Polymerization Of 1-hexene Research Articles

Polymeric α-diimine palladium catalysts for olefin (co)polymerization

In this contribution, a series of α-diimine palladium complexes with two vinyl units were designed and synthesized. Tandem ring opening metathesis polymerization/cross metathesis of cycloolefins in the presence of these complexes as chain-transfer agents resulted in a series of well-defined polymeric α-diimine Pd catalysts with improved catalytic performances. These polymeric Pd complexes can catalyze polymerization of ethylene and result in increased molecular weight of polyethylene products compared with their molecular analogues. In the polymerization of 1-hexene, the polymeric catalysts led to less isomerization, resulting in increased conversions of 1-hexene and higher molecular weights. Moreover, polymeric palladium catalysts show improved tolerance to polar comonomers, leading to higher activities as well as higher molecular weights in ethylene–methyl acrylate copolymerization. Most importantly, tuning of catalyst performance can be achieved by varying the structure or amount of cyclic monomer used in the preparation of these well-defined polymeric catalysts starting from the simple homogeneous platform.

Slow-chain-walking polymerization of ethylene and highly chain-straightening polymerization of 1-hexene to access semicrystalline polyolefins

The production of semicrystalline polyolefins using α-diimine late transition metal catalysts is highly desired but challenging in both ethylene and α-olefin polymerization, which relates to fundamental steps such as slow-chain-walking and highly chain-straightening events. In this work, by the combination of 4-(diphenylamino)phenyl moiety with different bulky substituents including H, Me, CHPh2, and Ph groups, a new family of unsymmetrical α-diimine nickel catalysts Ni1-Ni4 has been prepared. Under the activation of co-catalyst, these catalysts are highly active (107 g mol-1h−1) for ethylene polymerization, giving polymers from branched ethylene oligomers to linear ultrahigh molecular weight polyethylenes (UHMWPEs) over a wide temperature range of 30–70 °C. Notably, the preferred Ni4 even enables a slow-chain-walking process and thus is capable of producing linear, semicrystalline UHMWPE (Mn = 1056 kg mol−1, brs = 9.1/1000C, Tm = 123.5 °C) at low ethylene pressure of 1 bar. Likewise, in 1-hexene polymerization Ni4 is highly selective (88.1%) for uncommon 2,1-insertion followed by complete chain-walking. Thus, the chain-straightening polymerization of 1-hexene efficiently yields semicrystalline poly(1-hexene) with a high Tm of 102.1 °C that resembles low-density polyethylene (LDPE).

Synthesis of novel Ziegler Natta catalyst in the presence of internal promoter and electron donors for ethylene and ethylene/ 1-hexene polymerization

Synthesis of novel Ziegler Natta catalyst in the presence of internal promoter and electron donors for ethylene and ethylene/ 1-hexene polymerization

Catalyst Deactivation Processes during 1-Hexene Polymerization

The catalyst [Cp2Zr(μ-Me)2AlMe2]+[B(C6F5)4]− (1) has been studied by electrospray ionization mass spectrometry in order to better understand the complexities of catalyst deactivation in the polymerization of 1-hexene. Using off-line, online, and flow-based methods, we observe that zirconium π-allyl species are unstable in solution and previously unobserved dimethylalane complexes are more stable. The dimethylalane complexes are resistant to further 1-hexene additions, and their formation represents a previously unrecognized pathway for catalyst deactivation.

Determination and tracing of active and dormant propagation chains in 1-hexene polymerization with supported Ziegler-Natta catalyst

Propagation chains with 1,2 and 2,1 last-inserted monomer unit in 1-hexene polymerization with MgCl2-supported Ziegler-Natta catalysts were quench-labeled by thiophene-2-carbonyl chloride, and the two kinds of 2-thenoyl-labeled chain ends were determined by 1H NMR analysis. The number of labeled chains was noticeably smaller than the number of dead chains formed by chain transfer with alkylaluminum cocatalyst, and grew with time more slowly than the latter, showing that side reactions between the quencher and Al-polymeryl moieties are negligible. The active sites with 2,1 last-inserted monomer were halted in dormant state, which lead to their gradual accumulation in the 30 s polymerization process. The catalyst containing phthalate type internal donor has higher percentage of dormant sites as compared with the catalyst containing diol ester. The combination of acyl chloride quench-labeling and 1H NMR analysis forms a reliable and easily accessible method of tracing and characterizing active sites in transition metal catalyzed olefin polymerization.

1-Hexene Polymerization on a Highly Active Titanium–Magnesium Catalyst

The review summarizes the results obtained by the authors in a study of the polymerization of 1‑hexene on a supported titanium–magnesium catalyst. The effects of the composition of a complex titanium–magnesium catalytic system, the composition of a reaction medium, and the conditions of polymerization on the activity of the catalyst and the molecular weight, molecular-weight distribution, and isotacticity of the resulting polyhexene were considered. The main factors (the composition of a catalytic system and the polymerization conditions) that allow one to control the catalyst activity and the molecular structure of polyhexene over wide ranges were determined. Specific features of the polymerization of 1-hexene in comparison with the polymerization of ethylene and propylene on titanium–magnesium catalysts are discussed.

Solution XAS Analysis for Exploring Active Species in Syndiospecific Styrene Polymerization and 1-Hexene Polymerization Using Half-Titanocene–MAO Catalysts: Significant Changes in the Oxidation State in the Presence of Styrene

Mechanistic studies through Ti K-edge XANES and EXAFS spectra of the catalyst solution for 1-hexene polymerization using Cp*TiX2(O-2,6-iPr2C6H3) [X = Cl (1), Me (2)]–MAO catalysts and for syndiospe...

Kinetic Study of Chain Transfer Reactions upon 1-Hexene Polymerization on Highly Active Supported Titanium–Magnesium Catalysts

Data on the effect the concentrations of the monomer, triethylaluminium, and hydrogen on the molecular weight of polyhexene upon 1-hexene polymerization over supported titanium–magnesium catalyst are obtained. The ratios between propagation rate constant and the rate constants of the reactions of polymer chain transfer with monomer, triethylaluminium (AlEt3), triisobutylaluminium, and hydrogen are calculated. The data allow us to estimate the effect of individual reactions of chain transfer on the polymer’s molecular weight under different polymerization conditions. The data help to select polymerization conditions for obtaining polyhexene of a desired molecular weight. The heterogeneity of active centers is observed in the reaction of chain transfer with hydrogen when using AlEt3 as co-catalyst, which alters the polymer’s polydispersity when the concentration of hydrogen is varied in the reaction mixture. The molecular weight distribution is analyzed via resolution into Flory components for polyhexene characterized by different polydispersity.

Zirconocene-Catalyzed Polymerization of α-Olefins: When Intrinsic Higher Activity Is Flawed by Rapid Deactivation

Kinetic studies of homogeneous 1-hexene polymerization have been used for determining the propagation rates and active sites concentrations of industrially relevant zirconocene catalytic systems in...

Ethylene/1-hexene polymerization with bis(cyclopentadienyl) hafnium(IV) dichloride: A fundamental polymerization kinetics model

A mechanism for the polymerization of ethylene and 1-hexene with Cp2HfCl2 was proposed and its kinetic parameters were estimated to quantify ethylene uptake curves and the structure of the polymer made with Cp2HfCl2 when hydrogen concentration, 1-hexene concentration and temperature varied in a solution polymerization. The catalyst follows second order propagation kinetics, and first order catalyst decay kinetics over the range of conditions tested in this study. The Bernoullian model was combined with the Trigger mechanism to describe these copolymerizations, and the parameters for the proposed mechanism were successfully estimated. The models proposed for the conditions in this study describe adequately the polymerization kinetics, polymer Mn, and the average 1-hexene in the polymer made with Cp2HfCl2 for ethylene polymerization with/without hydrogen and ethylene/1-hexene copolymerization.

Catalyst Speciation During ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy-Formation and Partial Re-Activation of Zr-Allyl Intermediates.

Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)2AlMe2+ B(C6F5)4− (SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 °C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-σ-polyhexenyl cations arising from SBIZr-Me+ (formed from SBIZr(μ-Me)2AlMe2+ by release of AlMe3) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η3-allyl cations of composition SBIZr-η3-(1-R-C3H4)+ (R = n-propyl), formed by σ-bond metathesis between SBIZr-Me+ and 1-hexene under release of methane. At later reaction stages, all zirconocene-σ–polymeryl cations appear to decay to yet another SBIZr-allyl species, i.e., to cations of the type SBIZr-η3-(x-R-(3-x)-pol-C3H3)+ (pol = i-polyhexenyl, x = 1 or 2). Renewed addition of excess 1-hexene is proposed to convert these sterically encumbered Zr-allyl cations back to catalytically active SBIZr-σ–polymeryl cations within a few seconds, presumably by initial 1-hexene insertion into the η1- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η3-(1-R-C3H4)+ appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed.

Self-assisted stereospecific polymerization of unmasked polar 4-methylthio-1-butene

Stereospecific polymerization of polar olefins has always been an attractive but challenging project because the Lewis basic polar groups of monomers are usually poisonous to the Lewis acidic metal centers of the catalysts. In this contribution, thiophene-fused cyclopentadienyl scandium complexes 1—3 were successfully synthesized. Combined with alkylaluminium and organoborate, these complexes showed extremely low activity and no selectivity for 1-hexene polymerization. Surprisingly, highly stereo-selective coordination polymerization of unprotected polar 4-methylthio-1-butene has been achieved in high activity for the first time under the same polymerization conditions. High-molecular-weight (Mn=110×103) and perfectly syn-diotactic (rrrr>99%) poly(4-methylthio-1-butene) (P(MTB)) was afforded. Thus the methylthio-group-assisted mechanism that the unmasked methylthio group promoted the polymerization through σ-π chelation to the active scandium center together with the vinyl group was proposed. Moreover, the methylsulfonyl functionalized syndiotactic poly(1-butene) was also easily prepared by the oxidation of P(MTB). These results provided a new route for the synthesis of functionalized stereo-regular polyolefins.

Alkynyl Ether Labeling: A Selective and Efficient Approach to Count Active Sites of Olefin Polymerization Catalysts

Accurately measuring molecular kinetics of catalytic olefin polymerization has been a challenging objective. Many methods have been proposed in the literature, but all of them have drawback(s). In this paper, we introduce a labeling method to count active sites employing methyl propargyl ether (MPE) as the quench-labeling agent. It is commercially available, does not react with Al-alkyl species, and has a labeling efficiency close to 100%. The labeling reaction was evidenced by a mechanistic study on the reaction between the model system Cp2ZrMe2/MAO (Cp = cyclopentadienyl) and MPE that it may occur through a coordination–insertion mechanism without noticeable multiple insertions. The method was benchmarked by studying a MgCl2-supported Ziegler–Natta catalyst in 1-hexene polymerization. The fraction of the active transition metal χ* is found to be <1%. It rises in the very first few seconds and reaches a plateau within 10 s in the absence of precontact. With precontact, χ* remains constant over polymer yield from 0.3 up to 5.3 g(PH) g(cat)−1, demonstrating that χ* does not necessarily grow during polymerization. Longer precontact resulted in decreased χ* and decreased average rate constant of propagation <kp> which is in the order of 102 M–1 s–1.

Half-sandwich rare-earth metal complexes bearing a C5Me4-C6H4-o-CH2NMe2 ligand: synthesis, characterization and catalytic properties for isoprene, 1-hexene and MMA polymerization.

A new ortho-dimethylaminomethylphenyl-tetramethylcyclopentadienyl ligand C5Me4H-C6H4-o-CH2NMe2 (HL) and a series of rare-earth metal complexes bearing this ligand were synthesized. Of these complexes, two binuclear alkyl complexes [(C5Me4-C6H4-o-CH2N(Me)CH2-μ)Ln(CH2SiMe3)]2 (Ln = Sc (1a) and Y (1b)) were obtained from the alkane elimination reaction of the free ligand with Ln(CH2SiMe3)3(THF)2, followed by an intramolecular C-H activation process of a NMe group in the ligand with a CH2SiMe3 group, two binuclear dichloro complexes (C5Me4-C6H4-o-CH2NMe2)2Y2Cl4[LiCl(THF)2] (2a) and [(C5Me4-C6H4-o-CH2NMe2)LuCl(μ-Cl)]2 (2b) were synthesized by the reaction of anhydrous yttrium or lutetium trichloride with the lithium salt of the ligand LiL, and the binuclear bis(borohydrido) complexes [(C5Me4-C6H4-o-CH2NMe2)Ln(μ-BH4)BH4]2 (Ln = Sm (3a) and Nd (3b)) were synthesized by the reaction of Ln(BH4)3(THF)3 (Ln = Sm and Nd) with the lithium salt of the ligand. The molecular structures of all complexes 1a, 1b, 2a, 2b, 3a and 3b were determined by single-crystal X-ray crystallography. Upon activation with AlR3/Ph3CB(C6F5)4, MAO or MMAO, the binuclear alkyl complexes 1a and 1b show good catalytic activity for isoprene cis-1,4 enriched regioselective polymerization and moderate catalytic activity for 1-hexene polymerization. Complexes 3a and 3b were studied as catalysts for methyl methacrylate polymerization reaction under different conditions and were found to show moderate to high catalytic activity.

Quantitative Modeling of the Temperature Dependence of the Kinetic Parameters for Zirconium Amine Bis(Phenolate) Catalysts for 1-Hexene Polymerization

The chemical kinetics for a series of three zirconium amine bis(phenolate) catalysts for poly 1-hexene polymerization have been examined as a function of temperature. Detailed modeling of the experimental data has yielded the activation parameters for many of the reaction rate constants, including those for propagation, initiation, chain transfer, and monomer misinsertion and recovery. While existing literature is sparse, the results herein generally agree with previously published values; specifically, for the propagation rate constant, the magnitude of the enthalpy of activation is low (12 kcal mol–1 and below), and the magnitude of the entropy of activation is moderate (up to −27 cal mol–1 K–1). With regard to the remaining rate constants, Arrhenius behavior is observed in most cases despite the complexity of the temperature dependence in the two-step adsorption/insertion kinetics. The rate expression for these reactions approaches an Arrhenius form in certain limiting cases of the relative elementary rate constants. The reaction rate data are compared against these limiting cases, leading to the conclusion that docking, with an early transition state, is rate limiting for propagation and placing bounds on the interpretation of most of the remaining constants. The challenges encountered in assigning temperature-dependent rate constants for the polymerization reactions are indicative of both the significant complexity in modeling a reaction in which thousands of species are present and the extreme care that is required in generating reproducible data.

Synthesis, characterization, and olefin (co)polymerization behavior of unsymmetrical α-diimine palladium complexes containing bulky substituents at 4-position of aniline moieties

Three novel unsymmetrical α-diimine Pd(II) complexes containing bulky substituents at 4-position of aniline moieties were prepared and characterized. Unfortunately, the introduction of large substituents on para- N-aryl moieties did not slow the exchange between the anti and syn forms for these complexes. These unsymmetrical α-diimine Pd(II) complexes also did not improve thermal stability and broaden molecular weight distribution in ethylene polymerization. However, these α-diimine palladium catalysts could copolymerize ethylene with biorenewable comonomer acrylic acid (AA), with comonomer incorporation in the range of 1.1–2.7% and high copolymer molecular weights. The AA units are incorporated predominately at the end of the branches. In addition, a systematic investigation on the polymerization of 1-hexene, 1-octene and 1-decene using these complexes was also performed. Changes in the ligand sterics and monomer length can influence the branch density and molecular weight of poly(α-olefins). Interestingly, these α-olefin polymers show properties characteristic of thermoplastic elastomers, i.e., good elastomeric recovery and high strain at break. Pervious work has shown that ethylene or α-olefin polymerization using some nickel α-diimine catalysts can generate elastic polyolefin materials. This work may provide an alternative and effective strategy to synthesize thermoplastic elastomers by α-diimine Pd(II) catalysts in one step using only α-olefin as the feedstock.

The synthesis of ultra-high molecular weight poly(1-hexene)s by low-temperature Ziegler-Natta precipitation polymerization in fluorous reaction media

An effective method of 1-hexene polymerization in fluorous reaction media has been developed. When using perfluorinated compounds (FCs) as a solvent, the process, catalyzed by highly active titanium-magnesium catalysts modified with 3,3-bis(methoxymethyl)pentane (BMMP) as an electron-donor, proceeds as a precipitation polymerization, and the reaction products represent highly stereo- and regioregular poly(1-hexene)s in the form of microparticles. In freons, polymerization can be carried out at sub-zero temperatures with monomer conversion up to 50% within 1 h and the formation of UHMW poly(1-hexene)s with Mn ∼2·106 Da. The polymers prepared in FCs demonstrate a high drag reducing effect (up to 40% in n-heptane for 0.25 ppm concentration), exceeding the previously described UHMW poly(1-hexene)s. Polymerization products after mixing with rapeseed oil form stable dispersions of ready-to-use drag reducing agents (DRAs) for pipeline oil transportation.

1-Hexene polymerization with supported Ziegler-Natta catalyst: Correlation between catalyst particle fragmentation and active center distribution

1-Hexene was polymerized with a commercial MgCl2-supported Ziegler-Natta catalyst using triethylaluminum as cocatalyst at different monomer/catalyst mass ratio (mhexene/mcat = 5, 15, 30), and the number of active centers ([C*]/[Ti]) was determined by quench-labeling the catalyst with 2-thiophenecarbonyl chloride and monitoring sulfur content of the polymer. Changes of polymerization rate (Rp) and propagation rate constant (kp) with time were also determined. [C*]/[Ti] was found to increase with time for 3 − 5 folds in the first 10 min of polymerization, but the maximum [C*]/[Ti] value reached after the induction period markedly enhanced with increase of monomer/catalyst mass ratio. Gradual fragmentation of the catalyst particles in parallel with the [C*]/[Ti] increase was observed by SEM analysis. It means that a large proportion of active center precursors are inaccessible to cocatalyst and monomer at the beginning of reaction, and fragmentation of the particles by hydraulic force of the growing polymer chains leads to exposure and activation of these precursors. Raising the monomer concentration can provide larger hydraulic force to expose those active site precursors that are more tightly buried inside the catalyst particle. The polymer molecular weight distribution and related active center distribution was found to shift with increase of the monomer/catalyst ratio, meaning that there are different types of buried active center precursors, and their exposure requires different extent of particle fragmentation.

Bis-(salicylaldehyde-benzhydrylimino)nickel complexes with different electron groups: crystal structure and their catalytic properties toward (co)polymerization of norbornene and 1-hexene

Eight bis-(salicylaldehyde-benzhydrylimino)nickel complexes with different electron groups (Ni1–Ni8), Ni{(3-R1)(5-R2)C6H2(O)CHNCH(C6H5)2}2, (R1 = H, R2 = H, Ni1; R1 = H, R2 = CH3, Ni2; R1 = H, R2 = OCH3, Ni3; R1 = H, R2 = Br, Ni4; R1 = CH3, R2 = H, Ni5; R1 = OCH3, R2 = H, Ni6; R1 = Br, R2 = Br, Ni7; R1 = Cl, R2 = Cl, Ni8), were synthesized and their crystal structures were characterized using single crystal X-ray diffraction. The results revealed that Ni1–Ni6 belong to the monoclinic system (space group P2(1)/n), Ni7 belongs to the monoclinic system (space group C2/c) and Ni8 belongs to the triclinic system (space group P1̄). All nickel complexes exhibited high activities (0.46–2.07 × 106 gpolymer molNi−1 h−1) toward norbornene homopolymerization, and a strong electron-withdrawing group on the salicylaldimino aromatic ring can enhance the catalytic activity and favor polymerization. Ni1 and Ni2 exhibited high activities (0.55–2.40 × 105 gpolymer molNi−1 h−1) toward copolymerization of norbornene and 1-hexene in the presence of B(C6F5)3. The 1-hexene content in the copolymers could be controlled up to 7.98–12.50% by varying the comonomer feed ratio of 1-hexene from 10 to 50%. It is observed that when the 5-position of the salicylaldimino aromatic ring has a substituent (–CH3), the 1-hexene insertion rate is lower than that without a substituent. In addition, the polymers showed high molecular weights (1.5–2.4 × 105 g mol−1) and narrow molecular weight distributions (1.62–1.89). The obtained polymers were also verified to be amorphous copolymers and had high thermal stability, good solubility and optical transparency.

Bis(oxazoline)-derived N-heterocyclic carbene ligated rare-earth metal complexes: synthesis, structure, and polymerization performance

Bis(oxazoline)-derived N-heterocyclic carbene (IBiox) supported rare-earth (Sc, Y, Lu) trialkyl complexes have been synthesized and structurally characterized, and their catalytic activity in the (co)polymerization of α-olefins has been studied. The treatment of Ln(CH2SiMe3)3(THF)2 with one equivalent of freshly prepared IBiox afforded the rare-earth metal complexes (IBiox)Ln(CH2SiMe3)3THFn (Ln = Sc (1), n = 0; Y (2), n = 1; and Lu (3), n = 1) in good yields. Single crystal X-ray diffraction study showed that 1 is pseudo tetrahedral, while 2 and 3 are distorted trigonal bipyramidal with coordinated THF. The Ln-C(carbene) bond distances in 1, 2, and 3 are 2.352, 2.550, and 2.479 Å, respectively. DFT calculations were performed to study the bonding scheme and the structural stability. Complex 1 showed a high activity for 1-hexene polymerization by activation with 2 equivalents of [Ph3C][B(C6F5)4], and the resultant polymers are predominantly vinylene end groups (ca. 95%). Moreover, the catalyst system based on 1 proved to be effective for the copolymerization of 1-hexene with 1,7-octadiene, affording the copolymers with about 20% pendant vinyl groups. The hydrophilicity of the copolymers was improved by modifying the vinyl groups with carboxyls via a thiol-ene reaction.