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 Tp (temperature of polymerization). The PP&s are characterized by low melting temperature (Tm), 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 Tp. 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 (kp) and stereoselectivity and another with low kp 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 kp/ktrA, 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. 相似文献
The solution polymerization of ethylene in Isopar E in a semi-batch reactor using combined CGC-Ti and Et[Ind]2ZrCl2 catalysts was studied. Methylaluminoxane (MAO) and tris(pentafluorophenyl)borane were used as co-catalysts. Samples were analyzed by 13C NMR and gel permeation chromatography (GPC) for their branching content and molecular weight distribution. It was shown that there was an optimum ratio of CGC-Ti/Et[Ind]2ZrCl2 that maximizes the number of long-chain branches of the formed polyethylene. 相似文献
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. 相似文献
The copolymerization of ethylene and 5-ethylidene-2-norbornene (ENB) catalyzed by metallocene catalysts system is reported in this paper. The catalysts include Et(Ind)2 ZrCl2/MAO and Cp2ZrCl2/MAO. The resulting copolymer contains an ethylidene group which can be readily converted to a hydroxyl group by hydrogen borane. Then the hydroxyl group in turn can be utilized for grafting with ?-caprolactone. The dependence of the graft weight percentage on the reaction time was also studied. The graft copolymer is a compatibilizer for various polyethylene blends with engineering plastics. A functional polyethylene can be easily synthesized by the copolymerization of ethylene and 9-decen-l-ol using a homogeneous catalytic system of El(Ind)2ZrCl2/MAO. The resulting functional polyethylene was characterized by NMR, DSC, IR and TGA; and can also be utilized for grafting with ?-caprolactone. The grafted copolymer is also an effective compatibilizer. 相似文献
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. 相似文献
We investigated the ethylene copolymerization by utilizing Me2Si(Ind)2ZrCl2/MAO and Me2Si(Ind)2ZrCl2/MAO/SiO2 with 10-undecene-1-oxytrimethylsilane and 10-undecene-1-oxytriisopropylsilane and the ethylene copolymerization by using iPr(CpInd)ZrCl2/MAO and iPr(CpInd)ZrCl2/MAO/SiO2 with 5-norbornene-2-methyleneoxytrimethylsilane and 5-norbornene-2-methyleneoxytriisopropylsilane. The trimethylsilyl (TMS) protecting group could not prevent the catalyst deactivation caused by the addition of the polar comonomer. In contrast to that, good catalyst activities and comonomer contents were obtained with the triisopropylsilyl (TIPS) protected monomer. The homopolymerization of 10-undecene-1-OTIPS was carried out with Me2Si(Ind)2ZrCl2/MAO. 相似文献
Silica supported (butylcyclopentadienyl)2ZrCl2/MAO catalysts were synthesized according to the “incipient wetness” method from a solution of metallocene in a liquid monomer. The monomer was allowed to polymerize yielding a catalyst containing polyhexene (PH), polystyrene (PS) or polyoctadiene (PO). One catalyst containing no polymer was also synthesized. The catalysts were used to polymerize ethene at 70°C and 4 bar total pressure. The measured average activities were 5 300 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PH/SiO2, 8 600 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PS/SiO2, 3 400 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PO/SiO2 and 5 700 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/SiO2. The polyhexene, polystyrene or polyoctadiene in the catalyst forms a protective layer around the active sites. Even after exposure to air for five hours these catalysts retain some polymerization activity. 相似文献
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. 相似文献
A series of metallocenes, namely [Cp2ZrCl2], [(MeCp)2ZrCl2], [(nBuCp)2ZrCl2], [(iBuCp)2ZrCl2], [(tBuCp)2ZrCl2], [Cp2TiCl2], [Et(Ind)2ZrCl2], [Et(IndH4)2ZrCl2] and [MeSi2(Ind)2ZrCl2)], were combined in a 1:1 molar ratio within a reactor for ethylene polymerization, with MAO as the cocatalyst. The catalysts were characterized by cyclic and differential pulse voltammetry. The combined systems that showed the highest and lowest activities were combined in 1:3 and 3:1 molar ratios. The catalyst activity in the ethylene polymerization reaction is discussed in terms of the estimated consumption rate, decomposition rate constant and half‐life of the metallocene species formed with MAO in an ethylene atmosphere.
Inorganic siliceous porous materials such as MFI type zeolite, mesoporous silica MCM‐41 and silica gel with different average pore diameters were applied to the adsorptive separation of methylaluminoxane (MAO) used as a cocatalyst in α‐olefin polymerizations. The separated MAOs combined with rac‐ethylene‐(bisindenyl)zirconium dichloride (rac‐Et(Ind)2ZrCl2) were introduced to propylene polymerization, and their influences on the polymerization activity and stereoregularity of the resulting polymers were investigated. The polymerization activity and isotactic [mmmm] pentad of the produced propylene were markedly dependent upon the pore size of the porous material used for adsorptive separation. From the results obtained from solvent extraction of the produced polymers, it was suggested that there are at least two kinds of active species with different stereospecificity in the rac‐Et(Ind)2ZrCl2/MAO catalyst system. 相似文献
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. 相似文献
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. 相似文献
The copolymerization of propene and norbornene with the isospecific metallocene catalyst dimethylsilylenebis(η5-inden-1-yl)zirconium dichloride/methylaluminoxane ((CH3)2Si[Ind]2ZrCl2/MAO) was investigated. Because of the surprisingly high reactivity of the cyclic olefin copolymers with a norbornene content of 11 mol-% up to 98 mol-% were synthesized. The resulting copolymers are amorphous. The glass transition temperatures studied by differential scanning calorimetry measurements increase with rising norbornene content in the copolymer. High glass transition temperatures of Tg > 240°C were found for the copolymers with the highest content of norbornene. 相似文献