Hydrogen transfer reactions of supported metallocene catalysts

The evolution of methane from methylaluminoxane (MAO) solutions is enhanced in the presence of homogeneous metallocenes. This reaction serves as a model for the deactivation of metallocene catalysts. By supporting different metallocenes on a silica/MAO carrier the deactivation reaction by alpha-hydrogen transfer among metallocene active sites and aluminum alkyls can be suppressed. The suppression of alpha-hydrogen transfer is proven for different Al/Zr ratios and by near independence of the polymerization activity on the catalyst aging time, after reaching maximum activity. Aluminum alkyls and MAO leach Cp₂ZrCl₂ from the carrier, the leached metallocene is only active in polymerization if MAO is present.     

Catalytic activity during copolymerization of ethylene and 1-hexene via mixed TiO2/SiO2-supported MAO with rac-Et[Ind]2ZrCl2 metallocene catalyst

Activities during ethylene/1-hexene copolymerization were found to increase using the mixed titania/silica-supported MAO with rac-Et[Ind]2ZrCl2 metallocene catalyst. Energy Dispersive X-ray spectorcopy (EDX) indicated that the titania was apparently located on the outer surface of silica and acted as a spacer to anchor MAO to the silica surface. IR spectra revealed the Si-O-Ti stretching at 980 cm(-1) with low content of titania. The presence of anchored titania resulted in less steric hindrance and less interaction due to supporting effect.     

Synthesis and characterization of new organometallic complexes bonded stationary phases for high-performance liquid chromatography

Summary The preparation, characterization and potential liquid chromatographic applications of various organometallic iron complexes silica stationary phases are presented. These new supports are synthesized by covalently linking ferrocene, as well as some of its cationic derivatives, to appropriately derivatized silica support matrices. These columns exhibit moderate to high selectivity towards the separation of polycyclic aromatic hydrocarbons (PAHs). A charge transfer retention mechanism has been proposed. A comparison with a reference stationary phase, 3,5-dinitrobenzamide (DNB), to quantify the acceptor power of the new stationary bonded phases, is also reported. Finally, the effect of varying the derivatives of the bonded metallocene on PAHs retention is discussed.     

Mechanistic aspects of the olefin polymerization with metallocene catalysts

With C₁-, C₂- or C_s-symmetric metallocenes, different intermediates and types of copolymers can be obtained from randomly distributed to alternating structures. Substitution of the Cp-ring in [Me₂C-(tert-Bu Cp)(Flu)]ZrCl₂ yields ethene/norbornene copolymers with an alternating structure, because the rigid norbornene can only be inserted from the open side of the metallocene. By variation of the polymerization parameters, copolymers with glass transition temperatures above 180°C and molecular weights > 100 000 are synthesized. By supporting different metallocenes on a silica/methylaluminoxane (MAO) carrier the deactivation reaction under electron and hydrogen transfer can be suppressed. This is proved for different Al/Zr ratios when trimethylaluminum (TMA) is used as cocatalyst by the lack of methane evolution by metallocenes and by near independence of the polymerization activity on the prereaction time, after reaching maximum activity. Aluminumalkyls and MAO leach Cp₂ZrCl₂ from the carrier, the leached metallocene is only active in polymerization by adding MAO.     

茂金属催化剂负载对丙烯间规聚合的影响

茂金属催化剂具有活性高、定向性好的特点 .采用茂金属催化剂 ,Ｅｗｅｎ[1] 首次在常温、常压下实现了丙烯的间规聚合 ,得到了高间规度 (ｒｒｒｒ >80 % )的间规聚丙烯 (ｓＰＰ) .ｓＰＰ因其透明性好、耐冲击及耐辐射 ,室温韧性、热密封性及透气性好等特性 ,作为共混材料 ,在医疗产品、包装、纤维、薄膜和汽车配件等方面显示了广阔的应用前景 .国内外许多公司都投入大量人力、物力进行研究 .其中 ,Ｆｉｎａ公司处于技术领先地位 .Ｆｉｎａ公司继 1 987年开发出间规选择性茂金属催化剂后 ,成功地进行了中试聚合实验 ,得到了商用ｓＰＰ .1 994…     

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.     

Influence of Silica Support Size on the Polymerisation of Ethylene Using a Supported Metallocene Catalyst

In the current work, we will focus on the influence of support properties on the activity and molecular weights of polyethylene produced with a metallocene supported on silica treated with MAO. It is demonstrated that relatively small changes in the size of the silica particles have a profound effect on the activity of the growing particles, and that not all particles in a given batch of catalyst behave in the same manner.     

Synthesis of Modified Methylaluminoxane

Methylaluminoxane (MAO) is one of the most important cocatalysts of metallocene catalysts. The yield and activity of MAO is low when using Al2(SO4)3 nH2O and other inorganic hydrates to synthesize methylaluminoxane. The repeatability of this reaction is not good. The product cost is very high because one of the raw materials (Trimethylaluminium, TMA) to prepare MAO is very expensive. In addition, on standing, MAO toluene solution tends to gel. Gelled MAO can not be used to prepare su…     

Self-immobilizing catalysts and cocatalysts for olefin polymerization

Homogeneous catalysts for olefin polymerization such as metallocene or half-sandwich complexes containing the metals titanium, zirconium and hafnium, or other transition-metal coordination complexes can be functionalized with alkenyl groups and have then the potential to copolymerize with olefins to give heterogeneous catalysts. In a similar manner metallacyclic metallocene complexes with a metal-carbon sigma bond allow the catalytic insertion of olefins into this bond and produce heterogeneous catalysts. It is also possible to functionalize the active species of the cocatalyst methylalumoxane (MAO) and use it for self-immobilization processes. The high excess of MAO that is necessary in homogeneous solution can be reduced by more than 90% with this method.     

Ethylene polymerization and copolymerization with hexene-1 on supported metallocene catalysts based on (C<Subscript>5</Subscript>H<Subscript>5</Subscript>)<Subscript>4</Subscript>Zr and methylaluminoxane

New supported metallocene catalysts based on tetrakis(cyclopentadienyl)zirconium + methylaluminoxane (MAO) were prepared and tested for ethylene polymerization and copolymerization with hexene-1. It was shown that silica gel of the Davison 952 brand is the best support for such catalysts. The maximum catalyst activity was achieved on the support impregnated with the (C₅H₅)₄Zr-MAO complex. The addition of hexene-1 into the liquid phase resulted in acceleration of polymerization and an increase in the product yield. The morphological, rheological, and other properties of polymers and copolymers were studied. The test catalytic system can be used for manufacture of low-, medium-, and high-density polyethylenes with various stress-strain characteristics.     

C1桥联的茂金属化合物(Cp)CR1R2(Flu)MCl2的合成及其催化烯烃聚合活性

合成了6种单碳桥联的含芴(Flu)茂(Cp)基B族茂金属催化剂,研究了它们催化烯烃聚合的能力.通过IR,¹HNMR,EI-MS和元素分析对化合物进行了表征.用所合成的茂金属化合物与MAO所组成的催化体系对乙烯、丙烯的聚合进行了研究.其中金属为Ti的催化剂没有聚合活性或活性极低.金属为Zr的催化剂有一定的催化活性,用不同的催化剂得到的聚合物性质有一定的差异.     

A novel zirconocene/ultradispersed diamond black powder supported catalytic system for ethylene polymerization

A novel carrier of ultradispersed diamond black powder (UDDBP) was used to support metallocene catalyst. Al₂O₃ was also used as carrier in order to compare with UDDBP. Supported catalysts for ethylene polymerization were synthesized by two different reaction methods. One way was direct immobilization of the metallocene on the support, the other was adsorption of MAO onto the support followed by addition of the metallocene. Four supported catalysts Cp₂ZrCl₂/UDDBP, Cp₂ZrCl₂/Al₂O₃, Cp₂ZrCl₂/MAO/UDDBP and Cp₂ZrCl₂/Al₂O₃/MAO were obtained. The content of the zirconium in the supported catalyst was determined by UV spectroscopy. The activity of the ethylene polymerization catalyzed by supported catalyst was investigated. The influence of Al/Zr molar ratio and polymerization temperature on the activity was discussed. The polymerization rate was also observed.     

Electron transfer mechanism in olefin polymerization

Polymerization of olefins mediated by transition metal derivatives (Ziegler–Natta polymerization) is one of the most scientifically and industrially important processes of molecular conversion. Electron transfer mechanism could play a significant role in both heterogeneous and homogeneous catalysts. The catalytic activity strongly depends on the presence of two metallocene ligands attached to the transition metal (more commonly zirconium) which grants the valence form of zirconium in complexes of the type Cp₂ZrX₂(X=Cl or CH₃) followed by the formation of the (Cp₂ZrX)⁺ cation under the effect of a Lewis acid. On the other hand, Ti complexes with only one metallocene ligand give the syndiospecific polymerization of styrene, where the phenyl group appears to act as electron donor for the transition metal. The remarkable electronic effect of the metallocene groups in determining catalytic activity is demonstrated by the study of substituted metallocene ligands as well as other ligands around the metal. These effects cannot be, however, completely separated from steric effects which seem to be responsible for the impressive and versatile stereochemical control determined by symmetry properties of the transition metal complex.     

Heterogenization of racemic ethylenebis(1-indenyl)zirconium dichloride on trimethylaluminum vapor modified silica surface

Heterogeneous metallocene catalysts were prepared by adsorbing rac-Et(Ind)₂ZrCl₂ on a modified silica surface in solution. The modification of silica was conducted in gas phase with atomic layer chemical vapor deposition (ALCVD) technique, where the silica, preheated at either 350 or 600°C, was allowed to react with vaporized trimethylaluminum (TMA) at 250°C. Modified carriers and heterogeneous catalysts were characterized with FTIR, ¹H MAS (magic-angle spinning) NMR, ¹³C, and ²⁹Si CP (cross-polarization) MAS NMR spectroscopies and elemental analyses. In the reaction of TMA with silica, a saturated surface was formed consisting of different (---O)_4−nSi(CH₃)_n (n=1, 2 or 3) and ---AlCH₃ groups. The ratio of ---SiMe to ---AlMe groups was approximately 1.5 in the TMA/SiO₂ carriers. When the metallocene was adsorbed onto the carrier it seemed to react with the surface ---AlCH₃ groups and possibly ---ZrCH₃ groups were formed. Heterogeneous catalysts were tested in the polymerization of ethylene and propylene in the presence of methylalumoxane (MAO). And they produced similar polymer as the homogeneous rac-Et(Ind)₂ZrCl₂ catalyst, but with lower activity. A catalyst with the best activity was achieved from silica that was preheated at 600°C. Moreover, leaching of catalyst was examined whereupon a part of zirconium was observed to desorb from the carrier.     

Polymerization of styrene with supported half-sandwich complexes

Polymerizations of styrene were carried out with half-sandwich complexes supported on silica, CpTiX₃/MAO/SiO₂ (X = Cl, F). The optimum values for the polymerization time, the amount of cocatalyst and the Al_support/Ti ratio were found for the trichlorinated system. The highest activity obtained was 3,100 g sPS/(mol Ti × h × mol/L styrene). The trihalogenated complexes were compared to one another with respect to their polymerization rate. CpTiCl₃/MAO/SiO₂ and CpTiF₃/MAO/SiO₂ behave in a similar manner, suggesting that the active species of both half-sandwich complexes on the support are the same. Furthermore, aging experiments were carried out with CpTiCl₃/MAO/SiO₂ and, surprisingly, deactivation was observed, as opposed to supported zirconocenes which gain stability against deactivation reactions when anchored to a carrier. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2959–2968, 1999     

Advances in late transition metal catalysts for olefin polymerization/oligomerizarion

In this review article, we have consolidated our recent studies on late transition metal catalysts (mainly Fe, Co) for olefin polymerization/oligomerization. A series of bisiminopyridyl Co(II) and Fe(II) complexes were synthesized. These catalysts when activated with MAO in aromatic or aliphatic hydrocarbon solvents, oligomerize or polymerize ethylene to α-olefins or high molecular weight polymers with exceptionally high activities and selectivities. The electronic and steric effects of allyloxy and benzyloxy substituted bisiminopyridyl Fe(II) and Co(II) complexes were also investigated. The influence of catalyst structure and temperature on the polymerization activity, thermal properties and molecular weight were discussed. The effects of heterogenization of these catalysts on silica and modified SBA-15 were analyzed. The polymerization of polar monomers such as vinyl ethers and methyl methacrylate was tested and no specific trends in activity and polymer molecular weight with changes in steric bulkiness around the metal center were observed with the same catalyst system.     

Alkylidenverbrückte dissymmetrische zweikernige Metallocenkomplexe als Katalysatoren für die Ethylenpolymerisation

The synthesis is described of dissymmetric alkylidene bridged dinuclear metallocene complexes of titanium, zirconium and hafnium and some of the corresponding mononuclear reference complexes. The influence of structural parameters on the polymerization behaviour of the MAO activated complexes is systematically investigated for homogeneous ethylene polymerization. The dinuclear catalysts show higher polymerization activities than a mixture consisting of analogous mononuclear reference catalysts. The polyethylenes obtained from dinuclear complexes have higher polydispersities than those that were produced with mononuclear complexes.     

The combination of mononuclear metallocene and phenoxyimine complexes to give trinuclear catalysts for the polymerization of ethylene

Trinuclear complexes were synthesized by combination of metallocene and phenoxyimine zirconium complexes. After activation with methylalumoxane (MAO), these catalysts polymerize ethylene with moderate and good activities. Due to the presence of different catalytic centers, polyethylenes with broad or bimodal molecular weight distributions were obtained.     

有机-无机复合载体茂锆催化剂的制备及乙烯聚合

合成了组成为聚(4-乙烯基吡啶)-硅胶(SAV)的有机-无机复合载体茂锆催化剂,并用固体13C-NMR谱、元素分析(EA)、光电子能谱(XPS)等方法进行了表征.发现由SAV负载的茂锆催化剂可在相对较低的甲基铝氧烷(Al/Zr=600)用量下聚合乙烯.其活性(1.12×103kg PE/mol Zr.h)远高于SiO2负载的茂锆催化剂(0.22×103kg PE/mol Zr.h).     

SYNTHESIS OF NOVEL THIOPHENEDIMETHYLENE BRIDGED HOMOBINUCLEAR METALLOCENES AND THEIR CATALYTIC PROPERTIES FOR ETHYLENE POLYMERIZATION

By treating disodium(thiophenedirnethylene)dicyclopentadienide C_4H_2S(CH_2C_5H_4Na)_2 with two equivalent of CpTiCl_3 or CpZrCl_3 DME at 0℃ in THF,two new thiophenedimethylene bridged binuclear metallocenes [Cl_2MC_5H_5][C_5H_4CH_2C_4H_2SCH_2C_5H_4][C_5H_5MCl_2](M=Ti 3,M=Zr 4)were synthesized in high yield and their structures were characterized by ~1H-NMR.These complexes were used as catalysts for ethylene polymerization in the presence of methylaluminoxane(MAO).The effects of polymerization temperature,time,concentration of catalyst,molar ratio of MAO/Cat on polymerization were studied in detail.The catalytic activities of thiophenedimethylene bridged binuclear metallocene catalysts(3,4)reached 2.44×10~5 g PE mol~(-1)·cat~(-1)·h~(-1),9.61×10~5 g PE mol~(-1)·cat~(-1)·h~(-1) respectively,which are higher than that of pheneyldimethylene bridged binuclear metallocene catalysts and much higher than that of corresponding mononuclear metallocenes(Cp_2TiCl_2 and Cp_2ZrCl_2).The molecular weight distribution curves of polyethylenes produced by binuclear metallocene catalysts(3,4)and by mononuclear metallocene catalyst have only single peak,but the former(MWD=3.5-4.7)is obviously broader than the latter(MWD=2.0-2.2).