CN1365366A - Improvement in or relating to polymers - Google Patents

Abstract

Olefin homopolymers and copolymers, including novel products with essentially complete particle to particle homogeneity and having polymer chain defects introduced in a controlled manner across their molecular weight distribution, are prepared by a process comprising polymerisation under essentially constant conditions in a single reactor in the presence of a catalyst system comprising a support material coimpregnated with at least two metallocene olefin polymerisation catalysts having different propensities for incorporation of polymer chain defects.

Description

Improvements in or relating to polymers

The present invention relates to a process for the preparation of olefin polymers, including homopolymers and copolymers, and to the novel polymers obtained thereby. More particularly, the present invention relates to a process and product wherein polymer chain defects (i.e., irregularities in the otherwise regular structure of the polymer, such as side chains or crystallinity-disrupted monomer units) are introduced in a controlled manner across the molecular weight distribution of the polymer.

The molecular weight distribution of polymers affects their properties, in particular their mechanical strength and processability. Mechanical strength depends mainly on the higher molecular weight fraction, while extrudability depends on the lower molecular weight fraction. As a result, polyolefins with improved mechanical and processing properties can be obtained if the molecular weight distribution is to meet the end use requirements of the polymer. In many cases of use, for example extrusion and shaping processes, it is desirable to have a broad or multimodal molecular weight distribution. Polymers having a multimodal molecular weight distribution contain 2 or more polymer components and are generally characterized by having a broad molecular weight distribution, such polymers exhibiting good processability.

The mechanical properties of the polymer product are further controlled by the inclusion of polymer chain defects, for example, by incorporating alpha-olefin comonomers to alter their properties and the relative content of short chain branches present as side chains. Depending on the nature of the comonomer, such inclusion will result in an increase, or generally a lesser decrease, in the degree of branching in the main polymer backbone.

Not only the properties, but also the distribution of polymer chain defects in the individual polymer components, are important in determining the polymer properties. Thus, the ability to control such distribution over the entire molecular weight distribution of the polymer is particularly desirable, particularly the ability to produce multi-modes, such as bi-modal, copolymer molecular weight distributions in which polymer chain defects, such as comonomer molecules, are selectively incorporated in a portion of the molecular weight distribution. With multiple modes, such as bimodal polymers, defects in the molecular weight distribution, particularly the relative increase in the amount of side chains resulting from comonomer inclusion, are concentrated in the higher molecular weight fraction, which is particularly desirable. Such polymers exhibit good impact resistance, tear strength and environmental stress crack resistance. Without wishing to be bound by theory, it is believed that the presence of polymer chain defects, e.g., comonomer monomers in the higher molecular weight fraction of the polymer, helps to form or enhance the effect of "linking molecules" that can be incorporated into more than one crystalline sheet. This may be considered to improve the mechanical properties of the polymer, in particular the environmental stress crack resistance of the polymer.

In order to achieve an improved environmental stress crack resistance at the respective melt flow rates and densities, many have suggested combining low molecular weight copolymers with high molecular weight copolymers, for example using reactor mixing in series, or mixing the two separate components in an extruder (see US-A-3280220, US-A-4461873 and US-A-4547551). However, it is difficult to mix polymers having different molecular weights to obtain a uniform product. In order to achieve homogeneous mixing of polymers from two distinctly different molecular weights, it is generally necessary that at least 50% by weight of the mixture is the high molecular weight component. It is difficult to obtain a homogeneous mixture with > 50% by weight of low molecular weight components by mixing.

Various catalyst systems have been proposed for the polymerization of polymers and copolymers of olefins.

The preparation of olefin polymers with broad molecular weight distribution using a variety of transition metal catalysts, e.g., Ziegler catalysts, in a two reactor system is described in the examples of WO 92/12182. This is the case with a broad molecular weight distribution, and different reactor polymerization conditions favor the production of polymers of different molecular weights, e.g., one favors the production of high molecular weight polymers and the other favors the production of low molecular weight polymers.

Polyolefins of broad molecular weight distribution can be produced in a single reactor using a mixture of catalysts or a multi-site catalyst, for example, two or more metallocene hybrid catalysts. For example, WO95/04761 discloses the use of a combination of three metallocene complexes to produce a polymer product having a controlled molecular weight distribution. However, such catalyst systems provide lower control over the amount of incorporated polymer chain defects, such as comonomer molecules.

The use of two conventional Ziegler-NattｃA catalysts and Phillips-type catalysts (e.g.chromium oxide based) in combination with ｃA metallocene for the preparation of ethylene copolymers having ｃA bimodal molecular weight distribution or ｃA broad molecular weight distribution has been proposed (cf. for example EP-A-0676418, EP-A-0658571, U.S. A-5543376, U.S. A-5624877 and WO 97/27225). However, both Ziegler catalysts and Phillips catalysts have a tendency to produce polymer products having a molecular weight which is inversely related to the molecular weight of the comonomer, i.e., lower molecular weight polymer molecules contain a relatively higher proportion of comonomer than higher molecular weight polymer molecules. Thus, while a degree of comonomer molecular control is achieved, incorporation of comonomers in low molecular weight components is generally limited. The majority of the ethylene copolymers listed in EP-A-0676418 by way of example contain ｃA higher proportion of copolymer in the low molecular weight fraction and only one product has ｃA higher proportion of copolymer monomers in the high molecular weight fraction than in the low molecular weight fraction (factor 2: 1). Therefore, the products of the prior art tend to have a relatively poor balance of impact and stiffness and low environmental stress crack resistance.

Processes for preparing polyolefins having ｃA broad molecular weight distribution using paired metallocene catalysts in combination with ｃA suitable cocatalyst and ｃA support system are disclosed, for example, in EP-A-0619325, EP-A-0705851, and WO 98/57998. The first two documents disclose a single step reaction involving the use of a catalyst prepared by a multi-step procedure and the use of separate metallocene catalysts on separate supports. The third document relates to a multistage polymerization process, wherein a low molecular weight fraction containing little or no comonomer molecules can be produced in the first stage or early stage, while a bimodal high molecular weight fraction with comonomer inclusions can be produced in the second stage or later.

The present invention is based on the discovery that a catalyst system comprising a support material co-impregnated with at least 2 metallocenes and any necessary or desired cocatalyst (i.e. all catalyst and cocatalyst materials within the system, applied simultaneously to the support material during the preparation of the system) can be used in a single reaction step to prepare novel and useful olefin homopolymers and copolymers having superior properties. The use of metallocenes having different habits of incorporating polymer chain defects may have a high degree of control over the extent to which the polymer chain defects are incorporated into the higher and lower molecular weight fractions, despite the fact that the catalyst is co-impregnated in a single support material, which may ensure a high degree of inter-particle homogeneity of the polymer product. The polymerization process is carried out under substantially constant conditions (i.e., temperature, pressure, comonomer and/or appropriate hydrogen concentration, etc., do not vary significantly over time). Thus, within the reactor vessel, the steps can be simplified and operating costs reduced. The ability to produce such thorough mixing of two or more polymer components at different catalyst sites on a single support material under a single set of operating conditions is most unexpected.

It is therefore an object of the present invention to provide a process for the preparation of polymers of alkenes, wherein the polymerization of the alkenes is carried out in a single reactor under substantially constant conditions in the presence of a catalyst comprising a support material impregnated with at least two metallocene alkene polymerization catalysts having a different tendency to incorporate defects in the polymer chain.

It is known that the product of such a process can be further polymerized (i.e., by the process described above) if desired as part of a multi-step procedure for making more complex polymers.

The metallocene used in the catalyst system according to the present invention is preferably selected to produce an olefin polymer in which the polymer chain defect content in the higher molecular weight fraction of the polymer is at least 3 times, preferably at least 5 times, for example at least 10 times, that of the lower molecular weight fraction. The amount of polymer chain defects incorporated into the lower molecular weight fraction of such polymers, or the amount of polymer chain defects in the lower molecular weight fraction of such polymers, is preferably zero, or substantially zero, in which case such components constitute substantially a homopolymer, e.g., an ethylene homopolymer. It is particularly preferred that the catalyst is one which produces a copolymer in which incorporation of short chain branching derived from the comonomer is predominant, e.g. is present only in the higher molecular weight fraction. Incorporation of short chain branches at higher molecular weight chains is believed to be a higher level of comonomer incorporation into the polymer at a constant density, which in turn can contribute to achieving high environmental stress crack resistance.

It is a further object of the present invention to provide an alkene copolymer prepared according to the method of the present invention, and products (i.e., containers, fibers, films, sheets, pipes, etc.) produced therefrom. Thus, according to this object of the invention, there is provided a polyolefin having complete interparticle homogeneity and containing at least a higher molecular weight fraction and a lower molecular weight component, wherein the polymer chain defect content of said higher molecular weight fraction is at least three times that of said lower molecular weight fraction.

Preferred metallocenes for use in the catalyst system of the present invention have catalytic sites capable of producing a polymer component having a weight average molecular weight in the range of 1000 to 10000000, preferably 2000 to 1000000, such as 2000 to 500000. Especially preferred are catalyst systems comprising: a first metallocene capable of producing a polymer of relatively lower weight average molecular weight (Mw) (higher melt flow rate) (i.e. having a weight average molecular weight in the range 1000 to 1000000, preferably 2000 to 500000) with a lower amount of polymer chain defect incorporation, and a second metallocene capable of producing a polymer of relatively higher weight average molecular weight (lower melt flow rate) (e.g. having a weight average molecular weight in the range 10000 to 10000000, preferably 50000 to 1000000) with a higher amount of polymer chain defect incorporation. A representative content of polymer chain defect bonds in the lower molecular weight component of the polymer is 0 to 50, e.g., 0 to 25. A representative content of polymer chain defect bonds in the higher molecular weight component of the polymer is from 0.1 to about 333, such as from 5 to 100.

As used herein, the terms "amount of polymer chain defect", "amount of polymer chain defect incorporation", and "amount of polymer chain defect" are used interchangeably and are all defined as the average amount of polymer chain defect of any given polymer component or moiety within the entire molecular weight range. Typically, the amount of polymer chain defects, for example, is expressed as short chain branching frequency, i.e., the number of short chain branches per thousand carbon atoms, of the comonomer. This can be used to illustrate the case of propylene homopolymers in which a single monomer unit contains 2 backbone carbon atoms and a branched methyl group, so that all carbon atoms are branched by 1/3. This corresponds to a short chain branching frequency of 1000/3.

However, in polymers containing predominantly branched polymer units, i.e. polypropylene, the comonomer to be incorporated may comprise unbranched or linear comonomers, such as ethylene. The comonomer, which is used to reduce the degree of branching, may act as a crystallinity disrupting unit, which will result in a reduction in crystallinity of the polymeric material. In this case, the comonomer amount is determined by the average number of unbranched (or linear) units per thousand carbon atoms.

The process of the present invention can be used both for the homopolymerization of olefins and for the copolymerization of olefins. In the case of homopolymerization, such as ethylene homopolymerization, it is believed that the comonomer may be formed in situ by catalysis by one metallocene, while the other metallocene catalyzes the formation of a backbone with long chain branches derived from the comonomer generated in situ. Such long chain branches advantageously contain at least 10 monomer units each and are advantageously substantially homopolymerizable.

In the case of copolymerization, at least 50% by weight of the copolymer product, preferably from C_2-10Alpha-olefin monomers, more particularly from C_2-4Alpha-olefins, preferably ethylene or propylene. The other comonomer may be any monomer copolymerizable with the olefin monomer, preferably mono-or polyunsaturated C_2-20Compounds, especially mono-or dienes, especially C_2-10Alpha-olefins, for example, ethylene, propylene, but-1-ene, pent-1-ene, hex-1-ene, oct-1-ene, or mixtures thereof, and may include the in situ generated comonomers described above. Bulky comonomers, such as styrene or norbornene, can also be used.

The process is particularly effective for preparing copolymers of ethylene with one or more copolymerizable monomers, such as C_3-20Mono-and diene-copolymerizable monomers, more preferably C_3-10Alpha-olefin monomers, and for preparing polymers having one or more copolymerizable monomers, e.g. C_4-20Mono-and dienes, more preferably C_4-10Copolymers of propylene or ethylene of alpha-olefin monomers. The process of the present invention is particularly useful for the polymerization of ethylene and hex-1-ene.

Preferred polymer products are those having ethylene as the major monomer, i.e. in an amount of at least 50%, more preferably 50% by weight of the monomer residues are ethylene residues.

Catalyst systems comprising metallocenes having stereotactic and non-stereotactic sites, respectively, can be used according to the invention to produce fractions having different crystallinities, for example polypropylene having isotactic and atactic portions.

The metallocenes used according to the invention include: including organometallic compounds containing cyclopentadienyl groups, preferably containing a group 4, 5 or 6 metal, especially a group 4 metal. In the case of polymer components having different weight average molecular weights, it is desirable to have metallocenes, preferably containing group 4 metals, which produce lower molecular weight fractions.

Metallocenes are an example of complexes in which a metal is complexed by an η -ligand, i.e., the metal in the complex is complexed by an elongated H-orbital system of organic ligands. In the present invention, the metal may be used when it is coordinated with 1, 2 or more η -ligands: eta-ligand complex. The use of bis eta-ligand metallocenes and mono eta-ligand "half metallocenes (as developed by Dow) is particularly preferred. However, the term metallocene as used herein relates to all catalytically active complexes containing 1 or more η -ligands. The metal in such complexes is preferably a group 4, 5, 6, 7 or 8 metal or a metal of the lanthanide or actinide series, especially a group 4, 5 or 6 metal, especially Zr, Hf, Ti or Cr. The eta-ligand preferably comprises a cyclopentadienyl ring, optionally carbocyclic ring substituted by a heteroatom (e.g. N, B, S or P), optionally substituted by pendant or fused ring substituents, and optionally linked by a bridge (e.g. a bridge of 1 to 4 atoms, e.g. (CH)₂)₂、C(CH₃)₂Or Si (CH)₃)₂) To another optionally substituted homocyclic or heterocyclic cyclopentadiene hydrocarbon. The ring substituents may, for example, be halogen atoms or alkyl groups, alkyl groups optionally substituted with heteroatoms, for example O, N and Si, especially Si and O, and optionally substituted with mono-or polycyclic rings, for example phenyl or naphthyl. Examples of such homocyclic or heterocyclic cyclopentadienyl ligands are known from the scientific and patent literature, i.e.from the patent applications Hoechst, Montell, Borealis, Exxon and Dow, for example from EP-A-416815, WO 96/04290, EP-A-485821, EP-A-485823, US-A-5276208 and US-A-5145819.

Thus, η -binding ligands, for example, may be represented by formula I:

CpY_m(I) wherein Cp is an unsubstituted, mono-or polysubstituted homocyclic or heterocyclic cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, benzindenyl, cyclopenta (1) phenanthryl, azulene or octahydrofluorenyl ligand; m is zero or an integer having 1, 2, 3, 4 or 5; and each Y is the same or different substituent, which is attached to the cyclopentadiene of the Cp moiety and is selected from the group consisting of a halogen atom, and an alkyl group, an alkenyl group, an aryl group, an aromatic ring group, an alkoxy group, an alkylthio group, an alkylamino group, an (alkyl group)₂P, an alkylsilyloxy, an alkylmethylgermyloxy, an acyl, an acyloxy and an amido group, or a group wherein Y contains one atom or provides a chain of atoms containing 1 to 4 atoms selected from C, O, S, N, Si and P, particularly C and Si (i.e., a vinyl group), which is linked to a second unsubstituted, mono-or poly-substituted homocyclic or heterocyclic cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl or octahydrofluorenyl ligand group.

In the η -linked ligands of formula I, the ring fused to the cyclopentadienyl ring of the homocyclic or heterocyclic ring may itself be optionally substituted by a halogen atom or a group containing 1 to 10 carbon atoms.

Many examples of such η -linked ligands and their synthesis are known from the literature, for example Mohring et al, j. 1-29(1994), Brirntzinger et al, Angew. chem. int. Ed. Engl.34: 1143-1170(1995).

Examples of suitable η -linking ligands include the following: cyclopentadienyl, indenyl, fluorenyl, pentamethylcyclopentadienyl, methyl-cyclopentadienyl, 1, 3-dimethyl-cyclopentadienyl, isopropyl-cyclopentadienyl, 1, 3-diisopropylcyclopentadienyl, n-butyl-cyclopentadienyl, 1, 3-di-n-butylcyclopentadienyl, tert-butyl-cyclopentadienyl, 1, 3-di-tert-butylcyclopentadienyl, trimethylsilyl-cyclopentadienyl, 1, 3-bistrimethylsilyl-cyclopentadienyl, benzyl-cyclopentadienyl, 1, 3-dibenzyl-cyclopentadienyl, phenyl-cyclopentadienyl, 1, 3-diphenylcyclopentadienyl, naphthyl-cyclopentadienyl, 1, 3-dinaphthylcyclopentadienyl, cyclopentadienyl, benzyl-methyl-, benzyl-or benzyl-methyl-, benzyl-cyclopentadienyl, phenyl-cyclopentadienyl-1, 3-diphenyl-cyclopentadienyl-1, 3-dinaphthylcyclopentadienyl, 1-methyl-indenyl, 1, 3, 4-trimethylcyclopentadienyl, 1-isopropyl-indenyl, 1, 3, 4-triisopropylcyclopentadienyl, 1-n-butyl-indenyl, 1, 3, 4-tri-n-butylcyclopentadienyl, 1-tert-butyl-indenyl, 1, 3, 4-tri-tert-butylcyclopentadienyl, 1-trimethylsilyl-indenyl, 1, 3, 4-tri-trimethylsilyl-cyclopentadienyl, 1-benzyl-indenyl, 1, 3, 4-tribenzylcyclopentadienyl, 1-phenyl-indenyl, 1, 3, 4-triphenylcyclopentadienyl, 1-naphthyl-indenyl, 1, 3, 4-trinaphthylcyclopentadienyl, 1, 4-dimethyl-indenyl, 1-naphthyl-indenyl, 1, 4-diisopropyl-indenyl, 1, 4-di-n-butyl-indenyl, 1, 4-di-tert-butyl-indenyl, 1, 4-di-trimethylsilyl-indenyl, 1, 4-dibenzyl-indenyl, 1, 4-di-phenyl-indenyl, 1, 4-dinaphthyl-indenyl, methyl-fluorenyl, isopropyl-fluorenyl, n-butyl-fluorenyl, tert-butyl-fluorenyl, trimethylsilyl-fluorenyl, benzyl-fluorenyl, phenyl-fluorenyl, naphthyl-fluorenyl, 5, 8-dimethyl-fluorenyl, 5, 8-diisopropyl-fluorenyl, 5, 8-di-n-butyl-fluorenyl, 5, 8-di-tert-butyl-fluorenyl, 5, 8-di-trimethylsilyl-fluorenyl, 5, 8-dibenzyl-fluorenyl, 5, 8-diphenyl-fluorenyl, and 5, 8-dinaphthyl-fluorenyl.

In addition to the eta-ligands, the catalyst ligands used in the present invention may comprise other ligands: typically, it may be a halide, hydride, alkyl, aryl, alkoxy, aryloxy, amide, carboxamide, or other two electron donor group.

In a preferred embodiment, the catalyst composition comprises a mixture of di η -ligand catalysts, preferably non-bridged and bridged bis- η -ligand complexes of group 4, 5 or 6 metals, e.g. the non-bridged η -ligand complex is a metallocene with a cyclopentadienyl ligand having two homocyclic or heterocyclic rings, which are optionally substituted rings by fused or pendant substituents, and the bridged η -ligand complex contains two η -ligand groups connected by a chain of 1 to 4 atoms. An example of a metallocene composition is: (i) unbridged dicyclopentadienylDienyl Ti, Zr, or Hf compounds; and (ii) bridged bis-indenyl Ti, Zr or Hf compounds, e.g. substituted Cp₂ZrCl₂With optionally substituted CH₂CH₂(indenyl)₂ZrCl₂Or Si (CH)₃)₂(indenyl)₂ZrCl₂Are combined. Another composition is a dimethylsilylbis (fluorenyl) Ti, Zr or Hf complex (e.g., optionally substituted SiMe)₂(fluorenyl) ZrCl₂) And substituted biscyclopentadienyl Ti, Zr, or Hf complexes. Particularly preferred catalyst compositions for use in the present invention include: (i) cp^* ₂ZrCl₂(Cp^*Pentamethyl-substituted cyclopentadienyl) and rac-dimethylsilylbis (2-methyl-4-phenyl) indenyl zirconium dichloride; (ii) cp^* ₂ZrCl₂And bis (n-butylcyclopentadienyl) hafnium dichloride; and (iii) (nBuCp)₂ZrCl₂And Et (1-indenyl)₂HfCl₂。

The different types of catalyst sites of the catalyst material used in the process of the present invention are present in substantially the same number (i.e., in a 1: 1 or 1: 1 molar ratio for two or three catalyst type systems). However, one of the catalyst types which may be predominant may be present in a proportion of relative mol%, for example from 1 to 100% (100% representing a 1: 1 molar ratio), preferably from 5 to 80%, particularly preferably from 10 to 70%.

Catalyst systems useful in olefin polymerization may include: one or more cocatalysts or catalyst activators, and, in this regard, any suitable cocatalyst or activator may be used.

Examples of cocatalysts and catalyst activators suitable for use in the present invention include: trialkylaluminums (i.e. triethylaluminums), alumoxanes such as methylalumoxane, cationic activators such as boron-containing compounds, transition metal compounds (i.e. halide compounds), magnesium compounds, group iii organometallic compounds, i.e. aluminum or boron-based compounds. These materials may be solid, liquid or may be in solution in the catalyst liquid phase which is a solution in solution, solid, dispersion, suspension, slurry, or the like.

Preferred aluminoxanes include: c_1-10Alkylalumoxanes, in particular methylalumoxane, and also aluminoxanes in which the alkyl group contains an isobutyl group optionally in combination with a methyl group. This aluminoxane may be used as the sole cocatalyst or, alternatively, with other cocatalysts. Thus, in addition to alumoxane, other cationic complexes forming catalyst activators may be used. Silver and boron compounds known from the prior art may be mentioned in this connection. Such activators are desirable because they can react with η -ligand complexes to produce organometallic cations and non-coordinating cations (see, e.g., non-coordinating anion J-discussed in EP-A-61705 2 (Asahi)).

Aluminoxane cocatalyst, described by Hoechst in WO 94/28034. These are those having up to 40, preferably 3 to 20, - [ Al (R') O]Cage cyclic oligomers of repeating units (in which R' is a hydrogen atom, C)_1-10Alkyl (preferably methyl and/or isobutyl) or C_6-18Aryl groups or mixtures thereof).

The support material of the catalyst system may be an inorganic or organic support material, preferably a solid particulate material, which is preferably porous. Used herein are the usual catalyst support materials, for example porous inorganic or organic materials, for example oxides such as silica, alumina, silica-alumina, silica with Ti, zirconia and the like; non-oxides, e.g. magnesium halides, e.g. MgCl₂Aluminum phosphate, zeolite, etc.; and polymers, such as polystyrene, polymethacrylates, polystyrene-divinylbenzene, and polyolefins, such as polyethylene and polypropylene.

When an inorganic support material is used, it is preferably subjected to a treatment, for example, thermal or chemical treatment, to remove surface hydroxyl groups.

Preferably, the ratio of the different metallocenes is substantially uniform within the support particle, i.e., the preferred ratio is the same both on the surface of the particle and at different depths within the particle, and the ratio is substantially uniform from particle to particle.

The polymerization is carried out by a general method, for example, a slurry, gas phase, solution or high pressure polymerization method. Slurry polymerization comprises: polymerization under slightly supercritical conditions. Mixed gas phase and slurry reactors are preferred. Slurry polymerisation (e.g. bulk polymerisation) is preferably carried out, for example, in a tank reactor, or more preferably in a loop reactor. In a slurry reactor, if the primary monomer is propylene, it also acts as a solvent/diluent as well as a reactant. If the main monomer is ethylene, the non-polymerizable organic compound, e.g. C_3-10Alkanes, such as propane or isobutane, may be used as diluents. If this is the case, it is desirable to recover and reuse the volatile, non-reactive or non-reactive materials.

The reactor used in the process of the present invention may be any one of polymerization reactors generally used, for example, a reactor for solution polymerization, a slurry tank or a reactor for slurry loop polymerization or gas phase polymerization, etc.

For slurry reactors, the reaction temperature is typically in the range of 60 to 100 deg.C (e.g., 85 to 110 deg.C), and the reaction pressure is typically in the range of 5 to 80 bar (e.g., 25 to 65 bar), so that the residence time is typically in the range of 0.3 to 5 hours (e.g., 0.5 to 2 hours). The diluent used is generally an aliphatic hydrocarbon having a boiling point in the range-70 to +100 ℃. In such reactors, the polymerization is carried out, if desired, under supercritical conditions, in particular in a loop reactor.

For gas phase reactors, the reaction temperature is usually 60 to 115 ℃ (e.g., 70 to 110 ℃), the reactor pressure is usually 10 to 25 bar, and the residence time is usually 1 to 8 hours. The gas used is generally a non-reactive gas, such as nitrogen, used with the monomer (i.e., ethylene or propylene).

For solution phase reactors, the reaction temperature used is generally from 130 to 270 ℃, the reactor pressure is generally from 20 to 400 bar, and the residence time is generally from 0.1 to 1 hour. The solvent used is generally a hydrocarbon having a boiling point in the range of 80 to 200 ℃.

In the process of the present invention, the catalyst material is introduced into the reactor as a single material containing all the constituents of the catalyst material, which may be a solution, a solid, a dispersion, a suspension or a slurry, etc.

The amount of catalyst generally used depends on the nature of the catalyst, the type and conditions of the reactor, and the nature of the polymer product desired. Typical amounts of catalyst may be used, for example as described in the literature indicated herein.

In the process of the present invention, hydrogen is used to further control the molecular weight of the olefin copolymer produced in the reactor. The control of the molecular weight can be performed by controlling the hydrogen concentration, or by controlling the consumption of hydrogen in the polymerization process. In this case, it is preferred to use a catalyst system which is reactive towards hydrogen. By monitoring the consumption of hydrogen and monomer, i.e. the difference between the hydrogen input and output, and the difference between the monomer input and output, it is easy to achieve control of the overall molecular weight of the polymer. The ratio of hydrogen consumed to monomer consumed is closely related to the polymer molecular weight, and the molecular weight of the product can be adjusted accordingly using this relationship and by appropriately adjusting the hydrogen and monomer feed rates.

The process of the present invention, in addition to the polymerization step, may optionally comprise other steps, such as a drying step; a mixing step of the polymer product with one or more other materials such as other polymers, antioxidants, radiation (i.e. UV light) stabilizers, antistatic agents, fillers, plasticizers, carbon black, pigments, etc.; granulating, extruding and granulating; and the like.

The final polymer product of the process of the invention preferably has a melt flow rate of 0.1 to 500, a weight average molecular weight of 30000 to 500000 and a melting point of 70 to 165 ℃ (e.g., 70 to 136 ℃ for ethylene copolymers and 120 to 165 ℃ for propylene copolymers).

Such polymers may be compounded with conventional additives such as antioxidants, UV stabilizers, colorants, fillers, plasticizers, and the like, and may be used in making fibers or extruded films, in making raffia and pipes, as cables or wires, or in forming, i.e., injection molding, blow molding, rotational molding, and the like, using conventional forming and extrusion equipment.

The products of the invention have improved molecular weight and polymer chain defect distribution. With the process of the invention, there are particular advantages in being suitable for bringing the molecular weight distribution into the higher molecular weight fraction of the overall polymer, and it is possible to do so that the comonomer (mainly providing side chains, giving strength increase) is mainly in the high molecular weight fraction. For example, using the process of the present invention, the comonomer may be incorporated more into long chains than into shorter polymer chains, as a comparison, for example, improving the mechanical strength of the polymer product compared to that obtained using a ziegler or phillips-type catalyst in a similar process. At the higher molecular weight end, there is a bimodal or multimodal distribution, the homogenization is facilitated to be improved by the use of a suitable metallocene composition, the lower molecular weight component of the high molecular weight fraction reducing the viscosity of the high molecular weight fraction. Higher molecular weight fractions, if not having such lower molecular weight ends, would create melt homogenization problems and, therefore, result in a non-uniform melt.

Thus, the process of the present invention will allow the user to tailor the comonomer location into the high molecular weight fraction of the polymer and also tailor this high molecular weight fraction of the polymer to the molecular weight profile.

The polymers made using the catalyst or process of the present invention have many advantageous properties over polymers made using conventional techniques. For example, when comonomers such as but-1-ene or hex-1-ene are used, this is incorporated primarily into the long polymer chains rather than into the short polymer chains, resulting in improved mechanical strength and processability of the polymer product.

In addition, the polymer product has high inter-particle homogeneity. The homogeneity of the polymer is often a factor especially relevant to the end user, as inhomogeneities will give rise to the known phenomena of fish eyes, gelling or white spots. This is particularly important not only for films, but also for wires, cables, blow molded products, injection molded products, rotational molded products, pipes and fibers.

Highly homogeneous multimodal, e.g. bimodal, olefin production with controlled comonomer incorporation, carried out in a single polymerisation stage, has hitherto remained problematic. In the process of the present invention, the use of simultaneously co-impregnated catalyst support particles to prepare a supported catalyst having two or more catalytic sites prone to different comonomers can be used to prepare highly homogeneous polymers in a single polymerization step in a much simpler manner than hitherto thought.

The polymers prepared according to the process of the invention can be analysed using techniques known in the art. Techniques suitable for separating individual portions of a copolymer sample include temperature rising elution fractionation. A differential scanning calorimeter, preferably using a stepwise isothermal segregation technique, can be used to measure comonomer content (see j.a. parker, d.c. basett, r.h. olley)& P.Jaaskelainen，Polymer³⁵[1994],4140). Various methods are known in the art for determining the molecular weight distribution of a particular polymer sample; the measurement is usually carried out by gel permeation chromatography.

The contents of all the related information referred to above are hereby incorporated by reference.

The invention will now be further illustrated by the following non-limiting examples and the accompanying drawings. Wherein,

FIG. 1 is a differential scanning calorimetry curve for polymers made using a conventional single-site catalyst system.

FIGS. 2-5 and 7 are differential scanning calorimetry curves for polymers made according to the present invention using a dual site catalyst system and corresponding differential scanning calorimetry curves for polymers made using a conventional single site catalyst system.

FIG. 6 is a gel permeation chromatography curve for a polymer made according to the present invention and a corresponding gel permeation chromatography curve for a polymer made using a conventional single site catalyst system.

FIG. 8 is a gel permeation chromatography curve of an ethylene homopolymer made according to the present invention.

In the following examples, the following abbreviations are used:

Cp^*a pentamethyl-substituted cyclopentadienyl ligand,

(CH₃)₅Cp；

GPC ═ gel permeation chromatography

MAO-methylaluminoxane

MW ═ molecular weight

Mw-weight average molecular weight

MWD ═ molecular weight distribution

SIST (single-input single-output) stepwise isothermal segregation technology

TREF-temp. rising elution fractionation

Example 1 preparation of catalyst Supported catalyst (A)

The following chemicals were mixed to prepare a catalyst solution:

0.0024g of rac-dimethylsilylbis (2-methyl-4-phenylindenyl) zirconium dichloride

2.2ml of MAO solution (MAO in toluene, 30% by weight)

-1ml of toluene

The resulting solution was stirred at room temperature for 30 minutes.

The above solution was then added dropwise with stirring to 2g of porous granular silica supplied by 55SJ, Grace. The silica was previously calcined in a stream of dry air at 600 ℃. The catalyst solution was added dropwise in a ratio of 2g of the carrier to 3.2ml of the catalyst solution. Stirring was continued at room temperature for a further 60 minutes. The mixture was dried over 60 minutes with a stream of nitrogen to yield a supported catalyst. Supported catalyst (B)

The following chemicals were mixed to prepare a catalyst solution:

-0.0248gCp^* ₂ZrCl₂

2.2ml of MAO solution (MAO in toluene, 30% by weight)

-1ml of toluene

The resulting solution was stirred at room temperature for 30 minutes.

Then, the solution was added dropwise to the above 2g of 55SJ with stirring. Stirring was continued at room temperature for 60 minutes. The mixture was dried over 90 minutes with a stream of nitrogen to produce a supported catalyst. Supported catalyst (C)

The following chemicals were mixed to prepare a catalyst solution:

-0.0248gCp^* ₂ZrCl₂

-0.0028g of rac-dimethylsilylbis (2-methyl-4-phenylindenyl) zirconium dichloride

2.2ml of MAO solution (MAO in toluene, 30% by weight)

-1ml of toluene

The resulting solution was stirred at room temperature for 30 minutes.

Then, the solution was added dropwise to the above 2g of 55SJ with stirring. Stirring was continued at room temperature for a further 60 minutes. The mixture was dried for 90 minutes with a nitrogen stream to produce a supported catalyst. Supported catalyst (D)

The following chemicals were mixed to prepare a catalyst solution:

0.002 bis (n-butylcyclopentadienyl) hafnium dichloride

2.2ml of MAO solution (MAO in toluene, 30% by weight)

-1ml of toluene

The resulting solution was stirred at room temperature for 30 minutes.

Then, the solution was added dropwise to 2g of 55SJ above with stirring. Stirring was continued at room temperature for a further 60 minutes. The mixture was dried over 120 minutes with a stream of nitrogen to produce a supported catalyst. Supported catalyst (E)

The following chemicals were mixed to prepare a catalyst solution:

-0.0244gCp^* ₂ZrCl₂

0.002g of bis (n-butylcyclopentadienyl) hafnium dichloride

2.2ml of MAO solution (MAO in toluene, 30% by weight)

-1ml of toluene

The resulting solution was stirred at room temperature for 30 minutes.

Then, the solution was added dropwise to the above 2g of 55SJ with stirring. Stirring was continued at room temperature for 60 minutes more. The mixture was dried over a period of 120 minutes with a stream of nitrogen to produce a supported catalyst.

Example 2 polymerization

Ethylene polymerization was carried out in a 2-liter reactor using the catalysts (A) to (E). Isobutane (1 liter) containing 0.02% by weight of hexene and a catalyst were fed to the reactor, and the reaction was allowed to proceed to a desired extent under elevated temperature and pressure.

Pure ethylene gas was added through a pressure control valve and the polymerization was carried out under the following conditions: total pressure 24 bar, temperature 80 ℃ and polymerization time 60 minutes.

The results obtained are shown in table 1 below. TABLE 1

	Catalyst (A)	Catalyst (B)	Catalyst (C)	Catalyst (D)	Catalyst (E)
						Weight of catalyst (g)	0.424	0.31	0.331	0.478	0.417
Ethylene partial pressure (Bar)	10	10	10	10	10
						C6Ethylene cascade reaction (wt.% C)6)	5	5	5	5	5
Weight of Polymer (g)	177	41	34	235	70
						Productivity (g Polymer/g catalyst)	417	132	103	492	168
Activity (g/g. h)	1,565	132	103	492	168
						GPC，Mw	710,000	345,000	255,000	570,000	405,000
GPC，Mn	150,000	53,000	60,000	165,000	80,000
						GPC，MWD	4.7	6.5	4.3	3.5	5.1
Remarks for note	Foul smell			Foul smell

DSC analysis was performed with SIST annealing under the following conditions:

step temperature time at corresponding temperature to next temperature rate

(. degree. C.) (min) (K/min)

1 200 5 200

2 131 120 200

3 118 120 200

4 105 120 200

5 92 120 200

6 79 120 200

7 66 120 1

8 10 - -

Each sample was then heated at a rate of 10K/min to produce the melting curves given in FIGS. 1-5.

FIG. 1 shows the melting curves of the polymers prepared with catalysts (A) and (D). At different melting temperatures, the curves have the same height, indicating a greater proportion of polymer at the lower melting temperature than at the higher melting temperature. This is due to the difference in crystallinity and therefore, at lower melting temperatures, has a lower specific melting enthalpy. The relative concentration of polymer at each melting temperature is highly evident from the graph in FIG. 1. This means that the product obtained with catalyst (A) has a lower crystallinity than the product obtained with catalyst (D) and the crossing point is about 65 ℃. Both polymers were found to exhibit some degree of fouling in the reactor.

FIGS. 2 and 3 show the melting curves of the polymer made using the two-site catalyst (E) and the polymers made using the corresponding single-site catalysts (B) and (D). The dual-site catalyst does not generate foul smell. This is considered to be an unexpected result, each of the low crystalline polymer components having a melting temperature lower than the polymerization temperature. The two-site DSC curve corresponding to products with a low crystallinity component corresponds well to the melting curve of those products made with the catalyst component alone. The shift of the main peak can be explained by co-crystallization.

FIGS. 4 and 5 show the melting curves of the polymer made using the two-site catalyst (C) and the polymer made using the single-site catalysts (A) and (B). The dual site catalyst is foul free.

In FIGS. 1 to 5, the numbers appearing on the temperature scale indicate the% by weight of hexene corresponding to this melting temperature (calculated value). These numbers can be calculated from calibration of single site polyethylene and fractions collected by chemical structure fractionation. Calibration can be done by linear approximation of comonomer content (determined by C-13 NMR) and melting temperature (determined by DSC) according to the following equation:

y-0.5228 t +68.205 wherein Y is the% by weight of hexene and t is the melting temperature. Similarly, the comonomer content can be determined according to the following equation:

y-0.8714 t +113.67 wherein Y is the comonomer content (number of branches per 1000 carbon atoms) and t is the melting temperature.

The GPC analysis was carried out under the following conditions.

The device comprises the following steps: waters 150CV, plus No.1115

A detector: refractive Index (RI) and viscosity detector

Calibration (1115-9903): narrow molecular weight distribution PS

Column: 3 XHT 6E Styragel (polystyrene type crosslinked copolymer) from Waters corporation (140 ℃ C.)

The results are shown in FIG. 6. The high molecular weight tail peak of the polymer produced by the catalyst (E) is represented by the symbol ". sup.". This is believed to be higher than the result from the simple addition of molecular weights and may be evidence of the general synergistic effect of the dual site catalyst system of the present invention.

The low crystallinity/high comonomer/high Mw tail plot further demonstrates that products containing low and high molecular weight blends, homo-and copolymers, can be made in a single reaction step according to the present invention.

Example 3 catalyst preparation Supported catalyst (F)

The catalyst was produced by a method similar to that of the supported catalyst (D) except that zirconium was used in place of hafnium, and the relative amount was adjusted so that the supported catalyst contained 0.027mmol (nBuCp)₂ZrCl₂Per gram of support; and 5.6mmol Al (from MAO)/g support. Supported catalyst (G)

0.044g (n-butylCp)₂ZrCl₂0.0269g ethyl (1-indenyl)₂HfCl₂1.2ml of MAO solution in toluene (30% by weight MAO in toluene, from Albemarle SA) and 0.4ml of toluene were mixed to prepare a catalyst solution, which was used to prepare a double impregnated support as described above.

The supported catalyst product contained, by calculation, 0.011mmol (n-butylCp)₂ZrCl₂Per gram of support; 0.0531mmol of ethyl (1-indenyl)₂HfCl₂Per gram of support; and 5.5mmol Al (from MAO)/g support.

Example 4 polymerization

Ethylene polymerization was carried out in a 2-liter semi-batch reactor (ethylene continuous feed) using catalysts (F) and (G). Isobutane (1 liter) containing hexene and a catalyst were placed in the reactor, and the temperature and pressure were controlled to the desired values (85 ℃ and 29 bar). The polymerization was carried out in the absence of hydrogen for 60 minutes.

The results are shown in Table 2 below.

TABLE 2

	Catalyst (F)	Catalyst (G)	Catalyst (G)
				Hexene (wt% in isobutane)	2.9	2.9	0.18
Mw(g/mol)	105,000	130,000	175,000
				MWD	2.1	2.4	2.7
Tm (Peak) (. degree.C.)	122.6	125.2	132.2
				ΔHm	148.0	147.5	181.8
Activity of	6,692	1,533	737

The DSC curve of the final polymer product is shown in FIG. 7. These DSC measurements can be obtained using standard annealing, i.e. crystallization from 200 ℃ to 0 ℃ with a cooling rate of 10K/min, and melting by SIST.

The polymers prepared with high concentrations of hexene and catalyst (F) exhibit the typical DSC melting characteristics of single component copolymers during polymerization.

The polymers produced with catalyst (G) each contain 2 different crystalline components. This is particularly evident in products made with high concentrations of hexene, where clear shoulders are visible in the high crystallinity region. The overall curve also shifts towards higher melting temperatures. This is probably due to the reaction of high comonomer consuming the Hf sites of most of the added comonomer, thus causing lower incorporation of comonomer in the polymer created by the Zr sites. For products made with low hexene concentrations, perturbations on both sides of the peak were detected, demonstrating at least two components.

During the polymerization, a high concentration of hexene is used and the product made with catalyst (G) has a higher Mw and a higher molecular weight distribution than the product made with catalyst (F). The melting temperature increases together with the enthalpy of fusion held, which can be explained by the presence of two polymer fractions, one of which has a lower Mw and comonomer content than the other.

Example 5 polymerization

In a 2 l reactor, homopolymerization of ethylene was carried out with catalysts (C) and (E). The dried catalyst was placed in the reactor under a nitrogen purge, then hexene-free isobutane (650ml) was added and the temperature was rapidly increased from 15 ℃ to 80 ℃. Pure ethylene gas was added to increase the ethylene partial pressure from 0 liter to 10 bar over 2 minutes, giving a total reactor pressure of 24 bar. The polymerization time was 60 minutes. The results are shown in Table 3.

TABLE 3

	Catalyst (C)	Catalyst (E)
			Weight of catalyst (mg)	420	320
Weight of Polymer (g)	4	3
			GPC Mw	1,000,000	600,000
GPC Mn	40,000	38,000
			Weight average of g'	0.7	0.8

(in the table, g' is the ratio of the viscosity measured on a linear polymer having the same molecular weight to the theoretical viscosity)

Viscosity measurements on molecular weight demonstrate that these samples exhibit viscosity properties that lie between those of linear polyethylene (g '═ 0.95) and highly branched polyethylene (HPPE, g' ═ 0.61).

FIG. 8 shows the MWD of a sample from GPC measurements, with the abscissa representing log (MW) and the ordinate representing dW.MW/d (MW), where W is the polymer mass or mass fraction.

Example 6 catalyst preparation Supported catalyst (H)

The catalyst was prepared by a preparation process similar to that of the supported catalyst (F), giving a supported catalyst product containing 0.0314g of rac-dimethylsilylbis (indenyl) -zirconium chloride. Supported catalyst (I)

The catalyst was prepared by a preparation process similar to that of the supported catalyst (F) which gave a supported catalyst product containing 0.0384g of dimethylsilylbis (9-indenyl) -zirconium chloride. Supported catalyst (J)

A double impregnated support was made in a similar way to the supported catalyst (G), giving a supported catalyst containing: 90 mol% (0.0283g) rac-dimethylsilylbis (indenyl) zirconium chloride and 10 mol% (0.0038g) dimethylsilylbis (9-fluorenyl) zirconium chloride.

Example 7 polymerization

Propylene polymerization was carried out in a 2-liter reactor using the catalysts (H) to (J). The dried catalyst was placed in the reactor under a nitrogen purge, and then polypropylene (650ml) was added. After a prepolymerization at a temperature of 15 ℃ for 8 minutes, the temperature was rapidly raised to 70 ℃. The polymerization time was 60 minutes. The results obtained are shown in Table 4 below.

TABLE 4

	Catalyst (H)	Catalyst (I)	Catalyst (J)
				Mw	40000	200000	42000
Mn	20000	60000	15000
				MWD	2	3.3	2.8
Crystallinity of the compound	Height of	Is very low	Mixing of

The polymer produced with catalyst (J) dissolved 11% in xylene, this fraction having Mw120000 and Mn of 6000(MWD ═ 10), while the xylene insoluble crystalline phase has Mw 37000 and Mn of 19000(MWD ═ 2). This demonstrates the presence of both high and low crystalline fractions in this bimodal product.

Claims (19)

1. A process for preparing an olefin polymer, comprising: olefin polymerization is carried out in a single reactor under substantially constant conditions in the presence of a catalyst system comprising a support material co-impregnated with at least 2 metallocene olefin polymerization catalysts having different tendencies to bind polymer chain defects.

2. The process of claim 1 wherein said metallocene is selected for the production of an olefin polymer comprising at least a higher molecular weight fraction and a lower molecular weight fraction, wherein said higher molecular weight fraction has a polymer chain defect content of at least three times that of said lower molecular weight fraction.

3. The process of claim 2 wherein said metallocene is selected so that the polymer chain defect content of said higher molecular weight fraction is at least 10 times that of said lower molecular weight fraction.

4. The process of any preceding claim wherein at least one of said metallocenes comprises a group 4 metal.

5. The process of claim 4 wherein the catalyst system comprises at least a first metallocene selected from the group consisting of rac-dimethylsilylbis (2-methyl-4-phenylindenyl) zirconium dichloride, bis (n-butylcyclopentadienyl) hafnium dichloride, ethylbis (1-indenyl) hafnium dichloride, and rac-dimethylsilylbis (9-fluorenyl) zirconium dichloride; and a second metallocene selected from bis (pentamethylcyclopentadienyl) zirconium dichloride, bis (n-butylcyclopentadienyl) zirconium dichloride, and dimethylsilylbis (9-fluorenyl) zirconium dichloride.

6. A process as claimed in any one of the preceding claims, wherein the catalyst system further comprises a cocatalyst.

7. The process of claim 6, wherein the co-catalyst is methylalumoxane.

8. A method as claimed in any preceding claim, wherein the support material is porous particulate silica.

9. A process as claimed in any preceding claim, wherein ethylene or propylene is polymerised.

10. The process of claim 9 wherein the polymerization is carried out in the presence of an alpha-olefin comonomer containing up to 10 carbon atoms.

11. The process of claim 10, wherein ethylene is copolymerized with 1-hexene.

12. The process of any preceding claim wherein the olefin polymer is thereafter subjected to at least one further polymerization reaction.

13. The process of claim 12, wherein the further polymerization reaction comprises the process of claim 1.

14. A polyolefin having essentially complete interparticle homogeneity and comprising at least a higher molecular weight fraction and a lower molecular weight fraction, wherein the higher molecular weight fraction has a polymer chain defect content of at least 3 times that of the lower molecular weight fraction.

15. A polyolefin as claimed in claim 14 wherein the polymer chain defect content of said higher molecular weight fraction is at least 10 times that of said lower molecular weight fraction.

16. A polyolefin as claimed in claim 14 or claim 15 wherein the polymer chain defects are selected from side chains and crystallinity-perturbing monomer units.

17. A polyolefin as claimed in claim 16 wherein the polymeric chain defects comprise comonomer-derived short chain branching.

18. A polyolefin as claimed in claim 16 or claim 17 wherein the polymer chain defects comprise long chain branching comprising at least 10 monomer units.

19. A polyolefin as claimed in claim 18 wherein the long chain branching is substantially homopolymeric.

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