High performance catalysts switched by a series of silicon-bridged/N,P-based ancillary ligands have been explored. The precatalyst supported by L1 possessed a large steric bulk and exhibited a high activity of 16.8 × 106 g (mol Cr)−1 h−1 as well as a total selectivity of 99% toward 1-hexene and 1-octene. The selectivity for 1-hexene was adjustable from 59% to 88%. The catalyst bearing an L2 ligand, facilitated by a smaller steric bulk, displayed an identical activity of 13.0 × 106 g (mol Cr)−1 h−1 and a superior selectivity of 75% towards 1-octene under the appropriate conditions. The DFT calculations elucidated the reason for these excellent and tunable activities and selectivities.

New well-defined amphiphilic polymethylene-b-poly(vinyl acetate) (PM-b-PVAc) diblock copolymers were synthesized via a tandem strategy combining polyhomologation of ylides, chain-end functionalization and a visible light induced degenerative iodine transfer polymerization using decacarbonyldimanganese (Mn2(CO)10). Firstly, an iodo terminated polymethylene (PM-I) was prepared by polyhomologation of ylides initiated by a new organic borane based on catecholborane followed by functional group transformation using iodine as the end-capping reagent. Then, a series of amphiphilic PM-b-PVAc diblock copolymers with controlled molecular weight (Mn = 5530–17 020 g mol−1) and relatively narrow molecular weight distribution (Đ = 1.31–1.45) were obtained efficiently through a visible light induced degenerative iodine transfer polymerization of vinyl acetate (VAc) using PM-I as macroinitiator in the presence of Mn2(CO)10 under weak visible light irradiation at 40 °C. The micelles of such an amphiphilic diblock copolymer formed in tetrahydrofuran were observed by transmission electron microscopy (TEM). Moreover, the fabrication of porous films using PM-b-PVAc diblock copolymers via a static breath-figure process was investigated.

•The zeolite-grafted Cr(III)-PNP catalysts are prepared for improving reactivity of ethylene oligomerization.•The selectivity toward 1-hexene increased from 4.07% over Cr(III)-PNP to 73.24% over HY-grafted Cr(III)-PNP catalyst.•The increase of selectivity toward 1-hexene is attributed to the confinement effect of the pore channel.•The process can improve application of the confinement effect in the more complex catalyst system.Zeolite-supported Cr(III)-diphosphinoamine (Cr(III)-PNP) catalysts were prepared through grafting PNP on HY and NaY zeolites followed by complexing with CrCl3(THF)3 for ethylene oligomerization. The structure of supported Cr(III)-PNP catalysts was characterized by scanning electron microscopy, X-ray diffraction, nitrogen adsorption and desorption, thermogravimetric analyses and Fourier transform infrared, and the influence of the supported pattern on reactivity for ethylene oligomerization were investigated. The results revealed that the complex of Cr(III)-PNP was grafted on silicon hydroxyls in the pore channel of HY zeolite to decrease pore size but to maintain pore structure. Comparing with homogeneous Cr(III)-PNP producing 1-butene as main product, HY-supported catalyst had higher activity and selectivity toward 1-hexene increased from 4.07% to 73.24% using triisobutylaluminium as cocatalyst. The increase is attributed to confinement effect of the pore channel, which increases the stability of the chromacycloheptane intermediate to 1-hexene. The confinement effect for ethylene oligomerization was revealed in experiment.Download high-res image (167KB)Download full-size image

The effect of hydrogen addition on the catalytic activity and product selectivity of PNP/Cr(III)/MAO catalytic systems for ethylene tetramerization was investigated. The results showed that the catalytic activity could be increased twice and the polymer production could be reduced efficiently through hydrogen addition. It could be inferred from the analysis and characterization results of the products that there existed at least three sorts of catalytic active centers in the ethylene tetramerization reaction.

In this study, bis(diphenyl phosphine) dimethyl silane (L1), bis(diphenyl phosphine) methyl dimethyl silane (L2), bis(diphenyl phosphine methyl) dimethyl silane (L3) and their nickel (II) halide complexes, L1/NiBr2 (C1), L2/NiBr2 (C2), L3/NiBr2 (C3), were synthesized and characterized. The X-ray single-crystal analysis of C3 complex showed bidentate coordination on the Ni center. In combination with methylaluminoxane as co-catalyst, these complexes produced catalytic systems for ethylene dimerization to butylene with catalytic activities of up to 3.12 × 106 g mol−1 (cat.) h−1 and selectivities up to 97.6 %. With the fine-tuned ligand backbone, such a PSiP-based catalyst system provides a model for precise understanding of the impact of ligand variations on catalytic performance.

In this study, we examined catalyst systems comprising chromium(III) chloride tetrahydrofuran, diphenylphosphinoamine (PNP) ligand, and a mixed activator of methylaluminoxane (MAO) and alkylaluminum for the selective tetramerization of ethylene. By comparing the catalytic activities and the selectivities toward 1-hexene and 1-octene, we investigated the effects of various mixed aluminoxane systems on the ethylene tetramerization process. MAO/trimethylaluminum, MAO/triethylaluminum, and MAO/triisobutylaluminum were all effective cocatalysts for the PNP/Cr(III) ethylene tetramerization system, providing high catalytic activities and high selectivities. When using MAO/diethylaluminumchloride as the cocatalyst, PNP/Cr(III) exhibited an impressive switch in selectivity: from ethylene tetramerization to ethylene trimerization.

•The oligomerizations of 1-butene with higher α-olefins are catalyzed by metallocene.•The microstructure and chain termination of oligomers are characterized by NMR.•The influences of α-olefins on microstructure and reactivity are revealed.•The low-molecular-weight oily oligomers are suitable as lubricant base stocks.In this study we found that the oligomerizations of 1-butene with various higher α-olefins (1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene) in the presence of the catalyst (Me4Cp)2ZrCl2 and the co-catalyst methylaluminoxane yielded low-molecular-weight oily oligomers. 1H and 13C NMR spectroscopy revealed that the major olefinic bonds of these oligomers were terminal vinylidene and internal trisubstituted vinylidene units. The chain termination of oligomerization of 1-butene alone favored chain transfer to the co-catalyst, which process was favored after adding α-olefin and affected only slightly by the lateral size of the α-olefin. The addition of the α-olefin to 1-butene decreased the oligomerization activity, oligomer molecular weight and kinematic viscosity, but increased oligomer viscosity index. Moreover, the oligomerization activity, oligomer molecular weight and kinematic viscosity were presented as a function of the concentration of α-olefin, the oligomerization temperature and the Al/Zr ratio.

PNP/Cr(III)/MAO was proved to be an effective catalyst system for the tetramerization of ethylene toward 1-octene with high catalytic activity and high selectivity. In 1-n-butyl-3-methylimidazolium organoaluminate ionic liquid/cyclohexane biphasic systems, PNP/Cr(III)/MAO showed an impressive selectivity switch from ethylene tetramerization to ethylene trimerization. The influence of ionic liquid/Cr molar ratio, reaction temperature, reaction pressure and recycling runs on performance of the catalytic system were investigated in detail. These data suggest that the organoaluminate anion associates with the active chromium species, giving rise to more active and selective Cr-systems for trimerization of ethylene to 1-hexene.

PNP-type ligands showed very good property in the catalytic systems of PNP/Cr(III)/methylaluminoxane (MAO) for ethylene selective tetramerization toward 1-octene. In this research, two PNP analogues bis(diphenylphosphino)phenylborane and bis(diphenylphosphino)dimethylsilane have been synthesized and characterized. In combination with CrCl3(THF)3 as active center and MAO as cocatalyst, these ligands produced a new catalytic systems for ethylene oligomerization to linear α-olefins with catalytic activities of up to 3.07 × 106 g mol−1 (cat) h−1. Herein, we report the effects of the reaction temperature, ethylene pressure, and the molar ratio of Al/Cr on the catalyst activities and product selectivities.

A silica-supported Ziegler-Natta catalyst with dimethyldichlorosilane (DMDS) as modifier and small silica as support was successfully prepared and characterized. Results from pilot screen showed that the new catalyst exhibited higher catalytic activity, better hydrogen response ability and better copolymerization ability than the commercial M catalyst. Pilot screen in ethylene gas phase fluidized bed polymerization, the catalytic activity of the new catalyst was up to 8000 g PE/g cat, which was twice of that of the commercial M catalyst. The bulk density of polyethylene obtained with the new catalyst was 0.38 g/cm3. The new catalyst is suitable for condensed and super-condensed process in fluidized bed ethylene polymerization.

The synthesis and characterization of a novel trinuclear diphosphinoamine ligand 2 are reported. The ligand combined with Cr(III), activated with methylaluminoxane, lead to highly active and long-lifetime catalytic systems for the tetramerization of ethylene to form 1-octene. The effects of reaction temperature, reaction pressure, molar ratio of Al/Cr and bis(diphenylphosphino)amine/Cr on the catalytic activity and product selectivity were studied. Compared with its mononuclear analogue 1, ligand 2 showed a higher catalytic activity and longer lifetime for ethylene tetramerization in the presence of methylaluminoxane as cocatalyst. High molecular weight polyethylene was generated as a by-product with extremely broad molecular weight distributions.

Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-i-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction temperature, ethylene/propylene molar ratio, aluminium/vanadium (Al/V) molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated. The molecular weight, molecular weight distribution, sequence composition and crystallinity of the products were measured by gel permeation chromatography, 13C-NMR and differential scanning calorimetry analysis, respectively. In comparison to the vanadium and titanium catalysts, the bimetallic catalyst showed higher catalytic activity and better copolymerization performance. The obtained ethylene/propylene copolymers have high molecular weight (105), broad molecular weight distribution, high propylene content with random or short blocked sequence structures (rErP = 1.919), low melting temperatures and low crystallinities (Xc < 20%).

A series of novel N-halogen-substituted-aryl bisphosphinoamine ligands were synthesized and characterized by elemental analysis, 1H NMR and mass spectrometry. The combination of these ligands with Cr(III) and activation by methylaluminoxane leads to highly active catalytic systems for the tetramerization of ethylene to form 1-octene. The catalytic activities and product selectivities depend on the aryl ring substituents and the reaction conditions. We found that the location and size of the substituents are important in determining the catalytic activity and selectivity toward 1-octene. This trend is similar to that observed for their alkyl-substituted analogues.