Copolymerization Of 1-hexene Research Articles

Solvent-free preparation of well-dispersed and highly active CrOx/VOx/TiO2-SiO2 bimetallic catalyst for bimodal UHMWPE/ HDPE in-reactor blends

CrOx/VOx/TiO2-SiO2 was prepared via solvent-free and conventional wet-impregnation process with ethanol as solvent. The results of ICP-OES, N2 adsorption-desorption, SEM-EDX, Raman and DR-Uv-vis spectra indicate that well-dispersed Cr and V sites in isolated state were the main species. Bimodal ultra-high molecular weight polyethylene/high-density polyethylene in-reactor blends (UHMWPE/HDPE IRBs) could be synthesized with polymerization activity ＞ 1×107 gPE·mol−1Cr·h−1. Moreover, the two catalysts displayed similar catalytic behaviors in temperature sensitivity, H2 response and 1-hexene copolymerization efficiency, and their polymer products also show comparable molecular weight and molecular weight distribution, which implies analogous structures of their well-dispersed active sites. By contrast, the catalyst prepared by wet-impregnation process with water as solvent exhibited poor dispersity, which is reflected by its much lower activity and very different catalytic behaviors and polymer properties when compared with the well-dispersed catalysts. Therefore, the economic and green solvent-free process is promising for preparing highly-active CrOx/VOx/TiO2-SiO2.

Influence of the Main Blown Film Extrusion Process Parameters on the Mechanical Properties of a High-Density Polyethylene Hexene Copolymer and Linear Low-Density Polyethylene Butene Copolymer Blend Used for Plastic Bags

Polyethylene plastic bags manufactured via blown film extrusion have different quality specifications depending on their intended use. It is known that the mechanical properties of a film depend on the process parameters established, but little is known concerning how they affect one another, even more so due to the variety of polyethylene materials and processing techniques. This study focuses on establishing a proper correspondence of important mechanical properties like the dart impact, tensile strength at break, and elongation at break with commonly used process parameters like the blow-up ratio, take-up ratio, thickness reduction, and neck height, for a high-density polyethylene hexene copolymer and a linear low-density polyethylene butene copolymer blend film. Because this polyethylene mixture is an anisotropic material, interesting R2 values equal to or higher than 0.90 were found: a BUR with elongation at break and tensile strength at break in the MD and TD, a TUR with elongation at break in the MD and tensile strength at break in the MD and TD, and a TR with elongation at break and tensile strength at break in the MD. Also, a relationship between the dart impact and both the neck height and thickness were found.

Copolymerization of Ethylene with Alpha-Olefins over Supported Titanium–Magnesium Catalysts Containing Titanium Compounds in Different Oxidation and Coordination States

Data were obtained on the copolymerization of ethylene with α-olefins over supported titanium–magnesium catalysts (TMC) prepared on the same magnesium dichloride support but differing in the composition and oxidation state of titanium. The copolymerization kinetics of ethylene with 1-hexene over TMC of different compositions were studied. Data on the composition of the produced ethylene–1-hexene copolymers, their molecular weight distribution, thermophysical characteristics, and branching distribution were presented. The constants of ethylene–1-hexene copolymerization over catalysts with different compositions were calculated. The TMC containing only Ti(II) compounds as the active component exhibited increased copolymerizing ability compared to the conventional TiCl4/MgCl2 catalyst containing Ti(III) compounds as the active component. In addition, TMC with Ti(II) as an active component produces copolymers with a more uniform branching distribution. It was shown that the TMC containing isolated Ti(II) ions could be used to produce X-ray amorphous ethylene-propylene elastomers with a high yield.

Crystallization Behavior of Isotactic Propene-Octene Random Copolymers

The crystallization behavior of random propene-octene isotactic copolymers (iPPC8) prepared with a homogeneous metallocene catalyst has been studied. Samples of iPPC8 with low octene content up to about 7 mol% were isothermally crystallized from the melt at various crystallization temperatures. The samples crystallize in mixtures of the α and γ forms of isotactic polypropylene (iPP). The relative amount of γ form increases with increasing crystallization temperature, and a maximum amount of γ form (fγ(max)) is achieved for each sample. The crystallization behavior of iPPC8 copolymers is compared with the crystallization from the melt of propene–ethylene, propene–butene, propene–pentene, and propene–hexene copolymers. The results show that the behavior of iPPC8 copolymers is completely different from those described in the literature for the other copolymers of iPP. In fact, the maximum amount of γ form achieved in samples of different copolymers of iPP generally increases with increasing comonomer content, while in iPPC8 copolymers the maximum amount of γ form decreases with increasing octene content. The different behaviors are discussed based on the inclusion of co-monomeric units in the crystals of α and γ forms of iPP or their exclusion from the crystals. In iPPC8 copolymers, octene units are excluded from the crystals giving only the interruption effect that shortens the length of regular propene sequences, inducing crystallization of the γ form at low octene concentrations, lower than 2 mol%. At higher octene concentration, the crystallization of the kinetically favored α form prevails.

Statistical analysis of parameters involved in the synthesis of polar copolymers using a nickel (II) α-diimine complex

In this article, the copolymerization of 1-hexene and butyl acrylate in the presence of a nickel(II) complex (α-diimine nickel (II) catalyst consisting of bulky 2,6-di (isopropyl) phenyl groups as imine substituents and a planar acenaphthyl backbone) as catalyst and methylaluminoxane (MAO) or ethylaluminum sesquichloride (EASC) as activators has been investigated. The main aim of this article is to provide a deep investigation of the effect of the type of activator, polymerization time, temperature, and comonomer content in the reactor feed on activity, comonomer incorporation, and molecular weight of resulting copolymers. Then, a nonlinear regression method was used to fit analytical results to a numeric model, which is very useful for predicting the properties of the final copolymers only by having the polymerization parameters.

In‐reactor blends based on ultrahigh molecular weight polyethylene: Effect of microstructure of modifying fraction on the morphology and viscoelastic behavior of blends

AbstractA morphology and viscoelastic behavior of a wide range of in‐reactor blends (RBs) on the base of ultrahigh molecular weight polyethylene (UHMWPE) with Mw = 1000 kg mol−1 and polymer fractions of different microstructure were investigated to develop the understanding of relationships between the structure and properties of polyolefin materials. Linear low‐molecular weight polyethylene of high density (LMWPE) with Mw = 160 kg mol−1 as well as ethylene/1‐hexene copolymers (CEH‐n) containing from 3 to 19 mol% of 1‐hexene were used as the components of RBs. In‐reactor blends UHMWPE/CEH‐n and UHMWPE/LMWPE with a varied content of CEH‐n or LMWPE fractions were prepared in the two‐step polymerization processes of ethylene homo‐ and copolymerization over metallocene catalyst. It was found by the methods of differential scanning calorimetry (DSC) and Wide Angle X ray Scattering (WAXS) methods, that the percentages of crystalline and amorphous phases and the lamella sizes in the materials depend on the nature and amount of modifying polymer fractions. Linear dependences of α‐relaxation temperature on the lamella sizes in crystalline phase and β‐relaxation temperature on the density of butyl branches in copolymer fractions of in‐reactor blends UHMWPE/CEH‐n were found by the method of dynamic mechanical analysis (DMA) method. The mechanisms of the processes of α‐ and β‐relaxations in the in‐reactor blends including polymer fractions with different microstructure are discussed.

Tandem Synthesis of Ultra-High Molecular Weight Drag Reducing Poly-α-Olefins for Low-Temperature Pipeline Transportation.

Ultra-high molecular weight poly-α-olefins are widely used as drag reducing agents (DRAs) for pipeline transportation of oil and refined petroleum products. The synthesis of polyolefin DRAs is based on low-temperature Ziegler–Natta (ZN) polymerization of higher α-olefins. 1-Hexene based DRAs, the most effective at room temperature, typically lose DR activity at low temperatures. The use of 1-hexene copolymers with C8–C12 linear α-olefins appears to offer a solution to the problem of low-temperature drag reducing. The present work aims to develop two-stage synthesis of polyolefin DRAs that is based on selective oligomerization of ethylene in the presence of efficient chromium/aminodiphosphine catalysts (Cr-PNP), followed by polymerization of the olefin mixtures, formed at oligomerization stage, using efficient titanium–magnesium ZN catalyst. We have shown that oligomerization of ethylene in α-olefin reaction media proceeds faster than in saturated hydrocarbons, providing the formation of 1-hexene, 1-octene, and branched C10 and C12 olefins; the composition and the ratio of the reaction products depended on the nature of PNP ligand. Oligomerizates were used in ZN polymerization ‘as is’, without additional treatment. Due to branched character of C10+ hydrocarbons, formed during oligomerization of ethylene, resulting polyolefins demonstrate higher low-temperature DR efficiency at low polymer concentrations (~1 ppm) in comparison with benchmark polymers prepared from the mixtures of linear α-olefins and from pure 1-hexene. We assume that faster solubility and more efficient solvation of the polyolefins, prepared using ‘tandem’ ethylene-based process, represent an advantage of these type polymers over conventional poly(1-hexene) and linear α-olefin-based polymers when used as ‘winter’ DRAs.

Drag reduction assessment of some new copolymers of 1-hexene and maleic anhydride in light crude oil

Poly(1-hexene-co-maleic anhydride) derivatives containing various lengths of linear alkyl side chains (C11–C22) were experimentally evaluated as drag reduction agents in the turbulent flow of Iraqi crude oil using a circulating flow loop system. Good drag reduction performances were obtained. The results showed that the drag reduction has been influenced by the flow rate, concentration, chemical structure, molecular weight, and temperature. Their mechanical stabilities were also investigated using a cylindrical rotator device, and a good relationship was obtained between copolymers' drag reduction efficiency and branch length, in which longer branches significantly enhance copolymer mechanical stability.

A Multivariate Linear Regression Approach to Predict Ethene/1-Olefin Copolymerization Statistics Promoted by Group 4 Catalysts

We report a combined multivariate linear regression (MLR) and density functional theory (DFT) approach for predicting the comonomer incorporation rate in the copolymerization of ethene with 1-olefins. The MLR model was trained to correlate the incorporation rate of a set of 19 experimental group 4 catalysts to steric and electronic features of the dichloride catalyst precursors. Although the assembled experimental data were produced in different laboratories and both propene and 1-hexene copolymerization results were considered, the trained MLR model results in a R2 value of 0.82 and a leave-one-out Q2 value of 0.72. The trained model was validated against a validation set comprising 3 catalysts from the literature and not included in the training set plus one catalyst synthesized by us. Except for one literature catalyst, data in the validation set were predicted with reasonable accuracy. Additionally, a catalyst synthesized by us, for which the MLR model predicted a comonomer incorporation of 4.0%, resulted in a 1-hexene experimental incorporation of 4.5–5%. The trained MLR model was used to predict the comonomer incorporation rate of 10 related zirconocenes having structural features similar to the 19 systems in the training set. We further explored the impact of the precatalyst structure on the comonomer incorporation rate by analyzing a set of 15 zirconocenes having steric and electronic features different from those in the training set. These predictions were validated by DFT calculations.

Synthesis of ultra-high molecular weight poly(ethylene)-co-(1-hexene) copolymers through high-throughput catalyst screening.

A family of permethylindenyl titanium constrained geometry complexes, Me2SB(R′N,3-RI*)TiX2 ((3-R-η5-C9Me5)Me2Si(R′TiX2)), supported on solid polymethylaluminoxane (sMAO) are investigated as slurry-phase catalysts for ethylene/H2 homopolymerisation and ethylene/1-hexene copolymerisation by high-throughput catalyst screening. Me2SB(tBuN,I*)TiCl2 supported on sMAO [sMAO-Me2SB(tBuN,I*)TiCl2] is responsive to small quantities of H2 (<1.6%), maintaining high polymerisation activities (up to 4900 kgPE molTi−1 h−1 bar−1) and yielding polyethylenes with significantly decreased molecular weight (Mw) (from 2700 to 41 kDa with 1.6% H2). In slurry-phase ethylene/1-hexene copolymerisation studies, a decrease in polymerisation activity and polymer molecular weights compared to ethylene homopolymerisation is observed. Compared to many solid supported system, these complexes all display high 1-hexene incorporation levels up to a maximum incorporation of 14.2 mol% for sMAO-Me2SB(iPrN,I*)TiCl2). We observe a proportionate increase in 1-hexene incorporation with concentration, highlighting the ability of these catalysts to controllably tune the amount of 1-hexene incorporated into the polymer chain to produce linear low-density polyethylene (LLDPE) materials.

Microstructural study on MMA/1‐hexene copolymers made by mononuclear and dinuclear α‐diimine nickel (II) catalysts

Homogenous catalytic homopolymerization and copolymerization of 1‐hexene (H) with methyl methacrylate (MMA) were carried out in presence of two different types of mononuclear (MNC1 and MNC2) and dinuclear Ni‐based catalysts (BNC1 and BNC2). Modified methylaluminoxane was used as cocatalyst due to good reactivity in MMA/H copolymerization. Among the structures, BNC1 showed the highest catalyst activity (6.9 × 104 g P. mol−1Ni. h−1). Although Mw of the copolymer made by BNC1 was higher than its mononuclear, molecular weight distribution was broader. The optimum molar ratios for mononuclear and dinuclear were obtained at [Al]/[Ni] = 1,000:1 and [Al]/[Ni] = 1,500:1, respectively. Surprisingly, introduction of MMA (up to [MMA]/[H] = 50:50 molar ratio) into the polymerization solution increased the activity of all catalysts. 1H NMR analysis study revealed that increasing of MMA in the feed composition raised incorporation of the comonomer into the obtained copolymers. The result was consistent on the calculated reactivity ratio of monomers, using Kelen–Tudos method. In addition, BNC1 (at [MMA]/[H] = 70:30 molar ratio) demonstrated more incorporation of MMA to the main copolymer chain (95.2% mol). On the other side, study on tacticity of the PMMA sample was investigated that showed a distribution of stereoregularity in the order of atactic &gt; &gt; syndiotatic &gt; isotactic (53.2 &gt; 26.7 &gt; 20.1). In addition, for copolymers made by BNC1, an unusual pattern was observed as lower concentration of MMA in the feed (i.e., 30%) led to high isotactic blocks of MMA. The highest branching density of the polymer, however, was obtained by BNC1 (217/1000C) and the lowest by BNC2 (80/1000C). Higher extent of the polar comonomer (MMA) in the copolymer backbone led to increasing of Tg for the copolymer samples (from 74.4 to 98.9°C). The structural properties of the obtained copolymers were investigated using both Fourier transform infrared spectroscopy and Raman spectroscopies, as well.

PHYSICOMECHANICAL PROPERTIES OF NANOCOMPOSITES BASED ON COPOLYMERS OF ETHYLENE WITH α-OLEFINS AND CLINOPTILOLITE

The results of studying the effect of clinoptilolite concentration on the properties of nanocomposites based on of ethylene with butylene and of ethylene with hexene copolymer are presented. The effect of clinoptilolite particle size on ultimate tensile stress, elongation at break, flexural modulus, heat resistance, and melt flow index of composites was studied. It is shown that nanocomposites based on ethylene copolymers are characterized by higher values of physicomechanical properties. The additional use of ingredients such as alizarin and calcium stearate contributes to a significant improvement in the complex of properties of nanocomposites based on ethylene copolymers and clinoptilolite

Structural, Rheological, and Mechanical Properties of Binary Compounds Based on High-Density Polyethylene and Linear Low-Density Polyethylene

Rheological, molecular, thermal, and mechanical properties of binary blends based on bimodal high-density polyethylene (HDPE; ethylene–1-hexene copolymer) and unimodal linear low-density polyethylene (LLDPE; ethylene–1-butene–1-hexene terpolymer) were studied. Six blends with different HDPE/LLDPE weight ratios, 80/20, 70/30, 60/40, 50/50, 40/60, and 20/80, were prepared by blending in a double-worm extruder. The correlation of the rheological properties of the blends, analyzed by the capillary and rotation methods, with the melt flow index and molecular characteristics was demonstrated. LLDPE with increased flowability (MFI = 3 g/10 min) as a polymer additive is an effective plasticizer allowing control of the melt viscosity in a wide range and choice of the optimum target value of the melt flow index of the blend. The activation energy of the melt flow was calculated, and the relationship between this quantity and the content of short-chain branchings in polyethylene blends was revealed. The blends obtained are homogeneous, but an increase in the content of LLDPE in HDPE leads to a change in the polyethylene structure, which is confirmed by a decrease in the crystallinity and in the lamella thickness. The strength values at the yield point and at break decrease with an increase in the fraction of LLDPE in HDPE. Changes in the properties of these blends in their processing into a film by flat-die extrusion were studied.

Living coordination–insertion copolymerization of 1-hexene and ligated α-olefins using an α-diimine nickel catalyst and preparation of metal–ligand coordination crosslinked polymers

Metal–ligand coordination crosslinked polymers were prepared by coordination–insertion copolymerization of 1-hexene and ligated α-olefins.

Polymerization Kinetics and Microstructure of Ethylene/1‐Hexene Copolymers Made with Dual Metallocenes

AbstractMathematical models are developed to describe the polymerization of ethylene and 1‐hexene with a constrained geometry catalyst (CGC‐Ti) and with bis(cyclopentadienyl)‐zirconium (IV) dichloride (Cp2ZrCl2). Particle swarm optimization is used to fit these models to homo‐ and copolymerization data. The models are also used to describe copolymerizations with mixtures of CGC‐Ti and Cp2ZrCl2 to make copolymers with inverse short chain branching distribution. Copolymer molecular weight and short chain branch distributions, as well as polymerization rates with the dual metallocene system, are measured to test whether they agreed with model predictions. The results show that the two metallocenes do not interact strongly when used as a mixture to make ethylene/1‐hexene copolymers.

Strain hardening test on the limits of Slow Crack Growth evaluation in high resistance polyethylene resins: Effect of comonomer type

Long term performance assessment of polyethylene pipes is an issue that has greatly increased in importance in recent years due to the incorporation in the market of high resistance to crack polyethylene grades (PE100RC), where established Slow Crack Growth (SCG) evaluation using traditional tests such as Full Notch Creep Test (FNCT) or Pennsylvania Notch Tensile (PENT) Test is insufficient. The development in recent years of fast evaluation techniques such as Strain Hardening (SH) modulus has opened an important alternative for quick SCG evaluation since it correlates well with other conventional tests such as FNCT and PENT. In this work, a large number of commercial and experimental polyethylene pipe resins with different comonomer types were evaluated in order to define their SH values to rank the resins as PE100 or PE100RC. A relationship is proposed that utilizes SH test results to estimate the SCG resistance of PE pipes. 1-Butene copolymer resins display threshold SH values of 38 and 53 MPa that have been assigned to PE100 and 100RC grades, respectively. Moreover, dependence of the SH values on comonomer type used has been demonstrated. The experimental results show that 1-hexene copolymer resins exhibit higher SH values than 1-butene comonomer based resins.

Simultaneous Deconvolution of the Bivariate Molecular Weight and Chemical Composition Distribution of Ethylene/1‐Hexene Copolymers

AbstractThe bivariate molecular weight and chemical composition distribution (MWD×CCD) of ethylene/1‐hexene copolymers can be measured using TREF×GPC cross fractionation characterization (CFC). In this work, the experimental MWD×CCD of ethylene/1‐hexene copolymers made with a Ziegler–Natta catalyst under different polymerization conditions are measured by CFC and deconvoluted to identify the minimum number of site types present in the catalyst. Blends of ethylene/1‐hexene copolymers produced with a metallocene catalyst with known MWD×CCD are used to validate the proposed technique. This is a powerful methodology to better understand the nature of active sites on multisite catalysts, and can be beneficial for the development of copolymers with precisely controlled microstructures.

Concentration fluctuations in the early stages of LLPS and partial dissolution of melt-memory in broadly distributed ethylene copolymers

The mechanism of liquid-liquid phase separation (LLPS) is investigated in a random ethylene 1-hexene copolymer (E/H) with a broad comonomer content distribution. SANS measurements were first carried out using the original resin with deuterium added via direct isotope exchange to preserve the original branching distribution. Upon lowering the melt temperature, the upshift of SANS profile observed only below a critical scattering vector is consistent with the signature of nucleation and growth during LLPS in the metastable region. Differences in branching distribution between the original broad resin and a broad multi-components blend of narrow E/H copolymers studied previously, result in slower LLPS dynamics in the former that has a more continuous change of comonomer content between molecules. Time-resolved light scattering and light transmittance measurements in the metastable region of the broad resin, reveal the nucleation and growth stages of LLPS. Dissolution of crystalline melt-memory, associated with an inversion of the crystallization rate with decreasing the temperature of the initial melt, is found to occur mainly within the LLPS induction period and is associated with concentration fluctuations prior to the LLPS nucleation step. The typical sea-island morphology associated with LLPS via nucleation and growth is observed under bright-field optical microscopy after one-day annealing in the metastable region.

Polyolefins Made with Dual Metallocene Catalysts: How Microstructure Affects Polymer Properties

AbstractSlow crack growth resistance correlates with the lifetime of polyethylene pipes. Since this measurement may take considerable time, alternative ways to estimate it help expedite the development of new polyethylene resins. The primary structural parameter (PSP2), calculated from the distribution of molecular weight and short chain branching of polyethylenes, can predict the stress crack growth resistance of polyethylene resins without needing to measure it over long periods of time. In this investigation, a model is developed to calculate PSP2 of ethylene homopolymers and ethylene/1‐hexene copolymers made with two metallocene catalysts. For each metallocene, the effect of the following parameters on PSP2 is investigated: (1) polymer mass fraction, (2) polymer average molecular weight, and (3) average comonomer fraction. The simulation trends agree with previously published experimental results. The generated 3D surface response plots are useful guides for the design of polyethylenes having optimized slow crack growth resistance.

Rheological analysis of irradiated crosslinkable and scissionable polymers used for medical devices under different radiation conditions

The effects on different synthetic polymers of distinct types of radiation, gamma rays and electron beam, under different atmospheres are followed by changes in their viscoelastic behavior. Taking into account the two main radioinduced reactions, crosslinking and scissioning of polymeric chains, liquid polydimethylsiloxane has been used as example of crosslinkable polymer and semi crystalline polypropylene as example of scissionable polymer. Propylene − 1-hexene copolymers have been also evaluated, and the effects of both reactions were clearly noticed. Accordingly, samples of those aforementioned polymers have been irradiated with 60Co gamma irradiation in air and under vacuum, and also with electron beam, at similar doses. Sinusoidal dynamic oscillation experiments showed a significant increase in branching and crosslinking reactions when specimens are irradiated under vacuum, while scissioning reactions were observed for the different polymers when irradiation takes place under air with either gamma irradiation or electron beam.