Silolene-Bridged zirconocenium polymerization catalysts

A new silolene-bridged compound, racemic (1,4-butanediyl) silylene-bis (1-η⁵-in-denyl) dichlorozirconium ( 1 ) was synthesized by reacting ZrCl₄ with C₄H₈Si (IndLi)₂ in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta-fluorophenyl) borate ( 2 ) to produce in situ the zirconocenium ion ( 1 ⁺). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (T_p = ?55°C), producing refluxing n-heptane insoluble isotactic poly(propylene) (i-PP) with a yield of 99.4%, T_m = 164.3°C, δH_f = 20.22 cal/g and M?_w = 350 000. It has catalytic activities of 10⁷?10⁸ g PP/(mol Zr · [C₃H₆] · h) in propylene polymerization at the T_p ranging from ?55°C to 70°C, and 10⁸ polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1 ⁺ decreases gradually as T_p approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1 ⁺ is more stereospecific than the analogous cation derived from rac-dimethylsilylenebis (1-η⁵-indenyl)dichlorozirconium ( 4 ). The variations of polymerization activities in ethylene and in propylene for T_p from ?55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium-propylene π-complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π-complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude r_E ? 4r_p. Furthermore, r_E.r_p ? 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo-selectivity than the corresponding 1 ⁺ or 4 ⁺ system. © 1994 John Wiley & Sons, Inc.     

POISONING OF ACTIVE SITES ON ZIEGLER-NATTA CATALYST FOR PROPYLENE POLYMERIZATION

The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated.A minor amount of simple structure of Lewis base,i.e.,methanol,acetone,ethyl acetate,was introduced into the catalyst slurry for partial poisoning catalytic active centers.It was found that the variations in deactivation power were in the order of methanol>acetone>ethyl acetate.The kinetic investigation via stopped-flow polymerization showed that poisoning compounds caused...     

Hexene-1 polymerization by homogeneous zirconocene and heterogeneous-supported TiCl3 catalysts

MgCl₂-supported TiCl₃ catalysts, with and/or without electron donor modifier (internal B_i or external B_e), were compared with rac-ethylenebis(indenyl)zirconium dichloride ( 1 ) activated with either MAO or the cation forming agent, triphenyl carbenium tetrakis(pentafluorophenyl)borate ( 2 ), with triethylalumium (TEA). The activities of the heterogeneous catalysts depend on the presence or absence of the Lewis base, were relatively insensitive to the temperature of polymerization, and produce poly(hexene) with molecular weights up to 10⁶. The 1 /MAO catalyst has about five times higher activity at 50°C but is almost inactive at ?30°C; the overall activation energy is 12.4 kcal mol^?1. In contrast, the activity for hexene polymerization by the 1/2 /TEA catalyst is actually slightly greater at lower temperature. The MW's of poly(hexene) obtained with the zirconocenium catalysts are only in the tens of thousands because of rapid β-hydride elimination by the electrophilic cationic Zr center. © 1993 John Wiley & Sons, Inc.     

One-phase supported titanium-based catalysts for polymerization of ethylene. II. Effect of hydrogen

The relation between composition of the one-phase titanium-based silica supported catalysts for gas-phase ethylene polymerization, and the ability of these catalysts to control the molecular weight of polymer using hydrogen has been studied. Halogen containing alkylaluminium compounds and alkoxy groups on titanium promote the chain transfer process. A significant polymerization rate lowering effect is caused by hydrogen. However, catalyst activity fully revives after hydrogen removal from the polymerization system. The proportion of active titanium was found to be 18±4% in the presence of hydrogen, and the value of propagation rate constant (k_p) was calculated to be 190±45 L/mol.s. © 1993 John Wiley & Sons, Inc.     

Metallocene catalysts for olefin polymerizations. XXIV. Stereoblock propylene polymerization catalyzed by rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl)(1-η5-indenyl)dimethyltitanium: A two-state propagation

Racemic-anti-[ethylidene(1-η⁵-tetramethylcyclopentadienyl) (1-η⁵-indenyl)dimethyltitanium ( 6 ) has been synthesized and its molecular structure determined by x-ray diffraction methods. The two Ti?Me(1) and Ti?Me(2) units have bond distances differing by 0.08 Å and their proton NMR resonances are separated by over 1 ppm. Using this compound and methylaluminoxane (MAO) as the activator, at 25°C the 6 /MAO catalyst produced polypropylene having crystalline domain with physical crosslinks. The polymers obtained at lower polymerization temperatures are rheologically liquids. The behaviors of this catalyst system resembles closely the previously reported rac-[anti-ethylidene(1-η⁵-tetramethylcyclopentadienyl) (1-η⁵-indenyl)dichlorotitanium ( 4 )/MAO system. The structure of 6 determined here furnishes tangible support for the proposed two-state (isomeric)-switching propagation mechanism. Addition of MAO to 6 causes broadening of the Me(1) resonance in the ¹H-NMR spectra, and 6 is decomposed by Ph₃C⁺B(C₆F₅)^-₄. © 1992 John Wiley & Sons, Inc.     

Copolymerization of ethylene and propylene catalyzed by magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts

Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-i-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared.The effects of reaction temperature, ethylene/propylene molar ratio,aluminium/vanadium（Al/V）molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated.The molecular weight,molecular weight distribution,sequence composition and crystallinity of the products were measured by gel permeation chromatography,¹³C-NMR and differential scanning calorimetry analysis, respectively.In comparison to the vanadium and titanium catalysts,the bimetallic catalyst showed higher catalytic activity and better copolymerization performance.The obtained ethylene/propylene copolymers have high molecular weight （10⁵）,broad molecular weight distribution,high propylene content with random or short blocked sequence structures （r_Er_P=1.919）,low melting temperatures and low crystallinities（X_c<20%）.     

Probing the roles of diethylaluminum chloride in propylene polymerization with MgCl2-supported ziegler-natta catalysts

In this article, the effect of diethylaluminum chloride (DEAC) in propylene polymerization with MgCl₂-supported Ziegler-Natta catalyst was studied. Addition of DEAC in the catalyst system caused evident change in catalytic activity and polymer chain structure. The activity decrease in raising DEAC/Ti molar ratio from 0 to 2 is a result of depressed production of isotactic polypropylene chains. The number of active centers in fractions of each polymer sample was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and fractionating the polymer into isotactic, mediumisotactic and atactic fractions. The number of active centers in isotactic fraction ([C_i*]/[Ti]) was lowered by increasing DEAC/Ti molar ratio to 2, but further increasing the DEAC/Ti molar ratio to 20 caused marked increase of [C_i*]/[Ti]. The number of active centers that produce atactic and medium-isotactic PP chains was less influenced by DEAC in the range of DEAC/Ti = 0–10, but increased when the DEAC/Ti molar ratio was further raised to 20. The propagation rate constant of C_i* (k _pi) was evidently increased when DEAC/Ti molar ratio was raised from 0 to 5, but further increase in DEAC/Ti ratio caused gradual decrease in k _pi. The complicated effect of DEAC on the polymerization kinetics, catalysis behaviors and polymer structure can be reasonably explained by adsorption of DEAC on the central metal of the active centers or on Mg atoms adjacent to the central metal.     

石墨烯/二氯化镁负载钛系齐格勒-纳塔催化剂制备及其乙烯聚合性能

石墨烯自2004年发现以来,由于其独一无二的优异性迅速成为科学家们的研究热点.由于石墨烯具有极其优异的电学、力学和热学等性能,因此被广泛应用于高性能聚合物基复合材料的制备.众所周知,纳米填料在聚合物中的分散状态以及与基体间的界面作用是构筑高性能聚合物纳米复合材料的关键因素.由于石墨烯极易团聚,难以通过传统的熔融共混法制备均匀分散的石墨烯增强-聚烯烃纳米复合材料.另一方面,聚烯烃通常需要在较高温度下才能溶于部分有毒溶剂(如:三氯苯和二甲苯等),因此溶液共混法也不适用于聚烯烃-石墨烯纳米复合材料的制备.有鉴于此,本文开发了一种共沉积法制备石墨烯/二氯化镁负载钛系齐格勒-纳塔催化剂的路线.通过原位聚合直接制备出石墨烯均匀分散的聚烯烃/石墨烯纳米复合材料.考察了石墨烯的加入量对催化剂形态及其催化乙烯聚合行为的影响.当石墨烯加入量较低时,多个石墨烯片被包裹于较大的催化剂粒子中.随着石墨烯加入量的增加,催化剂趋向于在石墨烯表面聚集.继续增加石墨烯量将导致石墨烯包裹催化剂粒子,降低过渡金属钛的负载效率.通过三乙基铝活化后,所制备的催化剂具有非常高的乙烯催化活性,所生成的聚乙烯/石墨烯纳米复合材料复制了催化剂的片状结构.同时,通过对所制备的聚乙烯/石墨烯纳米复合材料进行电子显微镜和X射线衍射分析可知,石墨烯均匀分散于聚乙烯基体中,并且没有任何团聚现象发生.该复合材料的热重分析表明,仅加入非常少量的石墨烯就可以使其具有比纯聚乙烯更高的热稳定性,当石墨烯加入量为0.66 wt%时,其5 wt%热分解温度较纯聚乙烯升高了54°C.同时,所制备聚乙烯/石墨烯纳米复合材料具有更优异的机械性能.因此,本研究提供了一个简单高效的高性能聚烯烃/石墨烯纳米复合材料的制备方法.     

Propylene polymerization with catalysts containing divalent titanium

The behavior in propylene polymerization of divalent titanium compounds of type [η⁶-areneTiAl₂Cl₈], both as such and supported on activated MgCl₂, has been studied and compared to that of the simple catalyst MgCl₂/TiCl₄. Triethylaluminium was used as cocatalyst. The Ti–arene complexes were active both in the presence and in the absence of hydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. ¹³C-NMR analysis of low molecular weight polymer fractions indicated that the hydrogen activation effect observed for the MgCl₂-supported catalysts should be ascribed to reactivation of 2,1-inserted (“dormant”) sites via chain transfer, rather than to (re)generation of active trivalent Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indicating that for MgCl₂/TiCl₄ catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In ethylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activity during propylene polymerization may be due to the formation of clustered species that are too hindered for propylene but that allow ethylene polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2645–2652, 1997     

External Donor Induced Direct Contact Effects on Mg(OC2H5)2-Based Ziegler-Natta Catalysts for Propylene Polymerization

Effects of external donor induced direct contact without alkylaluminum were studied for Ziegler-Natta catalysts containing monoester and diester as internal donors on the catalytic performances such as activity and stereoselectivity. Traditional slurry polymerizations were carried out for rather short period after direct contact for a variety of time. GC analysis was also performed to observe replacement phenomena of donors during direct contact. It was postulated that the different performances of the catalysts were greatly affected by the pair of internal and external donors.     

甲基丙烯酸丁酯的Nd（Oct）3—Al（i—Bu）3配合催化聚合

甲基丙烯酸丁酯(BMA)在2-乙基己酸钕[Nd(Oct)_3]和三异丁基铝[Al(i-Bu)_3]配合催化下的聚合反应结果表明。以正己烷和石油醚为溶剂的聚合转化率高于甲苯和四氢呋喃体系。4种不同配体的钕盐的聚合转化率差别不大。但是,以Nd(Oet)_3-Al(i-Bu)_3为催化剂时聚甲基丙烯酸丁酯的分子量最高。聚合反应速度与单体浓度和催化剂浓度均成一次方关系。甲基丙烯酸丁酯的聚合反应活化能为47.40kJ/mol。     

New penta-ether as the internal donor in the MgCl2-supported Ziegler-Natta catalysts for propylene polymerization

The penta-ether compound was synthesized by the reaction of di(trimethylolpropane) with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl₂-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional Ziegler- Natta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl₂-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a penta-ether/Mg molar ratio equal to 0.21.     

Synthesizing UHMWPE Using Ziegler-Natta Catalyst System of MgCl2(ethoxide type)/ TiCl4/tri-isobutylaluminum

Summery: A Ziegler-Natta catalyst of MgCl₂ (ethoxide type)/TiCl₄ has been synthesized. In order to obtain ultra high molecular weight polyethylene (UHMWPE) tri-isobutylaluminum which is less active to chain transfer was used as cocatalyst. Slurry polymerization was carried out for the polymerization of ethylene while, dilute solution viscometry was performed for the viscosity average molecular weight (Mv) measurement. The effect of [Al]/[Ti] molar ratio, temperature, monomer pressure and polymerization time on the Mv and productivity of the catalyst have been investigated. The results showed increasing [Al]/[Ti] ratio in the range of 78–117, decreased the Mv of the obtained polymer from 7.8 × 10⁶ to 3.7 × 10⁶ however, further increase of the ratio, resulted in decreased of by much slower rate up to [Al]/[Ti] = 588. The higher pressure in the range of 1–7 bars showed the higher the Mv of the polymer obtained, while increasing temperature in the range of 50 to 90 °C decreased the Mv from 9.3 × 10⁶ to 3.7 × 10⁶. The Mv rapidly increase with polymerization time in the first 15 minutes of the reaction, this increase was slowly up to the end of the reaction (120 min). Increasing [Al]/[Ti] ratio raised productivity of the catalyst in the range studied. Rising reaction temperature from 50 to 75 °C increased the productivity of the catalyst however, further increase in the temperature up to the 90 °C decreased activity of the catalyst. Monomer pressure in the range 1 to 7 bars yields higher productivity of the catalyst. Also by varying polymerization conditions synthesizing of UHMWPE with Mv in the range of 3 × 10⁶ to 9 × 10⁶ was feasible.     

A study of polyethylene-gr-2-tert-butyl amino methacrylate-supported TiCl4 catalyst for ethylene polymerization

The use of a polyethylene-based copolymer with dual functional groups (polyethylene-gr-2-tert-butyl amino ethyl methacrylate) as the support for TiCl₄ catalyst in ethylene polymerization was studied. Different methods for treating the support were examined and treatment with BuMgCl was found to be the most effective. With the BuMgCl-modified support, a 12-run Plackett-Burman design was used to screen 11 factors in catalyst preparation. Statistical analysis of the results from this design identified significant factors with the amount of BuMgCl singled out to be the most important one for the four response variables of interest, Mg loading, Ti loading, catalyst activity per gram catalyst, and catalyst activity per gram Ti. © 1996 John Wiley & Sons, Inc.     

Stereospecific post-metallocene polymerization catalysts: the example of isospecific styrene polymerization

In the context of developing single-site stereoselective post-metallocene catalysts, the case for isospecific styrene polymerization catalysts based on methylaluminoxane-activated group 4 metal bis(phenolato) complexes is summarized. Ligands derived from the 1,4-dithiabutanediyl-linked bis(phenol)s have been found to induce stereochemical rigidity by the presence of the hemi-labile sulfide donor functions. Isospecific styrene polymerization was achieved using easily accessible catalyst precursors of the type [MX₂(OC₆H₂-^tBu₂-4,6)₂{S(CH₂)₂S}] (M = Ti, Zr, Hf; X = Cl, OⁱPr, CH₂Ph). Activating the dibenzyl titanium complex [Ti(CH₂Ph)₂(OC₆H₂-^tBu₂-4,6)₂{S(CH₂)₂S}] with B(C₆F₅)₃ and AlⁱBu₃, controlled isotactic polymerization became possible at lower temperatures. A remarkable dependence of both the activity and stereoselectivity on the ligand substitution pattern was observed. Analogous precursors with the 1,5-dithiapentanediyl-linked bis(phenolato) ligand gave syndiotactic polystyrene with lower activity.     

Modeling and Simulation of Liquid Phase Propylene Polymerizations in Industrial Loop Reactors

Liquid phase tubular loop polymerization reactors are widely used in the polyolefin industries because of their capabilities to promote high mixing of reactants in the reaction vessel and to allow for high heat transfer rates with the cooling jacket due to their high aspect ratio. Previous works on this subject focused on the modeling of the polymerization system, but only a few compared their results with real industrial data. A literature review about the propylene production in loop reactors shows that the validation of a distributed model with actual industrial data is yet to be presented. A distributed mathematical model is presented for industrial liquid phase loop polypropylene reactors and validated with actual industrial data for the first time. The model is able to represent the dynamic trajectories of production rates, MFI and XS values during grade transitions within the experimental accuracy. The model indicates that the polymer quality can change significantly along the reactor train and that manipulation of feed flow rates can be successfully used for production of more homogeneous polymer products.     

A kinetic approach to homogeneous Ziegler type polymerization. Steady state

In this paper we present a kinetic approach to the analysis of steady-state homogeneous Ziegler-Natta polymerization activity data. The influence of the number of monomeric species that are coordinated to the active site on the apparent rate law is discussed and the equations are fitted to the experimental results.     

A kinetic approach to homogeneous Ziegler type polymerization. Transient state

In this paper we present a kinetic approach to the analysis of transient-state homogenous Ziegler-Natta polymerization activity data. The main features of the experimental data are discussed and fitted to transient kinetic models.     

烯烃高效催化剂及聚合与共聚合的研究

为中山大学高分子研究所烯烃配位聚合研究室在高效Ziegler-Natta催化剂、茂金属催化剂烯烃聚合与共聚合方面部分研究工作的概述。重点叙述了催化剂的设计、过渡金属配合物配体结构及聚合条件对乙烯、丙烯、1-丁烯、丁二烯、苯乙烯等烯烃单体聚合及共聚合活性以及聚合产物结构和分子量的影响。     

Polymerization of 4-phenyl-1-butyne catalyzed by metathesis and Ziegler–Natta catalysts

The polymerization of 4-phenyl-1-butyne was carried out using metathesis and Ziegler-Natta catalysts. Especially, the Fe(acac)₃-AlEt₃ catalyst with toluene as a solvent produced an extremely high molecular weight polymer of M_w ≈ 10⁶. Solubility of the polymers at room temperature in organic solvents such as benzene, toluene, dichloromethane, chloroform, and THF was excellent despite their high molecular weights. It has been indicated that the polymer prepared by the Fe(acac)₃-AlEt₃ catalyst is of cis form with a high stereoregularity. © 1993 John Wiley & Sons, Inc.