Characterization of the Zr-polymeryl Species Present during Ethylene and Propylene Polymerizations by Homogeneous Zirconocene Catalysts
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Authors
Vatamanu, Mihaela
Date
2015-03-23
Type
thesis
Language
eng
Keyword
olefin polymerization , propene polymerization , alkene polymerization , ethene polymerization , metallocene catalysts , nonmetallocene catalysts , zirconocene , Ziegler-Natta catalysts , Zr-polymeryl intermediates , active species , dormant species , mechanism , metal alkyl , metal(alkyl)(olefin) , metal allyl , single-site , Zr(alkyl)(olefin)
Alternative Title
Abstract
A detailed investigation of Zr-polymeryl intermediates, present during ethylene and propylene polymerization by metallocene and non-metallocene catalysts, is presented. In this regard, the potential use of bromine as a quenching agent to give polymers with brominated end groups is investigated. Using NMR spectroscopy, these groups can be identified as primary or secondary and quantified, thus providing information on the nature of the Zr-polymeryl linkage(s) and their relative concentration(s). Bromine quenching was examined for ethylene polymerization by Cp2ZrMe2/B(C6F5)3, and for propylene polymerization by Cp2ZrMe2/B(C6F5)3, (indenyl)2ZrMe2/B(C6F5)3, and rac-{C2H4(1-indenyl)2}ZrMe2/B(C6F5)3. Polymers with primary alkyl bromide end groups were obtained. In the case of propylene polymerization by [ONNO]Zr(CH2C6H5)2/MAO/2,6-di-tbutylphenol, both primary and secondary alkyl bromide end groups were detected. Primary alkyl bromide end groups result from the cleavage by bromine of primary Zr-CH2~polymeryl linkages while secondary alkyl bromides are the result of the cleavage by bromine of secondary Zr-CH(Me)CH2~polymeryl linkages. The concentration of Zr-CH2~polymeryl intermediates was found to be low, suggesting that the catalyst deactivates during the polymerization.
A second objective of this research is to investigate the formation of Cp2Zr+-allyl complexes as these species are proposed to arise during the polymerization and deactivate the catalyst. Compounds of type [Cp2ZrMe]+ were found to react with vinylidene compounds of type CH2=C(Me)R, (R = CH2CHMe2 and CH2CH(Me)C3H7), to form methane and Cp2Zr+-allyl complexes. The reaction of Cp2ZrMe2/[Ph3C][B(C6F5)4] with CH2=C(Me)CH2CHMe2 involves the unprecedented [Cp2Zr(Me)(CH2CMeCH2CHMe2)]+ intermediate, detected by low temperature one- and two-dimensional NMR spectroscopy. The observation of this intermediate represents the first direct experimental evidence for a d0 metal-alkyl-olefin complex. The dynamic behavior and the kinetics of formation of Cp2Zr+-allyl complexes were also investigated by NMR spectroscopy. In situ propylene polymerization studies indicate that Cp2Zr+-allyl polymeryl intermediates form under catalytic conditions when either Cp2ZrMe2/B(C6F5)3 or Cp2ZrMe2/[Ph3C][B(C6F5)4] are used. Formation of Zr-allyl species occurs in the early stages of the polymerization process, even before the [Cp2ZrMe]+ catalyst is completely consumed, by recoordination of the polypropylene-containing vinylidene end groups, which are the normal products of chain transfer reactions via -H elimination, to the active catalyst.
Description
Thesis (Ph.D, Chemistry) -- Queen's University, 2008-12-04 19:26:27.564
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