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Semi‐Batch Polymerisations of Ethylene with Metallocene Catalysts in the Presence of Hydrogen, 3. Correlation Between Hydrogen Sensitivity and Molecular Parameters
Author(s) -
Blom Richard,
Swang Ole,
Heyn Richard H.
Publication year - 2002
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 - 10.1002/1521-3935(20020101)203:2<381::aid-macp381>3.0.co;2-b
Subject(s) - methylaluminoxane , metallocene , chemistry , zirconium , catalysis , hydrogen , reactivity (psychology) , polymer chemistry , ethylene , propene , reaction rate constant , chain transfer , post metallocene catalyst , hydrogen atom , polymer , polymerization , organic chemistry , kinetics , radical polymerization , alkyl , medicine , physics , alternative medicine , pathology , quantum mechanics
Semi‐batch ethylene polymerisations have been carried out with heterogenised Cp 2 ZrCl 2 /MAO, Ind 2 ZrCl 2 /MAO, Cp(Ind)ZrCl 2 /MAO and Cp(Flu)ZrCl 2 /MAO (MAO, methylaluminoxane) catalysts where hydrogen was added as the chain‐transfer agent. Modelling of molecular weight distributions of the polymer formed gave estimates of the relative rate constant for the chain transfer to hydrogen and the rate constant for propagation, k tH 2/ k p . Values of 0.7(2), 22(7), 13(3) and 35(4) were obtained for the Cp 2 , Ind 2 , (Cp,Ind) and (Cp,Flu) catalysts, respectively. The observed order of reactivity towards hydrogen has been correlated with chemical shifts from 91 Zr NMR and with the atomic charges of zirconium from DFT calculations for a series of metallocene complexes. The efficiency of hydrogen as a chain‐transfer agent is larger the more electron deficient the zirconium atom in the catalyst is.