Ethylene Homopolymerization Research Articles

Isobutylaluminum aryloxides as metallocene activators in Homo‐ and copolymerization of olefins

ABSTRACTThe article describes that sterically hindered isobutylaluminum aryloxides with bulky tBu substituents at 2,6‐ positions of aryl fragment, i.e. (2,6‐di‐tBu,4‐R‐C6H2O)AliBu2 (R = H (1‐DTBP), Me (1‐BHT), tBu (1‐TTBP)) and (2,6‐di‐tBu,4‐R‐C6H2O)2AliBu (R=H(2‐DTBP), Me(2‐BHT)) can serve as cocatalysts for metallocene complexes. Isobutylaluminum aryloxides have been applied for activation of rac‐Et(2‐MeInd)2ZrMe2 in homopolymerization of ethylene, propylene, copolymerization of ethylene and propylene, and terpolymerization of ethylene, propylene, and 5‐ethylidene‐2‐norbornene at Al/Zr = 300 mol/mol. The type of R substituent at 4‐position has a significant effect on catalyst activity. The catalytic system with 1‐TTBP showed the highest activity in all homo‐ and copolymerization processes. Diisobutylaluminum aryloxides provide much higher activity to the systems in all polymerization processes and stronger ability for propylene incorporation in copolymer than diaryloxides. The activities of the systems with isobutylaluminum aryloxides are similar or exceed that of the system with MAO as activator as have shown for propylene polymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43276.

Ligand-Unsymmetrical Phenoxyiminato Dinickel Catalyst for High Molecular Weight Long-Chain Branched Polyethylenes.

An unsymmetrical bimetallic catalyst, (CF3/SO2)FI2-Ni2, having a CF3-functionalized phenoxyiminato Ni(II) center, which produces linear high-Mw polyolefin (CF3/Ni) joined to an adjacent SO2-functionalized phenoxyiminato Ni(II) center, which produces highly branched low-Mw polyolefin (SO2/Ni), was synthesized and fully characterized. In ethylene homopolymerizations, (CF3/SO2)FI2-Ni2 affords monomodal (Đ = 1.7), highly, long-chain branched (69 branches/1000 C) polyethylenes with Mw = 24 kg/mol. In contrast, bimetallic (CF3)FI2-Ni2 and (SO2)FI2-Ni2 produce high-Mw (25 kg/mol) exclusively methyl-branched (40 branches/1000 C) and low-Mw (4.5 kg/mol) highly branched (105 branches/1000 C) polyethylenes, respectively, while tandem monometallic (CF3)FI-Ni + (SO2)FI-Ni catalyst mixtures yield a bimodal polyolefin mixture (Đ = 6.4).

Redox‐Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene‐Bridged Phosphine‐Sulfonate Palladium Complexes

AbstractThe facile and reversible interconversion between neutral and oxidized forms of palladium complexes containing ferrocene‐bridged phosphine sulfonate ligands was demonstrated. The activity of these palladium complexes could be controlled using redox reagents during ethylene homopolymerization, ethylene/methyl acrylate copolymerization, and norbornene oligomerization. Specifically in norbornene oligomerization, the neutral complexes were not active at all whereas the oxidized counterparts showed appreciable activity. In situ switching between the neutral and oxidized forms resulted in an interesting “off” and “on” behavior in norbornene oligomerization. This work provides a new strategy to control the olefin polymerization process.

Redox‐Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene‐Bridged Phosphine‐Sulfonate Palladium Complexes

The facile and reversible interconversion between neutral and oxidized forms of palladium complexes containing ferrocene-bridged phosphine sulfonate ligands was demonstrated. The activity of these palladium complexes could be controlled using redox reagents during ethylene homopolymerization, ethylene/methyl acrylate copolymerization, and norbornene oligomerization. Specifically in norbornene oligomerization, the neutral complexes were not active at all whereas the oxidized counterparts showed appreciable activity. In situ switching between the neutral and oxidized forms resulted in an interesting "off" and "on" behavior in norbornene oligomerization. This work provides a new strategy to control the olefin polymerization process.

Synthesis and properties of polyethylene/TiO2 nanocomposites using a vanadium catalyst

AbstractIn this study, a vanadium (III) complex bearing a salicylaldiminato ligand of the general formula [RN=CH(2,4‐tBu2C6H2O)]VCl2(THF)2, where R = 2,6‐iPr2C6H3, was used as a catalyst. Titanium dioxide doped with iron nanofillers was synthesized by a sol‐gel process and used to investigate the effect of nanofillers on ethylene homopolymer and ethylene/propylene copolymer properties. To the best of our knowledge, this is the first time titanium dioxide doped with iron has been used as a nanofiller in ethylene polymerization and ethylene/propylene copolymerization using a vanadium complex with methyl aluminum dichloride as a cocatalyst. Besides catalyst activity, the molecular mass (Mw) of the obtained polymer, molecular mass distribution, copolymer composition, crystallinity, and thermal characteristics of polyethylene and polyethylene/polypropylene nanocomposites were investigated.

Pyridylamido Bi-Hafnium Olefin Polymerization Catalysis: Conformationally Supported Hf···Hf Enchainment Cooperativity

Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 A, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 A). Once activated with Ph3C+B(C6F5)4– (B1) or PhNMe2H+B(C6F5)4– (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs ...

A low-symmetry nickel(II) α-diimine complex for homopolymerization of ethylene: study of interactive effects of polymerization parameters

A low-symmetry nickel(II) α-diimine complex [(2,4,6-trimethylphenyl)imino)-((2,6-diisopropylphenyl)imino)-acenaphthene nickel(II) dibromide] (C1) was synthesized and characterized crystallographically. Response surface method (RSM) was employed to study the interactive effects of critical factors on ethylene polymerization. The maximum activity of C1, when activated by methylaluminoxane (MAO) cocatalyst {4960 kgPE [(mol Ni)−1 h−1]} was achieved at 10 °C, 7 bar and CC (cocatalyst-to-catalyst ratio) equal to 1550, which is higher than most similar counterparts. Considering surface plots of MW, it is concluded that at high levels (>1000) of CC, there is competition between chain transfer to aluminum and reinsertion of macromonomer to newly formed metal-methyl bonds.

(α-Diimine)palladium catalyzed ethylene polymerization and (co)polymerization with polar comonomers

In this review, a recent development of cationic a-diimine palladium(II) complexes for ethylene polymerization and copoly-merization with polar functionalized comonomers was briefly described. First, the polymerization mechanism for this type of catalysts was discussed. Next, recent advances in ligand design were provided with special focus on the influence of ligand structures on the catalytic polymerization properties. Last, the ethylene homopolymerization and copolymerization with various polar comonomers, especially acrylate and vinyl ethers were summarized.

Effect of Ligand Structure on Olefin Polymerization by a Metallocene/Borate Catalyst: A Computational Study

We have carried out a systematic computational study on olefin polymerization by metallocene/borate catalysts, using three metallocenes: Cp2ZrMe2 (Cp), rac-SiMe2-bis(1-(2-Me-(4-PhInd))ZrMe2 (4-PhInd), and rac-SiMe2-bis(1-(2-Me-(4,5-BenzInd))ZrMe2 (4,5-BenzInd). Detailed reaction pathways, including the structure of the catalytically active ion pair, anion displacement, chain propagation, and chain termination steps, are reported for ethene homopolymerization, alongside with investigation of ethene–propene copolymerization reactions. Initially, all catalysts form inner-sphere ion pairs ([L2ZrMe]+–[B(C6F5)4]−) with a direct Zr–F interaction, which is weak enough to be displaced by the incoming monomer. In comparison to Cp, the bulky and electron-rich 4-PhInd and 4,5-BenzInd show higher barriers for anion displacement but lead to relative stabilization of the resulting π complexes. 4-PhInd enables the most feasible propene uptake, and both catalysts suppress the chain termination reactions relative to Cp. Th...

Homopolymerization of ethylene and copolymerization of ethylene and 5-ethylidene-2-norbornene with the use of C2-symmetric ansa-zirconozenes catalysts of different composition

The homopolymerization of ethylene and the copolymerization of ethylene and 5-ethylidene-2norbornene were investigated in the presence of C2-symmetric ansa-zirconozenes complexes with various types of bridges and substituents in the indenyl ligand—rac-Et(Ind)2ZrCl2 (1), rac-Et(H4Ind)2ZrCl2 (2), rac-Me2Si(Ind)2ZrCl2 (3), rac-Me2C(Ind)2ZrCl2 (4), and rac-Me2C(tert-BuInd)2ZrCl2 (5)—and with methylalumoxane as an activator. Catalyst 5, which has the Me2C bridge and the tert-Bu substituent in the indenyl ligand of zirconocene, was the most active in the homopolymerization of ethylene. Catalyst 1, which has the Et bridge, was the most active in the copolymerization of ethylene and 5-ethylidene-2-norbornene with respect to the yield of copolymer products. The introduction of the tert-Bu substituent into the ligand of zirconocene (catalyst 5) greatly slowed the incorporation of the cyclic comonomer into the polymer chain. In terms of the product of the calculated copolymerization constants, the trend of comonomer alternation was greater in the case of catalyst 1 (r 1 r 2 = 0.042) than that in the case of catalyst 3 (r 1 r 2 = 0.061). The amorphous copolymers synthesized with catalyst 1 possessed the highest glass-transition temperature.

Coordination chemistry to palladium(II) of pyridylbenzamidine ligands and the related reactivity with ethylene

The coordination chemistry to palladium of three pyridylbenzamidines (N-N′) was investigated in detail. The studied pyridylbenzamidines are featured by the bulky 2,6-diisopropylphenyl substituent at the azomethine nitrogen atom of the amidine unit, and differ in the substitution either at the amino atom, which bears a 2-pyridyl or a 6-methyl-2-pyridyl group, or at the bridging N-atom that, in one case, is substituted by a methyl group, leading to a molecule reported herein for the first time. The accurate NMR characterization of the free ligands points out the presence of dynamic phenomena in solution, due to the interconversion of several possible isomers, including tautomers. The coordination chemistry to Pd(II) is studied using both [Pd(cod)(CH3)Cl] and [Pd(cod)(CH3)(CH3CN)][PF6] as metal precursor. Depending on the palladium precursor and on the pyridylbenzamidine, different coordination compounds are obtained, demonstrating the capability of these molecules to act both as mono- and bidentate ligands. For the pyridylbenzamidine substituted with the methyl group on the bridging N-atom, the C–H activation of one of the isopropyl groups is observed with the formation of a six-membered palladacycle and methane. None of the isolated complexes generates active catalysts either for ethylene homopolymerization or for ethylene/methyl acrylate copolymerization. When reacting with ethylene, the complexes lead to the formation of propylene and the inactive dicationic [Pd(N-N′)2][PF6]2 complex.

Effect of Diethylzinc on the Activity of Ethylene Polymerization by Metallocene Catalyst

Adding a suitable amount of diethylzinc as the third compound to a metallocene/MAO catalytic system for ethylene (co) polymerization gives rise to a sharp increase in activity. For ethylene homopolymerization, the activity is enhanced from 2.28 (Zn/Zr = 0) to 10.92 × 106 g/mol‐Zr/h (Zn/Zr = 100), and the activity for ethylene/1‐hexene copolymerization is enhanced from 7.68 (Zn/Zr = 0) to 16.20 × 106 g/mol‐Zr/h (Zn/Zr = 100). The activity decreases when the amount of diethylzinc is further increased. UV‐vis analysis shows that a mixed aluminoxane (MEAO) may be generated by the reaction of diethylzinc with MAO.

ONNO]-type oxovanadium(V) complexes containing amine pyridine bis(phenolate) ligands: synthesis, characterization and catalytic behavior for ethylene (co)polymerization

A series of oxovanadium(V) complexes bearing dianionic [ONNO] chelate ligands 2-[bis(3-R1-5-R2-2 -hydroxybenzyl) aminomethyl]pyridine (2a: R1=tBu, R2=H; 2b: R1=CF3, R2=H; 2c: R1=OCH3, R2=H; 2d: R1=R2=tBu) and 2-[bis(3-R1-5-R2-2 -hydroxybenzyl) aminoethyl]pyridine (2e: R1=R2=tBu) have been synthesized by reacting VO(OnPr)3 with 1.0 equiv. of the ligands in CH2Cl2. All these complexes were characterized by 1H, 13C, 51V NMR spectra and elemental analysis. X-ray structural analysis for 2d revealed a six-coordinate distorted octahedral geometry around the vanadium center in the solid state. It was observed that these complexes existed as a mixture of two isomers, and the main isomer had the oxo moiety in trans configuration to the tripodal nitrogen atom. In the presence of Et2AlCl and CCl3COOEt, these complexes displayed high catalytic activities for ethylene polymerization even at elevated reaction temperature, depending on ligand structures. The resultant polymers possessed high molecular weights and unimodal molecular weight distributions, indicative of a single active site nature. In addition, copolymerizations of ethylene and norbornene using precatalysts 2a–e were also investigated, and the observed catalytic activity was nearly comparable with that for ethylene homopolymerization. When the concentration of comonomer in the feed amounted to 3.0mol/L, a NBE incorporation up to 41.5% could be achieved. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature and Al/V (molar ratio), are also examined in detail.

Homopolymerization of Ethylene by Palladium Phosphine Sulfonate Catalysts: The Role of Structural and Environmental Factors

Palladium phosphine sulfonate catalysts mediate the homopolymerization of ethylene and copolymerization with polar monomers very efficiently. Due to their great potential, a number of theoretical studies have complemented earlier experimental work in the quest of rationally improving their performance. In particular, structural features and reaction conditions are observed to tune the outcome of the polymerization reaction. In this work, we aim at understanding the contribution of factors such as the temperature, the structure of the catalyst, and the concentration of reactants toward production of polyethylene. The influence of each of these factors is studied separately, and trends in the reactivity that explain the experimental results are found. By pursuing a more realistic representation of the system, we traced back the length of the polymer chain obtained to the influence the temperature, the reactants’ concentration, and the catalyst structure have on the β-hydride elimination reaction that terminates the chain propagation. Finally, guidelines for the optimization of the catalyst performance are suggested.

Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts

Cationic Pd(II) catalysts incorporating bulky 8-p-tolylnaphthyl substituted diimine ligands have been synthesized and investigated for ethylene polymerization and ethylene/methyl acrylate copolymerization. Homopolymerization of ethylene at room temperature resulted in branched polyethylene with narrow Mw/Mn values (ca. 1.1), indicative of a living polymerization. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concentration. Copolymerization of ethylene and methyl acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concentration, and copolymers with up to 14 mol % MA were prepared. Mechanistic studies revealed that acrylate insertion into a Pd–CH3 bond occurs at −70 °C to yield a four-membered chelate, which isomerizes first to a five-membered chelate and then to a six-membered chelate. Barriers to migratory insertion of both the (diimine)PdCH3(C2H4)+ (19.2 kcal/mol) and (diimine)PdCH3(η2-C2H3CO2Me)+ (15.2 kcal/mol) were measured by low-temperature NMR kinetics.

CFD Derived Results Lead to An Installation of An Overflow Technique in A Microreactor for Gas‐Phase Ethene Homo Polymerization

AbstractThe presented micro gas‐phase reactor is a very suitable tool for the investigation of polymerizations. To achieve conditions which are closer to industry an overflow is installed in the microreactor. With this setup it is now possible to have a distinct exchange of ethene during the polymerization. CFD calculations have been performed to evaluate the reactor setup and according to these results the reactor has been modified to allow an exchange of the reactor volume two times per minute. The overflow leads to a better heat removal from the growing polymer particles and supplies the active centers with preheated ethylene. The performed overflow‐polymerizations are compared with polymerizations in static conditions and the results allow deeper understanding of the polymerization kinetics on particle level in gas phase conditions.

Methyl branching in polyethylene from homopolymerization of ethylene with N‐arylcyano‐β‐diketiminate methallyl nickel‐B(C6F5)3

ABSTRACTN‐Arylcyano‐β‐diketiminate methallyl nickel complexes activated with B(C6F5)3 were used in the polymerization of ethylene. The microstructure analysis of obtained polyethylene (PE) was done by differential scanning calorimetry and 13C nuclear magnetic resonance (NMR). The branched polymer structures produced by these catalysts were attributed to one step isomerization mechanism of the catalyst along the polymer chain. The ortho or para position of the cyano group with co‐ordinated B(C6F5)3 in both methallyl nickel catalysts influenced the polymer molecular weight, branching, and consequently melting and crystallization temperatures. NMR spectroscopic studies showed predominantly the formation of methyl branches in the obtained PE. Catalysts under study gave linear low‐density PEs with good crystallinities at temperatures of reaction between 50 °C and 70 °C at moderate pressures (12.3 atm). A propylene–ethylene copolymer produced by the metallocene catalyst had the same concentration of branches as the PE synthesized from methallyl nickel/B(C6F5)3. Comparing the two polyolefins with the same degree of branching, it was observed that the polymer obtained with the nickel catalyst proved to be twice more crystalline and had greater Tm. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 452–458

Effect of Solvent Type on High‐Temperature Thermal Gradient Interaction Chromatography of Polyethylene and Ethylene–1‐Octene Copolymers

The effects of the solvent type and operation conditions on the high‐temperature thermal gradient interaction chromatography (HT‐TGIC) of ethylene homopolymers, ethylene–1‐octene copolymers, and their blends are investigated. While the HT‐TGIC profiles of single polymers measured with 1,2,4‐trichlorobenzene (TCB) and chloronaphthalene (CN) are similar, they are always narrower when o‐dichlorobenzene (ODCB) is used, particularly for samples with lower 1‐octene fractions. Significant differences between the experimental and the calculated profiles of binary blends are observed with all three solvents, but better peak separation is seen when the ODCB is used. Having higher fractions of a 1‐octene‐poor component in the blend causes a more significant distortion of the shape expected for the peak from the component with the higher 1‐octene fraction. The effect of the molecular weight on HT‐TGIC profiles is also studied using samples with the same comonomer content and different molecular weights. Samples with low molecular weight have broader distributions and significant lower‐temperature tails, particularly when TCB is used. Chain crystallization after adsorption effects may also play a minor role for low‐comonomer samples. Finally, HT‐TGIC profiles are compared with their equivalent crystallization elution fractionation (CEF) profiles. The HT‐TGIC curves are broader than the equivalent CEF profiles, but these differences decrease as the comonomer content increases. image

Effects of supported metallocene catalyst active center multiplicity on antioxidant-stabilized ethylene homo- and copolymers

A silica-supported bis(n-butylcyclopentadienyl) zirconium dichloride [( n BuCp)2ZrCl2] catalyst was synthesized. This was used to prepare an ethylene homopolymer and an ethylene–1-hexene copolymer. The active center multiplicity of this catalyst was modeled by deconvoluting the copolymer molecular mass distribution and chemical composition distribution. Five different active site types were predicted, which matched the successive self-nucleation and annealing temperature peaks. The thermo-oxidative melt stability, with and without Irganox 1010 and Irgafos 168, of the above polyethylenes was investigated using nonisothermal differential scanning calorimetric (DSC) experiments at 150 °C. This is a temperature that ensures complete melting of the samples and avoids the diffusivity of oxygen to interfere into polyethylene crystallinity and its thermo-oxidative melt degradation. The oxidation parameters such as onset oxidation temperature, induction period, protection factor, and S-factor were determined by combining theoretical modeling with the DSC experiments. Subsequently, these findings were discussed considering catalyst active center multiplicity and polymer microstructure, particularly average ethylene sequence length. Several insightful results, which have not been reported earlier in the literature, were obtained. The antioxidant effect, for each polymer, varied as (Irganox + Irgafos) ≈ Irganox > Irgafos > Neat polymer. The as-synthesized homopolymer turned out to be almost twice as stable as the corresponding copolymer. The antioxidant(s) in the copolymer showed higher antioxidant effectiveness (AEX) than those in the homopolymer. Irganox exhibited more AEX than Irgafos. To the best of our knowledge, such findings have not been reported earlier in the literature. However, mixed with Irganox or Irgafos, their melt oxidation stability was comparable. The homopolymer, as per the calculated S-factor, showed Irganox–Irgafos synergistic effect five times that of the copolymer. This illustrates how the transition in backbone structure, from exceedingly high to low ethylene sequence length, influences antioxidant synergistic performance. Finally, this study shows a DSC-aided approach that can elucidate the effect of polyethylene structural backbone on its thermo-oxidative melt degradation as well as antioxidant synergism in a facile fashion.

Quantification of the steric influence of alkylphosphine-sulfonate ligands on polymerization, leading to high-molecular-weight copolymers of ethylene and polar monomers.

A series of palladium/alkylphosphine-sulfonate catalysts were synthesized and examined in the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. Catalysts with alkylphosphine-sulfonate ligands containing sterically demanding alkyl substituents afforded (co)polymers whose molecular weight was increased by up to 2 orders of magnitude relative to polymers obtained from previously reported catalyst systems. The polymer molecular weight was found to be closely correlated to the Sterimol B5 parameter of the alkyl substituents in the alkylphosphine-sulfonate ligands. Thus, the use of bulky alkylphosphine-sulfonate ligands represents an effective and versatile method to prepare high-molecular-weight copolymers of ethylene and various polar monomers, which are difficult to obtain by previously reported methods.