Youliang Hu

Late transition metal complexes bearing 2,9-bis(imino)-1,10-phenanthrolinyl ligands: synthesis, characterization and their ethylene activity

Abstract A series of iron, cobalt and nickel halide complexes, LMX2 (M=Fe, X=Cl; M=Co, X=Cl; M=Ni, X=Br) bearing 2,9-bis(imino)-1,10-phenanthrolinyl ligands [L=2,9-(ArNCH)2C12H6N2] were synthesized. The solid-state structures of 4 and 7 have been determined by single-crystal X-ray diffraction study. Treatment of the complexes LMX2 with methylaluminoxane (MAO) leaded to activate ethylene as oligomerization catalysts.

Cobalt and nickel complexes bearing 2,6-bis (imino) phenoxy ligands: syntheses, structures and oligomerization studies

Abstract A series of new cobalt and nickel complexes LMX2 (M=Co, X=Cl; M=Ni, X=Br) bearing 2, 6-bis(imino)phenoxy ligands were synthesized. The solid-state structures of 1 and 4 have been determined by single-crystal X-ray diffraction study. Treatment of the complexes LMX2 with methylaluminoxane (MAO) leads to active catalysts for oligomerization of ethylene with catalytic activities in the range of 1.2×105–2.1×105 g mol−1 h−1 atm−1 for Ni complexes, and ∼103 g mol−1 h−1 atm−1 for Co complexes. The oligomers were olefins from C4 to C16.

Ethylene oligomerization promoted by group 8 metal complexes containing 2-(2-pyridyl)quinoxaline ligands

Abstract Ni II , Co II and Fe II complexes of 2-(2-pyridyl)quinoxaline were synthesized and used in the ethylene oligomerization with methyl-aluminoxane (MAO) as cocatalyst. The nickel complex system mainly produced α-olefins with good activity, while the cobalt and iron complexes showed only marginal activity.

Facile synthesis of chain end functionalized polyethylenes via epoxide ring-opening and thiol–ene addition click chemistry

A wide range of low-molecular-weight, narrow-molecular-weight-distribution chain end functionalized polyethylenes (Cef-PEs), including hydroxyl-, amino-, carboxyl-, sulfo-, chloro-, azide- and trimethoxysilane-terminated polyethylenes, were synthesized under mild conditions via epoxide ring-opening and thiol–ene addition reactions with epoxy- and vinyl-terminated PEs as starting materials, respectively. The selectivities of the functionalizations were excellent. Similarly, amphiphilic polyethylene-block-poly(ethylene glycol) copolymer (PE-b-PEG) was prepared for the first time by simply treating epoxy terminated PE with hydroxyl terminated PEG and potassium hydroxide. A unique combination of primary (hindered-phenol) and secondary (thioester) antioxidants was introduced into the chain end of PE via successive thiol–ene addition and transesterification reactions. All Cef-PEs were characterized unambiguously by NMR, GPC, DSC and FTIR.

Study on the Activity of Constrained Geometry Metallocenes

The activities of a several titanium-based constrained geometry metallocenes (CGM) have been examined with respect to their central-metal net charges. A simple method consisting of a combination of the molecular mechanics and the charge equilibration method was adopted here to determine the structure and the net charge. The results obtained indicate that the net charge on the central-metal of the CGM does dominate the activity. A new CGM, (2,6-dipropylphenylamide) dimethyl (tetramethylcyclopentadienyl) silane titanium dichloride, was synthesized and analyzed.

Molecular modeling on the prediction of silolene‐bridged indenyl metallocene catalysts for isotactic polypropylene

Two new silolene-bridged metallocenes for isotactic polypropylene, racemic (1,4-butanediyl) silylene-bis (1-η5-2-methyl-indenyl) dichlorozironium and racemic diphenyl silylene-bis (1-η5-2-methyl-indenyl) dichlorozironium, were designed in terms of the mechanism and concept of the activity and selectivity of metallocenes. The predictions on which the designs were based were carried out for four metallocene catalysts through molecular modeling methods such as molecular mechanics and charge equilibrium. In a comparison of the data from three of the catalysts that were successfully synthesized, the predicted orders of the activity and selectivity were consistent. This shows that classical methods such as charge equilibrium are useful in predicting the activity of catalysts.

Study on the sequence length distribution of polypropylene by the successive self-nucleation and annealing (SSA) calorimetric technique

The effect of successive self-nucleation and annealing (SSA) parameters including the annealing time ts, annealing temperature interval and heating and cooling rates on the crystallization properties of polypropylene were researched in detail. Based on those results, the crystallization behavior and the sequence length distribution of polypropylene with different isotacticity and propylene/1-butene copolymer with different 1-butene comonomer content prepared by Ziegler–Natta catalyst were studied through SSA. With the increase of the isotacticity of polypropylene, the sequence length of the polypropylene gradually increases. The polypropylene prepared by propylene bulk polymerization has stronger crystallization ability and longer sequence length than that prepared by propylene sully polymerization. For the propylene/1-butene copolymer, the crystallization ability gradually reduces and the sequence length of each chain segment gradually decreases with the increase of 1-butene content in copolymer. In addition, the polypropylene samples with similar isotactic index prepared by Ziegler–Natta catalyst and metallocene catalyst under similar polymerization condition were also characterized through the SSA technique. The results show that the sequence length of polypropylene prepared by Ziegler–Natta catalyst is far longer than that prepared by metallocene catalyst. The interesting phenomenon that polypropylene prepared by metallocene catalyst has multiple melting peaks after SSA treatment, which is similar to the polypropylene prepared by Ziegler–Natta catalyst, was first reported.

Ethylene oligomerization by novel iron(II) diimine complexes/MAO

Two novel Fe(II) diimine complexes have been synthesized. In combination with MAO, they generate active catalytic systems that oligomerize ethylene with both high catalytic activity and high selectivity for α-olefins. The effects of substituents on the aryl ring, reaction temperatures and molar ratios of Al/Fe on catalytic activity and product distribution are studied.

A Novel Highly Active Iron/2,6-Bis(imino)pyridyl Catalyst for Ethylene Polymerization

A novel highly active catalyst 2,6-bis[1-(2-methylnaphthylimino)ethyl]pyridineiron(II) chloride (1) is reported for ethylene polymerization. Compared with 2,6-bis[(1-naphthylimino)ethyl]pyridineiron(II) chloride (2) reported recently, catalytic activities of this new complex are high with maximum activity 6.51×106 g PE·mol–1·Fe·h–1·bar–1 at 40°C. The activity of the catalyst, and the molecular weight and melting temperature of the polymers depend on the methylaluminoxane/1 molar ratio and polymerization temperature.

Ethylene polymerization with cycloalkylidene-bridged cyclopentadienyl metallocene catalysts

Ethylene was polymerized with cycloalkylidene-bridged cyclopentadienyl metallocene catalyst 1-9 in the presence of methyl aluminoxane (MAO) as the cocatalyst. Unlike the normal titanocene catalyst, the cycloalkylidene-bridge cyclopentadienyl titanocene catalyst show much higher activities than the corresponding zirconocene and hafnocene catalysts and show the highest activities at higher temperature. This indicates that the cycloalkylidene-bridge cyclopentadienyl titanocene system is very thermally stable and maybe a very promising catalyst system for industrial apllication.