Asymmetric silicon-bridged metallocenes useful as catalysts in the polymerization of a-olefins, process for their preparation and use of said metallocenes for the polymerization of a-olefins

Abstract: Asymmetric silicon-bridged metallocenes useful as catalysts in the polymerization of olefins and process for preparing said metallocenes. The metallocenes are represented by the general formula: wherein M represents a transition metal selected from Ti, Zr and Hf, X and X' represent a halogen atom, R 1 , R 2 , R 3 represent an alkyl group containing 1 or 2 carbon atoms or a hydrogen atom, providing that at least two of R 1 , R 2 , R 3 are alkyl groups, and R 4 and R 5 represent an alkyl or aryl group containing from 1 to 10 carbon atoms. Process for producing the metallocenes of general formula (I) comprising the steps of: a) reacting dichloro-dialkyl(or diaryl)silane with (substituted indenyl)lithium to produce (substituted indenyl)-dialkyl(or diaryl)-chlorosilane, b) reacting said chlorosilane with fluorenyllithium to produce the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor, c) reacting said (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor with butyllithium to produce its dilithium salt, and d) reacting said dilithium salt with a transition metal halide selected from halides of Ti, Zr and Hf to produce the metallocenes. Process for the polymerization of α-olefins such as ethylene and propylene by means of said metallocene.

Description: Technical Field The present invention relates to the use of asymmetric silicon-bridged metallocenes as catalysts for the polymerization of propylene. It relates more specifically to the use of silicon-bridged metallocenes containing fluorenyl and indenyl fragments. Finally it relates to a process for polymerization of propylene by using said asymmetric silicon-bridged metallocenes. Background of the invention Some asymmetric silicon-bridged metallocenes derived from group 4 metals and containing fluorenyl and indenyl fragments have already been proposed for the polymerization of α-olefins such as ethylene and propylene. For example, EP-A-0 754 698 discloses specifically dimethyl- or diphenyl-silylene (9-fluorenyl)-(2-methyl-1-indenyl) zirconium dichloride, dimethylsilylene (9-fluorenyl)-(2-methyl-4-phenyl-1-indenyl) zirconium dichloride, dimethylsilylene (9-fluorenyl)-(3-methyl-1-indenyl) zirconium dichloride and dimethylsilylene (9-fluorenyl)-(2-methyl-4-i-propyl-7-methyl-1-indenyl) zirconium dichloride in combination with aluminoxanes (MAO) for the polymerization of these α-olefins. However the productivity of such silicon-bridged metallocenes remains insufficient and they do not lead to polymers having optimal properties. In particular, according to EP 707 016, said compounds are producing polypropylene elastomers having very low isotacticity (about 20%). Silicon-bridged indenyl fluorenyl metallocenes are generally produced by processes involving the addition of the indenyl anion to the (9-fluorenyl) silylhalide (J. Organomet. Chem., 1995, 497, 1). The application of this known route to substituted indenyl compounds does not provide satisfactory results presumably due to unfavorable steric hindrance of the indenyl compound. Summary of the invention It is an object of the present invention to solve the above problems by using metallocenes as catalysts for olefin polymerization which are, in particular, able to produce polypropylene having high isotacticity. It is another objective of the present invention to provide a process for the polymerization of propylene by means of said metallocenes. The invention is thus related to the use of metallocenes represented by the general formula (I) wherein M represents a transition metal selected from Ti, Zr and Hf, X and X' represent a halogen atom, R 1 , R 2 , R 3 represent an alkyl group containing 1 or 2 carbon atoms or a hydrogen atom, providing that at least two of R 1 , R 2 , R 3 are alkyl groups, and R 4 and R 5 represent an alkyl or aryl group containing from 1 to 10 carbon atoms, as catalysts in the polymerization of propylene. Finally the present invention relates to a process for polymerization of propylene by means of said metallocenes. Detailed description According to a first aspect, the present invention relates to the use of metallocenes of the above general formula (I), for the polymerization of propylene. Preferably the transition metal is selected from hafnium and zirconium. Most preferably the transition metal is zirconium. The halogen atoms X and X' are preferably chlorine or bromine atoms and most preferably they are both chlorine atoms. The groups R 1 , R 2 , R 3 represent preferably a methyl group or a hydrogen atom, providing that at least two of R 1 , R 2 , R 3 are methyl groups. The groups R 4 and R 5 are preferably alkyl groups and more particularly alkyl groups containing from 1 to 3 carbon atoms. The most preferred metallocenes according to the present invention are dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride, dimethylsilylene (9-fluorenyl)-1-(2,4-dimethyl)indenyl zirconium dichloride or dimethylsilylene (9-fluorenyl)-1-(4,7-dimethyl)indenyl zirconium dichloride. When used in combination with a cocatalyst, such as for example aluminoxane, said metallocenes are able to produce polypropylene with high molecular weight. Moreover said metallocenes and more particularly those having an alkyl group in position 2 of the indenyl group provide surprisingly polypropylene having its isotacticity ; the use of polymerization temperatures higher than 50°C being generally advantageous for the obtention of said isotacticity. The metallocenes of general formula (I) may be prepared according to a process comprising the following steps : a) reacting dichloro-dialkyl(or diaryl)silane with (substituted indenyl)lithium to produce (substituted indenyl)-dialkyl(or diaryl)-chlorosilane, b) reacting said chlorosilane with fluorenyllithium to produce the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor, c) reacting said (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor with butyllithium to produce its dilithium salt, and d) reacting said dilithium salt with a transition metal halide selected from halides of Ti, Zr and Hf to produce the metallocenes. Preferably, step (a) is carried out with an excess of the chlorosilane. More preferably the (substituted indenyl)lithium is reacted with two molar equivalents of the silane. Preferably, step (b) is carried out by reacting the fluorenyllithium with the chlorosilane in equimolar quantity. Preferably, step (c) is carried with at least two molar equivalents of butyllithium per mole of the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor. Step (d) is most often carried out by reacting the dilithium salt with one equivalent of transition metal halide. Preferably, reaction step (a) is carried out in an inert solvent, for example an ether. Reaction step (a) is usually carried out at a temperature in the range of 0°C to room temperature. At the end of reaction of step (a), the solvent and the excess of dichloro-dialkyl(or aryl)-silane are generally removed in order to separate the produced substituted indenyl-alkyl(or aryl)-chlorosilanes which are oils. Preferably, the step (b) is carried out in the above-mentioned inert solvent, most often at room temperature. At the end of reaction, the suspension is usually hydrolyzed and the organic phase is isolated. After removal of the solvent, the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor is isolated. Preferably, step (c) is carried out in an inert solvent, such as toluene or an ether, often under the reflux of said solvent. The resulting Li salt is advantageously separated from the solvent and washed prior to being reacted, in step (d), with one equivalent of a transition metal halide selected from halides of Ti, Zr and Hf. Step (d) is preferably carried out in an inert solvent, such as toluene or an ether, often under the reflux of said solvent. After removal of the solvent, the solid metallocene is isolated. The metallocenes according to the present invention are useful as catalysts for the polymerization of propylene. The reaction is carried out by contacting said propylene with the said metallocene under polymerization conditions. It can be carried out in solution or in suspension in an hydrocarbon diluent or in suspension in the monomer maintained in the liquid form or in the gas phase. The polymerization conditions are well known by persons skilled in the art. The metallocenes according to the invention can be used in combination with one another. They can also be used in combination with aluminoxanes. Methylaluminoxane is preferred. They can also be used in combination with an ionizing agent. This ionizing agent can be chosen from the compounds comprising a first part which has the properties of a Lewis acid and which is capable of ionizing the metallocene and a second part that is inert towards the ionized metallocene. Examples of ionizing agents are triphenylcarbenium tetrakis(pentafluorophenyl) borate, N,N'-dimethylanilinium tetrakis(pentafluorophenyl) borate, tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, triphenylboron, trimethylboron, tri(trimethylsilyl)borate and organoboroxines. Organometallic compounds are generally used as cocatalysts and/or poison scavengers. They can be selected from organometallic compounds of lithium, magnesium, zinc, aluminium or tin. The best results are obtained with organoaluminium compounds and in particular with trialkylaluminium compounds. The metallocenes according to the present invention may be used for the homopolymerization of propylene or for the copolymerization - random or block copolymerization - of propylene with one or more comonomers. The preferred comonomers of propylene are ethylene, butene and their mixtures. The compounds of formula I in which R 1 and R 3 are alkyl groups containing 1 or 2 carbon atoms and R 2 is hydrogen are particularly suitable for the (co)polymerization of propylene. In addition to the foregoing description of the invention, the following examples are provided to illustrate the present invention. In these examples reactions are carried out under an argon atmosphere using standard Schlenk techniques. Toluene, diethyl ether, tetrahydrofuran (THF) and pentane were distilled from Na/K alloy under argon. Dichloromethane was distilled from CaH 2 under argon. Melting points of the polymers were determined by DSC with a Perkin-Elmer DSC-System. 13 C NMR spectra were determined on DPX300/AMX500 spectrometers in CDCl 3 at room temperature, and at 80°C in C 6 D 5 Cl. 1 H NMR spectra were recorded on a AC-200 spectrometer. 1. Preparation of metallocenes Example 1 - Preparation of the dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride a) production of (2,4,7-trimethyl)indenyl-dimethylsilane To a solution of 5.00 g (31.6 mmol) of (2,4,7-trimethyl)indene in 30 ml of dry diethyl ether and 10 ml of dry THF at 0 °C, was added dropwise a 1.6 M solution of butyllithium in hexane (19.70 ml, 31.6 mmol). The solution was stirred at room temperature for 5 h and then added dropwise via cannula to 7.67 ml (63.2 mmol) dichloro-dimethylsilane in 20 ml of dry diethyl ether at 20 °C. The addition was carried out over a 1 h period and the suspension was then stirred for 1 h at room temperature. The solvents and excess dichloro-dimethylsilane were then removed under vacuum. b) production of (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl-dimethylsilane The oil obtained in step (a) was suspended in 30 ml of dry diethyl ether at 0°C. To this was added dropwise by cannula, one equivalent of fluorenyllithium prepared from 5.25 g (31.6 mmol) of fluorene and 19.7 ml (31.6 mmol) of butyllithium in 30 ml of dry ether and 10 ml of dry tetrahydrofuran. The suspension was allowed to stir overnight at room temperature and hydrolyzed with aqueous NH 4 Cl. The organic phase was separated and the aqueous layer was extracted with ether. The combined organic phases were dried (MgSO 4 ), filtered and the solvent was removed. The residue was recrystallized from toluene/hexane 1:1 to give 9.05 g of (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl-dimethylsilane (75%); melting point 121-123 °C. 1 H NMR (CDCl 3 ): δ 7.90-7.34 (m, 8 H, arom), 6.95-6.88 (d, 1 H), 6.78-6.75 (d, I H), 6.66-6.65 (d, 1 H), 4.17, (s, 1 H, Flu sp 2 ), 3.85 (s, 1 H, Ind sp 2 ), 2.38 (s, 3 H, CH 3 ), 2.27 (s, 3 H, CH 3 ), 2.11 (s, 3 H, CH 3 ),-0.32 (s 3 H, Si-CH 3 ), -0.55 (s 3 H, Si-CH 3 ). Anal. Calcd for C 27 H 28 Si: C,85.21; H, 7.41. Found: C, 85.47; H, 7.35. c) production of the dilithium salt To a solution of 1.00 g (2.63 mmol) of (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl-dimethylsilane in 20 ml of dry toluene at 0 °C was added dropwise two equivalents of a 1.6 M solution of butyllithium in hexane (3.3 ml, 5.25 mmol). The solution was heated under reflux for 5 h giving an orange suspension. d) production of dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride The suspension obtained in (c) was cooled to -25 °C and zirconium tetrachloride (0.61 g, 2.63 mmol) was added as a solid. After stirring at room temperature overnight, the mixture was heated under reflux for an additional 4 h to ensure complete reaction. Upon cooling to room temperature, the suspension was filtered and the orange residue was extracted with dry methylene chloride. The solution was concentrated and stored at -20 °C to give 156 mg of dimethylsilylene-(9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride as an orange powder (11 %). 1 H NMR (CDCl 3 ): δ 8.00-6.62 (m, 11 H, arom), 2.72 (s, 3 H, CH 3 ), 2.38 (s, 3 H, CH 3 ), 2.23 (s, 3 H, CH3), 1.47-1.46 (d, 6 H, Si-CH 3 ). Anal. Calcd for C 27 H 26 SiCl 2 Zr.0.08C 27 H 28 Si: C,61.32; H, 4.98. Found: C, 61.80; H, 5.00. Example 2 - Preparation of dimethylsilylene (9-fluorenyl-1-(2,4-dimethyl)indenyl zirconium dichloride Following the procedure of steps a) to d) of example 1, using diethyl ether at room temperature as the solvent in steps c) and d), dimethylsilylene(9-fluorenyl)-1-(2,4-dimethyl)indenyl zirconium dichloride (225 mg, 15.6 %) was prepared using 2,4-dimethylindenyl lithium instead of 2,4,7-trimethylindenyl lithium in step a). It is an orange solid. 1 H NMR (CDCl 3 ):δ 7.76-6.73 (m, 11 H, arom), 6.62 (s, 1 H, Ind-C 5 ), 2.28 (s, 3 H, CH 3 ), 2.26 (s, 3 H, CH 3 ), 1.54-1.43 (d, 6 H, Si-CH 3 ). Anal Calcd. for C 26 H 24 Cl 2 SiZr.0.3CH 2 Cl 2 :C, 57.21; H, 4.49. Found : C, 57.28; H,4.30 2. Polymerization of propylene General conditions A 250 ml crown capped glass pressure reactor containing 50 ml of toluene was equilibrated with the appropriate monomer and pressure at the desired temperature. The desired amount of methylaluminoxane (MAO) was added and the solution was stirred for 5 min. 1 ml of the appropriate metallocene catalyst solution in toluene, in precontact with 1 ml MAO, was added and the mixture was stirred until the desired reaction time was reached. The mixture was quenched with 2% HCl in methanol, filtered and dried in a vacuum oven at an appropriate temperature for the polymer sample. Examples 3 and 4 These examples are related to the polymerization of propylene under the general conditions described hereabove by using the dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride. The conditions are as follows : Zr = 25µM Al/Zr = 4000:1 (molar ratio) pressure = 2,067.10 5 Pa (30 psi) The duration of the polymerization was 60 min, the temperature was 20°C for example 3 and 70°C for example 4. The yield was 1.8 g for example 3 (activity: 0.14 x 10 7 g polymer/(mol Zr.[propylene]. h) and 0.4 g for example 4 (activity: 0.23 x 10 7 g polymer/(mol Zr.[propylene]. h), the melting point was 74° C for example 4 and 125° C for example 5. Example 5 This example is related to propylene bulk polymerization with the dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride according to the following general procedure : the polymerization run is carried out in a 5 liters stainless steel reactor. Cocatalyst (MAO, 10 % by weight in toluene, 45 ml), catalyst (5 µmol Zr in precontact with 5 ml MAO, 10% by weight in toluene), Al/Zr = 15,000:1 (molar ratio), and liquid propylene (3,5 liters) are successively introduced under argon blanket and heated to the polymerization temperature (70 °C). The polymerization conditions are maintained for 60 minutes. The polymerization is then stopped by simultaneously flashing the residual monomer and cooling down the reactor. The results of polymerization were the following : activity : 0.074 10 8 g polypropylene/mmol Zr, melting temperature : 95.7°C Isotacticity [mmmm] measured by 13 C NMR: 79 mol%, Mw 43,000 Example 6 This example is related to polymerization of propylene under the conditions described in example 4 hereabove by using the dimethylsilylene (9-fluorenyl)-1-(2,4-dimethyl)indenyl zirconium dichloride. The results of said test were : activity 1.8 10 6 g polymer/mol Zr. [propylene].h, Isotacticity ([mmmm] pentad measured by 13 C NMR 83.8%; melting temperature : 119°C, Mw : 8000. Example 7 This example is related to polymerization of propylene under the condition described in example 5 hereabove by using the dimethylsilylene (9-fluorenyl)-1-(2,4-dimethyl)indenyl zirconium dichloride. The results of said test were : activity 0.11 10 8 g polymer/mol Zr. [propylene].h, Isotacticity ([mm] triad) 71%; melting temperature : 87°C, Mw : 49000.

Claims: Use of an asymmetric silicon-bridged metallocene as catalyst in the polymerization of propylene to produce isotactic polypropylene, said metallocene being represented by the general formula (I) wherein M represents zirconium, X and X' are chlorine atoms, R 1 , R 2 , R 3 represent methyl groups or hydrogen atoms, providing that at least two of R 1 , R 2 , R 3 are methyl groups, and R 4 and R 5 represent alkyl groups containing from 1 to 3 carbon atoms. Use of an asymmetric silicon-bridged metallocene according to claim 1, wherein the metallocene is dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride or dimethylsilylene (9-fluorenyl)-1-(2,4-dimethyl)indenyl zirconium dichloride or dimethylsilylene (9-fluorenyl)-1-(4,7-dimethyl)indenyl zirconium dichloride. Process for the polymerization of propylene to produce isotactic polypropylene, carried out in the presence of a catalyst comprising a metallocene according to claim 1.

Inventors: BETTONVILLE SERGE, RAUSCH MARVIN D, SIBERDT FABIAN, THOMAS EMMA J, BETTONVILLE, SERGE, RAUSCH, MARVIN D., SIBERDT, FABIAN, THOMAS, EMMA J.
Applicants: SOLVAY, SOLVAY POLYOLEFINS EUROPE - BELGIUM (SOCIETE ANONYME)
Application year: 2000
Main classification: C07F17
IPC codes: C08F10, C08F4, C07F17