Influence of the catalyst and polymerization conditions on the long‐chain branching of metallocene‐catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long‐chain branching, molecular weight, and end‐group types of polyethene produced with the metallocene‐catalyst systems Et[Ind]₂ZrCl₂/MAO, Et[IndH₄]₂ZrCl₂/MAO, and (n‐BuCp)₂ZrCl₂/MAO. Long‐chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]₂ZrCl₂/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n‐BuCp)₂ZrCl₂/MAO and Et[IndH₄]₂ZrCl₂/MAO, produced linear or only slightly branched polyethene. On the basis of an end‐group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]₂ZrCl₂/MAO at 80 °C in toluene. For the other catalyst systems, β‐H elimination dominated at low ethene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 376–388, 2000     

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     

Effective activation of metallocene catalysts with supported‐type Ph3CClO4 in ethylene polymerization

Supported type cocatalysts using triphenylcarbenium perchlorate (Ph₃CClO₄) were prepared by impregnation on inorganic carrier, magnesium chloride (MgCl₂) and applied to ethylene polymerizations with rac‐Et[Ind]₂ZrCl₂. Homogeneous polymerizations with Ph₃CClO₄ were also carried out for comparison. The activity of homogeneous polymerization was much lower than that obtained with methylaluminoxane (MAO). On the other hand, rac‐Et[Ind]₂ZrCl₂ activated by the supported type Ph₃CClO₄/MgCl₂ system displayed high activity comparable to that obtained with MAO. From the results of fractionation and polymerization of the rac‐Et[Ind]₂ZrCl₂‐Ph₃CClO₄/MgCl₂ catalyst system, it was found that the increased activity mainly came from the active species in the supernatant part. UV‐vis spectroscopic measurements combined with ICP analysis indicate that the active species in the supernatant fraction are composed of a stoichiometric amount of perchlorate and metallocene catalyst.     

Influences of methylaluminoxane separated by porous inorganic materials on the isospecific polymerization of propylene

Inorganic siliceous porous materials such as MFI type zeolite, mesoporous silica MCM‐41 and silica gel with different average pore diameters were applied to the adsorptive separation of methylaluminoxane (MAO) used as a cocatalyst in α‐olefin polymerizations. The separated MAOs combined with rac‐ethylene‐(bisindenyl)zirconium dichloride (rac‐Et(Ind)₂ZrCl₂) were introduced to propylene polymerization, and their influences on the polymerization activity and stereoregularity of the resulting polymers were investigated. The polymerization activity and isotactic [mmmm] pentad of the produced propylene were markedly dependent upon the pore size of the porous material used for adsorptive separation. From the results obtained from solvent extraction of the produced polymers, it was suggested that there are at least two kinds of active species with different stereospecificity in the rac‐Et(Ind)₂ZrCl₂/MAO catalyst system.     

UV‐Visible Spectroscopic Study of rac‐Et(Ind)2ZrCl2/Aluminoxanes

The UV‐visible spectroscopic study of the interaction between rac‐Et(Ind)₂ZrCl₂ and different aluminoxanes, such as isobutylaluminoxane (BAO) and ethyl(isobutyl)aluminoxane (EBAO), was conducted under normal polymerization conditions. UV‐visible absorption spectra of rac‐Et(Ind)₂ZrCl₂/aluminoxanes were correlated with the formation of ionic zirconium species. The influence of different aluminoxanes on the tightness of the metallocenium‐aluminoxane ionic pairs was interpreted in terms of the aluminoxane structure. The loose ionic pairs formed in the EBAO system causes a fast decaying kinetic profile, advantageous for copolymerization.     

Ethylene‐Norbornene Terpolymerization with 5‐Vinyl‐2‐norbornene Using Single‐Site Catalysts

The incorporation of 5‐vinyl‐2‐norbornene (VNB) into ethylene‐norbornene copolymer was investigated with catalysts [Ph₂C(Fluo)(Cp)]ZrCl₂ ( 1 ), rac‐[Et(Ind)₂]ZrCl₂ ( 2 ), and [Me₂Si(Me₄Cp)^tBuN]TiCl₂ ( 3 ) in the presence of MAO by terpolymerizing different amounts of 5‐vinyl‐2‐norbornene with constant amounts of ethylene and norbornene at 60°C. The highest cycloolefin incorporations and highest activity in terpolymerizations were achieved with 1 . The distribution of the monomers in the terpolymer chain was determined by NMR spectroscopy. As confirmed by XRD and DSC analysis, catalysts 1 and 3 produced amorphous terpolymer, whereas 2 yielded terpolymer with crystalline fragments of long ethylene sequences. When compared with poly‐(ethylene‐co‐norbornene), VNB increased both the glass transition temperatures and molar masses of terpolymers produced with the constrained geometry catalyst whereas decreased those for the metallocenes.     

Preparation of a PE/MT Composite by Copolymerization of Ethylene with In‐Situ Produced Ethylene Oligomers under a Dual Functional Catalyst System Intercalated into MT Layer

The catalyst dichlorobis(acetylacetone)zirconium was intercalated into montmorillonite (MT) together with AlEt₂Cl as a cocatalyst. Reacting ethylene in the presence of this catalyst yields α‐olefin oligomers with over 80% selectivity. [rac‐Et(Ind)₂ZrCl₂]/MAO was then added to form a dual functional catalyst system. An MT particle‐dispersed polyethylene composite was prepared by copolymerization of the in‐situ produced oligomers with ethylene using this dual system.     

The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization简

Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE.     

Insights into propylene/ω‐halo‐α‐alkenes copolymerization promoted by rac‐Et(Ind)2ZrCl2 and (pyridyl‐amido)hafnium catalysts

This article discussed the root causes of the interesting differences between rac‐Et(Ind)₂ZrCl₂ and dimethyl (pyridyl‐amido)hafnium in catalyzing the propylene/ω‐halo‐α‐alkene copolymerization. Confirmed by density functional theory (DFT) calculations, the larger spacial opening around the active center of rac‐Et(Ind)₂ZrCl₂ contributes to the coordination and insertion of the monomers, resulting in the higher catalytic activity, while the narrow spacial opening around the Hf center retards the chain transfer reaction, leading to the much higher molecular weights (M_ws) of the copolymers. The superior tolerability of Zr catalyst toward halogen groups might be attributed to that the dormant species generated from halogen coordination could be promptly reactivated. DFT calculations indicated the higher probability for the ω‐halo‐α‐alkene vinyl to coordinate with the Hf catalyst leading to the better ability to incorporate halogenated monomers. The high M_ws and the outstanding isotacticity achieved by the Hf catalyst determined the higher melting temperature values of the copolymers with a certain amount of halogen groups. In addition, the chain transfer schemes were employed to analyze why the presence of halogenated monomers greatly decreased the M_ws of the copolymers when rac‐Et(Ind)₂ZrCl₂ was used, while had no or little effect upon the M_ws in the copolymerization by the Hf catalyst. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3421–3428     

Synthesis of oxazoline functionalized polypropene using metallocene catalysts

Using two different zirconocene/MAO catalyst systems, propene was copolymerized with the comonomers 2‐(9‐decene‐1‐yl)‐1,3‐oxazoline and 2‐(4‐(10‐undecene‐1‐oxo)phenyl)‐1,3‐oxazoline, respectively. The catalysts used were rac‐Et[Ind]₂ZrCl₂ and rac‐Me₂Si[2‐Me‐4, 5‐BenzInd]₂ZrCl₂. Up to 0.53 mol‐% oxazoline could be incorporated into polypropene. Oxazoline content, molecular weight, degree of isotacticity and melting behavior were dependent on the catalyst system, comonomer structure and comonomer concentration in the feed.     

Synthesis and properties of poly‐1‐olefins

The oligomerization and polymerization of 1‐pentene using Cp₂ZrCl₂, Cp₂HfCl₂, [(CH₃)₅C₅]₂ZrCl₂, rac‐[C₂H₄(Ind)₂]ZrCl₂, [(CH₃)₂Si(Ind)₂]ZrCl₂, (CH₃)₂Si(2‐methylbenz[e]indenyl)₂ZrCl₂, Cp₂ZrCl{O(Me)CW(CO)₅}, Cp₂ZrCl(OMe) and methylaluminoxane (MAO) has been studied. The degree of polymerization was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1‐pentene to polymers of poly‐1‐pentene with a molar mass M_w = 149000 g/mol were formed. Cp₂ZrCl{O(Me)CW(CO)₅} is a new highly active catalyst for the oligomerization of 1‐pentene to low molecular weight products. The activity decreases in the order Cp₂ZrCl{O(Me)CW(CO)₅} > Cp₂ZrCl₂ > Cp₂ZrCl(OMe). Furthermore, poly‐1‐olefins ranging from poly‐1‐pentene to poly‐1‐octadecene were synthesized with (CH₃)₂Si(2‐methyl‐benz[e]indenyl)₂ZrCl₂ and methylaluminoxane (MAO) at different temperatures. The temperature dependence of the molar mass can be described by a common exponential decay function irrespective of the investigated monomer.     

Long‐chain‐branched polyethene by the copolymerization of ethene and nonconjugated α,ω‐dienes

Ethene was copolymerized (1) with 1,5‐hexadiene with rac‐ethylenebis(indenyl)zirconium dichloride/methylaluminoxane (MAO) used as a catalyst and (2) with 1,7‐octadiene with bis(n‐butylcyclopentadienyl)zirconium dichloride/MAO and rac‐ethylenebis(indenyl)hafnium dichloride (Et[Ind]₂HfCl₂)/MAO used as catalysts at 80 °C in toluene. The copolymer microstructure and the influence of diene incorporation on the rheological properties were examined. Ethene and 1,5‐hexadiene formed a copolymer in which a major fraction of the 1,5‐hexadiene was incorporated into rings and a small fraction formed 1‐butenyl branches. The copolymerization of ethene with 1,7‐octadiene resulted in a higher selectivity toward branch formation. Some of the branches formed long‐chain‐branching (LCB) structures. The ring formation selectivity increased with decreasing ethene concentration in the polymerization reactor. Melt rheological properties of the diene copolymers resembled those of metallocene‐catalyzed LCB homopolyethenes and depended on the vinyl content, the catalyst, and the polymerization conditions. At high diene contents, all three catalysts produced crosslinked polyethene. This was especially pronounced with Et[Ind]₂HfCl₂, where only 0.2 mol % 1,7‐octadiene in the copolymer was required to achieve significantly modified rheological properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3805–3817, 2001     

Renewable chain transfer agents for metallocene polymerizations: The effects of chiral monoterpenes on the polyolefin molecular weight and isotacticity

Monoterpenes were used as renewable chain transfer agents and polymerization solvents for metallocene/methylaluminoxane (MAO) catalysis. The polymerization of 1‐hexene, ethylene, and propylene in d‐limonene, hydrogenated d‐limonene and α‐pinene is reported. As detected by ¹H NMR analysis of the alkene region, chain transfer to d‐limonene yielded a higher percentage of trisubstituted alkenes. Size exclusion chromatography detected a decrease in molecular weight values resulting from chain transfer to d‐limonene. The [mmmm] pentads for isotactic polypropylene were characterized by ¹³C NMR and FTIR spectroscopy. Propylene polymerizations with the Et(Ind)₂ZrCl₂/MAO and Me₂Si(Ind)₂ZrCl₂/MAO catalyst systems in d‐limonene gave [mmmm] pentad values as high as 0.97. For the Et(Ind)₂ZrCl₂/MAO catalyst system at 0 °C, the mol fraction of [mmmm] pentads increased from 0.86 to 0.94 upon switching the solvent from toluene to d‐limonene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3150–3165, 2007     

Co- and terpolymerizations of ethene and α-olefins with metallocenes

The suitability of the (n-butCp)₂ZrCl₂/methylaluminoxane (MAO) catalyst system for the copolymerization of ethene with propene, hexene, and hexadecene was studied and Ind₂ZrCl₂/MAO was tested as a catalyst for ethene/propene and ethene/hexene copolymerizations. The synergistic effect of longer α-olefin on propene incorporation in ethene/propene/hexene and ethene/propene/hexadecene terpolymerizations was investigated with Et(Ind)₂ZrCl₂MAO and (n-butCp)₂ZrCl₂/MAO catalyst systems. The molar masses, molar mass distributions, melting points, and densities of the products were measured. The incorporation of comonomer in the chain was further studied by segregation fractionation techniques (SFT), by differential scanning calorimetry (DSC), studying the β relaxations by dynamic mechanical analysis (DMA) and by studying the microstructure of some copolymers by ¹³C-NMR. In this study (n-butCp)₂ZrCl₂ and Ind₂ZrCl₂ exhibited equal response in copolymerization of ethene and propene and both catalysts were more active towards propene than longer α-olefins. A nearly identical incorporation of propene in the chain was found for the two catalysts when a higher propene feed was used. A lower hexene feed gave a more homogeneous comonomer distribution curve than a higher hexene feed and also showed the presence of branching. In terpolymerizations catalyzed with (n-butCp)₂ZrCl₂, the hexadecene concentrations of the ethene/propene/hexadecene terpolymers were always very low, and only traces of hexene were detected in ethene/propene/hexene terpolymers. With hexene no clear synergistic effect on the propene incorporation in the terpolymer was detected and with hexadecene the effect of the longer α-olefin was even slightly negative. With an Et(Ind)₂ZrCl₂/MAO catalyst system both hexene and hexadecene were incorporated in the chain in the terpolymerizations. © 1997 John Wiley & Sons, Inc.     

Synthesis,characterization and polymerization of the novel carbazole‐based monomer 9‐(bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole

Synthesis and characterization of a novel carbazole‐based monomer, 9‐(bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) and its copolymerization with ethylene by using two metallocene/MAO catalyst systems are presented. The monomer was characterized by means of NMR spectroscopy, MS and elementary analysis. Copolymerization studies were conducted using [Ph₂C(Ind)(Cp)ZrCl₂] and [Ph₂C(Flu)(Cp)ZrCl₂] catalysts. The [Ph₂C(Ind)(Cp)ZrCl₂] catalyst gave a copolymer containing as much as 4.6 mol‐% of BHMCZ. Polymers were characterized using NMR spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC).     

Synthesis of Various Functional Propylene Copolymers Using rac‐Et[1‐Ind]2ZrCl2/MAO as the Catalyst System

Propylene copolymers with different polar groups were synthesised using rac‐Et[1‐Ind]₂ZrCl₂/MAO as the catalyst system. 10‐Undecen‐1‐ol, 10‐undecenoyl chloride, 10‐undecenoic acid, 2‐(9‐decen‐1‐yl)‐1,3‐oxazoline, 2‐(9‐decen‐1‐yl)‐4,4‐dimethyl‐1,3‐oxazoline, and 2‐[4‐(10‐undecene‐1‐oxy)phenyl]‐1,3‐oxazoline were used as comonomers. The addition of water to the 10‐undecenoyl chloride copolymer solution led to an acid‐functionalised copolymer. In the case of 2‐(9‐decen‐1‐yl)‐1,3‐oxazoline and its homopolymers, polymerisation temperature was varied. Up to 0.61 mol‐% comonomer were incorporated into the poly(propylene)s. The catalyst activities for 10‐undecen‐1‐ol, 10‐undecenoyl chloride and 10‐undecenoic acid were much higher than for the oxazoline comonomers.     

Effect of methylaluminoxane/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 the impregnation of TiCl₄ and rac-Et(Ind)₂ZrCl₂. The prepared rac-Et(Ind)₂ZrCl₂/TiCl₄/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)₂ZrCl₂/TiCl₄/MAO/SMB catalyst was investigated. The catalytic activity of rac-Et(Ind)₂ZrCl₂/TiCl₄/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)₂ZrCl₂/TiCl₄/MAO/SMB catalyst preferably produced a ethylene-hexene copolymer with non-blocky sequence ([EHE]) with increasing Al(MAO)/Zr ratio.     

Stereochemical control in homogeneous Ziegler-Natta catalysts

Racemic ethylenebis(η⁵-indenyl)zirconium dichloride (Et[Ind]₂ZrCl₂) activated with methylaluminoxane (MAO) catalyzed propylene polymerization with varying degree of stereochemical control which decreases greatly with the increase of T_p (temperature of polymerization). The PP&s are characterized by low melting temperature (T_m), high solubility, and prefers to crystallize in the γ-modification. The catalytic activity of Et[Ind]₂ZrCl₂/MAO becomes very small with the lowering of T_p. Very active and highly stereoselective cationic metallocene alkyl, Et[Ind]₂Zr⁺(CH₃), was produced by the reaction of Et[Ind]₂Zr(CH₃)₂ with Ph₃C⁺B(C₆F₅)₄⁻. Comparison of this system with the Et[Ind]₂ZrCl₂/MAO catalyst showed that in the latter case a quarter of the Et[Ind]₂ZrCl₂ was converted by MAO to Et[Ind]₂Zr⁺CH₃ at room temperature but less than 0.14% of the Zr was so activated at −20°C. The Et[IndH₄]ZrCl₂/MAO catalyst was shown to have two kinds of catalytic species one with high propagation rate constant (k_p) and stereoselectivity and another with low k_p and poor stereoselectivity. The very narrow molecular weight distribution of the PP produced may be attributed to the fact that the different types of active species have comparable k_p/k_tr^A, the latter is the rate constant of transfer. Non-symmetric, rac-[anti-ethylidene(1-η⁵-indenyl)(1-η⁵-tetramethylcyclopentadienyl)-Ti-Cl₂ and -(CH₃)₂ have been synthesized and structures determined. The complexes provide dissimilar steric environment to propagating chains to produce crystalline-amorphous multiblock thermoplastic elastomeric PP. The polymerization process here involves a two-state propagation mechanism.     

Functionalization of polyethylene with silane comonomers

We synthesized a new weakly interacting monomer with a reactive phenylsilane group that is an intermediate for many functional groups. The synthesis was performed in two steps: the hydrosilylation of 1,7‐octadiene with dimethylchlorosilane and a Grignard reaction with phenyl magnesium bromide. The new monomer, 7‐octenyldimethylphenylsilane, was isolated and copolymerized with ethylene via metallocene catalysts (Me₂Si(Me‐2‐Ind)₂ZrCl₂ and Et(Ind)₂ZrCl₂) and methylaluminoxane (MAO) as a cocatalyst. Electropositive silicon had no negative effect on the copolymerization reaction. The polymerization activity increased, and the molar mass of the product remained at a high level. The comonomer incorporation reached a significant 11.8 wt % (2.6 mol %). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1303–1308, 2002     

Copolymerization of Propene and 5‐Vinyl‐2‐Norbornene: A Simple Route to Polar Poly(propylene)s

Summary: The metallocenes rac‐C₂H₄(Ind)₂ZrCl₂ ( 1 ), rac‐Me₂Si(Ind)₂ZrCl₂ ( 2 ), and rac‐Me₂Si(2‐Me‐benz[e]Ind)₂ZrCl₂ ( 3 ) efficiently copolymerize propene and 5‐vinyl‐2‐norbornene (VNB). 1 and 2 give a high VNB content and high productivities, whereas 3 gives moderate incorporation. Surprisingly, precatalysts 1 and 2 , which have very closely related structures, showed very different reactivities toward VNB, with 1 having a greater affinity for VNB than for propene. The copolymers are quantitatively converted into polyolefins with polar functionalities.