WO2002079272A1

WO2002079272A1 - Process for the preparation of a high-molecular-weight polyethylene

Info

Publication number: WO2002079272A1
Application number: PCT/NL2002/000194
Authority: WO
Inventors: Gerardus Johannes Maria Gruter; Bing Wang; Adrianus Hendricus Joseph Franciscus De Keijzer
Original assignee: DSM NV
Current assignee: Koninklijke DSM NV
Priority date: 2001-03-29
Filing date: 2002-03-27
Publication date: 2002-10-10
Anticipated expiration: 2003-09-29

Abstract

The invention relates to a process for the preparation of a high-molecular-weight homo- or copolymeric polyethylene having a weight-average molecular weight (as determined by Size Exclusion Chromatography combined with a viscosity detector) of between 500,000 and 10,000,000, the homo- or copolymeric polyethylene being prepared by polymerization of ethylene and optionally a minor amount of another α-olefin with a metallocene catalyst composition containing a double-bridge bisindenyl metal complex of Formula (1).

Description

PROCESS FOR THE PREPARATION OF A HIGH-MOLECULAR-WEIGHT POLYETHYLENE

The invention relates to a process for the preparation of a high- molecular-weight homo- or copolymeric polyethylene having a weight-average molecular weight (as determined via Size Exclusion Chromatography combined with a viscosity detector (SEC-DV)) of between 500,000 and 10,000,000 g/mol, in the presence of a metallocene catalyst composition.

Metallocene catalysts for the production of polyethylene with a relatively high molecular weight have recently been developed, as described in for instance WO-A-99/02.540. The metallocene catalysts used therein contain highly complex cyclopentadienyl ligands with at least four fused rings.

A drawback of the known process is that it only rarely results in a polyethylene having a weight-average molecular weight of more than 500,000 g/mol. Most of the polyethylenes obtained have a weight-average molecular weight of less than 300,000 g/mol. It has now been found that a high-molecular-weight homo- or copolymeric polyethylene having a weight-average molecular weight of between 500,000 and 10,000,000 g/mol (as determined via SEC-DV) can be obtained when ethylene and optionally a minor amount of another α-olefin is polymerized in the presence of a metallocene catalyst composition comprising a double-bridged bisindenyl metal complex of Formula 1 :

where: Ri to R₁₀ are substituents which are equal or different and are each independently chosen from the group comprising a hydrogen atom, a halogen atom, a hydrocarbon group with 1-20 carbon atoms, and a hydrocarbon group with 1-20 carbon atoms in which one or more hydrogen and/or carbon atoms have been replaced by hetero atoms;

Bi and B₂ are bridging groups which are equal or different; in the case of a homopolymerization of ethylene, B^ and B₂ each independently represent a group chosen from the group comprising a hydrocarbon group having 1 to 20 carbon atoms, a halogen-containing hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing group, a germanium-containing group, a tin-containing group, -O-, -CO-, -S-, -SO₂-, -Se-, -NR-, -PR-, -P(O)R-, -BR-, and -AIR-, wherein, for each group independently, R is chosen from the group comprising a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, and a halogen- containing hydrocarbon group having 1 to 20 carbon atoms; in the case of a copolymehzation of ethylene with a minor amount of another α-olefin as the comonomer B^ represents a group chosen from the group comprising a silicon- containing group, a germanium-containing group, a tin-containing group, -O-, -CO-, -S-, -SO₂-, -Se-, -NR-, -PR-, -P(O)R-, -BR- or -AIR-, wherein R is defined as above, and B₂ represents a group chosen from the group comprising a hydrocarbon group having 1 to 20 carbon atoms, a halogen-containing hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing group, a germanium-containing group, a tin-containing group, -O-, -CO-, -S-, -SO₂-, -Se-, -NR-, -PR-, -P(O)R-, -BR-, and -AIR-, wherein R is as defined above;

M is a transition metal of the lanthanides and/or of Group 3, 4, 5 or 6 of the Periodic Table of the Elements;

Q is an anionic ligand and k is the number of Q groups.

Double-bridged bisindenyl metal complexes according to Formula 1 are known from JP-A-00095820 for the polymerization of propylene. Said publication does not teach, however, that such double-bridged bisindenyl metal complexes are suitable as catalysts for the polymerization of ethylene to a high-molecular-weight polyethylene.

A method for the preparation of double-bridged bisindenyl metal complexes according to Formula 1 is described in JP-A-00095820. A description in further detail of the various components of the double-bridged bisindenyl metal complex used in the process according to the present invention is given in the following.

The substituents R^ to R₁₀ on the indenyl rings can be equal or different and are chosen form the group comprising a hydrogen atom, a halogen atom, a hydrocarbon group with 1-20 carbon atoms, and a hydrocarbon group with 1-20 carbon atoms in which one or more hydrogen atoms have been replaced by hetero atoms. The hydrocarbon group with 1-20 carbon atoms can be linear, branched, cyclic or aromatic.ln the hydrocarbon groups in which one or more hydrogen atoms have been replaced by hetero atoms, the hydrogen atoms have preferably been replaced by halogen atoms or organic silyl substituents. Also, two adjacent substituents of the indenyl compound can be bonded with each other to form a ring system. Preferably these are hydrocarbon substituents forming a ring. This may for instance result in the formation of benzoindenyl. The substituents on the indenyl ring are for instance alkyl, aryl, aralkyl, trialkylsilyl, dialkylaminoalkyl, alkoxyalkyl and haloalkyl, such as for instance methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, 2-ethylhexyl, decyl, phenyl, benzyl, trimethylsilyl, triethylsilyl, phenyldimethylsilyl, diphenylmethylsilyl, triphenylsilyl, dimethylaminoethyl, methoxyethyl, (dimethyl)(dimethylamino)silyl and 2-chloroethyl. In the case of a homopolyme zation of ethylene, B^ and B₂ preferably each independently represent an ethylene group, a silicon-containing group, a germanium-containing group or a tin-containing group.

In the case of a copolymerization of ethylene with a minor amount of another α-olefin as the comonomer, , and B₂ preferably each independently represent a silicon-containing group, a germanium-containing group or a tin-containing group.

More preferably, in the case of a homopolymerization of ethylene or a copolymerisation of ethylene with a minor amount of another α-olefin as the comonomer, B_T and B₂ are of the following structure:

-(ER'₂)_p-(CR"₂)_q-

where p = 1-4; q = 0-4; E is a Si, Ge or Sn atom and the R' and R" groups each independentlly represent hydrogen, a hydrocarbon group with 1-20 carbon atoms, or a hydrocarbon group with 1-20 carbon atoms in which one or more hydrogen atoms have been replaced by hetero atoms. The hydrocarbon group with 1 -20 carbon atoms can be linear, branched, cyclic or aromatic. In the hydrocarbon group in which one or more hydrogen atoms have been replaced by hetero atoms, the hydrogen atoms have preferably been replaced by halogen atoms or organic Si, Ge or Sn substituents. Examples of hydrocarbon groups are a methylene group, an ethylene group, a propylene group, and a butylene group. E is preferably a Si atom.

Examples of suitable bridging groups B^ and B₂ are dialkyl silylene, dialkyl germylene, tetraalkyl disilylene, dialkyl silaethylene (-SiR'₂-CH₂-), and tetraalkyl silaethylene (-SiR'₂-CR"₂). The R' and R" groups in such bridging groups preferably each independently represent hydrogen, an alkyl group containing 1-4 carbon atoms or an aryl group, for example a phenyl group. The R' and R" groups preferably each independently represent a methyl group or an ethyl group. In particular, Bj and B₂ each are of the following formula:

-Si(R"')₂-

where R'" is an alkyl group with 1-4 C atoms. Catalysts with two dialkylsilylene bridges exhibit a higher activity. Polymerization of ethylene by means of such catalysts results in a polyethylene having a higher molecular weight.

M is a transition metal chosen from the lanthanides or from Groups 3,

4, 5 or 6 of the Periodic System of the Elements. By the Periodic System of the

Elements is understood the new IUPAC version as printed on the inside of the Handbook of Chemistry and Physics, 70th edition, CRC Press,

1989-1990.

M is by preference a transition metal from Group 4, in particular Ti, Zr or Hf.

Q is an anionic ligand which is sigma-bonded to the transition metal M. Examples of such ligands, which can be identical or different, are a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an arylalkyl group, an alkoxy group, an aryloxy group, and a group with a hetero atom chosen from Groups 14, 15 or 16 of the

Periodic System of the Elements, such as:

- an amine group or an amide group, - a sulphur-containing group, such as a sulphide, - a phosphorus-containing group, such as a phosphine.

The ligand Q can also be an anionic ligand which is bonded to the transition metal M via a covalent metal-carbon bond and additionally shows a non-covalent interaction with M via one or more functional groups. Such a functional group can be an atom, but also a group of atoms which are bonded to each other. The functional group preferably is an atom from Group 17 of the Periodic System of the Elements or a group which contains one or more elements of Group 15, 16 or 17 of the Periodic System of the Elements. Examples of functional groups are F, CI, Br, a dialkylamino^'group, and an alkoxy group. Q can for instance be a phenyl group with one of the ortho positions substituted with a functional group which is capable of donating electron density to the transition metal M. Q can also be a methyl group with one or more of the positions on the α-carbon atom being substituted with a functional group which is capable of donating electron density to the transition metal M. Examples of methyl groups which are substituted at one or more α-positions are benzyl, diphenylmethyl, ethyl, propyl and butyl substituted with a functional group which is capable of donating electron density to the transition metal M. Preferably at least one of the ortho positions of the benzyl group is substituted with a functional group which is capable of donating electron density to the transition metal M. Examples of such Q groups are: 2,6-difluorophenyl, 2,4,6-trifluorophenyl, pentafluorophenyl, 2-alkoxyphenyl, 2,6-dialkoxyphenyl, 2,4,6-tri(trifluoromethyl)phenyl,

2,6-di(trifluoromethyl)phenyl, 2-thfluoromethylphenyl, 2-(dialkylamino)benzyl and 2,6-(dialkylamino)phenyl.

Preferably, Q is a monoanionic ligand which is sigma-bonded to the transition metal M. Most preferably, Q is CI or a methyl group. k is the number of Q groups in the indenyl compound, and depends on the valency of the transition metal M and the valency of the Q groups themselves. In the double-bridged bisindenyl compound according to Formula 1 , k is equal to the valency of M minus 2, divided by the valency of Q.

In the process according to the invention it is preferred to make use of a cocatalyst. The cocatalyst can be an organometal compound with a metal chosen from Group 1 , 2, 12 or 13 of the Periodic System of the Elements. Examples of suitable compounds, without being restricted thereto, are organoaluminium compounds, amyl sodium, butyl lithium, diethyl zinc, butyl magnesium chloride and dibutyl magnesium. Preference is given to organoaluminium compounds, such as for instance thalkylaluminium compounds (for example triethylaluminium and triisobutylaluminium); alkylaluminium hydrides (for example diisobutyl aluminium hydride); alkylalkoxy organoaluminium compounds; halogen-containing organoaluminium compounds (for example diethyl aluminium chloride, diisobutyl aluminium chloride, and ethyl aluminium sesquichloride); and aluminoxanes. Preferably, aluminoxanes are used as organoaluminium compound. These aluminoxanes can contain a minor amount of thalkylaluminium, preferably 0.5 - 15 mol% trialkylaluminium.

Supplementary to or as an alternative to the organometal compounds used as cocatalyst, the catalyst composition according to the invention can contain an ion complex. This ion complex consists of a cation and a compatible non-coordinating anion which is relatively big and which can stabilize the active catalyst particle that is formed when the ion complex and the double-bridged bisindenyl metal complex are combined. The bond between such a compatible non-coordinating anion and the transition metal is sufficiently labile to enable the compatible non-coordinating anion to be replaced by an unsaturated monomer during the olefin polymerization. Such ion complexes have already been described for instance in EP-A-426,637, and are also known from EP-A-277,003 and EP-A-277,004. Preferably, such a complex contains a triaryl borate, a tetraaryl borate, or an aluminium or silicon equivalent thereof. Examples of suitable ion complexes are: - dimethylanilinium tetrakis (pentafluorophenyl) borate; dimethylanilinium bis(7,8-dicarbaundecaborate)-cobaltate (III); tri(n-butyl)ammonium tetraphenyl borate; triphenylcarbenium tetrakis (pentafluorophenyl) borate; dimethylanilinium tetraphenyl borate; and - tris(pentafluorophenyl) borane.

In addition to the metallocene catalyst and optionally a cocatalyst the reaction mixture can also contain a minor amount of scavenger. A scavenger is an organometal compound which reacts with impurities in the reaction mixture. Organoaluminium compounds are commonly used as scavenger. Examples of scavengers are trioctylaluminium, triethylaluminium and triisobutylaluminium.

The metallocene catalyst composition on the basis of the double- bridged bisindenyl metal complex and optionally a cocatalyst can be applied on a carrier as well as without a carrier. Examples of suitable carrier materials are silica, alumina and MgCI₂. Preferably silica is used as the carrier material. The weight-average molecular weight of the high-molecular-weight polyethylene according to the invention is preferably between 750,000 and 10,000,000 g/mol, more preferably between 750,000 and 5,000,000 g/mol, as determined by SEC- DV.

The high-molecular-weight polyethylene is obtained by the homopolymerization of ethylene or by the copolymerization of ethylene with a minor amount of another α-olefin as the comonomer to yield an ethylene copolymer. The amount of comonomer in the ethylene copolymer generally varies from 0.25 to at most 45 wt.%. The other α-olefin is preferably an α-olefin with 3-12 carbon atoms, more preferably an α-olefin chosen from the group comprising propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene, or a mixture of two or more of these α-olefins; most preferably an α-olefin chosen from the group comprising propene, 1-butene, 1-hexene, and 1-octene.

The polymerization can be carried out in the known manner, in the gas phase as well as in a liquid medium. In a liquid medium both solution and suspension polymerization are possible. The amount of catalyst used in a liquid medium normally is such that the catalyst concentration during the polymerization is between 10^"8 and 10^~2 mol/l of the reaction mixture.

The polymerization can be carried out at atmospheric pressure, but also at elevated pressure, up to 500 MPa, continuously or discontinuously. The polymerization is preferably carried out at a pressure of between 0.1 and 25 MPa. High pressures of 100 MPa and more can be used if the polymerization is carried out in a so-called high-pressure reactor. If the polymerization is carried out at elevated temperature the polymerization rate is usually higher. The polymerization is therefore preferably carried out at a temperature of 95 to 300°C, more preferably at a temperature of 100 to 200°C, in particular at a temperature between 100 and 180°C.

The polymerization can be carried out in several steps, in series as well as parallel. If required the metallocene catalyst composition, the temperature, the hydrogen concentration, the pressure, the residence time, etc. can be varied from step to step. In this way it is possible to obtain products with a controllable, for example broad, molecular weight distribution.

High-molecular-weight polyethylenes, i.e. with a weight average molecular weight higher than 500,000 g/mol, are commercially produced using a Ziegler catalyst. In such a process, however, relatively large amounts of catalyst are required, which remain in the product or need to be removed. The resulting polyethylenes usually feature a relatively broad molecular weight distribution.

The invention will now be elucidated by means of the following Examples without being restricted thereto, however.

Examples

Experimental methods

The polyethylenes (PE) produced according to Examples l-V were analysed by^*SEC-DV using a Waters M150C GPC (including a DRI detector) connected via a heated transfer line with a Viscotek H502B viscosimeter. Four TSK GMHxL-HT columns were applied. 1 ,2,4-trichlorobenzene was used as the eluent. Universal and conventional calibration was done using polyethylene standards. The flow was 1.0 ml/min, the injection volume 300 μl, the column temperature 140°C and the injection temperature 150°C. The data were processed using Viscotek TriSEC 2.7 software.

Examples l-V

400 ml of pentamethyl heptane (PMH), ethylene and, in the case of Example III, 25 ml (17.8 g) of 1-octene (C8), were supplied to a 1.3-litre reactor and heated until the polymerization temperature was reached; the pressure being 2 MPa. Then 0.78 ml (1.6 M solution in toluene) of methylaluminoxane (from Witco) and the catalyst compound in solution (0.001 M solution in toluene) were pre-mixed at room temperature for 1 minute and subsequently supplied to the reactor. The catalyst supply vessel was rinsed with 100 ml of PMH. The pressure in the reactor was kept constant by supplying ethylene. By cooling of the reactor the temperature was kept within a deviation band of maximally 5°C relative to the set temperature. After 10 minutes the polymerization was stopped and the polymer was worked up by draining the solution and evaporation at 50°C in vacua.

The polymerization conditions, the catalyst activity and the weight average molecular weight (Mw) of the products are given in the Table below. Table

Catalyst:

1. (1 ,2'-dimethylsilylene)(2,1'-dimethylsilylene)bis(3-trimethylsilylindenyl)zirconium dichloride

2. (1 ,2'-dimethylsilylene)(2,1'-dimethylsilylene)bis(indenyl)hafnium dichloride

3. (1 ,2^,-dimethylsilylene)(2,1 '-dimethylsilylene)bis(3-methylindenyl)zirconium dichloride

4. (1,2'-dimethylsilylene)(2,1'-dimethylsilylene)bis(indenyl)zirconium dichloride

5. (1 ,2'-ethylene)(2,1'-ethylene)bis(indenyl)zirconium dichloride

Claims

Process for the preparation of a high-molecular-weight homo- or copolymeric polyethylene having a weight-average molecular weight (as determined via

Size Exclusion Chromatography combined with a viscosity detector) of between 500,000 and 10,000,000, in the presence of a metallocene catalyst composition, characterized in that the high-molecular-weight homo- or copolymeric polyethylene is prepared by polymerization of ethylene and optionally a minor amount of another α-olefin in the presence of a metallocene catalyst composition comprising a double-bridged bisindenyl metal complex of the following formula:

where:

RT to Rio are substituents which are equal or different and are each independently chosen from the group comprising a hydrogen atom, a halogen atom, a hydrocarbon group with 1-20 carbon atoms, and a hydrocarbon group with 1-20 carbon atoms in which one or more hydrogen atoms have been replaced by hetero atoms;

BT and B₂ are bridging groups which are equal or different; in the case of a homopolymerization of ethylene, Bi and B₂ each independently represent a group chosen from the group comprising a hydrocarbon group having 1 to 20 carbon atoms, a halogen-containing hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing group, a germanium-containing group, a tin-containing group, -O-, -CO-,

-S-, -SO₂-, -Se-, -NR-, -PR-, -P(O)R-, -BR-, and -AIR-, wherein, for each group independently, R is chosen from the group comprising a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, and a halogen-containing hydrocarbon group having 1 to 20 carbon atoms; in the case of a copolymerization of ethylene with a minor amount of another α-olefin as the comonomer, B^ represents a group chosen from the group comprising a silicon-containing group, a germanium-containing group, a tin-containing group, -O-, -CO-, -S-, -SO₂-, -Se-, -NR-, -PR-,

-P(O)R-, -BR- or -AIR-, wherein R is as defined above, and B₂ represents a group chosen from the group comprising a hydrocarbon group having 1 to 20 carbon atoms, a halogen-containing hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing group, a germanium-containing group, a tin-containing group, -O-, -CO-, -S-, -SO₂-, -Se-, -NR-, -PR-,

-P(O)R-, -BR-, and -AIR-, wherein R is as defined above; M is a transition metal of the lanthanides or of Group 3, 4, 5 or 6 of the Periodic System of the Elements; Q is a monoanionic ligand and k is the number of Q groups.

2. Process according to Claim 1 , wherein the polymerization of ethylene and optionally a minor amount of another α-olefin as the comonomer is carried out at a temperature of 95 to 300°C.

3. Process according to Claim 2, wherein the polymerization of ethylene and optionally a minor amount of another α-olefin as the comonomer is carried out at a temperature of 100 to 180°C.

4. Process according to any one of Claims 1-3, wherein M is a transition metal of Group 4.

5. Process according to any one of Claims 1-4, wherein the polymerization is a homopolymerization of ethylene, and wherein B^ and B₂ each represent a group chosen from the group comprising an ethylene group, a silicon- containing group, a germanium-containing group, and a tin-containing group.

6. Process according to any one of Claims 1-4, wherein the polymerization is a copolymerization of ethylene with a minor amount of another α-olefin as the comonomer, and wherein B^ and B₂ each represent a group chosen from the group comprising a silicon-containing group, a germanium-containing group, and a tin-containing group.

7. Process according to any one of Claim 5 and Claim 6, characterized in that B_T and B₂ have the following formula: -(ER'₂)p-(CR"₂)q-

where p = 1-4; q = 0-4; E is a Si, Ge or Sn atom and the R' and R" groups each independently are hydrogen or or a hydrocarbon radical with 1-20 carbon atoms or a hydrocarbon group with 1-20 carbon atoms in which one or more hydrogen atoms have been replaced by hetero atom.

8. Process according to Claims 7, characterized in that B, and B₂ each contain at least one Si atom.

9. Process according to Claim 8, characterized in that B^ and B₂ have the following formula:

-Si(R'")₂-

where R'" is an alkyl group with 1-4 C atoms.

10. Process according to any one of Claims 1-9, characterized in that the weight-average molecular weight is between 750,000 and 5,000,000.