The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization简

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.     

Propene homo- and copolymerization using homogeneous and supported metallocene catalysts based on Me2Si(2-Me-Benz[e]lnd)2ZrCl2

The isoselective propene polymerization using the supported catalyst SiO₂/MAO/Me₂Si(2-Me-Benz[e]Ind)₂ZrCl₂/AlR₃ was investigated and compared with propene polymerization using the corresponding homogeneous catalyst system. The influence of propene concentration, polymerization medium, temperature, comonomer, and external aluminium alkyls on polymerization kinetics and polypropene properties such as molecular mass, stereo- and regioselectivity, morphology, and bulk density was studied. © 1997 John Wiley & Sons, Inc.     

Functionalization of polyethylene with silane comonomers

We synthesized a new weakly interacting monomer with a reactive phenylsilane group that is an intermediate for many functional groups. The synthesis was performed in two steps: the hydrosilylation of 1,7‐octadiene with dimethylchlorosilane and a Grignard reaction with phenyl magnesium bromide. The new monomer, 7‐octenyldimethylphenylsilane, was isolated and copolymerized with ethylene via metallocene catalysts (Me₂Si(Me‐2‐Ind)₂ZrCl₂ and Et(Ind)₂ZrCl₂) and methylaluminoxane (MAO) as a cocatalyst. Electropositive silicon had no negative effect on the copolymerization reaction. The polymerization activity increased, and the molar mass of the product remained at a high level. The comonomer incorporation reached a significant 11.8 wt % (2.6 mol %). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1303–1308, 2002     

SYNTHESIS AND PROPERTIES OF HOMOPOLYMER AND COPOLYMERS OBTAINED FROM 1-OCTADECENE WITH ZIRCONOCENE CATALYSTS

Studies related to the behavior of different metallocene catalysts for the homopolymerization of 1-octadecene andits copolymerization with ethylene will be presented. The metallocenes: rac-Et(Ind)_2ZrCl_2, rac-Me_2Si(Ind)_2ZrCl_2 andPh_2C(Flu)(Cp)ZrCl_2 were chosen for the homopolymerization study. They show important differences in catalytic activity athigh temperatures (≥70℃), with rac-Et(Ind)_2ZrCl_2 showing the highest activity. At lower temperatures (≤30℃) thedifferences are negligible. For the copolymerization of ethylene with 1-octadecene only the catalysts rac-Et(Ind)_2ZrCl_2 andrac-Me_2Si(Ind)_2ZrCl_2 were studied. The results show that their catalytic activity is just like that for the homopolymerizationof 1-octadecene, with higher activity for the metallocene with the Et-bridged catalyst. ~(13)C-NMR analysis shows that thecomposition of the copolymerization products depends on the catalytic systems. Copolymers obtained with rac-Me_2Si(Ind)_2ZrCl_2 have greater comonomer incorporation. Thermal analysis shows that poly-1-octadecene synthesized withthe catalyst rac-Et(Ind)_2ZrCl_2 is very dependent on the polymerization temperature. The homopolymer obtained at 70℃presents two endothermal peaks at 41℃ and 53℃, as compared with the one obtained at 30℃ which presents one wider peakwith a maximum at 67℃. For the catalyst rac-Me_2Si(Ind)_2ZrCl_2 this trend is not observed. The type of metallocene and thereaction time do not significantly change the intrinsic viscosity, but the polymerization temperature changes it drastically,giving higher values at lower temperature. Viscosity measurements on the copolymers show that an increase of comonomerconcentration in the feed reduces the molecular weight of the copolymer, and it was also found that for homopolymer, themolecular weight is independent of the catalytic systems.     

Functionalization of polyolefins via the reaction of ozone with double bonds

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.     

Synthesis of oxazoline functionalized polypropene using metallocene catalysts

Using two different zirconocene/MAO catalyst systems, propene was copolymerized with the comonomers 2‐(9‐decene‐1‐yl)‐1,3‐oxazoline and 2‐(4‐(10‐undecene‐1‐oxo)phenyl)‐1,3‐oxazoline, respectively. The catalysts used were rac‐Et[Ind]₂ZrCl₂ and rac‐Me₂Si[2‐Me‐4, 5‐BenzInd]₂ZrCl₂. Up to 0.53 mol‐% oxazoline could be incorporated into polypropene. Oxazoline content, molecular weight, degree of isotacticity and melting behavior were dependent on the catalyst system, comonomer structure and comonomer concentration in the feed.     

Polymer materials based on ethylene copolymers with substituted norbornene

The copolymers of ethylene with 5-ethylidene-2-norbornene containing 10–65% of the cyclic comonomer have been prepared with the use of three ansa-metallocene catalysts, namely, Et[Ind]₂ZrCl₂-methylaluminoxane, Et[IndH₄]₂ZrCl₂-methylaluminoxane, and Me₂Si[Ind]₂ZrCl₂-methylaluminoxane. Side groups >C=CH-CH₃ capable of participation in the ozonolysis reaction have been incorporated into polymer chains via the copolymerization of ethylene with the cyclic comonomer. As evidenced by DSC, and X-ray diffraction, and very cold neutron scattering measurements of the supramolecular structure of the copolymers, the enrichment of the copolymer with the cyclic comonomer causes transformation of the ethylene-5-ethylidene-2-norbornene copolymer from the semicrystalline state to the amorphous state. This effect is accompanied by an increase in the density and optical transparency of the material and a rise in its glass transition temperature. Among the copolymers under study, the highest T _g (83°C) is exhibited by the copolymer synthesized with the Et[Ind]₂ZrCl₂-methylaluminoxane catalyst and containing 30 mol % 5-ethylidene-2-norbornene.     

Results coming from homogeneous and supported metallocene catalysts in the homo- and copolymerization of olefins

Ethylene, propylene and α-olefins were homo- and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind)₂ZrCl₂ (I), Me₂Si(Ind)₂ZrCl₂ (II), Et(2-Me-Ind)₂ZrCl₂ (III), Ph₂C(Flu)(Cp)ZrCl₂ (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol-gel preparation technique. The homo- and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed.     

Ethylene/hexene copolymerization with the heterogeneous catalyst system SiO2/MAO/rac‐Me2Si[2‐Me‐4‐Ph‐Ind]2ZrCl2: The filter effect

The main focus of this study is the ethylene/hexene copolymerization with the silica supported metallocene SiO₂/MAO/rac‐Me₂Si[2‐Me‐4‐Ph‐Ind]₂ZrCl₂. Polymerizations were carried out in toluene at a reaction temperature of 40°C–60°C and the cocatalyst used was triisobutylaluminium (TIBA). The kinetics of the copolymerization reactions (reactivity ratios r_E/H, monomer consumption during reaction) were investigated and molecular weights M_w, molecular weight distributions MWD and melting points T_m were determined. A schematic model for the blend formation observed was developed that based on a filtration effect of monomers by the copolymer shell around the catalyst pellet.     

Defined synthesis of copolymers using metallocene catalysis

The copolymerization of propene with small amounts of ethene, catalyzed by tetrahydroindenyl zirconocenes such as [En(H₄Ind)₂]ZrCl₂ or [Me₂Si(H₄Ind)₂]ZrCl₂ and MAO in liquid propene produces polymers with much higher activities and molecular weights than the homopolymerization of propene. The normal bisindenyl complexes doesn't present such differences. The investigation of the microstructure shows for the tetrahydroindenyl catalyst that after a 2,1-insertion of a propene unit the system is in a sleeping state and can be activated when an ethene unit is inserted. In this case these catalysts become faster than the ansa bis-indenyl catalysts. An active catalyst for the copolymerization of ethene and norbornene is the more temperature stable [Me₃PhPen(Flu)]ZrCl₂. This catalyst produces atactic copolymers with high molecular weights of over 900 000 g/mol at 30°C and 38 mol% of norbornene content.     

Renewable chain transfer agents for metallocene polymerizations: The effects of chiral monoterpenes on the polyolefin molecular weight and isotacticity

Monoterpenes were used as renewable chain transfer agents and polymerization solvents for metallocene/methylaluminoxane (MAO) catalysis. The polymerization of 1‐hexene, ethylene, and propylene in d‐limonene, hydrogenated d‐limonene and α‐pinene is reported. As detected by ¹H NMR analysis of the alkene region, chain transfer to d‐limonene yielded a higher percentage of trisubstituted alkenes. Size exclusion chromatography detected a decrease in molecular weight values resulting from chain transfer to d‐limonene. The [mmmm] pentads for isotactic polypropylene were characterized by ¹³C NMR and FTIR spectroscopy. Propylene polymerizations with the Et(Ind)₂ZrCl₂/MAO and Me₂Si(Ind)₂ZrCl₂/MAO catalyst systems in d‐limonene gave [mmmm] pentad values as high as 0.97. For the Et(Ind)₂ZrCl₂/MAO catalyst system at 0 °C, the mol fraction of [mmmm] pentads increased from 0.86 to 0.94 upon switching the solvent from toluene to d‐limonene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3150–3165, 2007     

Evidence of the Quasi‐Living Character of the ansa‐Zirconocene/MAO‐Catalyzed Copolymerization of Ethylene and Norbornene

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.     

Synthesis and characterization of ethylene‐propylene‐1‐pentene terpolymers

Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)₂ZrCl₂/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me₂C(Cp)(Flu)ZrCl₂/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp₂ZrCl₂/MAO/SiO₂/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of ¹³C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008     

Enantioselective methylalumination of α-olefins

The ability of various enantiopure zirconocenes to catalyze the asymmetric methylalumination of allylbenzene has been tested. The enantioselectivity of an ethylene(Ind)₂ZrCl₂/MAO system is the same as that of authentic methyl cation generated with Ph₃C⁺ from ethylene(Ind)₂ZrMe₂, confirming that the methyl cation is the active catalyst from ethylene(Ind)₂ZrCl₂/MAO.     

Tuning the ligand structure in metallocene polymerization catalysts

Meso-[Me₂Si(2-Me-4,6-ⁱPr₂Ind)₂ZrCl₂ was synthesized in a pure form and used as catalyst for the copolymerization of ethene and α-olefins. The results are compared with polymers obtained by C₁-symmetric metallocenes and constrained geometry catalysts. The activity of the meso form is remarkable high and reaches more than 100000 kg polymer/mol Zr · h. The ligand structure has large influence on the incorporation of 1-octene forming thermoplastics (LLDPE) and thermoplastic elastomers (POE).     

Determination of reactivity ratios for ethylene/α-olefin copolymerization catalysed by the C2H4[Ind]2ZrCl2/methylaluminoxane system

The present study reports values of reactivity ratios for ethylene/1-hexene, ethylene/1-octene and ethylene/1-decene copolymerizations promoted by C₂H₄[Ind]₂ZrCl₂/MAO. The comonomer reactivities are markedly influenced by the number of carbon atoms of the α-olefin. The ethylene/1-decene copolymerization depends on the concentration of α-olefin in the feed.     

Study of the compositional heterogeneity of ethylene-1-hexene copolymers via thermal fractionation with the use of differential scanning calorimetry

The compositional heterogeneity of ethylene-1-hexene copolymers synthesized with various types of supported catalysts, namely, the titanium-magnesium catalyst TiCl₄/MgCl₂ and the zirconocene catalyst SiO₂(MAO)/Me₂Si(Ind)₂ZrCl₂, is studied via the method of successive self-nucleation-annealing (SSA) with the use of differential scanning calorimetry. On the basis of the data on the temperatures of individual peaks on SSA curves, the thickness of lamellas composed of macromolecules with a certain degree of short-chain branching is estimated. The copolymer synthesized with the zirconocene catalyst has a narrower range of fusion and does not contain large lamellas composed of molecules with a low degree of short-chain branching. With the use of the broadness index, it is shown that the copolymer synthesized with the zirconocene catalyst has a more uniform distribution of the comonomer than does the copolymer synthesized with the titanium-magnesium catalyst. For the copolymers synthesized with the titanium-magnesium catalyst, the compositional heterogeneity increases with an increase in the content of 1-hexene.     

Shape and diffusion of the monomer‐controlled copolymerization of ethylene and α‐olefins over Cp2ZrCl2 confined in the nanospace of the supercage of NaY

Cp₂ZrCl₂ confined inside the supercage of NaY zeolites [NaY/methylaluminoxane (MAO)/Cp₂ZrCl₂] exhibited the shape and diffusion of a monomer‐controlled copolymerization mechanism that strongly depended on the molecular structure of the monomer and its size. For the ethylene–propylene copolymerization, NaY/MAO/Cp₂ZrCl₂ showed the effect of the comonomer on the increase in the polymerization rate in the presence of propylene, whereas the ethylene/1‐hexene copolymerization showed little comonomer effect, and the ethylene/1‐octene copolymerization instead showed a comonomer depression effect on the polymerization rate. Isobutylene, having a larger kinetic diameter, had little influence on the copolymerization behaviors with NaY/MAO/Cp₂ZrCl₂ for the ethylene–isobutylene copolymerization, which showed evidence of the shape and diffusion of a monomer‐controlled mechanism. The content of the comonomer in the copolymer chain prepared with NaY/MAO/Cp₂ZrCl₂ decreased by about one‐half in comparison with that of Cp₂ZrCl₂. A differential scanning calorimetry study on the melting endotherms after the successive annealing of the copolymers showed that the copolymers of NaY/MAO/Cp₂ZrCl₂ had narrow comonomer distributions, whereas those of homogeneous Cp₂ZrCl₂ were broad. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2171–2179, 2003     

Co- and terpolymerizations of ethene and α-olefins with metallocenes

The suitability of the (n-butCp)₂ZrCl₂/methylaluminoxane (MAO) catalyst system for the copolymerization of ethene with propene, hexene, and hexadecene was studied and Ind₂ZrCl₂/MAO was tested as a catalyst for ethene/propene and ethene/hexene copolymerizations. The synergistic effect of longer α-olefin on propene incorporation in ethene/propene/hexene and ethene/propene/hexadecene terpolymerizations was investigated with Et(Ind)₂ZrCl₂MAO and (n-butCp)₂ZrCl₂/MAO catalyst systems. The molar masses, molar mass distributions, melting points, and densities of the products were measured. The incorporation of comonomer in the chain was further studied by segregation fractionation techniques (SFT), by differential scanning calorimetry (DSC), studying the β relaxations by dynamic mechanical analysis (DMA) and by studying the microstructure of some copolymers by ¹³C-NMR. In this study (n-butCp)₂ZrCl₂ and Ind₂ZrCl₂ exhibited equal response in copolymerization of ethene and propene and both catalysts were more active towards propene than longer α-olefins. A nearly identical incorporation of propene in the chain was found for the two catalysts when a higher propene feed was used. A lower hexene feed gave a more homogeneous comonomer distribution curve than a higher hexene feed and also showed the presence of branching. In terpolymerizations catalyzed with (n-butCp)₂ZrCl₂, the hexadecene concentrations of the ethene/propene/hexadecene terpolymers were always very low, and only traces of hexene were detected in ethene/propene/hexene terpolymers. With hexene no clear synergistic effect on the propene incorporation in the terpolymer was detected and with hexadecene the effect of the longer α-olefin was even slightly negative. With an Et(Ind)₂ZrCl₂/MAO catalyst system both hexene and hexadecene were incorporated in the chain in the terpolymerizations. © 1997 John Wiley & Sons, Inc.     

Ethylene‐Norbornene Terpolymerization with 5‐Vinyl‐2‐norbornene Using Single‐Site Catalysts

The incorporation of 5‐vinyl‐2‐norbornene (VNB) into ethylene‐norbornene copolymer was investigated with catalysts [Ph₂C(Fluo)(Cp)]ZrCl₂ ( 1 ), rac‐[Et(Ind)₂]ZrCl₂ ( 2 ), and [Me₂Si(Me₄Cp)^tBuN]TiCl₂ ( 3 ) in the presence of MAO by terpolymerizing different amounts of 5‐vinyl‐2‐norbornene with constant amounts of ethylene and norbornene at 60°C. The highest cycloolefin incorporations and highest activity in terpolymerizations were achieved with 1 . The distribution of the monomers in the terpolymer chain was determined by NMR spectroscopy. As confirmed by XRD and DSC analysis, catalysts 1 and 3 produced amorphous terpolymer, whereas 2 yielded terpolymer with crystalline fragments of long ethylene sequences. When compared with poly‐(ethylene‐co‐norbornene), VNB increased both the glass transition temperatures and molar masses of terpolymers produced with the constrained geometry catalyst whereas decreased those for the metallocenes.