Journal
ACS CATALYSIS
Volume 9, Issue 4, Pages 3338-3348Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.9b00250
Keywords
alkene polymerization; active site counting; chain transfer; kinetics; mechanism; copolymerization
Categories
Funding
- Dow Chemical Company
- NSF through the University of Wisconsin Nanoscale Science and Engineering Center [DMR-0832760, 0425880]
- NSF [CHE-1048642]
- NIH [1S10 OD020022-1, S10 OD012245]
- Paul and Margaret Bender Fund
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Copolymerization of ethene and 1-octene is catalyzed by the Hf-pyridyl amido complex used in chain-shuttling polymerization. Active site counts and the molar mass distribution of catalystbound polymeryls are determined by chromophore quench-labeling. Catalytic data for copolymerization (1-octene consumption, active site counts, molar mass distributions of polymers, and I-2-labeling of Znpolymeryls) are compared with similar data for the homopolymerization of 1-octene. Such comparisons reveal that small amounts of ethene have a significant impact on catalysis. The rate of 1-octene consumption increases in a copolymerization similar to 3-fold compared to a homopolymerization; this likely results from in situ ligand modification. The first insertion of alkene occurs into the Hf-naphthyl bond of the Hf-pyridyl amido catalyst; in copolymerization, competition between ethene and 1-octene for this insertion creates multiple active species. We propose that ethene insertion into the Hf-naphthyl bond leads to a faster polymerization catalyst than insertion of 1-octene. In the presence of diethyl zinc, the homopolymerization of 1-octene produces broader molar mass distributions than those seen for the copolymerization of octene and ethene. Narrowing of the distribution by ethene presumably reflects increased reversibility of chain transfer between Hf and Zn. I-2-labeling of Zn-polymeryls and subsequent NMR chain end analysis reveals that more than one polymer chain per Zn is produced under copolymerization conditions. The steric requirements for reversible chain transfer are assessed by I-2-labeling of sequential copolymerization reactions.
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