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     

Homopolymerization of Higher 1‐Olefins with Metallocene/MAO Catalysts

Linear 1‐olefins from 1‐pentene to 1‐octadecene are polymerized by non‐stereospecific Cp₂HfCl₂ ( 1 ), syndiospecific Me₂C(Cp)(9‐fluorenyl)ZrCl₂ ( 2 ) and isospecific Et(Ind)₂ZrCl₂ ( 3 ) catalysts in the presence of MAO. The molecular weight of the resulting polymers (GPC) is highly dependent on the nature of the catalyst, but more or less independent of the monomer chain length. The stereoregularity of the poly(1‐olefins) obtained with 2 and 3 as determined by NMR spectroscopy decreases linearly with increasing monomer chain length. A decrease in isotacticity occurs for the poly(1‐olefins) synthesized with 3 when increasing the catalyst concentration. Vinylidene, 1,2‐disubstituted and 1,1,2‐trisubstituted double bonds attributed to different chain termination mechanisms are generated during the polymerization processes.     

Copolymerization of ethylene and 1‐decene by metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

Copolymerizations of ethylene with 1‐decene have been carried out by using two syndiospecific metallocenes synthesized by modifying the bridge: highly syndiospecific isopropylidene(1‐η⁵‐cyclopentadienyl)(1‐η⁵‐fluorenyl)‐dimethylzirconium (Me₂C(Cp)(Flu)ZrMe₂, 1 ) and less syndiospecific (1‐fluorenyl‐2‐cyclopentadienylethane)‐dimethylzirconium (Et(Cp)(Flu)ZrMe₂, 2 ), in the presence of [Ph₃C][B(C₆F₅)₄] as a cocatalyst. The ethano bridged 2 compound of smaller dihedral angle showed much higher activity than 1 compound. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1‐decene comonomer is present in the feed. The compound 1 showed better comonomer reactivity than 2 . The properties (T_m, density, and crystallinity) of copolymers seem not to be affected by the type of bridge of the metallocenes, and mainly depend on 1‐decene content in the copolymer.     

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.     

Synthesis and characterization of elastoplastic poly(styrene‐co‐ethylene) using novel mono(η5‐cyclopentadienyl) titanium and modified methylaluminoxane catalysts

Elastoplastic poly(styrene‐co‐ethylene) with high molecular weight was synthesized using novel mono(η⁵‐pentamethylcyclopentadienyl)tribenzyloxy titanium [Cp*Ti(OBz)₃] complex activated with four types of modified methylaluminoxanes (mMAO) containing different amounts of residual trimethylaluminum (TMA). The ideal mMAO, used as a cocatalyst for the copolymerization of styrene with ethylene, contains TMA approaching to 17.8 wt %. The oxidation states of the titanium‐active species in different Cp*Ti(OBz)₃/mMAO catalytic systems were determined by the redox titration method. The results show that both active species may exist in the current system, where one [Ti(IV)] gives a copolymer of styrene and ethylene, and the second one [Ti(III)] only produces syndiotactic polystyrene (sPS). Catalytic activity, compositions of copolymerization products, styrene incorporation, and copolymer microstructure depend on copolymerization conditions, including polymerization temperature, Al/Ti, molar ratio, and comonomers feed ratio. The copolymerization products were fractionated by successive solvent extractions with boiling butanone and tetrahydrofuran (THF). The copolymer, chiefly existing in THF‐soluble fractions, was confirmed by ¹³C‐NMR, GPC, DSC, and WAXD to be an elastoplastic copolymer with a single glass transition temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1851–1857, 1999     

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     

Study on chain end structures of polypropylenes prepared with different symmetrical metallocene catalysts

Propylene homopolymerizations were conducted by using three kinds of metallocenes: Cp₂ZrCl₂, En(Ind)₂ZrCl₂ and iPr(Cp)(Flu)ZrCl₂, all of which were activated with methylaluminoxane. Detailed NMR analyses of the chain ends in the resulting polymers were carried out to discuss the chain end structures of the polypropylenes and the mechanism of polymerization. The characteristic of each metallocene for the mechanism of polymerization was also described.     

Copolymerization and characterization of ethene–1‐hexene copolymers prepared by using the (Me5Cp)2ZrCl2–MAO catalyst system

It is demonstrated that the catalyst system bis(pentamethylcyclopentadienyl)‐zirconium dichloride (Me₅Cp)₂ZrCl₂–methylaluminoxane (MAO) is able to produce random copolymers of ethene and 1‐hexene. The 1‐hexene incorporation in the copolymers is extremely small. Even in the case of a molar ratio of [ethene] to [1‐hexene] of 1/20 in the monomer feed, only 1.4 mol % 1‐hexene are incorporated according to ¹³C nuclear magnetic resonance (NMR) spectra. Nevertheless, the physical properties of the random copolymers change significantly in this small range of 1‐hexene incorporation, from a high‐density polyethene to a linear low‐density polyethene. Thus, the melting temperature, the degree of crystallinity, the density and lamella thickness, and the long period of the alternating crystalline and amorphous regions decrease with increasing 1‐hexene content in the random copolymers. Blends of high‐density polyethene prepared with the system (Me₅Cp)₂ZrCl₂–MAO and an elastomeric random copolymer of ethene and 1‐hexene are phase‐separated and show good compatibility, as demonstrated by transmission electron microscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 439–447, 1999     

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     

Study of the influence of the reaction parameters on the composition of the metallocene‐catalyzed ethylene copolymers using temperature rising elution fractionation and 13C nuclear magnetic resonance

Polyethylene copolymers prepared using the metallocene catalyst rac‐Et[Ind]₂ZrCl₂ were fractionated by preparative Temperature Rising Elution Fractionation (p‐TREF) and characterized by ¹³C nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC) to study the heterogeneity caused by experimental conditions. Two ethylene–1‐hexene copolymers with different 1‐hexene content and an ethylene–1‐octene copolymer all obtained using low (1.6 bar) ethylene pressure were compared with two ethylene–1‐hexene copolymers with different 1‐hexene content obtained at high ethylene pressure (7.0 bar). Samples obtained at low ethylene pressure and with low 1‐hexene concentration in the reactor presented narrow distributions in composition. Samples prepared with high comonomer concentration in the reactor or with high ethylene pressure showed an heterogeneous composition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 155–163, 2002; DOI 10.1002/app.10284     

Study on unsaturated structures of polyhexene,poly(4-methylpentene) and poly(3-methylpentene) prepared with metallocene catalysts

Hex-1-ene (hexene), 4-methylpent-1-ene (4-MP-1) and 3-methylpent-1-ene (3-MP-1), homopolymerizations were conducted by using metallocenes, En(Ind)₂ZrCl₂ and iPr(Cp)(Flu)ZrCl₂, with methylaluminoxane. ¹H NMR analyses of the resulting polymers were carried out to identify the unsaturated structures of these polymers. In polyhexene and poly(4-MP-1), the detected main unsaturated structure was di-substituted vinylene. On the other hand, in poly(3-MP-1), vinylidene and tri-substituted vinylene structures were mainly observed for the first time.     

Highly active ethylene/hydroxyl comonomers copolymerization using metallocene catalysts

Ethylene was copolymerized with 10‐undecen‐1‐ol and 5‐hexen‐1‐ol using stereorigid [rac‐ethylene(Ind)₂ZrCl₂], [rac‐ethylene(H₄Ind)₂ZrCl₂], and the new catalyst systems [rac‐norbornane(Ind)₂TiCl₂] and [mesonorbornane(Ind)₂TiCl₂], activated with methylaluminoxane. The characterization of the copolymers by ¹³C NMR spectroscopy revealed that the polymerization products were copolymers and that the conversion of the polar comonomer was strongly favored in the case of the zirconocene precursors. Very high catalytic activity values, nearly independent on the amount of comonomer in the feed, and comonomer incorporations up to 25.4%‐weight have been found for 10‐undencen‐1‐ol comonomer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The detailed analysis of the vinylidene structure of metallocene-catalyzed polypropylene

The vinylidene structures in polypropylenes produced by ethylenebis(indenyl)zirconiumdichloride (En(Ind)₂ZrCl₂), 1, and isopropyl(cyclopentadienyl)(fluorenyl)zirconiumdichloride (iPr(Cp)(Flu)ZrCl₂), 2, were analyzed by ¹H NMR. The vinylidene group adjacent to the chain end was clearly distinguished from other internal vinylidene structures for the first time using 1,2-dichlorobenzene as solvent. The polypropylene produced by 2 had much internal vinylidene groups compared with one by 1.     

Copolymerization of propylene and norbornene with different metallocene catalysts

Propylene and norbornene were copolymerized by metallocene/MAO catalysts. The organometallic compounds rac-[Me₂C(Ind)₂]ZrCl₂ (1) and [Me₂C(Cp)(Flu)]ZrCl₂ (2), [Ph₂C(Cp)(2,7-di^tBuFlu)]ZrCl₂ (3) and [Me₂Si(3-^tBuCp)(N^tBu)]TiCl₂ (4) were used to catalyze polymerization series, in which the influence of the molar fraction of norbornene in the feed and of the polymerization temperature were investigated in detail. The obtained polymers, which exhibit a wide range of properties with glass transition temperatures above 200 °C, were characterized by ¹³C NMR spectroscopy, differential scanning calorimetry and gel permeation chromatography techniques.In this article, the emphasis is placed on the copolymerization behaviour of the catalysts and the properties of the obtained polymers, while other articles concentrate on NMR investigations of propylene/norbornene copolymers.     

Preparation and properties of ethylene/POSS copolymer with rac‐Et(Ind)2ZrCl2 catalyst

The various monovinyl‐functional polyhedral oligomeric silsesquioxane (POSS) monomers had been copolymerized with ethylene (E) using rac‐Et(Ind)₂ZrCl₂ and a modified methylaluminoxane (MMAO) cocatalyst. The unreacted POSS monomer could be removed completely by washing the copolymerization product with n‐hexane. And the copolymers were characterized with ¹H NMR, TEM, DSC, TGA, and GPC to know the composition, thermal properties, molecular weight and its distribution, respectively. According to ¹H NMR data, the monomer reactivity ratios of various POSS monomers were calculated by the Fineman‐Ross and Kelen‐Tudos methods. Thermogravimetric analysis of E/POSS copolymers exhibited an improved thermal stability with a higher degradation temperature and char yields, demonstrating that the inclusion of inorganic POSS nanoparticles made the organic polymer matrix more thermally robust. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

Stereochemical and compositional assignments of trans‐4‐methacryloyloxyazobenzene–methyl methacrylate copolymers by one‐ and two‐dimensional NMR spectroscopy

The microstructure of trans‐4‐methacryloyloxyazobenzene–methyl methacrylate copolymers prepared by solution polymerization process using AIBN as initiator is analyzed by one‐and two‐dimensional spectroscopy. Sequence distribution was calculated from the ¹³C(¹H)‐NMR spectra of the copolymers. Comonomer reactivity ratios were determined using the Kelen–Tudos and the nonlinear error‐in‐variables methods are r_A = 1.14 ± 0.08 and r_M = 0.51 ± 0.03; r_A = 1.13 ± 0.1 and r_M = 0.50 ± 0.04, respectively. The sequence distribution of A‐ and M‐centered triads determined from ¹³C(¹H)‐NMR spectra of copolymer is in good agreement with triad concentration calculated from a statistical model. The 2‐D heteronuclear single‐quantum correlation and correlated spectroscopy (TOCSY) was used to analyze the complex ¹H‐NMR spectrum. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3016–3025, 1999     

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     

Residual metal content in Ethylene‐Propylene‐Diene Monomers synthesized using vanadium‐ and zirconocene‐based catalysts

Ethylene‐propylene‐diene monomer (EPDM) terpolymers were prepared using either vanadium (VOCl₃/Al₂Et₃Cl₃) or zirconocene (Et(Ind)₂ZrCl₂/MAO) catalyst systems. Residual metal contents in EPDM films were determined by Rutherford backscattering spectrometry. Metallocene catalyst systems exhibited a higher activity, producing EPDM with lower molecular weight and narrower molecular weight distribution. The highest activity guaranteed lower residual metal content (Zr/C = 10⁻⁵) than in the case of EPDM produced by VOCl₃/Al₂Et₃Cl₃ (V/C = 10⁻⁴). Subsequent steps of dissolution of the polymer and its reprecipitation were seen to reduce the metal contents in both metal systems. Concerning the cocatalyst retention, despite initial use of a very high amount of methylaluminoxane/metallocene (Al/Zr = 3000) in the reactor, only about 4% of this initial concentration remained in the polymer. On the other hand, in the case of vanadium‐based catalyst, almost all Al present in the initial conditions (≃8.3) remained in the polymer. In both cases, the residual Al/M ratio was close to the value generally proposed for the generation/stabilization of the active species. In the case of vanadium systems, a test in the synthesis of ethylene propylene rubbers indicated that the absence of diene in the polymer structure leads to a reduction in the residual vanadium content, indicating that the diene double bond might be responsible for partially vanadium coordination. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1997–2003, 1999