TY - JOUR
T1 - Switching from ethylene polymerization to nonselective oligomerization over a homogeneous model catalyst
T2 - A triphenylsiloxy complex of chromium(VI)
AU - Qiu, Pengyuan
AU - Cheng, Ruihua
AU - Liu, Zhen
AU - Liu, Boping
AU - Tumanskii, Boris
AU - Eisen, Moris S.
N1 - Funding Information:
National Natural Science Fund of China (No. 20774025 ) and Key Projects in the National Science & Technology Pillar Program during the 11th Five-Year Plan Period (2007BAE50B04) are thanked for financial support. This work is also financially supported by the Research Program of the State Key Laboratory of Chemical Engineering , the Program of Introducing Talents of Discipline to Universities ( B08021 ) and the Fundamental Research Funds for the Central Universities . Dr I. Barzilai (Technion-Israel Institute of Technology) is thanked for GC measurements. Dr. B. Tumanskii is grateful for support from the Center for Absorption in Science, State of Israel Ministry of Immigrant Absorption.
PY - 2012/2/15
Y1 - 2012/2/15
N2 - SiO 2-supported silyl chromate catalyst (UCC S-2 catalyst) is an important heterogeneous catalyst for the commercial production of polyethylene (PE). However, it has not been fully investigated during the past several decades. A large obstacle has been the lack of homogeneous model systems for this chromium-based heterogeneous catalyst. In this work, bis(triphenylsilyl) chromate (BC), as a homogeneous model for UCC S-2 catalyst, was studied for its polymerization behavior with aluminum alkyl cocatalysts, namely, triisobutylaluminum (TIBA) and methylaluminoxane (MAO). Moreover, activation of BC was investigated by NMR and ESR spectroscopy, radical trapping on fullerene, and MALDI-TOF mass spectroscopy. In the case of TIBA, only an activity of ethylene polymerization were observed; In the case of MAO, BC exhibits an interesting transformation from ethylene polymerization (Al/Cr ≤ 200) to nonselective oligomerization (Al/Cr ≥ 500) with an increase of Al/Cr molar ratio. The obtained PE display a switching from a unimodal molecular weight distribution (MWD) (Al/Cr ≤ 100) to a bimodal MWD (Al/Cr ≥ 200), and the obtained oligomers are main even-numbered linear α-olefins (C 6-C 16). The butyl radical and [Cr(η 6-arene) 2] + cation was identified during activation of BC with TIBA, and the [Cr(η 6-arene) 2] + cation was proved to be inactive for ethylene polymerization by temperature-dependent ESR experiments.
AB - SiO 2-supported silyl chromate catalyst (UCC S-2 catalyst) is an important heterogeneous catalyst for the commercial production of polyethylene (PE). However, it has not been fully investigated during the past several decades. A large obstacle has been the lack of homogeneous model systems for this chromium-based heterogeneous catalyst. In this work, bis(triphenylsilyl) chromate (BC), as a homogeneous model for UCC S-2 catalyst, was studied for its polymerization behavior with aluminum alkyl cocatalysts, namely, triisobutylaluminum (TIBA) and methylaluminoxane (MAO). Moreover, activation of BC was investigated by NMR and ESR spectroscopy, radical trapping on fullerene, and MALDI-TOF mass spectroscopy. In the case of TIBA, only an activity of ethylene polymerization were observed; In the case of MAO, BC exhibits an interesting transformation from ethylene polymerization (Al/Cr ≤ 200) to nonselective oligomerization (Al/Cr ≥ 500) with an increase of Al/Cr molar ratio. The obtained PE display a switching from a unimodal molecular weight distribution (MWD) (Al/Cr ≤ 100) to a bimodal MWD (Al/Cr ≥ 200), and the obtained oligomers are main even-numbered linear α-olefins (C 6-C 16). The butyl radical and [Cr(η 6-arene) 2] + cation was identified during activation of BC with TIBA, and the [Cr(η 6-arene) 2] + cation was proved to be inactive for ethylene polymerization by temperature-dependent ESR experiments.
KW - Bis(triphenylsilyl)chromate
KW - Ethylene polymerization
KW - Homogeneous model
KW - Nonselective oligomerization
KW - UCC S-2 catalyst
UR - http://www.scopus.com/inward/record.url?scp=84855672946&partnerID=8YFLogxK
U2 - 10.1016/j.jorganchem.2011.10.033
DO - 10.1016/j.jorganchem.2011.10.033
M3 - 文章
AN - SCOPUS:84855672946
SN - 0022-328X
VL - 699
SP - 48
EP - 55
JO - Journal of Organometallic Chemistry
JF - Journal of Organometallic Chemistry
ER -