Evidence of the Quasi‐Living Character of the ansa‐Zirconocene/MAO‐Catalyzed Copolymerization of Ethylene and Norbornene

The kinetics of the ethylene‐norbornene copolymerization, catalyzed by rac‐Et(Ind)₂ZrCl₂/MAO, 90%rac/10%meso‐Et(4,7‐Me₂Ind)₂ZrCl₂/MAO and rac‐H₂C(3‐tert‐BuInd)₂ZrCl₂/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi‐living polymerization.     

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.     

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.     

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     

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     

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.     

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.     

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.     

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.     

Copolymerization of Ethylene and Propylene Using Silicon Tetrachloride‐Modified Silica/MAO with Et[Ind]2ZrCl2 Metallocene Catalyst

For the copolymerization of ethylene with propylene or a higher α‐olefin, using Et[Ind]₂ZrCl₂ metallocene catalyst, modification of silica with silicon tetrachloride prior to MAO adsorption can increase the activity, which is more pronounced for ethylene/1‐hexene copolymerization at higher pressure and temperature. The molecular weight of the copolymer produced was lower and the polydispersity tends to be decreased. No significant effect of SiCl₄ addition on the microstructure and the chemical composition distribution of the copolymer produced was observed.     

Isospecific Polymerization of Propylene By ansa-Zirconocene Diamide Compound Cocatalyzed by Mao

Abstract

The kinetics of propylene polymerization initiated by racemic ethylene-1,2-bis(1-indenyl) zirconium bis(dimethylamide) [rac-(EBI) Zr(NMe₂)₂(rac-1)] cocatalyzed by methylaluminoxane (MAO) were studied. The polymerization behaviors of rac-1/MAO catalyst investigated by changing various experimental parameters are quite different from those of rac-(EBI) ZrCl₂ (rac-2)/MAO catalyst, due to the differences in the generation procedure of cationic actives species of each metallocene by the reaction with MAO. The activity of rac-1/MAO catalyst showed maximum when [Al]/[Zr] is around 2000, when [Zr] is 137.1 μM, and when polymerization temperature is 30°C. The negligible activity of rac-1/MAO catalyst at a very low MAO concentration seems to be caused by the instability of the cationic active species. The meso pentad values of polymers produced by rac-1/MAO catalyst at 30°C are in the range of 82.8% to 89.7%. The rac-1/MAO catalyst lost stereorigid character at the polymerization temperature above 60°C. The molecular weight of polymer decreased as [Al]/[Zr] ratio, polymerization temperature, and [Zr] increased. The molecular weight distributions of all polymers are in the range of 1.8–2.3, demonstrating uniform active species present in the polymerization system.     

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     

Low-temperature isospecific polymerization of propylene catalyzed by alkylzirconocene-type ‘cations’

The rac-ethylenebis(indenyl)methylzirconium ‘cation’ (1), generated from rac-Et(Ind)₂ZrMe₂ and Ph₃CB(C₆F₅)₄, has recently been shown to be exceedingly active and stereoselective in propylene polymerization. The ethyl analog (2) can be produced by an alternate, efficient route involving a reaction between rac-Et(Ind)₂ZrCl₂ and AlEt₃ (TEA), followed by addition of Ph₃CB(C₆F₅)₄. The use of excess AlEt₃ serves both to alkylate the zirconium complex as well as to scavenge the system. The propylene polymerization activity of the ‘cation’ 2 is about 7000 times greater than the activity of rac-Et(Ind)₂ZrCl₂/methylaluminoxane (MAO) at T_p=?20°C. The related catalyst system rac-Me₂Si(Ind)₂ZrCl₂/TEA/Ph₃CB(C₆F₅)₄ (3) was found to produce 98.3% i-PP with T_m 156.3°C and an activity of 1.8 × 10⁹ g PP {(mol Zr) [C₃H₆]h}^?1.     

Functionalization of polyolefins via the reaction of ozone with double bonds

Polar groups are introduced into polyolefin chains via the postpolymerization polymer-analogous transformations using the ozonolysis of side ethylidene groups of ethylene (propylene) copolymers with the cyclic comonomer 5-ethylidene-2-norbornene. The copolymers are synthesized using ansa-zirconocene catalysts Me₂Si[Ind]₂ZrCl₂/MAO, Et[Ind]₂ZrCl₂/MAO and Et[IndH₄]₂ZrCl₂/MAO, which provide insersion of the cyclic monomer into the polymer chain without ring opening. The study of number-average molecular mass and compositions of homo- and copolymers of ethylene and propylene with 5-ethylidene-2-norbornene confirms a high selectivity of the ozonolysis of unsaturated double bonds of polyolefins. The formation of polar groups in the ozonized ethylene and propylene copolymers with 5-ethylidene-2-norbornene is proved by IR and Raman spectroscopy. The thermophysical characteristics of the initial and ozonized copolymers are compared.     

Silica-supported metallocenes: stereochemical comparison between homogeneous and heterogeneous catalysis

Propylene was polymerized in the presence of the isospecific Et(Ind)₂ZrCl₂ (Et: ethylene, Ind: indenyl) and the aspecific (Ind)₂ZrCl₂ complexes in solution and anchored to SiO₂ and SiO₂/MAO (MAO: methylaluminoxane) supports. From the stereochemical analysis of the polypropene samples obtained it can be deduced that (i) the same active species is formed when a metallocene is in solution and when it is anchored to the SiO₂/MAO support and (ii) a completely different active species is formed when the metallocene is anchored to the silica. The fact that both systems Et(Ind)₂ZrCl₂ SiO₂ and (Ind)₂ZrCl₂ SiO₂ produce the same prevailingly isospecific polymer suggests that only isospecific centers are formed in this case, independently of the metallocene stereochemical structure.     

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp₂ZrCl₂ and rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂ as a catalyst) and styrene (Cp*Ti(OMe)₃ as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp₂ZrCl₂/MAO, whereas it became less effective when the catalyst changed to rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp₂ZrCl₂/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂/MAO. In the case of styrene polymerization with Cp*Ti(OMe)₃/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as B? H‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010     

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     

Gas phase polymerization of ethylene with a silica-supported metallocene catalyst: influence of temperature on deactivation

Ethylene was polymerized at 5 bar in a stirred powder bed reactor with silica supported rac-Me₂Si[Ind]₂ZrCl₂/methylaluminoxane (MAO) at temperatures between 40°C and 80°C using NaCl as support bed and triethylaluminium (TEA) as a scavenger for impurities. For this fixed recipe and a given charge of catalyst. the average catalyst activity is reproducible within 10% for low temperatures. The polymerization rate and the rate of deactivation increase with increasing temperature. The deactivation could be modeled using a first order dependence with respect to the polymerization rate.     

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.