Ethylene-hexene Copolymer Research Articles

Physico-mechanical properties of dynamically vulcanized basaltoplastics based on compatibilized ethylene-hexene copolymer

Physico-mechanical properties of dynamically vulcanized basaltoplastics based on compatibilized ethylene-hexene copolymer

Technological features of reactive dynamic extrusion of nanocomposites based on polyolefins, aluminum and technical carbon

The effect of the concentration of aluminum powder and technical carbon nanoparticles on the main physical and mechanical properties of nanocomposites based on high density polyethylene, low density polyethylene and an ethylene-hexene copolymer is considered. The optimal technological parameters of the reaction extrusion of nanocomposites vulcanized with sulfur and dicumyl peroxide have been determined. The influence of the type of polyolefin, fillers and crosslinking agents on the formation of isotropic nanocomposites during the production of sheet products has been investigated.

Kinetic Regularities of Crystallization of Nanocomposites Based on Clinoptilolite and Ethylene-Hexene Copolymer

The paper presents the results of experimental studies of the crystallization process of nanocomposites based on clinoptilolite and an ethylene-hexene copolymer. The temperature dependence of the specific volume and free volume was investigated by the method of dilatometric measurements. In accordance with the theory of Avrami, the kinetic regularity of the isothermal crystallization process at the temperature of the first-order phase transition has been studied. The mechanism and type of crystal growth for the initial polymer matrix and nanocomposites are determined.

Deformation transitions of ethylene-hexene copolymers under creep loading

Creep tests were conducted in the temperature range from 296 to 358 K, on three commercial ethylene-hexene copolymers (PE) with mass density of 0.938, 0.941 and 0.952 g/cc. PE with the highest density shows the well-known ductile-brittle (DB) transition in the relationship between applied stress and failure time, and PE with the medium density a different transition which was detected through the change in the dependence of failure time on the applied stress, but the failure mode remained ductile. Therefore, this transition is named ductile-ductile (DD). The work shows feasibility of establishing creep master curves to include the two transitions, and discusses exclusiveness between DD and DB transitions so that detection of the DD transition can be used to determine the likelihood of the DB transition to occur in the long-term service. The work also examines applicability of the Monkman-Grant relationship to PEs that involve DD or DB transition.

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.

Analyses of Short Chain Branches in Polyolefins with Improved 1H NMR Spectroscopy.

Polyolefin microstructures, for example, short chain branching (SCB) and short chain branch distribution (SCBD), have a direct impact on properties and thus ultimately influence end-use applications. The 1H NMR approach to analyze SCB and SCBD is particularly useful when only a limited amount of sample is available, for example, polyolefin film layers or the fractions from polyolefin separation techniques, such as gel permeation chromatography (GPC), crystallization elution fractionation (CEF), high temperature liquid chromatography (HTLC), and thermal gradient interaction chromatography (TGIC). In this paper, we discuss the best approach to find a good decoupling frequency and propose an improved 1H pulse sequence with homonuclear decoupling for better measuring SCB. With this new pulse it is possible to reach a S/N of 10 (level of quantification) for the methyl signal from SCB in an ethylene-hexene copolymer (EH, 3.6 mol % H) in 3.5 min with 0.5 μg of sample. We also show an easy method to calculate SCB/1000C and demonstrate the proper use of heteronuclear single quantum coherence (HSQC) to measure SCB in a complicated system. A very quick approach to examine the presence of a small amount of LDPE in a polyolefin sample is also suggested, which can reduce NMR acquisition time from a couple of days to a few minutes.

Elucidation of the relationships of structure-process-property for different ethylene/α-olefin copolymers during film blowing: An in-situ synchrotron radiation X-ray scattering study

The copolymerization of ethylene and different α-olefins could result in polyethylene (PE) with different structural topologies, and lead to polyethylene products with different macroscopic performances. Herein, three different polyethylene samples, namely low-density polyethylene (l-PE), metallocene catalyzed ethylene-hexene copolymer (h-PE) and ethylene-octene copolymer (o-PE), were selected as representatives to construct the structure-process-property relationship during film blowing. The detailed crystal-based network evolution during film blowing was first characterized by in-situ synchrotron radiation X-ray scattering. The crystallization process of l-PE film is determined by the coupling effects of temperature and flow, while those of h-PE and o-PE films are dominated by the temperature. Furthermore, the hierarchical crystal structure from the molecular scale to micrometers of final films and segmental dynamics were systematically characterized by multiple ex-situ characterization techniques, i.e. Solid-State NMR, FTIR, SEM. l-PE film shows the crystalline morphology of the row-nucleated structure, whereas h-PE and o-PE show spherulite-like superstructure with better mechanical properties. The current study tentatively constructs the relation of primary chemical structure, microstructural evolution and macroscopic performances of different polyethylene copolymers during film blowing.

Polyolefin-Polar Block Copolymers from Versatile New Macromonomers.

A new metallocene-based polymerization mechanism is elucidated in which a zirconium hydride center inserts α-methylstyrene at the start of a polymer chain. The hydride is then regenerated by hydrogenation to release a polyolefin containing a single terminal α-methylstyrenyl group. Through the use of the difunctional monomer 1,3-diisopropenylbenzene, this catalytic hydride insertion polymerization is applied to the production of linear polyethylene and ethylene-hexene copolymers containing an isopropenylbenzene end group. Conducting simple radical polymerizations in the presence of this new type of macromonomer leads to diblock copolymers containing a polyolefin attached to an acrylate, methacrylate, vinyl ester, or styrenic segments. The new materials are readily available and exhibit interfacial phenomena, including the mediation of the mixing of immiscible polymer blends.

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.

SANS Evidence of Liquid–Liquid Phase Separation Leading to Inversion of Crystallization Rate of Broadly Distributed Random Ethylene Copolymers

Aiming to understand the inversion of crystallization kinetics observed by DSC, detailed SANS investigations of the melt structure of a broadly distributed ethylene–1-hexene copolymer have been undertaken in a wide range of temperatures that were reached either by heating the solid or cooling from the homogeneous melt state. In both cases, the observed SANS signal transitions from a scattering cross section consistent with a homogeneous melt state (high temperature range) to an intensity that in the low Q region displays the characteristics of the Porod region for particles dispersed in a homogeneous matrix (low melt temperature range). The latter structure is consistent with demixing of the highly branched molecules and corroborates the postulated liquid–liquid phase separation (LLPS) as an explanation for the peculiar crystallization kinetics observed by DSC. The solution temperature is found at 160 °C by heating the solid and at 150 °C when cooling from the one-phase melt, thus denoting the effect of c...

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.

Tandem Action of SNS-Cr and CGC-Ti in Preparation of Ethylene-1-Hexene Copolymers from Ethylene Feedstock

Ethylene–1-hexene copolymer materials, ranging from semicrystalline linear low-density poly­ethylene (LLDPE) to completely amorphous polyethylenes (PEs), are prepared from ethylene alone in a single reactor by the tandem polymerization of bis(2-dodecylsulfanyl-ethyl)amine–CrCl3 (SNS–Cr) and (N-tert-butylamido) (tetramethylcyclopentadienyl)–titanium dichloride (CGC–Ti) at 75 °C and under atmospheric pressure. The polymerization activities are on the order of 105–106 g (mol Ti)−1 h−1. 1-Hexene incorporation in the resulting copolymers can be adjusted by varying the Cr–Ti molar ratio and/or applying a short period of pre-trimerization. Copolymers with high 1-hexene incorporation up to 15 mol% are obtained. Few vinyl and vinylene chain ends are detected by 13C NMR, suggesting that 1-hexene does not act as a chain-transfer agent. Narrow molecular-weight distributions with polydispersities from 1.9 to 2.6 are obtained, characteristic of a single-active-site nature of the catalyst system.

Effects of supported (nBuCp)2ZrCl2 catalyst active center multiplicity on crystallization kinetics of ethylene homo- and copolymers

Two different supported zirconocene, that is, bis(n-butylcyclopentadienyl) zirconium dichloride (nBuCp)2ZrCl2, catalysts were synthesized. Each catalyst was used to prepare one ethylene homopolymer and one ethylene–1-hexene copolymer. Catalyst active center multiplicity and polymer crystallization kinetics were modeled. Five separate active center types were predicted, which matched the successive self-nucleation and annealing (SSA) peak temperatures. The predicted crystallinity well matched the differential scanning calorimetric (DSC) values for a single Avrami–Erofeev index, which ranged between 2 and 3 for the polymers experimented. The estimated apparent crystallization activation energy Ea did not vary with cooling rates, relative crystallinity α, and crystallization time or temperature. Therefore, the concept of variable/instantaneous activation energy was not found to hold. Ea linearly increased with the weight average lamellar thickness Lwav DSC-GT; and for each homopolymer, it exceeded that of the corresponding copolymer. Higher Ea, hence slower crystallization, was identified as a pre-requisite to attain higher crystallinity. Crystallization parameters were correlated to polymer backbone parameters, which are influenced by catalyst active center multiplicity.

Silica-supported (n BuCp)2 ZrCl2 : effect of catalyst active center distribution on ethylene-1-hexene copolymerization

Metallocenes are a modern innovation in polyolefin catalysis research. Therefore, two supported metallocene catalysts—silica/MAO/(nBuCp)2ZrCl2 (Catalyst 1) and silica/nBuSnCl3/MAO/(nBuCp)2ZrCl2 (Catalyst 2), where MAO is methylaluminoxane—were synthesized, and subsequently used to prepare, without separate feeding of MAO, ethylene–1-hexene Copolymer 1 and Copolymer 2, respectively. Fouling-free copolymerization, catalyst kinetic stability and production of free-flowing polymer particles (replicating the catalyst particle size distribution) confirmed the occurrence of heterogeneous catalysis. The catalyst active center distribution was modeled by deconvoluting the measured molecular weight distribution and copolymer composition distribution. Five different active center types were predicted for each catalyst, which was corroborated by successive self-nucleation and annealing experiments, as well as by an extended X-ray absorption fine structure spectroscopy report published in the literature. Hence, metallocenes impregnated particularly on an MAO-pretreated support may be rightly envisioned to comprise an ensemble of isolated single sites that have varying coordination environments. This study shows how the active center distribution and the design of supported MAO anions affect copolymerization activity, polymerization mechanism and the resulting polymer microstructures. Catalyst 2 showed less copolymerization activity than Catalyst 1. Strong chain transfer and positive co-monomer effect—both by 1-hexene—were common. Each copolymer demonstrated vinyl, vinylidene and trans-vinylene end groups, and compositional heterogeneity. All these findings were explained, as appropriate, considering the modeled active center distribution, MAO cage structure repeat units, proposed catalyst surface chemistry, segregation effects and the literature that concerns and supports this study. While doing so, new insights were obtained. Additionally, future research, along the direction of the present work, is recommended. © 2013 Society of Chemical Industry

Effects of Supported (nBuCp)2ZrCl2Catalyst Active-Center Distribution on Ethylene–1-Hexene Copolymer Backbone Heterogeneity and Thermal Behaviors

Two catalysts, denoted as catalyst 1 [silica/MAO/(nBuCp)2ZrCl2] and catalyst 2 [silica/nBuSnCl3/MAO/(nBuCp)2ZrCl2] were synthesized and subsequently used to prepare, without separate feeding of methylaluminoxane (MAO), ethylene homopolymer 1 and homopolymer 2, respectively, and ethylene–1-hexene copolymer 1 and copolymer 2, respectively. Gel permeation chromatography (GPC), Crystaf, differential scanning calorimetry (DSC) [conventional and successive self-nucleation and annealing (SSA)], and 13C nuclear magnetic resonance (NMR) polymer characterization results were used, as appropriate, to model the catalyst active-center distribution, ethylene sequence (equilibrium crystal) distribution, and lamellar thickness distribution (both continuous and discrete). Five different types of active centers were predicted in each catalyst, as corroborated by the SSA experiments and complemented by an extended X-ray absorption fine structure (EXAFS) report published in the literature. 13C NMR spectroscopy also supported this active-center multiplicity. Models combined with experiments effectively illustrated how and why the active-center distribution and the variance in the design of the supported MAO anion, having different electronic and steric effects and coordination environments, influence the concerned copolymerization mechanism and polymer properties, including inter- and intrachain compositional heterogeneity and thermal behaviors. Copolymerization occurred according to the first-order Markovian terminal model, producing fairly random copolymers with minor skewedness toward blocky character. For each copolymer, the theoretical most probable ethylene sequences, nE MPDSC-GT and nE MPNMR-Flory, as well as the weight-average lamellar thicknesses, Lwav DSC–GT and Lwav SSA DSC, were found to be comparable. To the best of our knowledge, such a match has not previously been reported. The percentage crystallinities of the homo- and copolymers increased linearly as a function of LMPDSC-GT. This indicates that the homo- and copolymer chains folded excluding the butyl branch. The results of the present study will contribute to developing future supported metallocene catalysts that will be useful in the synthesis of new grades of ethylene−α-olefin linear low-density polyethylenes (LLDPEs).

Effect of cocatalyst on the chemical composition distribution and microstructure of ethylene-hexene copolymer produced by a metallocene/Ziegler-Natta hybrid catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for metallocene/Ziegler-Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl4 and rac-Et(Ind)2ZrCl2. The prepared rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst was applied to the ethylenehexene copolymerization with a variation of cocatalyst species (polymerization run 1: triisobutylaluminum (TIBAL) and methylaluminoxane (MAO), polymerization run 2: triethylaluminum (TEA) and methylaluminoxane (MAO)). The effect of cocatalysts on the chemical composition distributions (CCDs) and microstructures of ethylene-hexene copolymers was examined. It was found that the catalytic activity in polymerization run 1 was a little higher than that in polymerization run 2, because of the enhanced catalytic activity at the initial stage in polymerization run 1. The chemical composition distributions (CCDs) in the two copolymers showed six peaks and exhibited a similar trend. However, the lamellas in the ethylene-hexene copolymer produced in polymerization run 1 were distributed over smaller sizes than those in the copolymer produced in polymerization run 2. It was also revealed that the rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst preferably produced the ethylene-hexene copolymer with non-blocky sequence when TEA and MAO were used as cocatalysts.

Effect of triethylaluminum/transition-metal ratio on the physical properties and chemical composition distributions of ethylene-hexene copolymers produced by a rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB Catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for a metallocene/ Ziegler-Natta hybrid catalyst. The prepared rac-Et(Ind)2ZrCl2/TiCl4/MAO(methylaluminoxane)/SMB catalyst was applied to the copolymerization of ethylene with 1-hexene using a variable triethylaluminum (TEA)/transitionmetal (Ti) ratio and fixed MAO/transition-metal (Zr) ratio. The effect of the Al(TEA)/Ti ratio on the physical properties and chemical composition distributions (CCDs) of the ethylene-hexene copolymers produced by the hybrid catalyst was investigated. In the ethylene-hexene copolymers, two melting temperatures attributed to the metallocene and Ziegler-Natta catalysts were clearly observed. The number of CCD peaks was increased from six to seven and the temperature region in which the peaks for the short chain branches of the ethylene-hexene copolymer were distributed became lower as the Al(TEA)/Ti ratio was increased from 300 to 400. Furthermore, the temperature regions corresponding to the lamellas in the copolymer became lower and those corresponding to the small lamellas in the copolymer became higher as the Al(TEA)/Ti ratio was increased from 300 to 400. In the copolymer produced with Al(TEA)/Ti = 500, however, only four CCD peaks were observed and the short chain branches were poorly distributed.

Effect of methylaluminoxane/transition-metal ratio on the physical properties and chemical composition distributions of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst

A silica–magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for the impregnation of TiCl 4 and rac-Et(Ind) 2ZrCl 2. The prepared rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO(methylaluminoxane)/SMB catalyst was applied to the ethylene–hexene copolymerization under the conditions of variable Al(MAO)/Zr ratio and fixed Al(TEA, triethylaluminum)/Ti ratio. The effect of Al(MAO)/Zr ratio on the physical properties and chemical composition distributions of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst was investigated. The catalytic activity of rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB was steadily increased with increasing Al(MAO)/Zr ratio from 200 to 500. The ethylene–hexene copolymer produced with Al(MAO)/Zr = 300, 400, and 500 showed two melting points at around 110 °C and 130 °C, while that produced with Al(MAO)/Zr = 200 showed one melting point at 136 °C. The number of chemical composition distribution (CCD) peaks was increased from 4 to 7 and the short chain branches of ethylene–hexene copolymer were distributed over lower temperature region with increasing Al(MAO)/Zr ratio. The lamellas in the copolymer were distributed over lower temperature region and the small lamellas in the copolymer were increased with increasing Al(MAO)/Zr ratio. The rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst preferably produced a ethylene–hexene copolymer with non-blocky sequence ([EHE]) with increasing Al(MAO)/Zr ratio.

Chemical composition distributions and microstructures of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for a metallocene/Ziegler–Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl 4 and rac-Et(Ind) 2ZrCl 2. The prepared rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst was applied to the ethylene–hexene copolymerization with variable amounts of 1-hexene used. The catalytic activity of rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB showed a volcano feature with respect to the amount of comonomer used. The melting point attributed to the Ziegler–Natta catalyst was not changed significantly, while that attributed to the metallocene catalyst was broadened and gradually shifted to the lower temperature with increasing 1-hexene content. The number of chemical composition distribution (CCD) peaks was increased and the short chain branches were distributed over the lower temperature region with increasing 1-hexene content. The majorities of lamella distributions whose content was more than 50 wt.% shifted to the smaller lamella size with increasing 1-hexene content. The average sequence length of ethylene was steadily decreased with increasing comonomer content, while that of 1-hexene was not changed significantly. Both blocky sequence ([EHH]) and non-blocky sequence ([EHE]) were increased with increasing comonomer content. However, the increasing rate of blocky sequence formation was much higher than that of non-blocky sequence.

Physical property and chemical composition distribution of ethylene–hexene copolymer produced by metallocene/Ziegler–Natta hybrid catalyst

Silica–magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for metallocene and metallocene/Ziegler–Natta hybrid catalysts. SMB was treated with methylaluminoxane (MAO) prior to catalyst immobilization. The supported heterogeneous catalysts were applied to the ethylene copolymerization with 1-hexene. The h-copolymer (ethylene–hexene copolymer produced by metallocene/Ziegler–Natta hybrid catalyst) showed two melting points and broad molecular weight distribution. The differences in physical properties between h-copolymer and m-copolymer (ethylene–hexene copolymer produced by metallocene catalyst) could be explained by the differences in chemical composition and side chain distributions of the produced copolymers.