydrogen) on catalyst’s activity, molecular weight distribution (MWD) and microstructure of polyhexene (PH) are obtained.
The cocatalyst has an extremely strong effect on the molar mass and MWD of polyhexene. When triisobutylaluminum is used as a cocatalyst, PH with high Mw and narrow MWD is produced. The use of triethylaluminum (TEA) results in decrease in the Mw of PH and MWD broadening.
Addition of hydrogen causes an abrupt increase in activity of TMC.
Decreasing of polymerization temperature from 700C to 300C results in the unusual effect of the increase of activity at polymerization over catalyst TMC/TEA without hydrogen. Pronounced broadening of MWD of PH at decreasing of polymerization temperature was found (see figure).
On the base of kinetic data on the effect of concentrations of hydrogen, monomer and TEA the values of ktrH/kр, ktrM/kр and ktrAl/kр were determined. It is found that the ratio of the rate constant of chain transfer to TEA (ktrAl) to the propagation rate constant (kр) is about two orders of magnitude higher than the ktrAl/kр value calculated for polymerization of ethylene and propylene.