Ethylene Polymerization Behavior Research Articles

Synthesis of vanadium (V) complex with bulky phenoxy ligand and the study of catalysis behavior in ethylene (co)polymerization

A series of imido-vanadium complexes containing bulky aryloxo ligand have been isolated and employed as catalyst in ethylene (co)polymerization. The introduction of bulky ligand in the vanadium complex structure could promote the thermal stability of catalyst in ethylene polymerization. Especially the corresponding catalysts remain good activity in the ethylene copolymerization with polar monomers such as 10-undecen-1-ol (UOH) and methyl 10-undecenoate (UA). In the attempted copolymerization with acrylate monomer, the vanadium catalysts still show moderate activity but only afford polyethylene.

Pd-Iminocarboxylate Complexes and Their Behavior in Ethylene Polymerization.

Designing co-catalyst-free late transition metal complexes for ethylene polymerization is a challenging task at the interface of organometallic and polymer chemistry. Herein, a set of new, co-catalyst-free, single-component catalytic systems for ethylene polymerization have been unraveled. Treatment of anthranilic acid with various aldehydes produced four iminocarboxylate ligands (L1-L4) in very good to excellent yield (75-92 %). The existence of 2-((2-methoxybenzylidene)amino) benzoic acid (L1) has been unambiguously demonstrated using NMR spectroscopy, MS and single-crystal X-ray diffraction. A neutral Pd-iminocarboxylate complex [{N O}PdMe(L1)] (N O=κ2 -N,O-ArCHNC6 H4 CO2 with Ar=2-MeOC6 H4 ) C1 was prepared by treating stoichiometric amount of L1.Na with palladium precursor. The identity of C1 was confirmed by 1-2D NMR spectroscopy and single-crystal X-ray diffraction studies. Along the same lines, palladium complexes C2-C4 were prepared from ligands L2-L4 respectively. In-situ high-pressure NMR investigations revealed that these Pd complexes are amenable to ethylene insertion and undergo facile β-H elimination to produce propylene. These palladium complexes were then evaluated in ethylene polymerization reaction and various reaction parameters were screened. When C1-C4 were exposed to ethylene pressures of 10-50 bar, formation of low-molecular-weight polyethylene was observed.

Synthesis and structural characterization of zirconium complexes supported by tridentate pyrrolide-imino ligands with pendant N-, O- and S-donor groups and their application in ethylene polymerization

Zirconium complexes supported by pyrrolide-imino ligands been synthesized and their catalytic behavior in ethylene polymerization has been investigated.

Hydrogen effects in TiCl4/MgCl2/THF catalysts with second Lewis acid addition on ethylene polymerization behaviors

In this study, four Ziegler–Natta (ZN) catalysts with the absence and presence of Lewis acids including TiCl4/MgCl2/THF (None–THF), TiCl4/ZnCl2/MgCl2/THF (Zn–THF), TiCl4/ZnCl2/AlCl3/MgCl2/THF (ZnAl–THF), and TiCl4/ZnCl2/FeCl2/MgCl2/THF (ZnFe–THF) were synthesized, characterized, and used for ethylene polymerization. This research aims to elucidate the hydrogen effects in different Lewis acid-doped ZN catalysts on ethylene polymerization behaviors in terms of catalytic activity and polymer properties. With the absence of hydrogen during polymerization, it was found that ZnCl2 decreased the catalytic, because it acted as a catalyst poison. The catalytic activity was in the order of None–THF > ZnFe–THF > ZnAl–THF > Zn–THF. Thus, the addition of second Lewis acids such as AlCl3 and FeCl2 was able to improve the catalytic activity of Zn–THF catalyst. In addition, ZnFe–THF catalyst exhibited slightly higher activity than ZnAl–THF catalyst. This is because FeCl2 may better participate in MgCl2 structure due to similar atomic radius, leading to more efficiently removal of the remaining THF in the final catalyst. With the presence of hydrogen during polymerization, the decrease in catalytic activity was in the order of ZnFe–THF < ZnAl–THF < Zn–THF < None–THF with increasing H2/C2H4 molar ratio from 0.08 to 0.60. The hydrogen response on molecular weight was also observed for all catalysts in this study.

Oxo-bridged azaallylzirconium complexes: Synthesis, characterization and ethylene polymerization behavior

The oxo-bridged azaallylzirconium chlorides (μ-O){η3-(2,6-Et2-4-R-C6H2) N(Ph)CCHSiMe2NMe2ZrCl2}2, [R=Me (C1) and H (C2)] have been prepared in reasonable yields from the reactions of zirconium tetrachloride and the correspondent ligands, Me2NMe2SiCH2(Ph)CN(2,6-Et2-4-R-C6H2). The representative complex C1 was crystallized and identified by the single-crystal X-ray diffraction, indicating oxo-bridged dinuclear azaallylzirconium structure. Both azaallylzirconium complexes exhibited notable catalytic activities toward ethylene polymerization in the presence of MAO, and obtained polyethylenes possess high molecular weights.

(α-Diimine)nickel Complexes That Contain Menthyl Substituents: Synthesis, Conformational Behavior, and Olefin Polymerization Catalysis

We describe the synthesis and coordination chemistry of the (1R,2S,5R)-menthyl-substituted N,N′-diaryl-α-diimine ligands N,N′-(2-Men-4-Me-Ph)2-BIAN (L1, Men = menthyl, BIAN = bis(imino)acenaphthene) and N,N′-(2-Men-4,6-Me2-Ph)2-BIAN (L2), the conformational properties of these ligands and their metal complexes, and the ethylene and 1-hexene polymerization behavior of the corresponding (α-diimine)Ni complexes. Free ligands L1 and L2 and square-planar (L1)PdCl2 and (L1,2)Ni(acac)+ complexes exhibit a preference for the syn conformation, in which the two menthyl units are located on the same side of the N═CC═N plane, while tetrahedral (L1,2)MX2 (MX2 = ZnCl2, NiBr2) complexes exhibit a preference for the anti conformation, in which the menthyl units are located on opposite sides of the N═CC═N plane. Both the anti and the syn conformers of [(L2)Ni(acac)][B(C6F5)4] can be activated by Et2AlCl to generate highly active ethylene polymerization catalysts (activity (2.5–6.6) × 106 g of PE/((mol of Ni) h) at 15 psi ...

Mechanisms for the effects of fluorine and α-diimine backbone structure on the catalyst behavior and catalyst deactivation in ethylene polymerization by Ni catalysts

Ethylene polymerizations were carried out via three fluorinated late transition metal (LTM) catalysts activated by methylaluminoxane (MAO) as a co catalyst. The effects of polymerization conditions, the fluorine of ligand and the α-diimine backbone structure on the catalysts performance and polymer properties were studied. Modification of the α-diimine ligand had a notable effect on the catalysts behavior. The catalyst [bis(N,N/-2-fluorophenylimino)acenaphthene] nickel (ΙΙ) dibromide (catalyst 1) showed the highest activity compared to other catalysts used in this study. Moreover, the catalyst 1 produced a polymer with the highest molecular weight, while the catalyst [bis(N,N/-2-fluorophenylimino)ethan] nickel (II) dibromide (catalyst 2) produced a polymer with the lowest molecular weight. A mechanism was proposed for the effects of fluorine and α-diimine backbone structure on the catalysts behavior, catalyst deactivation and molecular weight of the polymers obtained. Our mechanistic hypothesis was strongly verified by computational approaches, we used to describe the system. The probable reactive electronic interactions of fluorine substitution were accurately distinguished to explain the influence of the ligand backbone on the molecular weight of the obtained polymer.

Chromium(III) complexes bearing bis(benzotriazolyl)pyridine ligands: synthesis, characterization and ethylene polymerization behavior

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)3 in THF to form neutral complexes, [CrCl3{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV–Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH2 (complex 3) and from the fac configuration when the spacer is CO (complex 4).

Preparation of Polyethylene/Graphene Nanocomposites with Octadecylamine‐Modified Graphene Oxide‐MgCl‐Supported Ziegler–Natta Catalyst

ABSTRACTIn this work, an octadecylamine‐modified graphene oxide (ODA‐GO)‐MgCl‐supported Ziegler–Natta catalyst was synthesized by reacting ODA‐GO with a Grignard reagent, followed by anchoring TiCl4 to the structure. The effect of the ODA‐GO on the catalyst morphology and ethylene polymerization behavior was examined. The resultant polyethylene (PE)/ODA‐GO nanocomposites directly mirrored the catalyst morphology by forming a layered morphology, and the ODA‐GO fillers were well dispersed in the PE matrix and showed strong interfacial adhesion with it. The resultant PE/ODA‐GO nanocomposites exhibited better thermal stability and mechanical properties than neat PE, even with a small amount of ODA‐GO added. Thus, this work provides a facile approach to the production of high‐performance PE. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 855–860

Preparation of graphene/MgCl2-supported Ti-based Ziegler-Natta catalysts by the coagglomeration method and their application in ethylene polymerization

We report a facile coagglomeration method for preparing graphene (G)/MgCl2-supported Ti-based Ziegler-Natta catalysts. The effects of graphene feed ratio on catalyst morphology and ethylene polymerization behavior were examined. The synthesized catalyst exhibited very high activity for ethylene polymerization. The resultant polyethylene (PE)/G nanocomposites showed a layered morphology, and the graphene fillers were well dispersed in the PE matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced with the introduction of a very small amount of G fillers (0.05 wt%). This work provides a facile approach to the production of high-performance PE.

Preparation and properties of PE/MoS2 nanocomposites with an exfoliated-MoS2/MgCl2-supported Ziegler-Natta catalyst via an in situ polymerization

Here, we report the first example of preparation of polyethylene (PE)/exfoliated-MoS2 nanocomposites through in-situ Ziegler-Natta polymerization. The exfoliated-MoS2/MgCl2-supported Ti-based Ziegler–Natta catalyst was synthesized via a facile coagglomeration method. The effects of MoS2 on the catalyst morphology and the ethylene polymerization behavior were examined. The resultant PE/MoS2 nanocomposites had a flake shape morphology, and the MoS2 fillers were well dispersed throughout the entire PE matrix. In addition, the thermal stability and mechanical properties of the PE base material were significantly enhanced by the introduction of a very small amount of the MoS2 filler (0.08wt%). Therefore, this work provides a facile method to produce of high-performance PE.

Fabrication of polyethylene/graphene nanocomposites through in situ polymerization with a spherical graphene/MgCl2-supported Ziegler-Natta catalyst

In this study, a spherical grapheme (G)/MgCl2-supported Ti-based Ziegler-Natta catalyst was prepared by a facile spray-coagglomeration method. The effects of graphene on catalyst morphology, ethylene polymerization behavior, and polymer properties were investigated. The resultant product was spherical, and the G was well dispersed in the whole polyethylene (PE) matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced with the introduction of a very small amount of G (0.09 wt%) due to good dispersion of the graphene fillers in the PE matrix. Thus, this work provides a facile approach for the production of high-performance PE.

Half-titanocene complexes bearing bulky dibenzhydryl-substituted aryloxide ligand: Syntheses, characterization, and ethylene (Co-)polymerization behaviors

Abstract Three half-titanocene complexes 2a-3a bearing dibenzhydryl-substituted aryloxide ligands CpTiCl2(O-2,6-Ph2CH C6H2-4-Me), 2a; CpTiCl2 (O-2,6-Ph2CH C6H2-4-OMe), 2b; Cp*TiCl2(O-2,6-Ph2CH C6H2-4-Me), 3a were synthesized. All the complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complex 2a and 2b were further determined by single crystal X-ray diffraction, both of them adopt a three-legged distorted tetrahedral geometry in which the aryl substituents are orthogonally to the aryloxide group. Activated by methylaluminoxane (MAO), these complexes showed high activities (up to 2100 kg mol−1 (Ti) h−1) for ethylene polymerization. The resultant polyethylenes had high molecular weight and narrow molecular weight distributions. Furthermore, for the ethylene/1-hexene copolymerization, these complexes exhibited moderate activites and moderate to high 1-hexene incorporation ability. The sequence distributions of poly (ethylene-co-1-hexene)s are greatly influenced by the substituent on the cyclopentadineyl group of titanium complexes.

β-Oxo-δ-diimine Nickel Complexes: A Comparison of Tautomeric Active Species in Ethylene Polymerization Catalysis

A series of mono- and bimetallic Ni alkyl complexes of a β-oxo-δ-diimine (BODDI) ligand are reported. The monometallic complexes have a second binding pocket, of which the free “arm” can exist as either an enamine (e.g., 8, BODEI, β-oxo-δ-enamineiminato) or imine (e.g., 3, BODII, β-oxo-δ-imineiminato) tautomer. The identity of the tautomer in the secondary Ni coordination sphere has a significant effect on ethylene polymerization behavior: the enamine tautomer, which hydrogen bonds to the central O atom and is in conjugation with the N,O backbone chelate, is significantly more electron rich and yields a much lower molecular weight polymer than the imine tautomer, which rotates away from Ni to a distal position and has little effect on polymerization. Deprotonation of the second binding pocket with M(HMDS) (M = Li, Na, K) yields the Ni-alkali metal heterobimetallic complexes 3Li, 3Na, and 3K. The deprotonated alkali metal enamides display ethylene polymerization behavior similar to the neutral imine comple...

Nickel(II) complexes with mono(imino)pyrrole ligands: preparation, structure and ethylene polymerization behavior

A series of unsymmetrical mono(imine)pyrroles (L1–L3) were synthesized by microwave irradiation from 2-acetylpyrrole and a series of dimethylanilines with two methyl groups at different positions on the aniline ring. A simplified synthetic method was initiated to prepare the corresponding nickel complexes NiL2 (1–3) with direct condensation of mono(imine)pyrrole and nickel chloride. The compounds were determined using a suite of techniques (i.e. 1H NMR, 13C NMR, IR, EA, MS). L1–L3 and 3 were further characterized by X-ray crystal diffraction. The structure of 3 showed that the ligand chelated to nickel with 2 : 1 M ratio, in spite of a 1 : 1 rate of charge. Application of 1–3 in ethylene polymerization indicated that mono(imino)pyrrole nickel complexes showed low activities. The polymerization reaction time and temperature, as well as the ligand structure, influenced the catalytic performance to some extent. Experimental data showed higher activity as –CH3 on the aniline ring is closer to the imine group.

Synthesis, characterization, and ethylene polymerization behavior of Cr(III) catalysts based on bis(pyrazolylmethyl)pyridine and its derivatives

New chromium(III) [Cr(III)] catalysts based on 2,6-bis(pyrazol-1-ylmethyl) pyridine derivatives have been synthesized, characterized, and evaluated for ethylene polymerization. All ligands with substituents on the pyrazole rings were analyzed by single-crystal X-ray diffraction to clearly identify isomer structures. Additionally, X-ray analyses of the new Cr(III) complex bearing 2,6‑bis[(4,5-dimethyl-1H-pyrazol-1-yl) methyl]pyridine showed tridentate coordination on the mer-octahedral chromium sphere. Upon activation with dry methyaluminoxane, the precatalysts produce polyethylene (PE) as a major product, and their catalytic performances were affected by the substituents on the pyrazole units; the introduction of functional groups on the pyrazole raised PE compositions and the molecular weight of the PE.

Novel Ni-based FI catalyst for ethylene polymerization

Novel nickel based FI catalysts with different ligands from well known salicylaldehyde imine ligand, to naphthoxy-imine ligand were designed, synthesized, and characterized. The effect of synthesized ligand on ethylene polymerization was investigated. Extensive experimentations have been carried out using the nickel catalysts after activation with methylaluminoxane (MAO) to study the ethylene polymerization behavior of the prepared catalysts comparably. Substituents on the arene moiety and/or the backbone of the ligand influence the activities of the active sites of the catalyst during the polymerization. Therefore, not only polymerization behavior varied, but also versatile products regarding molecular weight, crystallinity and melting point were obtained. The crystallinities and melting points of the polymer obtained at the temperatures of 10, 30 and 60°C were 58%, 39%, and 14% and 130, 97 and 88°C respectively.

Synthesis, structural investigations and ethylene polymerization of titanium complexes with tripodal oxazoline ligands

A series of tripodal nitrogen containing ligands including amidine and aminopyridines with extra oxazoline functionality were synthesized. The corresponding titanium complexes bearing such ligands were synthesized by diethylamine elimination route. Diethylamidotitanium trichloride [Et2NTiCl3] reacts with the functionalized anilines, 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-(2-fluorophenyl)-aniline (FOxH) and 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-(2-methoxyphenyl)aniline (MeOOxH), the amidine(E)-N’-(2,6-diisopropylphenyl)-N-(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl)benzimidamide ( Am OxH), and the aminopyridines N-(2-(4,4-dimethyl-4,5-dihydro oxazol-2-yl)phenyl)-6-(piperidin-1-yl)pyridin-2-amine (ApOxH) and N-(2-(4,4- dimethyl- 4,5-dihydrooxazol-2-yl)phenyl)-6-(2,4,6-triisopropyl phenyl)pyridin-2-amine (Ap*OxH), under diethylamine elimination to form the corresponding titanium trichlorides [FOxTiCl3], [MeOOxTiCl3], [AmOxTiCl3], [ApOxTiCl3] and [Ap*OxTiCl3] in excellent yields. These compounds were characterized by spectroscopic methods, and X-ray crystal structure analysis (selected complexes). Furthermore, their behavior in ethylene polymerization was explored. The complexes show moderate activity towards ethylene if activated with MAO. The observed PEs were analyzed by HT-GPC and were found to be of low molecular weight for the amidinate AmOxTiCl3 but of very high one (Mp up to 3.5 million g/mol) for the aminopyridinate Ap*OxTiCl3 titanium complex.

Lewis Acid Modification and Ethylene Oligomerization Behavior of Palladium Catalysts That Contain a Phosphine-Sulfonate-Diethyl Phosphonate Ancillary Ligand

The multifunctional phosphine-sulfonate-diethyl phosphonate ligand [1-(P(4-tBu-Ph)(2-PO3Et2-5-Me-Ph)-2-SO3-5-Me-Ph]− ([OP-P-SO]−) was used to form complexes of type [κ2-(OP-P-SO)]PdMe(L) (L = 2,6-lutidine, 2b; L = pyridine, 2c). B(C6F5)3 abstracts the Pd-bound sulfonate group of 2b and induces a switch to a phosphine-diethyl phosphonate coordination mode, affording [κ2-(OP-P-SO-B(C6F5)3)]PdMe(2,6-lutidine) (3). In contrast, MgCl2 binds to the sulfonate and diethyl phosphonate units of 2b, generating the dipalladium species [{κ2-(OP-P-SO)PdMe}2(μ-Cl)][MgCl] (4) by simple self-assembly. AgB(C6F5)4 reacts with 4 in the presence of THF to selectively abstract the Mg-Cl to form [{κ2-(OP-P-SO)PdMe}2(μ-Cl)Mg(THF)][B(C6F5)4] (5). The ethylene polymerization behaviors of 2b, 2c, 3, and 5 are quite similar (Mn: 120–1170 Da, activity: 60–290 kg (mol Pd)–1 h–1). All of these catalysts produce low-molecular-weight polyethylene with predominantly internal unsaturation, but little branching. The reaction of 4 with 2 equiv of AgB(C6F5)4 to abstract both chloride ions generates an active ethylene polymerization catalyst that produces linear polyethylene with a bimodal molecular weight distribution.

Synthesis, characterization, and ethylene polymerization behaviors of late-transition metal complexes coordinated with chlorinated bis(arylimino)pyridine ligand

A series of late-transition metal complexes supported with chlorinated bis(arylimino)pyridine ligands [2,6-(ArNCCl)2C5H3N]MtCl2 (Ar = 2,4,6-Me3C6H2, Mt = Fe (1a), Co (2a), Ni (3a); Ar = 2,6-iPr2C6H3, Mt = Fe (1b), Co (2b); Ar = 2,6-Et2C6H3, Mt = Co (1c), Ni (3c); Ar = 2,6-Me2C6H3, Mt = Fe (1d), Co (2d); Ar = 4-Cl-2,6-Me2C6H2, Mt = Fe (1e), Co (2e); Ar = 4-Br-2,6-Me2C6H2, Mt = Fe (1f), Co (2f)) were synthesized. At the presence of methylaluminoxane (MAO), Fe(II)- and Co(II)- based complexes were highly active towards ethylene polymerization, affording polymers with bimodal and unimodal molar mass distributions, respectively, while the Ni(II)-based complexes gave no polymer products. Moreover, the obtained polyethylenes were predominately saturated and vinyl-terminated for Fe(II)- and Co(II)-based complexes, respectively. Changing the ligand environment, polymerization parameters also posed a great influence on the catalytic activities and the properties of the resulting polymers.