Diethylaluminum Chloride Research Articles

A Novel Catalytic System of [O,O] Bidentate Titanium Complexes and Et2AlCl/Bu2Mg for the Production of Ultra‐High Molecular Weight Polyethylene

AbstractA bidentate ligand, 2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranol (ddbfOH), is used to synthesize the titanium complexes, ddbfOTi(OiPr)3(1) and (ddbfO)2Ti(OiPr)2(2). Combined with diethylaluminium chloride (Et2AlCl) and di‐n‐butylmagnesium (Bu2Mg), complexes 1 and 2 exhibit super high activity towards ethylene polymerization, and giving the ultra‐high molecular weight polyethylene (UHMWPE). After rationally optimizing the experimental conditions, the highest polymerization activity is achieved in both 1/ and 2/Et2AlCl/Bu2Mg catalytic systems (213.6×106 g‐PE⋅mol‐Ti−1 h−1, 142.8×106 g‐PE⋅mol‐Ti−1 h−1). The highest molecular weight (Mv =1905×104) can be achieved under a low polymerization temperature (−30 °C) at the expense of activity (3000 g‐PE⋅mol‐Ti−1 h−1). Additionally, through the investigation of various polymerization conditions on the activity and molecular weight of the catalytic system, we have found that the ratio of the catalyst and cocatalyst has a more significant impact on both activity and molecular weight.

Nickel catalyzed synthesis of branched polyethylene waxes using a hybrid steric strategy

Previous work suggests that the mixing of different substituents may have an unexpected effect on transition metal-catalyzed polymerization of ethylene. In this study, we synthesized a series of pyridine-imine Ni(II) complexes bearing o-diarylmethyl and o-aryl substituents. The hybrid steric Ni(II) complexes exhibited moderate activities (0.80–8.5 × 105 g·mol−1·h−1) and yielded branched (54–79/1000 C) polyethylene waxes with appropriate molecular weights (1.8 to 6.8 kg/mol) in ethylene polymerization. Surprisingly, methoxy and bimethoxy nickel catalysts exhibited very low polymerization activity commonality as well as significant different molecular weight polyethylene variability. The complexation of methoxy with diethylaluminum chloride resulting in simultaneous suppression of chain growth and chain transfer may be responsible for the above phenomenon. In addition, high temperature carbon spectra show that these polyethylene waxes are predominantly methyl branched.

Copolymerization of norbornene with 1-hexene catalyzed by sulfur-containing Schiff base titanium complex and density functional theory analysis

Sulfur-containing salicylaldimine ligand and corresponding titanium complex were synthesized and characterized this work, indicating structural conformity with the design. By using diethylaluminum chloride (EADC) as a cocatalyst, the titanium complex exhibited high activity (∼106 g·mol−1·h−1) in the copolymerization of norbornene (NB) and 1-hexene (1-C6), producing oligomer with a molecular weight of approximately 500. The catalytic copolymerization results were interpreted by combining experimental analysis and density functional theory (DFT). The results indicated that the insertion of norbornene and 1-hexene into Ti catalysts was thermodynamically feasible. Although the reaction barrier for norbornene monomer insertion into the metal active center was lower than that of 1-hexene, the strong steric hindrance between NBE monomer and NBE units in the oligomer chain hindered continuous NBE insertion. By comparing the reaction rates in equimolar systems, the initial insertion step of 1-hexene monomer into the Ti-Et structure was found to be much easier than norbornene insertion, resulting in a lower quantity of norbornene groups in the copolymerization product than 1-hexene groups.

Synthesis, Characterization, and Catalytic Behaviors in Isoprene Polymerization of Pyridine-Oxazoline-Ligated Cobalt Complexes.

A family of pyridine-oxazoline-ligated cobalt complexes L2CoCl23a-h were synthesized and characterized. Determined via single-crystal X-ray diffraction, complexes 3a and 3d, ligated by two ligands, displayed a distorted tetrahedral coordination of a cobalt center. The X-ray structure indicated the pyridine-oxazoline ligands acted as unusual mono-dentate ligands by coordinating only to Noxazoline. Upon activation with AlEt2Cl (diethylaluminum chloride), these cobalt complexes all exhibited high catalytic activity (up to 2.5 × 106 g·molCo-1·h-1), affording cis-1,4-co-3,4-polyisoprene with molecular weights of 4.4-176 kg mol-1 and a narrow Ð of 1.79-3.42, suggesting a single-site nature of the active sites. The structure of cobalt catalysts and reaction parameters, especially co-catalysts and the reaction temperature, all have significant influence on the polymerization activity but not on the microstructure of polyisoprene.

Vanadium (III) catalysts with bulky Bis-NHCs ligands for ethylene-norbornene (co)polymerization

A series of vanadium catalysts with bulky bis(N-heterocyclic carbenes) (bis-NHCs) ligands were synthesized by in-situ reaction. With diethylaluminum chloride (AlEt2Cl) as cocatalyst and ethyl trichloroacetate (ETA) as activator, these catalysts exhibit good activity when used to catalyze ethylene (co)polymerization. The structure of the catalyst, especially the bridging carbons number of the bis-NHCs ligands, is related to the performance of the (co)polymer. When the bis-NHCs ligand with tBu substituted, increased the bridging carbons number of the bis-NHCs ligand is easier to obtain higher molecular weight polymers. But when the bis-NHCs ligand with 2,6-diisopropyl phenyl substituted, the increase of the bridging carbons number is not conducive to obtaining higher molecular weight polymers. Under the same concentration of comonomer, the increase of the bis-NHCs ligand bridged carbon number of the V-complexes is more beneficial to obtain the copolymer with high norbornene (NB) content.

Synthesis of Low Molecular Weight Butadiene Polymers Using Cationic Catalytic Systems Based on Diethylaluminium Chloride

Сationic polymerization of butadiene with the catalytic systems based on diethylaluminium chloride (AlEt2Cl) in combination with tertiary alkyl halides (AH), such as tert-butyl chloride, tert-butyl bromide and 2-chloro-2-methylbutane, is an effective method for obtaining fully soluble butadiene polymers at a industrially relevant temperature of 20°C. It is shown that, regardless of the nature of AH in the catalytic system, with an increase in the duration of the polymerization process of butadiene, the values of the weight-average molecular weight and polydispersity of the polymers significantly increase with the simultaneous decrease of polybutadiene unsaturation, which is associated with the transfer reaction of the growing chain to the polymer double bond during polymerization. Using the 13C NMR spectroscopy method, it was found that polybutadiene macromolecules synthesized on the AlEt2Cl–tert-butyl chloride catalytic system consist mainly of 1,4-trans units, contain two types of initial tert-butyl units and two types of end chlorine-containing units formed as a result of the transfer reaction of the growing chain to tert-butyl chloride. Based on the data of 13C NMR spectra of polybutadiene, a method for calculating the conversion of butadiene during polymerization has been developed, and a mechanism of the process of cationic butadiene polymerization has been proposed. It is shown that the synthesized “cationic” polybutadiene is characterized by high film-forming properties and can be a promising component in the production of paint and varnish materials.

Vanadium complexes bearing 8-anilide-5,6,7-trihydroquinoline ligands for ethylene (co-)polymerization.

Several trivalent and pentavalent vanadium complexes bearing 8-anilide-5,6,7-trihydroquinoline ligands were synthesized. These vanadium complexes were identified by elemental analysis, FTIR spectroscopy and NMR. Single crystals of trivalent vanadium complexes V2, V3', and V4 and pentavalent vanadium complexes V5 and V7 were further obtained and identified by X-ray single crystal diffraction. In addition, the catalytic performance of these catalysts was adjusted by controlling the electronic and steric effects of substituents in the ligands. In the presence of diethylaluminium chloride, complexes V5-V7 displayed high activity (up to 82.8 × 106 g molV-1 h-1) and good thermal stability toward ethylene polymerization. In addition, the copolymerization ability of complexes V5-V7 was evaluated, and complexes V5-V7 displayed high activity (up to 105.6 × 106 g molV-1 h-1) and high copolymerization ability toward ethylene/norbornene copolymerization. By adjusting the polymerization conditions, copolymers with norbornene insertion ratios of 8.1%-30.9% can be obtained. Complex V7 was further studied for ethylene/1-hexene copolymerization, and the obtained copolymer displayed a moderate 1-hexene insertion ratio of 1.2%. Complex V7 displayed high activity and high copolymerization ability while having thermal stability. The results showed that 8-anilide-5,6,7-trihydroquinoline ligands with fused rigid-flexible rings were beneficial for vanadium catalysts.

A systematic study on the effect of co-catalysts composition on the performance of Ziegler-Natta catalyst in ethylene/1-butene co-polymerizations

Effect of the type and composition of conventional co-catalysts on the catalytic performance of Ziegler-Natta catalysts has been investigated by means of a combined experimental and theoretical study. Two fully alkylated co-catalysts (triethylaluminium, TEA, and triisobuthylaluminium, TIBA) and their combinations with two chlorinated ones, DEAC (diethylaluminiumchloride) and EADC (ethylaluminiumdichloride), were employed in ethylene/1-butene co-polymerization using a commercial TiCl4/MgCl2 catalyst. The highest co-polymerization rate was found for TEA and TIBA, without the addition of chlorinated co-catalysts. According to the high temperature gel permeation chromatography and the rheometric mechanical spectrometer analyses, the composition of DEAC with TEA and TIBA lead to the production of polymers with the highest molar mass and longer relaxation times. The promising influence of chlorinated Al-alkyl co-catalysts was on the comonomer incorporation since the combination of TIBA + DEAC could promote it up to 34%. Eventually, to elucidate the role of the co-catalysts on the comonomer response, density functional calculations were performed using ethylene and propylene as monomers. Lower energy barrier was observed in propylene insertions in the presence of DEAC and TIBA co-catalysts, demonstrating their positive impact on comonomer response, in comparison to TEA and EADC, which confirm the experimental evidence.

Preparation of highly branched polyolefins by controlled chain‐walking olefin polymerization

AbstractA series of α‐diimine nickel(II) catalysts bearing different para‐substituted groups, {[(4‐R‐2,6‐Me2‐C6H2NC)2Nap]NiBr2, Nap: 1,8‐naphthdiyl; R = CHMePh (C1); R = CHPh2 (C2); R = tBu (C3); R = Br (C4); R = Me (C5)}, were synthesized and characterized. The molecular structures of C1 and C3 were determined by single crystal X‐ray analysis and show distorted tetrahedron geometry with C2v symmetry. The catalytic behaviors of these catalysts toward ethylene polymerization were investigated in the presence of diethylaluminum chloride (Et2AlCl) as a cocatalyst. The fast chain‐walking process in N,N‐chelated nickel system can be efficiently modulated via the introduction of para‐sec‐phenethyl substituents with improved thermal stability and catalytic performance. C1‐Et2AlCl exhibited high thermal stabilities and high activities reaching 4.61 × 106 g PE (mol Ni h)−1, producing highly branched amorphous polyethylenes (up to 143 branches/1000C) with high molecular weight and narrow polydispersity. This catalyst system conducted successfully conducted 2‐octene polymerization in comparison with the corresponding 1‐octene polymerization. The result demonstrated 2‐octene polymerized slower than 1‐octene and produced the highly‐branched poly(2‐octene)s with approximately 120 branches/1000C, including methyl, ethyl, amyl, and hexyl branches and a small amount of the long methylene sequence due to monomer isomerization.

Exploring cocatalyst type effect on the Ziegler–Natta catalyzed ethylene polymerizations: experimental and DFT studies

Due to the important role of cocatalyst in the polymerization process employing industrially favored Ziegler–Natta catalysts, its effect on kinetic behavior, catalyst activity, and polymer properties is discussed. In this paper, triethyl aluminum (TEA) and triisobutyl aluminum (TIBA) have been used as the main cocatalyst ingredient with 10–20 mol percent of diethyl aluminum chloride (DEAC) and ethyl aluminum dichloride (EADC) cocatalysts, being neat TEA the cocatalysts with the highest activity. Moreover, TEA-DEAC and TEA-EADC cocatalysts revealed a built-up kinetic profile, while TIBA-DEAC and TIBA-EADC show a decay-type kinetic curve. According to melt flow index results, no considerable change in flowability was detected in the synthesized polyethylenes (PE). On the other hand, the ethylene insertion and chain termination mechanisms were investigated by means of density functional calculations using Ti active center located in (110) and (104) facets of the MgCl2 surface. To shed light on the bulkiness level of employed cocatalysts, buried volume (VBur) together with the two-dimensional map of cocatalyst systems were considered. Higher VBur of TIBA complex can explain its lower activity and decay type kinetic profile obtained by experimental studies.

Formation and Functioning of Nickel Bis-(acetylacetonate)-Based Multicomponent Catalytic Systems for Di- and Oligomerization of Ethylene: New Mechanistic Aspects

The paper summarizes new information on the formation and functioning of Ni(acac)2-based multicomponent (Ziegler) systems for oligo- and polymerization of ethylene. It turns out that catalytically active sites formed in these systems are deposited on nickel-containing nanoparticles generated via the interaction of the starting components directly in the reaction system. It is shown that the activity, productivity, and composition of the target products depend on the water content in the initial solvent, all other things being equal. A model of nanosized nickel-containing particles formed during the interaction of Ni(acac)2 and diethylaluminum chloride or ethylaluminum sesquichloride is presented.

Copolymerization of Butadiene with Ethylene in the Presence of Ni-containing Organometallic Catalytic Systems and Different Modifiers

Copolymerization of ethylene with butadiene was carried out in the presence of nickel diethyldithiocarbamate and various modifiers. Triphenylphosphines were selected as modifiers. Solutions of nickel diethyldithiocarbamates and said modifiers in aromatic solvents of various concentrations have been prepared. Their physicochemical parameters, particle sizes in solutions, as well as mutual solubility were determined. It was demonstrated that these complexes are readily soluble in aromatic solvents, and the particle size in solution is in the nanometer range. These complexes were tested in the processes of copolymerization of ethylene with butadiene in combination with various cocatalysts - (tri-, diethylaluminum chloride). The products synthesized in their presence were analyzed by various physicochemical methods and their structure was confirmed. It has been shown that oligomeric and copolymer products with the required structure can be in fact synthesized in the presence of these catalytic systems. The activity and selectivity of catalytic systems have been comparatively tested in liquid phase (co) polymerization processes. The composition and conditions have been found to have a significant effect on the activity and structure of the resulting products.

Design and synthesis of base-metal nickel(II) based catalysts: studies on nearly selective formation of 1-butene from ethylene

A new family of base-metal nickel complexes [Ni(L1-10)2] (1-10) were synthesized from tridentate meridional ligands L1H to L10H (where H stands for dissociable proton). Different spectroscopic studies were utilized for the characterization of these complexes [Ni(L1-10)2] (1-10). Molecular structures of complexes [Ni(L1)2] (1), [Ni(L3)2] (3) and [Ni(L8)2] (8) were determined by X-ray crystallography. Electronic properties of complexes [Ni(L1)2] (1) [Ni(L3)2] (3) and [Ni(L8)2] (8) were elucidated with the help of DFT and TD-DFT calculations. Complexes [Ni(L1-10)2] (1-10) were utilized as catalysts for the synthesis of 1-butene from ethylene using diethyl aluminium chloride as a co-catalyst. A nearly selective formation of 1-butene was observed and productivity up to 17.50 [kg (product/gm catalyst)] h−1 bar−1 was found after examining the catalytic activity of complexes 1-10. A reaction pathway was also proposed for the conversion of ethylene to 1-butene.

Structural modification of phenoxyimine titanium complexes and activation studies with alkylaluminum compounds

AbstractThe synthesis and characterization of three complexes of the type (N‐(3‐tert‐butylsalicylidene)‐R)2TiCl2 [R=2,6‐difluorophenyl 1, R=2,6‐dimethylphenyl 2, R=phenyl 3] is reported and compared with the highly active R=2,3,4,5,6,–pentafluorophenyl 4. The complexes were tested for ethylene polymerization when activated with different co‐catalysts, giving high catalytic activity when activated with methylaluminoxane for complexes 3 and 4. Complex 3 is the only catalyst to be inactive when activated with diethylaluminum chloride. Unexpectedly, for complexes 1 and 2, no catalytic activity is recorded when butylated hydroxytoluene in methylaluminoxane is used to remove the trimethylaluminum, while the catalytic activity for complex 3 is retained. NMR study on the activation of the four complexes in the presence of common alkyl aluminum co‐catalysts suggests the formation of Ti(III) species in the presence of tri‐iso‐butylaluminum, and also the formation of NR−CH2 (R: −Al(CH2CH(CH3)2)2) bond from the N=C−H bond of the ligand explaining the absence of catalytic activity. Density functional theory calculations using B3LYP and a combination of basis sets (6‐31+G and cc‐pVTZ) were performed on the catalyst precursors and the activated species showing insights into the frontier orbitals, localizing the LUMO on the imino bond elucidating their reactivity. Mulliken charges are also reported and an unexpected relationship between the nitrogen on the ligands and the molecular weight is observed.

The influences of alkylaluminium as cocatalyst on butene-1 polymerization with MgCl2-supported TiCl4 Ziegler-Natta catalysts

The influences of alkylaluminium compounds including triethylaluminium (TEA), triisobutylaluminium (TIBA) and diethylaluminium chloride (DEAC) on the catalyst activity, isotacticity and weight-average molecular weight (Mw) of the products in butene-1 (Bt-1) polymerizations with MgCl2-supported TiCl4 Ziegler-Natta catalysts were investigated. The catalytic activity of polybutene-1 (PB) increased in the order of TEA > TIBA > DEAC, while the Mw of PB synthesized with TEA was the lowest when compared with that with other alkylaluminium compounds. Solvent extracted fractionation combining with differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and carbon-13 nuclear magnetic resonance spectrometry (13C-NMR) were used to conduct composition analysis of PB. Fractions including atactic polybutene-1 (aPB), high isotactic polybutene-1 with high Mw (HiPB) and medium high isotactic polybutene-1 with medium high Mw (MHiPB) were isolated for the first time from the PB. Using TIBA resulted more HiPB fractions with higher Mw. A minor incorporation of TIBA or DEAC in TEA increased the HiPB fractions of PB. The contribution mechanism of alkylaluminium compound in TiCl4/MgCl2 Ziegler-Natta catalyst was proposed to explain the influence of alkylaluminium compound with different structures on the active species and polymer components in PB.

Synthesis and application of chromium complexes bearing hyperbranched PNP ligands in the ethylene oligomerization

Series of hyperbranched PNP ligands (L1–L3) were prepared using three low‐generation hyperbranched molecules with the same branching chains and functional groups but different alkyl chain length as backbones in a mixed solvent of acetonitrile and dichloromethane. The chromium complexes (Cr1–Cr3) were obtained by reacting with CrCl3(THF)3 and the corresponding ligands (L1–L3). Both L1–L3 and Cr1–Cr3 were characterized by elemental analysis, Fourier transform infrared and electrospray ionization–mass spectrometry as well as 1H nuclear magnetic resonance (NMR) and 31P NMR measurements in the case of the ligands. When activated with different aluminum co‐catalysts, all three chromium complexes were able to catalyze the ethylene oligomerization, but the products of the ethylene oligomerization were mainly dependent on ethylene pressure, co‐catalyst and ligand backbone. Upon activation with methylaluminoxane, the catalytic activity and the selectivity of C8 olefin increased with increasing of ethylene pressure for Cr1, the catalytic activity was 13.83 × 105 g·(mol Cr·h)−1 and the main product was C8 olefin (50.68%) at the ethylene pressure of 4.0 MPa. When activated with diethylaluminium chloride, ethylaluminium dichloride and ethylaluminum sesquichloride, Cr1 showed the lower catalytic activity and the higher selectivity of C4 olefin in toluene. An increase in the length of alkyl chain in the hyperbranched PNP ligand backbone caused a decrease in the catalytic activity and an increase in the selectivity of C8 + olefin. The PNP chromium complexes exhibited higher selectivity for higher carbon number olefins compared with the dendritic PNP chromium complex (Cr5).

Silica‐Grafted Tris(neopentyl)aluminum: A Monomeric Aluminum Solid Co‐catalyst for Efficient Nickel‐Catalyzed Ethene Dimerization

AbstractA silica‐supported monomeric alkylaluminum co‐catalyst was prepared via surface organometallic chemistry by contacting tris(neopentyl)aluminum and partially dehydroxylated silica. This system, fully characterized by solid‐state 27Al NMR spectroscopy augmented by computational studies, efficiently activates (nBu3P)2NiCl2 towards dimerization of ethene, demonstrating comparable activity to previously reported dimeric diethylaluminum chloride supported on silica. Three types of aluminum surface species have been identified: monografted tetracoordinated Al species as well as two types of bisgrafted Al species—tetra‐ and pentacoordinated. Of them, only the monografted Al species is proposed to be able to activate the (nBu3P)2NiCl2 complex and generate the active cationic species.

Silica-Grafted Tris(neopentyl)aluminum: A Monomeric Aluminum Solid Co-catalyst for Efficient Nickel-Catalyzed Ethene Dimerization.

A silica-supported monomeric alkylaluminum co-catalyst was prepared via surface organometallic chemistry by contacting tris(neopentyl)aluminum and partially dehydroxylated silica. This system, fully characterized by solid-state 27 Al NMR spectroscopy augmented by computational studies, efficiently activates (n Bu3 P)2 NiCl2 towards dimerization of ethene, demonstrating comparable activity to previously reported dimeric diethylaluminum chloride supported on silica. Three types of aluminum surface species have been identified: monografted tetracoordinated Al species as well as two types of bisgrafted Al species-tetra- and pentacoordinated. Of them, only the monografted Al species is proposed to be able to activate the (n Bu3 P)2 NiCl2 complex and generate the active cationic species.

Immobilization of [VCl3(N-2,6-Me2C6H3)] Complex on Silica Supports: Synthesis and Catalytic Testing for Ethylene Polymerization

The heterogenization of 2,6-dimethylarylimido–vanadium(V) dichloride via chemical tethering on insoluble silica supports is reported. The effects of the silica particle size, drying conditions, and the reaction time were investigated. The drying conditions of the support were found to be a crucial parameter: drying temperatures over 400 °C were needed to achieve successful catalysis. The supported catalytic systems were characterized by Fourier-transform infrared (FT-IR) spectroscopy, transmission electron microscopy–energy-dispersive X-ray (TEM-EDX), and inductively coupled plasma mass spectroscopy (ICP-MS), while the polymers were characterized by FT-IR, differential scanning calorimetry (DSC), and rheology. Ethylene polymerization tests were performed employing the prepared heterogenized catalysts with methylaluminoxane/diethylaluminum chloride as a cocatalyst. The supported catalyst precursor, when activated with diethylaluminum chloride, promotes the synthesis of polyethylene with seemingly controlled particle size in the absence of reactor fouling, suggesting the successful immobilization of the complex over the inert support. The resulting polymer shows features of ultrahigh-molecular-weight polyethylene (UHMWPE). These findings present a proof-of-concept for a new approach toward the heterogenization of arylimido–vanadium complexes.

Molecular structure, magnetic properties and catalytic activity in selective ethylene dimerization of nickel (II) complexes with bis(3,5-dimethylpyrazol-1-yl)methane

Nickel(II) complexes with neutral bidentate nitrogen-containing ligands are of great interest as promising precatalysts for the selective oligomerization of ethylene. Complexes of compositions 0.75[LNiCl2]2•0.25[LNiClBr]22 and LNiBr23 where L = bis-(3,5-dimethylpyrazol-1-yl)methane have been synthesized and characterized by single crystal X-ray diffraction, IR and 1H NMR spectroscopies and elemental analysis. The 1H NMR spectra of paramagnetic complexes indicate that the structures of these complexes in solution are similar to ones in the solid state. Magnetic susceptibility of the compounds has been investigated and discussed in the context of their structures. Treatment of these complexes with diethylaluminum chloride (DEAC) or ethylaluminum sesquichloride (EASC) generates active catalysts that oligomerize ethylene to yield mostly butenes with activities up to 930 kg(oligomers)·mol[Ni]−1·h−1 (DEAC).