Ethylene polymerization reactions with multicenter Ziegler‐Natta catalysts—Manipulation of active center distribution

This article describes ethylene/1‐hexene copolymerization reactions with a supported titanium‐based, multicenter Ziegler‐Natta catalyst. The catalyst was modified by pretreating its solid precursor with AlEt₂Cl and with similar organoaluminum chlorides, Al₂Et₃Cl₃, AlEtCl₂, and AlMe₂Cl. Testing of the untreated and the pretreated catalysts in copolymerization reactions under standard reaction conditions demonstrated that the modifying agents produce two changes in the catalyst. First, the pretreatment significantly reduces the reactivity of active centers that produce high molecular weight, highly crystalline copolymer components with a low 1‐hexene content. Second, the pretreatment noticeably increases the reactivity of active centers that produce low molecular weight copolymer components with a high 1‐hexene content. The first effect is caused by Lewis acid‐base interactions of the modifiers with the active centers, whereas the second (activating) effect is due to the removal of catalyst poisons (organosilicon compounds generated in the process of the catalyst synthesis) by AlEt₂Cl. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4219–4229, 2010     

Chemistry of olefin polymerization reactions with chromium‐based catalysts

Detailed GC analysis of oligomers formed in ethylene homopolymerization reactions, ethylene/1‐hexene copolymerization reactions, and homo‐oligomerization reactions of 1‐hexene and 1‐octene in the presence of a chromium oxide and an organochromium catalyst is carried out. A combination of these data with the analysis of ¹³C NMR and IR spectra of the respective high molecular weight polymerization products indicates that the standard olefin polymerization mechanism, according to which the starting chain end of each polymer molecule is saturated and the terminal chain end is a C?C bond (in the absence of hydrogen in the polymerization reactions), is also applicable to olefin polymerization reactions with both types of chromium‐based catalysts. The mechanism of active center formation and polymerization is proposed for the reactions. Two additional features of the polymerization reactions, co‐trimerization of olefins over chromium oxide catalysts and formation of methyl branches in polyethylene chains in the presence of organochromium catalysts, also find confirmation in the GC analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5330–5347, 2008     

Kinetic modeling studies of ethylene polymerization reactions using supported chromium catalysts

Kinetic models for ethylene polymerization based on a general coordination–insertion mechanism, in which either a monocoordinated species or a bicoordinated species could lead to migratory insertion, were constructed. These models were implemented through the solution of a set of differential equations resulting from the material balances for all the species involved. The application of these kinetic models to monomer consumption for different supported catalysts produced very good fittings and allowed the estimation of the kinetic rate constants of each elementary step. Although the same kinetic scheme was used to describe all the observations, the results of the fitting showed that the supported chromium species behaved very differently according to the support. Only in the case of the silica‐supported catalysts was mechanical fragmentation of the particles observed during the course of the reaction, and this implied the inclusion of a new term in the model. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3464–3472, 2004     

Comparison of silyl chromate and chromium oxide based olefin polymerization catalysts

A comparison of the ethylene polymerization performance conducted with an oxo and a triphenylsilyl chromate catalyst on silica was performed. The oxo catalyst has higher activity and better comonomer response. The silylchromate catalyst has a much longer induction time and made a much broader molecular weight distribution polymer compared to the oxo analogue. Performance similar to silylchromate on silica was observed when triphenylsilanol (TPS) was added to the oxo chromium catalyst. The oxo catalyst was converted to the silyl chromate catalyst by ligand substitution. Analysis of the catalyst components when TPS was added to the oxo chrome analogue showed that bis triphenylsilyl chromate can form and be removed from the support.     

AlR2Cl/MgR2 combinations as universal cocatalysts for Ziegler–Natta,metallocene, and post‐metallocene catalysts

Combinations of dialkylaluminum chlorides and dialkylmagnesium compounds, when used at molar [AlR₂Cl]:[MgR₂] ratios ≥ 2, act as universal cocatalysts for all three presently known types of alkene polymerization catalysts—Ziegler–Natta, metallocene, and post‐metallocene. When these cocatalysts are used with supported Ti‐based Ziegler–Natta catalysts, they produce catalyst systems which are 1.5–2 times more active than the systems utilizing AlR₃ compounds as cocatalysts. Combinations of AlR₂Cl/MgR₂ cocatalysts and various metallocene complexes produce single‐center catalyst systems similar to those formed in the presence of MAO. The same cocatalysts activate numerous post‐metallocene Ti complexes containing bidentate ligands of a different nature and produce multicenter systems of very high activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3271–3285, 2009     

The active species of the chromium (phillips type) catalysts for the polymerization of ethylene: A unifying approach

From literature data it is concluded that the rate of the reduction, alkylation, polymer chain growth, and chain transfer reactions of three chromium(II) and one chromium(III) surface species all increase with decreasing electron density at the chromium ion. This electron density has previously been measured by the IR shift of the stretching vibration of one CO molecule terminally adsorbed on these chromium ions. It is observed that the reduction half time decreases proportional to the increasing Lewis acidity and that the rate of the polymer chain growth reaction increases exponentially for three chromium surface species with increasing CO stretching vibration. Due to the large difference of the polymer chain growth rates for the two chromium (II) species (A_d and C_d), common in the normal Phillips catalyst, both contribute almost equally to the polymer product, although the A_d species outnumbers the C_d one by more than 3 to 1.     

A kind of novel nonmetallocene catalysts for ethylene polymerization

A kind of novel bridged nonmetallocene catalysts was synthesized by the treatment of N,N‐imidazole and N,N‐phenylimidazole with n‐BuLi, and MCl₄ (M = Ti, Zr) in THF. Those catalysts were performed for ethylene polymerization after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M ratio, pressure of monomer, and concentration of catalysts on ethylene polymerization behaviors were investigated in detail. Those results revealed that the catalyst system was favorable for ethylene polymerization with high catalytic activity. The polymer was characterized by ¹³C NMR, WAXD, GPC, and DSC. The result confirmed that the obtained polyethylene featured broad molecular weight distribution around 20, linear structure, and relative low melting temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 33–37, 2008     

Copolymerization of ethylene and α‐olefins with combined metallocene catalysts. II. Mathematical modeling of polymerization with single metallocene catalysts

The relation between the polymerization conditions and the distributions of molecular weight (MWD) and chemical composition (CCD) of poly(ethylene‐co‐1‐hexene) made with single supported metallocene catalysts was investigated. Understanding the behavior of each metallocene under different polymerization conditions is necessary for designing combined metallocene catalysts to produce tailor‐made polyolefins. In this article, a simple mathematical model based on experimental results is developed and combined with the bimodality criterion developed in Part I of this series to predict polymerization conditions and metallocene combinations that will produce polymers with desired MWDs and CCDs. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1417–1426, 2000     

Ethylene polymerization behavior of Cr(III)‐containing montmorillonite: Influence of chromium compounds

Montmorillonite was treated with Cr(NO₃)₃, Cr(acetate)₃, and Cr(acac)₃ to give three catalyst precursors, Cr‐MMT‐1 , Cr‐MMT‐2 , and Cr‐MMT‐3 , respectively. Application of these catalysts to the ethylene polymerization reaction revealed Cr‐MMT‐1 to be much more reactive than the other two while the molecular weight distributions of the polymers were practically the same. Elemental analysis, XRD, and TEM measurements suggested that chromium occupied the interlayer section in Cr‐MMT‐1 and mostly the outer surface region for the other two catalysts. Aluminosilicate‐supported Cr catalysts exhibited reactivity similar to that of Cr‐MMT‐2 and Cr‐MMT‐3 . However, more of the low‐molecular‐weight polymer was formed. These data suggested that there is a relationship between the sites of the Cr ions and catalytic reactivity, and between supporting solid identity and molecular weight distribution of the polymer. The use of n‐Bu₂Mg and Et₂Zn in the place of Et₃Al led to lower activity but gave polymers of narrower molecular weight distribution, with more of the high‐molecular‐weight material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2272–2280, 2009     

Styrene‐ethylene co‐oligomerization with bis‐(diphenylphosphino)‐amine/chromium catalysts and the use of the co‐oligomerization products in copolymerization reactions with metallocenes

Ethylene‐styrene (or 4‐methylstyrene) co‐oligomerization using various bis(diphenylphoshino)amine ligands in combination with chromium is discussed. GC analysis of the reaction mixture shows that various phenyl‐hexene and phenyl‐octene isomers are formed either through cotrimerization or cotetramerization. It seems that the more bulky ligands display lower selectivity to co‐oligomerization and favor ethylene homo‐oligomerization. Subsequent copolymerization of the oligomerization reaction mixture using a metallocene polymerization catalyst results in a copolymer with a branched structure as indicated by Crystaf and ¹³C NMR analysis. Assignments of the ¹³C NMR spectrum are proposed from an APT NMR experiment combined with calculated NMR chemical shift data using additivity rules. An indication of the ability of the different co‐oligomerization products to copolymerize into the polyethylene chain could be established from these assignments. Unreacted styrene and the more bulky isomers, 3‐phenyl‐1‐hexene and 3‐phenyl‐1‐octene, are not readily incorporated while branches resulting from the other isomers present in the co‐oligomerization reaction mixture are detected in the NMR spectrum. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 1488–1501, 2008     

Supported titanium‐magnesium catalysts for ethylene polymerization: A comparative study of catalysts containing isolated and clustered titanium ions in different oxidation states

Supported titanium–magnesium catalysts (TMC) comprising isolated and clustered titanium ions in different oxidation states, which are obtained using titanium compounds of different composition (TiCl₄, TiCl₃?nDBE (DBE – dibutyl ether), [η⁶–BenzeneTiAl₂Cl₈]), were synthesized and tested in ethylene polymerization. The state of titanium ions was studied by the ESR method both for the procatalysts and after their interaction with triisobutilaluminum. For identification of ESR‐silent Ti³⁺ ions and Ti²⁺ ions, special procedures of additional catalyst treatment with pyridine, water, and chloropentafluorobenzene were used to obtain Ti³⁺ ions that are observable in ESR spectra. In distinction to numerous earlier works performed with the TiCl₄/MgCl₂ catalyst comprising after the interaction with AlR₃ the Ti³⁺ surface compounds both as isolated ions and clusters (ESR‐silent), this work considers the [η⁶–BenzeneTiAl₂Cl₈]/MgCl₂ catalyst (TMC‐3) comprising mainly the isolated Ti²⁺ ions and a new catalyst TMC‐4 obtained by treating the TMC‐3 with chloropentafluorobenzene. This catalyst comprises only the isolated Ti³⁺ ions both before and after the interaction with triisobutylaluminum. It was shown that in spite of sharp distinctions between the catalysts under consideration concerning titanium oxidation state and the ratio of isolated Ti³⁺ ions to clustered ones, all these catalysts produce polyethylenes with similar molecular weights and molecular‐weight distributions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6362–6372, 2009     

Effects of amino groups and microstructure of organic mesoporous silica supported metallocene catalysts on ethylene polymerization

<正>Mesoporous silica(MS),3-aminopropyltriethoxysilane(APTES) modified mesoporous silica(AMS),bis(3- trimethoxysilylpropyl)amine modified mesoporous silica(BAMS) and APTES modified solid spherical silica(AS) were prepared and used to immobilize metallocene catalysts for ethylene polymerization.Gel permeation chromatography results showed that polyethylenes(PEs) catalyzed by AMS(or BAMS) supported metallocene catalysts at the molar ratios of Al/Zr =100,300 and 500 were of bimodal molecular weight distribution(BMWD);while PEs catalyzed by the above catalysts at the molar ratios of Al/Zr≥800 were of monomodal molecular weight distribution(MMWD).However,MS(or AS) supported metallocene catalysts could only produce PEs with MMWD in spite of the molar ratio of Al/Zr.It was because that AMS(or BAMS) supported catalysts possessed two active sites for ethylene polymerization at low molar ratios of Al/Zr due to the combination effects of mesopore geometrical constraint and amino groups of the supports,which was confirmed by X-ray photoelectron spectroscopy.This brings forward a novel and easy method for the synthesis of polyolefin with BMWD.     

Ethylene polymerization and ethylene/hexene copolymerization with vanadium(III) catalysts bearing heteroatom‐containing salicylaldiminato ligands

A series of novel vanadium(III) complexes bearing heteroatom‐containing group‐substituted salicylaldiminato ligands [RN?CH(ArO)]VCl₂(THF)₂ (Ar = C₆H₄, R = C₃H₂NS, 2a ; C₇H₄NS, 2c ; C₇H₅N₂, 2d ; Ar = C₆H₂tBu₂ (2,4), R = C₃H₂NS, 2b ) have been synthesized and characterized. Structure of complex 2c was further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et₂AlCl. Complexes 2a–d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmol_V h bar), and affording polymer with unimodal molecular weight distributions at 25–70 °C in the first 5‐min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 °C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a–d were also explored in the presence of Et₂AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled over a wide range by the variation of catalyst structure and the reaction parameters, such as comonomer feed concentration, polymerization time, and polymerization reaction temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3573–3582, 2009     

凝胶色谱法测定顺丁橡胶平均分子量及其分布的研究

通过一系列的条件试验,包括样品浓度、样品量及流动相流速对柱效的影响,确定了最佳的凝胶色谱（ＧＰＣ）试验条件;采用普适校正法将聚苯乙烯（ＰＳ）标定曲线转换成顺丁橡胶（ＰＢ）标定曲线,并对Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程式中Ｋ,α值的选择进行了讨论;采用４种分子量加宽方程对色谱柱加宽效应进行改正计算,通过比较,选定适合本试验系统的加宽效应的改正方法;用粘度法测得的顺丁橡胶特性粘度（η）吻合ＧＰＣ所测得特性粘度值,证明了方法的可靠性。     

Synthesis and ethylene polymerization of 8‐(fluorenylarylimino)‐5,6,7‐trihydroquinolylnickel chlorides: Tailoring polyethylenes by adjusting fluorenyl position and adduct Et2Zn

A series of 8‐(arylimino)‐5,6,7‐trihydroquinolines ligand pendant fluorenyl group at N‐aryl ring, and their nickel complexes ( Ni1 ? Ni5 ) have been prepared and characterized. Once activated with Et₂AlCl, the complexes Ni1 , Ni2 , and Ni3 bearing ligands from para‐fluorenylaniline produced unimodal polyethylenes; on the contrary complexes Ni4 and Ni5 gave bimodal polyethylenes due to steric influence of ligands from ortho‐fluorenyl anilines. With a increment of Et₂Zn/ Ni4 ratio from 0 to 400, the distinct bimodel polyethylenes were obtained with molecular weights shifted from 14.3 to 57.6 kg·mol^?1; apart shiftment to higher molecular weights, the portion of low molecular weight decreased along with higher portion of high molecular weight. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1910–1919     

Effect of interchange reactions on the molecular weight distribution of poly(ethylene terephthalate): A Monte Carlo simulation

The effect of the interchange reactions of poly(ethylene terephthalate) (PET) on its molecular weight distribution (MWD) was analyzed using a Monte Carlo simulation method. Three kinds of motions, which correspond to the direct ester(SINGLEBOND)ester interchange reaction, alcoholysis, and internal alcoholysis in polyester, were performed in this simulation: bond flip, end attack, and backbite. Two systems with two different types of nonequilibrium distribution (monodisperse and bimodal distribution) were initially prepared. The initial biases from equilibrium MWD are rapidly relaxed to an equilibrium MWD as the reaction progresses. The MWD at equilibrium is well described by the most probable MWD proposed by Flory. From the polydispersity data, it is concluded that about 0.3 interchanges per segment are sufficient to equilibrate the nonequilibrium system. For the validity of the simulation, the variation of MWD of the mixtures of two PETs having different molecular weights were monitored using gel permeation chromatography. The agreement between simulation and experiment is remarkably good. © 1996 John Wiley & Sons, Inc.     

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     

Imino‐indolate half‐titanocene chlorides: Synthesis and their ethylene (co‐)polymerization

A series of imino‐indolate half‐titanocene chlorides, Cp′Ti(L)Cl₂ ( C1 – C7 : Cp′ = C₅H₅, MeC₅H₄, C₅Me₅, L = imino‐indolate ligand), were synthesized by the reaction of Cp′TiCl₃ with sodium imino‐indolates. All complexes were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. Moreover, the molecular structures of two representative complexes C4 and C6 were confirmed by single crystal X‐ray diffraction analysis. On activation with methylaluminoxane (MAO), these complexes showed good catalytic activities for ethylene polymerization (up to 7.68 × 10⁶ g/mol(Ti)·h) and ethylene/1‐hexene copolymerization (up to 8.32 × 10⁶ g/mol(Ti)·h), producing polyolefins with high molecular weights (for polyethylene up to 1808 kg/mol, and for poly(ethylen‐co‐1‐hexene) up to 3290 kg/mol). Half‐titanocenes containing ligands with alkyl substituents showed higher catalytic activities, whereas the half‐titanocenes bearing methyl substituents on the cyclopentadienyl groups showed lower productivities, but produced polymers with higher molecular weights. Moreover, the copolymerization of ethylene and methyl 10‐undecenoate was demonstrated using the C1 /MAO catalytic system. The functionalized polyolefins obtained contained about 1 mol % of methyl 10‐undecenoate units and were fully characterized by several techniques such as FT‐IR, ¹H NMR, ¹³C NMR, DSC, TGA and GPC analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 357–372, 2009     

Simulation of gel permeation chromatography measurement for long chain branched metallocene polyethylene

The research about the polymerization reaction mechanism of long chain branched polymer provides a method to simulate the generation of LCB mPE (long chain branched metallocene polyethylene).^[1-3] In this work, after simulating the generation of one million LCB mPE molecules, we calculate the sizes (i.e. radii of gyration) of molecules in good solvents to obtain the molecular size distributions. Then we simulate the fractionation in GPC (gel permeation chromatography) measurement and the different GPC detector responses to obtain simulated GPC MWDs (molecular weight distributions). The simulated MWDs are compared to the real GPC results provided by the Dow Chemical Company.