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Ethylene Polymerization over Homogeneous and Supported Catalysts Based on Bis(imino)pyridine Co(II) Complex: Data on the Number of Active Centers and Propagation Rate Constant
Author(s) -
Barabanov Artem A.,
Bukatov Gennady D.,
Zakharov Vladimir A.,
Semikolenova Nina V.,
Echevskaja Ljudmila G.,
Matsko Michail A.
Publication year - 2008
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200800376
Subject(s) - catalysis , polymerization , chemistry , reaction rate constant , chain propagation , ethylene , carbon monoxide , pyridine , polyethylene , homogeneous , molar mass distribution , quenching (fluorescence) , polymer chemistry , degree of polymerization , homogeneous catalysis , hydrogen , medicinal chemistry , kinetics , polymer , organic chemistry , physics , thermodynamics , fluorescence , quantum mechanics
The number of active centers ( C P ) and propagation rate constant ( k P ) for ethylene polymerization with homogeneous catalyst LCoCl 2 + MAO and supported catalyst LCoCl 2 /SiO 2 + Al( i ‐Bu) 3 , where L is 2,6‐(2,6‐(Me) 2 C 6 H 3 N = CMe) 2 C 5 H 3 N, have been determined using the method of polymerization quenching by radioactive carbon monoxide ( 14 CO). The unstable rate profile of the reaction was attributed to a decrease in the number of active centers from 0.23 to 0.14 mol · mol −1 (Co) corresponding to an increase in the reaction time from 5 to 15 min, whereas the k P value remained constant, amounting to 3.5 × 10 3 L · mol −1 · s at 35 °C. A narrow molecular weight distribution of the obtained polyethylene (PE) samples ( $\overline M _{\rm w} /\overline M _{\rm n}$ = 1.9) testifies that the homogeneous catalyst LCoCl 2 + MAO can be regarded as a single‐site system. The activity of the supported catalyst was stable and noticeably lower than that of the homogeneous catalyst due to the low concentration of the active centers (0.02–0.03 mol · mol −1 (Co)). PE with a broad molecular weight distribution ( $\overline M _{\rm w} /\overline M _{\rm n}$ = 36) and noticeably higher molecular weight is formed in the presence of the supported catalysts. The activity of the supported catalyst increases sharply at polymerization in the presence of hydrogen. The data obtained on the C P and k P values allow suggesting the formation of the “dormant” centers at polymerization without hydrogen and regeneration of the active centers in the presence of hydrogen. The average k P values for the supported catalyst containing multiple active centers were determined to be 5.9 × 10 3 and 10.5 × 10 3 L · mol −1 · s, respectively, at 35 and 50 °C.