Molecular Mass Characteristics of Polyethylene Produced with Supported Vanadium-Magnesium Catalysts
, E-ISSN: 1097-0126
||Ethylene polymerization, Gel permeation chromatography (GPC), Molecular mass distribution, Polyethylene (PE), Size exclusion chromatography (SEC), Vanadium-magnesium catalyst
Echevskaya Ludmila G.
Matsko Mikhail A.
Mikenas Tatiana B.
Zakharov Vladimir A.
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Science, Prospekt Akademika Lavrentieva 5, Novosibirsk, 630090, Russia
Highly active supported vanadium-magnesium catalysts (VMC) produce polyethylene (PE) with broad and bimodal molecular mass distribution (MMD) in comparison with the famous titanium-magnesium catalysts (TMC). The effect of hydrogen as an efficient chain-transfer agent on the MMD of PE has been studied. Increasing hydrogen concentration causes a considerable broadening of MMD of PE due to the shift of the low molecular weight peak on the MMD curve. At the same time, the high molecular weight shoulder stays at the same position even at high hydrogen concentration. This means that VMC contain two types of active centre. One type is very reactive in the chain-transfer reaction with hydrogen. These centres produce low molecular weight PE in polymerization in the presence of hydrogen. The other type of active centre is not active in chain transfer with hydrogen. These centres produce high molecular weight PE ((1–3) × 106) and hydrogen does not affect the position of the high molecular weight shoulder. MMD data were used to analyze the kinetics of the chain-transfer reaction with hydrogen and to calculate the rate constants of this reaction.