Zeolite‐supported metallocene catalyst for ethylene/1‐hexene copolymerization

Commercial zeolite acid mordenite was thermally treated for use as a support for bis(n‐butyl‐cyclopentadienyl)zirconium dichloride [(n‐BuCp)₂ZrCl₂] for the further evaluation of ethylene/1‐hexene copolymerization. The polymerization time, temperature, and solvent, as well as the addition of tri(isobutyl)aluminum in the hexane medium, were evaluated. The catalytic activity and 1‐hexene content in the copolymer synthesized with the supported system were very near those obtained with the homogeneous precursor. A comonomer effect was observed for both systems. The polymerization rate profiles were obtained for ethylene polymerization, and the activation energy and monomer reactivity were calculated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3038–3048, 2004     

Ethylene/1‐hexene copolymers synthesized with a single‐site catalyst: Crystallization analysis fractionation,modeling, and reactivity ratio estimation

A series of poly(ethylene‐co‐1‐hexene) samples made with rac‐ethylene bis(indenyl)zirconium dichloride/methylaluminoxane were analyzed by crystallization analysis fractionation (CRYSTAF). The nine samples had comonomer contents of 0–4.2 mol % 1‐hexene with a narrow range of molecular weights (34,000–39,000 g/mol). Because all the copolymer samples had narrow, unimodal chemical composition distributions, they were ideal as calibration standards for CRYSTAF. A linear calibration curve was constructed relating the peak crystallization temperature from CRYSTAF operated at a cooling rate of 0.1 °C/min and the comonomer content as determined by ¹³C NMR. Reactivity ratios for ethylene and 1‐hexene were estimated by the fitting of reactant liquid‐phase compositional data to the Mayo–Lewis equation. It was found that a value of the 1‐hexene reactivity ratio could not be unequivocally determined from the set of samples analyzed because the range of comonomer incorporation was too narrow. Stockmayer's bivariate distribution was used to model the fractionation process in CRYSTAF, and although a good fit to experimental CRYSTAF profiles was attained, the model did not fully describe the underlying crystallization phenomena. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2595–2611, 2002     

Ethylene/1‐hexene copolymerization with tetramethyldisiloxane‐bridged bis(indenyl) metallocenes

Ethylene/1‐hexene copolymerizations with disiloxane‐bridged metallocenes, rac‐ and meso‐1,1,3,3‐tetramethyldisiloxanediyl‐bis(1‐indenyl)zirconium dichloride (rac‐ 1 , meso‐ 1 ) activated by modified methylaluminoxane were performed to investigate the influence of conformational dynamics on comonomer selectivity. Although ¹H NOESY (nuclear Overhauser and exchange spectroscopy) analysis indicated that the most stable conformation for the meso isomer in solution was that in which both indenes project over the metal coordination site, this isomer showed higher 1‐hexene selectivity in copolymerization (r_e = 140 ± 30, r_h = 0.024 ± 0.004) than the rac isomer with only one indene over the coordination site (r_e = 240 ± 20, r_h = 0.005 ± 0.001). The meso isomer showed high 1‐hexene selectivity, a high product of reactivity ratios (r_er_h = 3.3 ± 0.5) and produced copolymers that could be separated into fractions with different ethylene content suggesting that the active species exhibited multisite behavior and populated conformations with different comonomer selectivities during the copolymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3323–3331, 2004     

Tacticity of poly‐α‐olefins from poly‐1‐hexene to poly‐1‐octadecene

A systematic study of the influence of the α‐olefin size, the catalyst stereospecificity and the reaction temperature was done on the catalytic activity and tacticity of poly‐α‐olefins from 1‐hexene to 1‐octadecene. The metallocenes used were rac‐Et[Ind₂]ZrCl₂ ( 1 ) and Me₂C[Cp(9‐Flu)]ZrCl₂ ( 2 ) to obtain isotactic and syndiotactic polyolefins. Some catalysts giving atactic polymers were also used in order to study all the possible ¹³C NMR pentades. Catalytic activities increased and isotacticity and syndiotacticity decreased with temperature, but no real trend was found with the α‐olefin size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4744–4753, 2005     

Copolymerization of ethylene with 1‐hexene promoted by novel multi‐chelated non‐metallocene complexes with imine bridged imidazole ligand

A series of novel bridged multi‐chelated non‐metallocene catalysts is synthesized by the treatment of N,N‐imidazole, N,N‐dimethylimidazole, and N,N‐benzimidazole with n‐BuLi, 2,6‐dimethylaniline, and MCl₄ (M = Ti, Zr) in THF. These catalysts are used for copolymerization of ethylene with 1‐hexene after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M molar ratio, and pressure of monomer on ethylene copolymerization behaviors are investigated in detail. These results reveal that these catalysts are favorable for copolymerization of ethylene with 1‐hexene featured high catalytic activity and high comonomer incorporation. The copolymer is characterized by ¹³C NMR, WAXD, GPC, and DSC. The results confirm that the obtained copolymer features broad molecular weight distribution (MWD) about 33–35 and high 1‐hexene incorporation up to 9.2 mol %, melting temperature of the copolymer depends on the content of 1‐hexene incorporation within the copolymer chain and 1‐hexene unit in the copolymer chain isolates by ethylene units. The homopolymer of ethylene has broader MWD with 42–46. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 417–424, 2010     

Effect of excess halide on the palladium‐catalyzed insertion‐triggered radical copolymerization of methyl acrylate and 1‐hexene

[Pd₂(μ‐Cl)₂(C₆F₅)₂(tht)₂] ( 1 ) is a very efficient initiator of the radical polymerization of methyl acrylate, but it is not active in the polymerization of methyl methacrylate or in the copolymerization with 1‐hexene. The addition of an excess of NBu₄Cl to solutions of [Pd₂(μ‐Cl)₂(C₆F₅)₂(tht)₂] ( 1 ) provides an initiator system that copolymerizes methyl acrylate and 1‐hexene by an insertion‐triggered radical mechanism. Random copolymers are obtained with 11% incorporation of 1‐hexene in moderate yields (about 35%). Studies of the decomposition products obtained after the first insertion of methyl acrylate in the Pd? C₆F₅ bond of 1 show that the addition of excess halide in the presence of monomer favors the homolytic cleavage of the Pd? C bond, and the generation of the radicals that are active species in the polymerization, versus alternative evolution pathways. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5682–5691, 2006     

Permeation measurements in ethylene‐1‐hexene,ethylene‐1‐octene,and ethylene‐1‐dodecene copolymers synthesized with metallocene catalysts

The permeation behavior of different ethylene‐1‐hexene, ethylene‐1‐octene, and ethylene‐1‐dodecene copolymers synthesized with metallocene catalysts has been analyzed. These copolymers cover a wide range of comonomer contents, so their crystallinities display rather considerable variations. The results for the permeability to oxygen of the different ethylene copolymers show that the main factor influencing the permeability is the noncrystalline fraction, although some influence of the kind of comonomer may also be present, which may be explained by the fact that when the alkyl branch of the α‐olefin is longer, there is an increase in the free volume in the amorphous and interfacial regions, causing slightly higher values of the permeability coefficient. From the results with different gases, it follows that, in general, an increase in the size of the penetrant (as expressed by its kinetic diameter or critical molar volume) leads to an increase in the solubility and a decrease in the diffusion coefficient. A wide range of permeability values is covered by these ethylene copolymers, depending basically on the crystallinity of the sample, but the permselectivity of CO₂ with respect to oxygen (and probably between other pairs of gases) does not differ very much among the different copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2174–2184, 2003     

Synthesis and characterization of ethylene‐propylene‐1‐pentene terpolymers

Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)₂ZrCl₂/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me₂C(Cp)(Flu)ZrCl₂/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp₂ZrCl₂/MAO/SiO₂/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of ¹³C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008     

Copolymerization of norbornene with ω‐alkenylaluminum as a precursor comonomer for introduction of carbonyl moieties

Norbornene copolymers functionalized with methyl ester group or carboxy group are facilely synthesized by the copolymerization of norbornene and 7‐octenyldiisobutylaluminum (ODIBA) with ansa‐dimethylsilylene(fluorenyl)(t‐butylamido)dimethyltitanium ( 1 ) activated by Ph₃CB(C₆F₅)₄, and the sequential CO₂/methanolysis reactions or CO₂/hydrolysis reactions, respectively. The methanolysis and the hydrolysis are simply switched by engaging acidic methanol or acidic aqueous acetone as the quenching/washing solution, respectively. Meanwhile, the increase of ODIBA in the copolymerization abruptly decreases the yield and number–average molecular weight (M_n) of the product. However, the addition of triisobutylaluminum (8 mM) and the use of excess Ph₃CB(C₆F₅)₄ (twofold of 0.4 mM of 1 ) significantly increase the yield, accompanying the increase in the M_n and the narrowing of the molecular weight distribution (M_w/M_n), especially in the case of the use of excess Ph₃CB(C₆F₅)₄. The yield (g polymer/g monomers), M_n, and M_w/M_n reach up to 0.82, 341,000, and 1.46, respectively, at a copolymerization condition. The carboxy groups in the norbornene copolymers are controlled in the range of 0–1.8 mol % in high polymer yields with high M_n and narrow M_w/M_n accompanied by the decrease in the contact angle with water from 104° to 89°. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5085–5090     

Copolymerization of ethylene with 1‐hexene over metallocene catalyst supported on complex of magnesium chloride with tetrahydrofuran

The study of ethylene/1‐hexene copolymerization with the zirconocene catalyst, bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂)/methylaluminoxane (MAO), anchored on a MgCl₂(THF)₂ support was carried out. The influence of 1‐hexene concentration in the feed on catalyst productivity and comonomer reactivity as well as other properties was investigated. Additionally, the effect of support modification by the organoaluminum compounds [(MAO, trimethlaluminum (AlMe₃), or diethylaluminum chloride (Et₂AlCl)] on the behavior of the MgCl₂(THF)₂/Cp₂ZrCl₂/MAO catalyst in the copolymerization process and on the properties of the copolymers was explored. Immobilization of the Cp₂ZrCl₂ compound on the complex magnesium support MgCl₂(THF)₂ resulted in an effective system for the copolymerization of ethylene with 1‐hexene. The modification of the support as well as the kind of organoaluminum compound used as a modifier influenced the activity of the examined catalyst system. Additionally, the profitable influence of immobilization of the homogeneous catalyst as well as modification of the support applied on the molecular weight and molecular weight distribution of the copolymers was established. Finally, with the successive self‐nucleation/annealing procedure, the copolymers obtained over both homogeneous and heterogeneous metallocene catalysts were heterogeneous with respect to their chemical composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2512–2519, 2004     

Chain microstructure of homogeneous ethylene‐1‐alkene copolymers and characteristics of single site catalysts using a direct 13C NMR peak method I. Theory and models

To describe the detailed microstructure of homogeneous ethylene‐1‐alkene copolymer chains and to study the characteristics of single site catalysts, Markov statistics are used to fit peak intensities of all relevant ¹³C NMR signals of series of copolymers. In the case of the occurrence of inverted comonomer units, a first‐order Markov terpolymer is applied, otherwise a second‐order Markov copolymer model. Chain propagation probabilities are obtained via modeling of the entire NMR spectrum. This procedure results in an accurate reproduction of the chain microstructure, including ethylene, 1‐alkene, and methylene sequence length distributions. If the experimental (co)monomer feeds are known, the reactivity ratios and the theoretical (co)monomer feeds are also found providing information about the copolymerization kinetics and the characteristics of the catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 722–737, 2006     

Structure–property transition‐state model for the copolymerization of ethene and 1‐hexene with experimental and theoretical applications to novel disilylene‐bridged zirconocenes

Ethene homopolymerization and copolymerization with 1‐hexene were performed with three new tetramethyldisilylene‐bridged zirconocene catalysts with 2‐indenyl ligand ( A ), 2‐tetrahydroindenyl ligand ( B ), and tetramethyl‐cyclopentadienyl ligand ( C ) and with methylaluminoxane as a cocatalyst. Catalysts A and B showed substantial comonomer incorporation, resulting in a copolymer melting temperature more than 20° lower than that of the corresponding homopolymer. In contrast, catalyst C produced a copolymer with a low 1‐hexene content and a high melting temperature. The reduction in the molecular weight with 1‐hexene addition also correlated well with the comonomer incorporation. For all three catalysts, the homopolymer and copolymer unsaturations indicated frequent chain termination after 1‐hexene insertion and a high degree of chain‐end isomerization during the homopolymerization of ethene. The chain transfer to Al in the cocatalyst also appeared to be important. The comonomer response could be correlated with the structural properties of the catalyst, as derived from quantum chemical calculations. A linear model, calibrated against recent experiments with unbridged (Me_nC₅H_5?n)₂ZrCl₂ catalysts, suggested that the low comonomer incorporation obtained with catalyst C was caused partly by a narrow opening angle between the aromatic ligands and partly by steric hindrance in the transition state of comonomer insertion. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1622–1631, 2003     

Chain microstructure of homogeneous ethylene‐1‐alkene copolymers and characteristics of single site catalysts using a direct 13C NMR peak method. Part III. Application to ethylene–propylene copolymers showing no inversion

All relevant ¹³C NMR signals of two series of seven homogeneous ethylene–propylene copolymers were used to fit the second‐order Markov reactivity ratios of the catalysts and the theoretical feeds. The copolymers cover a very broad range of comonomer incorporations, from about 10 to 93%, and show only primary (1,2) insertions. For both series, solutions are found with reliabilities >>99.5%. The reactivity ratios, r₁₁₂ = 2.54, r₁₂₁ = 0.12, r₂₁₂ = 2.05, and r₂₂₁ = 0.29 for the used Zirconocone and r₁₁₂ = 1.69, r₁₂₁ = 0.32, r₂₁₂ = 1.56, and r₂₂₁ = 0.51 for the hafnocene, provide direct information about the metallocenes, the kinetics, and the chain microstructure. With these results, the direct peak method demonstrates that the use of all relevant ¹³C NMR peaks enables accurate second‐order Markov modeling, revealing subtle differences between copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 747–755, 2006     

Microstructure of metallocene isotactic propylene‐co‐1‐pentene‐co‐1‐hexene terpolymers

This study aims at characterizing in depth the microstructure of propylene‐co‐1‐pentene‐co‐1‐hexene terpolymers, which have been recently reported to develop the isotactic polypropylene δ trigonal polymorph when the total comonomer content is high enough. Such a specific crystalline form had been only reported so far in the analogous copolymers containing either 1‐pentene or 1‐hexene. A comparative ¹³C NMR study in solution of the aforementioned terpolymers and copolymers allows asserting the random insertion of both comonomers during chain growth under the polymerization conditions used. The reaction parameters, mainly catalyst and temperature, have been chosen for the purpose of assuring relatively high molar mass polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2537–2547     

Supported Metallocene Catalysts Prepared by Impregnation of Silica with Metallocene/Aluminoxane/1‐Hexene Solutions

A novel method for the preparation of supported metallocene/alkylaluminoxane catalysts has been developed. An incipient wetness impregnation of silica at ca. –40°C is performed in one step employing a solution of catalyst and cocatalyst in 1‐hexene. A prepolymerization of this system at ambient temperature yields a catalyst robust towards exposure to air, as demonstrated by a reasonable activity during ethene polymerization. A special feature of the catalyst is a uniform impregnation across the silica particles.     

Direct synthesis of linear low‐density polyethylene of ethylene/1‐hexene from ethylene with a tandem catalytic system in a single reactor

Tandem catalysis offers a promising 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‐hexene copolymers from ethylene stock as the sole monomer. The reported catalytic systems employ the tandem action between an ethylene trimerization catalyst, (η⁵‐C₅H₄CMe₂C₆H₅)TiCl₃ ( 1 )/modified methylaluminoxane (MMAO), and a copolymerization metallocene catalyst, [(η⁵‐C₅Me₄)SiMe₂(^tBuN)]TiCl₂ ( 2 )/MMAO or rac‐Me₂Si(2‐MeBenz[e]Ind)₂ZrCl₂ ( 3 )/MMAO. During the reaction, 1 /MMAO in situ generates 1‐hexene with high activity and high selectivity, and simultaneously 2 /MMAO or 3 /MMAO copolymerizes ethylene with the produced 1‐hexene to generate butyl‐branched polyethylene. 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 60–128 °C, crystallinities of 5.4–53%, and hexene percentages of 0.3–14.2 can be efficiently produced. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4327–4336, 2004     

Copolymerization of ethylene with 1,1‐disubstituted olefins catalyzed by ansa‐(fluorenyl)(cyclododecylamido)dimethyltitanium complexes

A series of titanium complexes with ansa‐(fluorenyl)(cyclododecylamido) ligands, Me₂Si(η³‐R)(N‐c‐C₁₂H₂₃)TiMe₂ [R = fluorenyl ( 5 ), 2,7‐^tBu₂fluorenyl ( 6 ), 3,6‐^tBu₂fluorenyl ( 7 )], was synthesized. The crystal structure of complex 6 revealed η³‐coordination of the fluorenyl moiety to the metal. Upon activation with trialkylaluminum‐free modified methylaluminoxane, complexes 5 – 7 as well as the corresponding ^tBu amide complexes, Me₂Si(η³‐R)(N^tBu)TiMe₂ [R = fluorenyl ( 2 ), 2,7‐^tBu₂fluorenyl ( 3 ), 3,6‐^tBu₂fluorenyl ( 4 )], were adopted as the catalysts for the copolymerization of ethylene (E) and isobutylene (IB). Among these complexes, complex 6 was found to achieve the highest IB incorporation to produce alternating E‐IB copolymers. Complex 6 system also achieved copolymerization of E and limonene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Pressure and trimethylaluminum effects on ethene/1‐hexene copolymerization with methylaluminoxane‐activated (1,2,4‐Me3Cp)2ZrCl2: Trimethylaluminum suppression of standard termination reactions after 1‐hexene insertion

Ethene homopolymerizations and copolymerizations with 1‐hexene were catalyzed by methylaluminoxane‐activated (1,2,4‐Me₃Cp)₂ZrCl₂. Investigations of the effects of various pressures on the homopolymerizations and copolymerizations and of the effects of different concentrations of trimethylaluminum (TMA) on the copolymerizations were performed. The characteristics of the ethene/1‐hexene copolymers agreed with expectations for changes in the ethene concentration: the incorporation of 1‐hexene decreased, whereas the melting point and crystallinity increased, with increasing pressure. The main termination mechanism of the homopolymerizations was β‐hydrogen transfer to the monomer. Termination mechanisms resulting in vinylidene unsaturations dominated in the copolymerizations. Standard termination mechanisms producing vinyl and trans‐vinylene unsaturations occurred in parallel and were not influenced by the ethene or TMA concentration. In addition, some chain transfer to TMA, producing saturated end groups after hydrolysis, occurred. Copolymerizations with different additions of TMA, with the other polymerization conditions kept constant, showed that the catalytic productivity [tons of polyethylene/(mol of Zr h)], the 1‐hexene incorporation, and the molecular weight (from gel permeation chromatography) were independent of the TMA concentration. Surprisingly, the vinylidene content decreased almost linearly with increasing TMA concentration. TMA might have coordinated to the catalytic site after 1‐hexene insertion and rotation to the β‐agostic state and, therefore, suppressed the standard termination reactions after 1‐hexene insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2584–2597, 2005