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Preparation of Hafnium and Chromium Complexes for Olefin Poly/Oligomerizations
- Author(s)
- 백준원
- Alternative Author(s)
- Jun Won Baek
- Advisor
- 이분열
- Department
- 일반대학원 분자과학기술학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2022-08
- Language
- eng
- Keyword
- catalyst; chromium; hafnium; poly(alpha-olefin); polyolefin
- Alternative Abstract
- ABSTRACT This dissertation covers hafnium (Hf) and chromium (Cr) catalysts for polyolefin and poly(α-olefin). The catalysts we designed were aimed at improving catalytic performance in terms of activity and properties of products. Chapter 1 reviews background information to produce polyolefin and poly(α-olefin) and the history of organometallic catalysts for them. Chapter 2 shows Hf catalysts capable of coordinative chain transfer polymerization. Hf complexes have drawn attention for their application as post-metallocene catalysts with unique performance in olefin polymerization. In this work, a series of half-metallocene HfMe2 complexes, bearing a tetrahydroquinoline framework, as well as a series of [Namido,N,Caryl]HfMe2-type post-metallocene complexes, bearing a tetrahydrophenanthroline framework, were prepared; the structures of the prepared Hf complexes were unambiguously confirmed by X-ray crystallography. When the prepared complexes were reacted with anhydrous [(C18H37)2N(H)Me]+[B(C6F5)4]−, desired ion-pair complexes, in which (C18H37)2NMe coordinated to the Hf center, were cleanly afforded. The activated complexes generated from the half-metallocene complexes were inactive for the copolymerization of ethylene/propylene, while those generated from post-metallocene complexes were active. 8-(Tetramethylcyclopentadienyl)-1,2,3,4-tetrahydroquinoline dimethylhafnium complex (12), which bears bulky isopropyl substituents, exhibited the highest activity; however, the activity was approximately half that of the prototype pyridylamido-Hf Dow catalyst. The comonomer incorporation capability was also inferior to that of the pyridylamido-Hf Dow catalyst. However, 12 performed well in the coordinative chain transfer polymerization performed in the presence of (octyl)2Zn, converting all the fed (octyl)2Zn to (polyolefinyl)2Zn with controlled lengths of the polyolefinyl chain. Chapter 3 indicates that a poly(α-olefin)(PAO) prepared by trimerization of 1-octene and 1-dodecene using supported chromium catalyst, has better properties than commercial PAO-4.0. The demand for PAOs, which are high-performance group IV lubricant base oils, is increasingly high. PAOs are generally produced via the cationic oligomerization of 1-decene, wherein skeleton rearrangement inevitably occurs in the products. Hence, a transition-metal-based catalytic process that avoids rearrangement would be a valuable alternative for cationic oligomerization. In particular, transition-metal-catalyzed selective trimerization of α-olefins has the potential for success. In this study, (N,N’,N’’-tridodecyltriazacyclohexane)CrCl3 complex was reacted with MAO-silica (MAO, methylaluminoxane) for the preparation of a supported catalyst, which exhibited superior performance in selective α-olefin trimerization compared to that of the corresponding homogeneous catalyst, enabling the preparation of α-olefin trimers at ~200 g scale. Following hydrogenation, the prepared 1-decene trimer (C30H62) exhibited better lubricant properties than those of commercial-grade PAO-4 (kinematic viscosity at 40 °C, 15.1 vs. 17.4 cSt; kinematic viscosity at 100 °C, 3.9 vs. 3.9 cSt; viscosity index, 161 vs. 123). Moreover, it was shown that 1-octene/1-dodecene mixed co-trimers (i.e., a mixture of C24H50, C28H58, C32H66, and C36H74), generated by the selective supported Cr catalyst, exhibited outstanding lubricant properties analogous to those observed for the 1-decene trimer (C30H62). Chapter 4 describes catalysts system for the selective trimerization of α-olefins with high activity by a modified Phillips ethylene trimerization catalyst system despite the original Phillips system being inactive for α-olefin. α-Olefin trimers are used at a bulk scale as top-tier lubricant base oils, with putative future applications as diesel fuels obtainable from renewable ethylene. In this context, catalysts that can selectively convert α-olefin to its trimers are valuable. However, few examples have been reported. Herein, we report selective α-olefin trimerization catalysts and avoiding the use of expensive activators, such as methylaluminoxane (MAO), B(C6F5)3, and [B(C6F5)4]− salt. A catalytic system Cr(acac)3/[2,5-Me2C4H2N-Al(iBu)3]−Na+/(iBu)3Al demonstrating high turnover numbers (TONs) exceeding 10000 (31 kg/g-Cr for 1-decene), generating trimers selectively without other higher or lower fractions, was developed, confirmed by simulated distillation gas chromatography (SimDis GC) analysis. The hypothesized 2,5-pyrrolide chromium active species was partially confirmed by the structure elucidation of [2,5-Me2C4H2N-AlMe3]Cr(Me)[CH2C6H4(ortho-NMe2)-κ2C,N]. The prepared 1-decene trimers (after hydrogenation) exhibited an advantageously higher viscosity index (VI) than the commercial product PAO-4.0 (128 vs. 123). Fluids demonstrating similar lubricant characteristics as either the 1-decene trimers or 1-decene derived PAO-4.0 were obtained by using 1-octene/1-dodecene blend.
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- Graduate School of Ajou University > Department of Molecular Science and Technology > 4. Theses(Ph.D)
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