桥联稀土异双核Mt-Sm(Mt=Zr,Ti)茂金属配合物催化乙烯聚合研究

在合成新型的碳桥联前过渡金属-稀土异核茂金属化合物[(C5H5)MtCl2][(C5H4)CMe2(C9H6)][(C5H5)SmCl][Mt=Zr(5),Ti(7)]之后,经甲基铝氧烷活化催化乙烯聚合,考察了催化剂浓度、[Al]/[Cat]、温度、聚合时间对聚合反应的影响.与相应的单核茂金属相比,发现Ti-Sm体系(7)的催化活性升高,而Zr-Sm体系(5)的活性有所下降;然而,随着时间的延长,前者所得的聚乙烯分子质量逐步下降,而后者所得的聚乙烯分子质量逐步上升.TiSm体系(7)与Zr-Sm体系(5)不同的催化性能也许与Sm和不同的前过渡金属间的组合有关.所得聚乙烯的GPC分析呈双峰,相对分子质量分布较宽(＞3.00).     

Polyethylene nanocomposites by gas‐phase polymerization of ethylene in the presence of a nanosilica‐supported zirconocene catalyst system

BACKGROUND: Much of the current research related to the development of in situ nanocomposites of olefins by polymerizing them with metallocenes in the presence of surface‐treated fillers is carried out in the slurry phase. In slurry‐phase methods a large amount of solvent is required and there is always a need of purification of the final product due to the possibility of traces of solvents present in the product. To overcome these drawbacks, to perform solvent‐free metallocene‐catalysed polymerizations with in situ incorporation of inorganic nanoparticles, we have used a gas‐phase polymerization technique as this does not require solvents and also utilizes monomer feed stocks efficiently. RESULTS: The catalyst used for the synthesis of in situ polyethylene nanocomposites by gas‐phase polymerization was nanosilica‐supported zirconocene. The fillers used were Cloisite‐20A, kaolin and nanosilica. Three different in situ polyethylene nanocomposites, i.e. Cloisite‐20A‐filled polyethylene (CFPE), kaolin‐filled polyethylene (KFPE) and nanosilica‐filled polyethylene (SFPE), were prepared by gas‐phase polymerization. The nanocomposites were obtained in the form of fine powder. The polyethylene content in the developed nanocomposites is in the orthorhombic crystalline phase. Using our approach, it is observed that the nanofillers are completely encapsulated by a thin layer of polyethylene. Significantly higher molecular weight polyethylene was formed in the case of KFPE in comparison to CFPE and SFPE. The thermal decomposition temperature, melting temperature and enthalpy are also observed to be higher for KFPE. CONCLUSIONS: The gas‐phase polymerization technique has been successfully carried out for the synthesis of in situ polyethylene nanocomposites. Copyright © 2007 Society of Chemical Industry     

茂金属化合物[(C_(13)H_8)Si(CH_3)_2(C_5H_4)]ZrCl_2的制备及其乙烯、丙烯共聚的催化研究

实验以芴基锂、二氯二甲基硅烷和环戊二烯基钠为原料,在四氢呋喃溶剂中合成了茂锆催化剂[(C_(13)H_8)Si(CH_3)_2(C_5H_5)]ZrCl_2,总收率51%。经核磁共振氢谱和碳谱分析,确定了化合物的结构。经甲基铝氧烷活化,该化合物催化乙烯、丙烯共聚反应显示出较高的催化活性,其催化活性(每1 mol Zr)常压下可以达到10~3g/h,聚合物的相对分子质量约1.0×10~4。     

Polymerization of ethylene by zirconocene—B(C6F5)3catalysts with aluminum compounds

Ethylene polymerization by zirconocene—B(C₆F₅)₃ catalysts with various aluminum compounds has been investigated. It is found that the catalytic activity depended on zirconocenes used, and especially on the type of aluminum compounds. For Et(H₄Ind)₂ZrCl₂ (H₄Ind: tetrahydroindenyl), the activity decreases in the following order: Me₃Al > i-Bu₃Al > Et₃Al ≫ Et₂AlCl. While for Cp₂ZrCl₂(Cp : cyclopentadienyl), it varies as follows: i-Bu₃Al > Me₃Al ≫ Et₃Al. Furthermore, the activity is significantly affected by the addition mode of the catalytic components, which may imply that the formation of active centers is associated with an existing concentration of catalytic components. Results of thermal behavior of polyethylene (PE) studied by differential scanning calorimetry (DSC) show that crystallinity of the polymer prepared with Et₃Al is higher than that with Me₃Al or i-Bu₃Al. It is also found that the number-average molecular weight (M ) of the polymers prepared with Me₃Al or i-Bu₃Al is much higher than that with Et₃Al. ¹H-NMR studies substantiate that i-Bu₃Al is a more efficient alkylation agent of Cp₂ZrCl₂ in comparison with Me₃Al. © 1997 John Wiley & Sons, Inc. JAppl Polym Sci 66: 1715–1720, 1997     

Supported SiO2‐nBuSnCl3/MAO/(nBuCp)2ZrCl2 catalyzing MAO cocatalyst‐free ethylene polymerization: Study of hydrogen responsiveness

A supported metallocene catalyst was synthesized by sequentially loading methylaluminoxane (MAO) (30 wt % in toluene) and (ⁿBuCp)₂ZrCl₂ on partially dehydroxylated silica ES 70 modified by ⁿBuSnCl₃. Its shock load hydrogen responsiveness was evaluated by polymerizing ethylene for 1 h at 8.5 bar (g) and 75°C without separately feeding the MAO cocatalyst. The shock load hydrogen feeding increased the ethylene consumption (at a fairly constant rate), catalyst productivity, as well as the resin bulk density and average particle size at ΔP (of hydrogen) ≥～3.0 psi. The bulk density increased from 0.25 to 0.31 g/cm³. This shows a procedure for overcoming the inherent drop in catalyst productivity caused by heterogenization of metallocenes (that is a method for catalyst activation) and improving the resulting resin bulk density. The volume‐weighted mean particle diameter of the resulting polyethylenes was found to be 5.80–11.12‐fold that of the catalyst corresponding to ΔP = 0.00–7.11 psi, respectively. The resulting kinetic profiles showed to be fairly stable. However, M_w and polydispersity index were not affected. The particle size distribution, average particle size, and the scanning electron microscope photographs of the resulting resin particles confirmed the occurrence of the replication phenomenon. On the basis of the above findings, the mechanism of ethylene polymerization under the present experimental conditions has been revisited. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Supported metallocene polymerization catalysis

Zirconocene supported on alumina or magnesium chloride exhibits modest olefin polymerization activity but not when it is supported directly on silica. The surface silanol as well as siloxane groups must be passivated with appropriate reagents. A very active and stereospecific supported catalyst was obtained by first reacting silica with methylalumoxane and bisphenol A before the impregnation of the ansa-zirconocene precursor. The main difference between a homogeneous and supported catalyst is that at the same gross amount of metallocene, the net concentration of it in the pores of a support material is several orders of magnitude greater than it exists in solution thus the rate of deactivation in the former case is correspondingly faster than in the latter. Most other supported metallocene catalysts based on supports such as zeolites, cyclodextrin, polymeric MAO, synthetic polymers, etc., are poor in olefin polymerization for this and other reasons discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Chain transfer reactions in propylene polymerization with zirconocene catalysts

The chemical structures of end groups of medium-low molecular weight atactic and isotactic polypropylenes (a-PP and i-PP), produced with zirconocene/methylalumoxane catalysts, have been analyzed and used to infer the chain-transfer reaction mechanisms, which are then correlated with the zirconocene ligand structure and the polymerization conditions. For the chiral, isospecific ansa-zirconocenes such as rac-[ethylenebis(1-indenyl)]ZrCl₂/methylalumoxane (1/MAO) and rac-[ethylenebis(4,7-dimethyl-1-indenyl)]ZrCl₂/methylalumoxane (2/MAO) catalysts, i-PP molecular weight is dependent on the regiospecificity of the catalyst, as shown by the presence of cis-2-butenyl end groups, formed by chain transfer to the monomer after a secondary propylene insertion. At low monomer concentration, chain-transfer with 2/MAO shifts from predominant transfer to the monomer after a secondary propylene insertion to β-methyl (allyl end groups) and β-hydrogen transfers after a primary insertion (2-propenyl, or vinylidene, end group). Ansa-bis(3-R-indenyl)ZrCl₂ (ansa = CH₂CH₂, Me₂Si, Me₂C; R = Me, t-Bu, Me₃Si) catalysts, which are highly regiospecific, produce polypropylenes with chain transfer via both β-hydrogen transfer after a primary insertion and β-methyl transfer. For example, rac-Me₂C(3-t-Bu-Ind)₂ZrCl₂ (4) exhibits the highest selectivity for β-methyl transfer so far observed in an isospecific zirconocene. As for 2/MAO, the rate of β-methyl transfer in 4/MAO increases by lowering [propylene]. This revised version was published online in June 2006 with corrections to the Cover Date.     

Polymerization characteristics of in situ supported pentamethylene bridged dinuclear zirconocene

An in situ supporting method was applied to newly synthesized [(CH₂)₅(C₅H₄)₂][(C₉H₇)ZrCl₂]₂ catalyst and other commercial catalysts, and its effects on the polymerization characteristics of these catalysts were examined through reaction experiments. The changes in the molecular weight distribution varied depending on the metallocene catalyst while the changes in the catalytic activity, average molecular weight and the melting point showed the same trend. The reason for the decrease in the molecular weight with in situ supporting was discussed in relation to the co-catalysts. The polymerization characteristics of each catalyst also varied according to the alkyl aluminum, and so it is important to select a proper co-catalyst or a combination of co-catalysts to obtain a desired polymer product from each metallocene catalyst supported by in situ method.     

Preparation of branched polyethene using a soluble zirconocene catalyst

[Me₂C(Cp) (Ind)]ZrCl₂ metallocene catalyst has been prepared and employed in a study of ethene polymerization in the presence of the cocatalyst methylaluminoxane. C₁ and C₂ signals are detected in the ¹³C NMR spectra of the resultant polymers; this reveals that the resultant polymer is a branched polyethene (polyethylene). The influence of polymerization temperature, catalyst concentration and [Al]/[Zr] ratio on catalytic activities and polymerization kinetics is investigated. A plausible mechanism for forming branched polyethene is suggested. © 2000 Society of Chemical Industry     

Residual metal content in Ethylene‐Propylene‐Diene Monomers synthesized using vanadium‐ and zirconocene‐based catalysts

Ethylene‐propylene‐diene monomer (EPDM) terpolymers were prepared using either vanadium (VOCl₃/Al₂Et₃Cl₃) or zirconocene (Et(Ind)₂ZrCl₂/MAO) catalyst systems. Residual metal contents in EPDM films were determined by Rutherford backscattering spectrometry. Metallocene catalyst systems exhibited a higher activity, producing EPDM with lower molecular weight and narrower molecular weight distribution. The highest activity guaranteed lower residual metal content (Zr/C = 10⁻⁵) than in the case of EPDM produced by VOCl₃/Al₂Et₃Cl₃ (V/C = 10⁻⁴). Subsequent steps of dissolution of the polymer and its reprecipitation were seen to reduce the metal contents in both metal systems. Concerning the cocatalyst retention, despite initial use of a very high amount of methylaluminoxane/metallocene (Al/Zr = 3000) in the reactor, only about 4% of this initial concentration remained in the polymer. On the other hand, in the case of vanadium‐based catalyst, almost all Al present in the initial conditions (≃8.3) remained in the polymer. In both cases, the residual Al/M ratio was close to the value generally proposed for the generation/stabilization of the active species. In the case of vanadium systems, a test in the synthesis of ethylene propylene rubbers indicated that the absence of diene in the polymer structure leads to a reduction in the residual vanadium content, indicating that the diene double bond might be responsible for partially vanadium coordination. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1997–2003, 1999