Synthesis and characterization of ethylene-1-hexene copolymers using homogeneous Ziegler-Natta catalysts

Summary This study investigated the copolymerization of ethylene with 1-hexene using the homogeneous Et[Ind]₂ZrCl₂ and [Ind]₂ZrCl₂ catalysts. The Et[Ind]₂ZrCl₂ catalyst gave a higher catalytic activity than the [Ind]₂ZrCl₂ and also showed a better incorporation of 1-hexene for the same comonomer concentration in the feed. Thermal analysis (DSC) and viscosity measurements showed that an increase of the 1-hexene incorporated in the copolymer results in a decrease of the melting point, crystallinity and molecular weight of the polymer formed. The reactivity ratios for ethylene and 1-hexene confirmed the more successful incorporation of the comonomer for the polymerization catalyzed by Et[Ind]₂ZrCl₂.     

Ethylene polymerization with catalysts on the base of Zr-cenes and methylaluminoxanes synthesized on zeolite support

Summary The fixed aluminoxanes have been prepared on zeolite support Na-form of ZSM-5 (Si/Al=42) in reaction of partial hydrolysis of trimethylaluminium (TMA) with inside zeolite water. It was shown that aluminoxanes synthesized on zeolite surface form the heterogenized complexes with Cp₂ ZrCl₂ and Et[Ind]₂ ZrCl₂ which are active in ethylene polymerization without addition of other aluminiumorganic cocatalyst for a long time. The activation energy of ethylene polymerization in the presence of ZSM-5(H₂O)/TMA - Et[Ind]₂ ZrCl₂ is equal to 32 kJ/mol. Molecular weight and melting point of polyethylene obtained with such zeolite supported Zr-cene catalysts are higher than those of polyethylene formed with appropriate homogeneous metallocene systems. Received: 15 February 2000/Revised version: 10 May 2000/Accepted: 10 May 2000     

In situ copolymerization of ethylene to produce linear low‐density polyethylene by Ti(OBu)4/AlEt3‐MAO/SiO2/Et(Ind)2ZrCl2

Linear low‐density polyethylene (LLDPE) is produced in a reactor from single ethylene feed by combining Ti(OBu)₄/AlEt₃, capable of forming α‐olefins (predominantly 1‐butene), with SiO₂‐supported Et(Ind)₂ZrCl₂ (denoted MAO/SiO₂/Et(Ind)₂ZrCl₂), which is able to copolymerize ethylene and 1‐butene in situ with little interference in the dual‐functional catalytic system. The two catalysts in the dual‐functional catalytic system match well because of the employment of triethylaluminum (AlEt₃) as the single cocatalyst to both Ti(OBu)₄ and MAO/SiO₂/Et(Ind)₂ZrCl₂, exhibiting high polymerization activity and improved properties of the obtained polyethylene. There is a noticeable increment in catalytic activity when the amount of Ti(OBu)₄ in the reactor increases and 1‐butene can be incorporated by about 6.51 mol % in the backbone of polyethylene chains at the highest Ti(OBu)₄ concentration in the feed. The molecular weights (M_w), melting points, and crystallinity of the LLDPE descend as the amount of Ti(OBu)₄ decreases, which is attributed mainly to chain termination and high branching degree, while the molecular weight distribution remains within a narrow range as in the case of metallocene catalysts. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2451–2455, 2004     

The production of ethene/propene/5-ethylidene-2-norbornene terpolymers using metallocene catalysts: Polymerization,characterization and properties of the metallocene EPDM

Metallocene catalysts Et(Ind)₂ZrCl₂/MAO and Et(Ind)₂HfCl₂/MAO were used in ethene/propene copolymerization and in ethene/propene/5-ethylidene-2-norbornene (E/P/ENB) terpolymerization. The copolymerization activity of the Et(Ind)₂ZrCl₂/MAO system was 20 × 10³ kg_polym/mol_Mt *h, the Et(Ind)₂HfCl₂/MAO yielding 5 × 10³ kg_polym/mol_Mt *h. The polymerization activity decreased with diene addition, but this effect was significant only at very large diene feeds. The catalysts incorporated diene readily. Materials with an ethene content of 55 to 70 mol % and an ENB content of 2 to 16 mol % were produced. Et(Ind)₂HfCl₂ produced a considerably higher molar mass material than the Et(Ind)₂ZrCl₂ catalyst. The molar mass distributions were narrow. Copolymers and terpolymers with up to 3 mol % ENB content had some crystallinity. Copolymer T_gs were between −59°C and −55°C. The terpolymer glass transition temperature rose 1.5°C per wt % of ENB in the polymer. Polymer characteristics reported include composition, molar mass distribution, melt flow rate, density, and thermal behavior. The dynamic mechanical and rheological properties of the materials in comparison with commercial E/P/ENB terpolymers are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 35–44, 1997     

Copolymerization of ethylene and 1-octene by homogeneous and different supported metallocenic catalysts

In this work, the performance of the homogeneous catalyst system based on Et(Flu)₂ZrCl₂/MAO was evaluated on the copolymerization of ethylene and 1-octene. Characteristics of some of the produced polymers were also investigated. A study was performed to compare this system with that of Cp₂ZrCl₂/MAO. The influence of different support materials for the Cp₂ZrCl₂ was also evaluated, using silica, MgCl₂, and the zeolite sodic mordenite NaM. An increase in activity was observed in relation to the comonomer addition for the two homogeneous catalysts. The copolymers produced by the Et(Flu)₂ZrCl₂/MAO system showed higher molecular weight and narrower molecular weight distribution. We verified that the catalyst supported on SiO₂ was the most active one, although the copolymers produced with the catalyst supported on NaM showed higher molecular weight and lower molecular weight distribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 724–730, 2001     

Investigation of styrene/1‐hexene copolymerization by homogeneous and heterogeneous bisindenyl ethane zirconium dichloride catalyst system

Homogeneous copolymerization of styrene and 1‐hexene was carried out in toluene at room temperature using bisindenyl ethane zirconium dichloride/methylaluminoxane (MAO). The supported catalyst was prepared with immobilization of Et(Ind)₂ZrCl₂/MAO on silica (calcinated at 500°C) with premixed method. Heterogeneous copolymerization of styrene/1‐hexene with different mole ratios was carried out in the presence of supported catalyst system. The copolymers obtained from homogeneous and heterogeneous catalyst system were characterized by ¹H NMR and ¹³C NMR. Composition of the resulting copolymers was determined by ¹H NMR data. Analysis of ¹³C NMR spectra of obtained copolymers by homogeneous and heterogeneous catalyst systems present isotactic olefin‐enriched copolymers. Molecular weight and thermal behavior of resulting copolymers was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4008–4014, 2007     

Synthesis and functionalization of poly(ethylene‐co‐dicyclopentadiene)

Copolymerizations of ethylene with endo‐dicyclopentadiene (DCP) were performed by using Cp₂ZrCl₂ (Cp = Cyclopentadienyl), Et(Ind)₂ZrCl₂ (Ind = Indenyl), and Ph₂C(Cp)(Flu)ZrCl₂ (Flu = Fluorenyl) combined with MAO as cocatalyst. Among these three metallocenes, Et(Ind)₂ZrCl₂ showed the highest catalyst performance for the copolymerization. From ¹H‐NMR analysis, it was found that DCP was copolymerized through enchainment of norbornene rings. The copolymer was then epoxidated by reacting with m‐chloroperbenzoic acid. ¹³C‐NMR spectrum of the resulting copolymer indicated the quantitative conversion of olefinic to epoxy groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 103–108, 1999     

Preparation of linear low‐density polyethylene by in situ copolymerization of ethylene with Zr supported on montmorillonite/Fe/methylaluminoxane catalyst system

Linear low‐density polyethylene (LLDPE) was prepared by in situ copolymerization of ethylene with dual‐functional catalysts that were composed of rac‐Et(Ind)₂ZrCl₂ supported on montmorillonite (MMT) and {[(2‐ArN?C(Me))₂C₅H₃N]FeCl₂} [Ar = 2,4‐C₆H₄(Me)₂] oligomerization catalyst. A series of polyethylenes with different degrees of branching were obtained by adjusting the ratio of Fe and Zr (Fe/Zr). DSC, NMR, GPC, SEM, and density‐gradient method were used to characterize the polymers. With increasing Fe/Zr ratio, the densities and melting points of polymers decreased, whereas the branching degrees and molecular weights increased. When the Fe/Zr ratio was increased, the activities of the catalysts decreased at atmospheric pressure and increased at 0.7 MPa ethylene pressure. SEM micrographs revealed that the morphology of branched polyethylene, produced with the catalyst supported on MMT, is better than that produced by the catalyst in a homogeneous system. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1690–1696, 2004     

Preparation of ethylene/1‐octene copolymers from ethylene stock with tandem catalytic system

Tandem catalysis offers a novel synthetic route to the production of linear low‐density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1‐octene copolymers from ethylene stock as the sole monomer. The reported catalytic systems involving a highly selective, bis(diphenylphosphino)cyclohexylamine/Cr(acac)₃/methylaluminoxane (MAO) catalytic systems for the synthesis of 1‐hexene and 1‐octene, and a copolymerization metallocene catalyst, rac‐Et(Ind)₂ZrCl₂/MAO for the synthesis of ethylene/1‐octene copolymer. Analysis by means of DSC, GPC, and ¹³C‐NMR suggests that copolymers of 1‐hexene and ethylene and copolymers of 1‐octene and ethylene are produced with significant selectivity towards 1‐hexene and 1‐octene as comonomers incorporated into the polymer backbone respectively. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 101.1–134.1°C and density of 0.922–0.950 g cm^?3 can be efficiently produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Organic Nanoparticles with Polypropyleneoxide Chains as Support for Metallocene Catalysts: Ethylene Homopolymerization and Ethylene/α-olefin Copolymerization

Summary Novel organic nanoparticles functionalized with nucleophilic polypropyleneoxide (PPO) chains on their surfaces for supporting metallocene catalysts in heterogeneous olefin polymerization are presented. The nanoparticles (60–100 nm) were obtained by miniemulsion polymerization of styrene, divinylbenzene and PPO functionalized styrene. It is demonstrated that Me₂Si(2MeBenzlnd)₂ZrCl₂/MAO supported on these nanoparticles is suitable for the homopolymerization of ethylene, resulting in excellent product morphologies and high activities. lt is shown that by varying the MAO/Zr ratios and Zr concentrations the activities and productivities of the catalysts as well as the qualities of the polyethylene products can be tuned. These new supported catalysts are also suitable for the copolymerization of ethylene with several comonomers (1-hexene, 1-octene, 1-decene or norbornene). As the obtained product properties like crystallinity, melting temperature or bulk density match the results of silica supported systems, these organic nanoparticles can be considered as alternative carriers in comparison to the established inorganic ones.     

Modification of a Ziegler-Natta catalyst with a metallocene catalyst and its olefin polymerization behavior

A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl₄ catalyst supported on MgCl₂ (MgCl₂-Ti) with a rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)₂ZrCl₂, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non-isospecific site and modify a Ti-active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co-catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl₄/VOCl₃, Ti-V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp₂ZrCl₂ and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.     

Influence of process parameters on ethylene-norbornene copolymers made by using [2,2′-methylenebis(1,3-dimethylcyclopentadienyl)]-zirconium dichloride and MAO

Ethylene-norbornene copolymerization was investigated by using metallocene catalysts, [2,2′-methylenebis( 1,3-dimethylcyclopentadienyl)]zirconium dichloride(2,2′-CH₂ (1,3-Me₂Cp)₂ZrCl₂, Catalyst A) and racemicethylenebis( indenly)zirconium dichloride (rac-Et(Ind)₂ ZrCl₂, Catalyst B), in the presence of methylaluminoxane as a cocatalyst. The influences of different process parameters such as polymerization temperature and ethylene pressure were studied by using a 56 wt% norbornene solution in toluene. The results show that Catalyst A has a higher activity in copolymerization than Catalyst B. Catalyst A also has a superior norbornene insertion performance to Catalyst B, resulting in polymers with higher glass transition temperatures, by approximately 70 ‡C, at similar polymerization conditions, indicative of a great commercial potential of Catalyst A.     

13C-NMR study of ethylene/1-hexene and ethylene/1-octene copolymers obtained using homogeneous catalysts

Summary This study employed the ¹³C-NMR spectroscopy to investigate the influence of the increase of the comonomer concentration on the microstruture of ethylene/1-hexene and ethylene/1-octene copolymers obtained by the use of MeSiCp₂ZrCl₂, Cp₂ZrCl₂, Et[Ind]₂ZrCl₂ and [Ind]₂ZrCl₂ catalysts. For both comonomers butyl or hexyl branches were isolated between ethylene blocks. As the -olefin concentration in the copolymer increased, butyl or hexyl branches became closer, some of them, separated by only one or two ethylene units. Incorporation of -olefin in the copolymer was higher for the bridged catalysts, MeSiCp₂ZrCl₂, and Et[Ind]₂ZrCl₂ than for the unbridged ones. The -olefin size did not seem to effect its reactivity towards ethylene.     

(nBuCp)2ZrCl2‐catalyzed ethylene‐4M1P copolymerization: Copolymer backbone structure,melt behavior,and crystallization

The judicious design of methylaluminoxane (MAO) anions expands the scope for developing industrial metallocene catalysts. Therefore, the effects of MAO anion design on the backbone structure, melt behavior, and crystallization of ethylene?4‐methyl‐1‐pentene (E?4M1P) copolymer were investigated. Ethylene was homopolymerized, as well as copolymerized with 4M1P, using (1) MAO anion A (unsupported [MAOCl₂]^?) premixed with dehydroxylated silica, (ⁿBuCp)₂ZrCl₂, and Me₂SiCl₂; and (2) MAO anion B (Si?O?Me₂Si?[MAOCl₂]^?) supported with (ⁿBuCp)₂ZrCl₂ on Me₂SiCl₂‐functionalized silica. Unsupported Me₂SiCl₂, opposite to the supported analogue, acted as a co‐chain transfer agent with 4M1P. The modeling of polyethylene melting and crystallization kinetics, including critical crystallite stability, produced insightful results. This study especially illustrates how branched polyethylene can be prepared from ethylene alone using particularly one metallocene‐MAO ion pair, and how a compound, that functionalizes silica as well as terminates the chain, can synthesize ethylene?α‐olefin copolymers with novel structures. Hence, it unfolds prospective future research niches in polyethyne systhesis. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1688–1706, 2016     

PE/OMMT nanocomposites catalyzed by the OMMT‐intercalated Et[Ind]2ZrCl2 in slurry polymerization: Effects of organic solvent on ethylene polymerization behaviors and the nanocomposite structures

In situ intercalative polymerization for ethylene monomers was carried out to produce PE‐based hybrids through a slurry polymerization method. In this approach, organic solvent for olefin polymerization was found to be one of the most significant factors for the dispersion of the OMMT‐intercalated Et[Ind]₂ZrCl₂ catalysts, which determines that whether olefin monomers polymerize is in a well‐defined confinement environment or not. Understanding the olefin polymerization occurring in between the nanoscale silicate layers of OMMT as well as the corresponding structure of OMMT in an organic polymerization solvent is a critical step toward tailoring and characterizing nanocomposites formed by OMMT in a polyolefin matrix. As we know, the Et[Ind]₂ZrCl₂ catalyst and MAO are both better dissolved in toluene than that in hexane because of the larger polarity of toluene. Thus, in hexane the active sites of the OMMT/Et[Ind]₂ZrCl₂ catalyst exist in the silicate layers of OMMT and the PE chains grow in the middle of them, while in toluene the active specimens are exposed in the gel formed by the OMMT‐intercalated catalyst with MAO, which cause that the PE chains propagated in the mixture liquids. Consequently, when hexane is selected as the polymerization solvent, the formed PE‐based nanocomposites have a good dispersion of OMMT and the nanofiller content (TGA measurement residue at 600°C) is thus higher (>7.0 wt %). However, in toluene, most of the silicate layers of OMMT are agglomerated in the PE matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Self‐Immobilizing Precatalysts: Norbornene‐Bridged Zirconium ansa‐Metallocenes

We report here the synthesis of new tethered biscyclopentadienyl and bisindenyl zirconocenes, bearing one unsaturation on the interannular bridge, and their use as self‐immobilizing catalysts. They proved to be active catalysts towards ethylene polymerization in solution, with activities comparable to those displayed by commercial rac‐Et(Ind)₂ZrCl₂. When tested as self‐polymerization catalysts under suitable experimental conditions, they gave colored precipitates that, once reactivated with MAO, were significantly active in ethylene polymerization, although lower than those of the corresponding catalytic systems in solution. The molecular weights of the produced polymers were similar to those obtained with the same catalysts in solution, but their distribution resulted to be broader, with values typical of heterogeneous catalytic systems. From ¹³C NMR studies we had the first spectroscopic evidence of the actual incorporation of a metallocene of this type into a polymeric chain.     

Catalysis of ethylene to linear low‐density polyethylene with iron‐based diimine complex immobilized on calcosilicate and silica‐supported rac‐Et(Ind)2ZrCl2

Iron‐based diimine complex was immobilized on calcosilicate (CAS‐1) to form heterogeneous precatalyst, which oligomerized ethylene to α‐olefins even without the use of aluminum alkyl compounds as activators. The α‐olefins, upon the catalysis of another catalyst, i.e., silica‐supported rac‐Et(Ind)₂ZrCl₂, copolymerized with ethylene to produce linear low‐density polyethylene (LLDPE). The copolymerization reactions could be performed with the addition of triethylaluminum alone because of the introduction of methylaluminoxane to CAS‐1 and silica during the supporting process. In addition to the formation of more α‐olefins with lower molar mass, the layered structure of CAS‐1 acted well in the controlled release of α‐olefins in the copolymerization process. The simultaneous employment of the aforementioned two catalysts hence resulted in high catalytic activities, smooth kinetic process, well‐regulated branching degree, higher molecular weights (M_n), improved thermal stability, and better morphology of the LLDPE obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polymer-supported metallocene catalysts for gas-phase ethylene polymerization

The use of hydroxylated chloromethylated-styrene/divinylbenzene copolymer as a support for three different catalysts, Cp₂ZrCl₂, [Ind]₂ZrCl₂ and (CH₃)₂Si[Ind]₂ZrCl₂ has been examined for the polymerization of ethylene in gas phase. The gas phase polymerization experiments were performed in a horizontal reactor by using Box-Behnken experimental design [Box and Wilson, 1951] to study the effects of temperature, ethylene partial pressure, and MAO cocatalyst level on polymerization. The measured average catalyst activities were empirically correlated with these three factors. Temperature appears to be the most important factor, which shows a first and second order effect on activity and also interacts with pressure and MAO. The kinetic study shows that these supported catalysts might contain two types of active sites, and the deactivation of sites follows a first order kinetic. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Ethylene/propylene copolymerization over three conventional C2‐symmetric metallocene catalysts: Correlation between catalyst configuration and copolymer microstructure

This work reports on a correlation between catalyst configuration and copolymer microstructure for ethylene/propylene (E/P) copolymerization using three conventional C₂‐symmetric metallocene catalysts, namely, rac‐Et(Ind)₂ZrCl₂ (EBI), rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ZrCl₂ (SiPh), and rac‐CH₂(3‐tBu‐Ind)₂ZrCl₂ (MBu), with MAO as a common cocatalyst. Copolymerization reactions were conducted in toluene at three different temperatures with varied E/P ratios. Some typically obtained copolymers were characterized in detail using ¹³C‐NMR spectroscopy, by which triad distribution data were elaborated in a statistical method to determine the reactivity ratios (r_E and r_P) of the comonomers, which were also obtained by Fineman‐Rose estimation. The production of alternating‐like copolymers from EBI is attributed to the rapid interconversion between two conformation states of the active site, one of which favors the incorporation of propylene but the other one does not. Both SiPh and MBu are structurally more rigid and of larger dihedral angles than EBI; however, SiPh which owns open active site conformation tend to produce random copolymers at all studied temperatures, and for MBu, sterically hindered catalyst, block‐like copolymers were obtained. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymerization and characterization of ethylene/propylene and ethylene/1-octene copolymers produced with bridged Zr- and Hf-based metallocenes

Ethylene/propylene (E/P) and ethylene/1-octene (E/O) copolymers were polymerized with two bridged metallocene catalyst systems, Et(Ind)₂ZrCl₂/MAO and Et(Ind)₂HfCl₂/MAO, respectively. The copolymers produced and some commercial reference copolymers were characterized by DSC, SEC, DMA and ¹³C NMR. The Hf-catalysed E/P polymerizations showed much lower activities than the corresponding Zr-catalysed polymerizations but gave polymers with high molar mass. The Hf-based copolymers also showed two melting peaks which may be indicative of several active sites of the catalyst. A comparison of E/P copolymers, containing about 20 mol-% propylene and produced with Zr, Hf and homogeneous V-catalysts, respectively, indicated that the Hf and V-catalysts gave material more similar to each other. The E/O copolymers produced with Zr-catalysts gave very low molar masses and the reactivity ratios, calculated from the NMR data, indicated that the Hf-catalyst has a slightly higher reactivity for 1-octene and the Zr-catalyst some better reactivity for ethylene. Segregation fractionation studies by DSC indicated that a lower 1-octene feed gives more heterogeneous copolymers and the DMA measurements reveal the existence of a linear correlation between the 1-octene content and the intensity of the tan δ_max peak.