TW202438539A - Process for producing a high-flow polypropylene homopolymer - Google Patents

Abstract

The present invention relates to a process for the production of a polypropylene homopolymer, the process comprising the steps of (a) polymerizing in a first reactor propylene in the presence of a metallocene catalyst yielding a first polypropylene homopolymer fraction having a MFR2 of 1 to 50 g/10min measured according to ISO 1133, (b) transferring the first polypropylene homopolymer fraction to a second reactor, (c) polymerizing in the second reactor propylene in the presence of the first polypropylene homopolymer fraction yielding a second polypropylene homopolymer fraction, (d) withdrawing the polypropylene homopolymer comprising the first polypropylene homopolymer fraction and the second polypropylene homopolymer fraction from the second reactor, wherein the polypropylene homopolymer has a MFR2 of 20 to 200 g/10min measured according to ISO 1133, wherein the metallocene catalyst comprises a metallocene complex and a support, wherein the support comprises silica, and wherein a split ratio between the first polypropylene homopolymer and the second polypropylene homopolymer is 20:80 to 80:20.

Description

Method for producing high fluidity polypropylene homopolymer

The present invention relates to a method for preparing a polypropylene homopolymer, and more particularly to a metallocene-catalyzed high-flow polypropylene homopolymer with improved rigidity.

As the need to save energy, downsizing and lightweighting become more important, the demand for polypropylene homopolymers with excellent stiffness at high flowability continues to increase. High-flow polypropylene is often used for molding, especially in the automotive industry, where injection molding is the preferred conversion process. Especially in glass fiber reinforced applications, high-flow homopolymers with good mechanical properties and high thermal stability are required. In addition, the addition of high-flow homopolymers with excellent impact-stiffness balance can allow the manufacture of automotive compounds with higher melt flow rates (MFR) without losing the required mechanical properties.

From the perspective of a multi-stage propylene polymerization process, balancing the production rates in different reactors can be a challenge.

For example, in a multi-stage polymerization process using, for example, a two-reactor system, two important parameters that need to be controlled are the reactor balance and the reactor split between the reactors. This is important from a plant economics perspective, but also from a product properties perspective.

Typically, the reactor split in a two-reactor system (also called "production split") is between 40/60 and 60/40%, and, if a third reactor is used to produce heterophasic copolymer elastomers, the reactor split in the last reactor is typically between 5 and 30%. In a four-reactor mode, typically two rubber gas phase reactors (GPRs) are used, and the total split in the last reactor for making heterophasic products can be between 10% and 40%, with the split between the rubber GPRs being between 50/50 and 90/10%. In the case of a three-mode process, typically, the first three reactors produce polypropylene homopolymer (homo PP) or random polypropylene copolymer (random PP), and the split can be, for example, 45/35/20%.

However, in each of the above reactor systems, one challenge is the same, that is, controlling the production distribution according to the plant design. Otherwise, the plant operation is slow, the output is low, and the plant economics are poor.

Therefore, it may be an object of the present invention to provide a method for producing polypropylene homopolymer that overcomes the above challenges.

Another object of the present invention may be to provide a method for producing a high-flowability polypropylene homopolymer, particularly a metallocene-catalyzed high-flowability polypropylene homopolymer with improved rigidity.

Another object of the present invention may be to provide a method that is beneficial from a process point of view, for example, enabling increased throughput and plant speed, thereby improving reactor balance and plant economics.

The expression "homopolymer" as used herein refers to a polypropylene consisting essentially of propylene units, i.e., a polypropylene consisting of at least 99.5 wt%, more preferably at least 99.8 wt% of propylene units. In a preferred embodiment, only propylene units can be detected in the propylene homopolymer.

The "modality" of a polymer refers to the shape of its molecular weight (Mw) distribution curve, that is, the appearance of the curve of the polymer weight fraction as a function of its molecular weight. For example, when a polymer is produced in a continuous step process, utilizing reactors connected in series and using different conditions in each reactor, the different fractions produced in the different reactors will each have their own molecular weight distribution. When the molecular weight distribution curves of these fractions are superimposed on the molecular weight distribution curve of the total resulting polymer product, the latter will show two or more maxima, or at least be significantly broadened compared to the curves of the individual fractions. Such a polymer product produced in two or more continuous steps is called bimodal or multimodal, respectively, depending on the number of steps. In the following, for simplicity, all polymers produced in two or more consecutive steps are referred to as "multimodal". It should be noted that the chemical composition of the different distillates may also be different.

It has now surprisingly been found that the above objects can be achieved by a method for producing a polypropylene homopolymer, the method comprising the steps of: a) polymerizing propylene in a first reactor in the presence of a metallocene catalyst to produce a first polypropylene homopolymer distillate, the first polypropylene homopolymer distillate having an MFR ₂ of 1 to 50 g/10min, measured according to ISO 1133; b) transferring the first polypropylene homopolymer distillate to a second reactor; c) polymerizing propylene in the presence of the first polypropylene homopolymer distillate in the second reactor to produce a second polypropylene homopolymer distillate; and d) discharging a polypropylene homopolymer containing the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate from the second reactor, wherein the MFR ₂ of the polypropylene homopolymer is 20 to 200 g/10min, measured according to ISO 1133, wherein the metallocene catalyst comprises or consists of a metallocene complex and a carrier, wherein the carrier comprises or consists of silicon dioxide, and wherein the distribution ratio between the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate is 20 wt%:80 wt% to 80 wt%:20 wt%,

Wherein, the metallocene complex is an organic metal compound (C), and the organic metal compound (C) is represented by the following chemical formula (Ia): (L) ₂ R _n MX ₂ (Ia) wherein, "M" is zirconium or einsteinium; each "X" is a σ-ligand; each "L" is an optionally substituted cyclopentadienyl, indenyl or tetrahydroindenyl; "R" is a SiMe ₂ bridging group connecting the organic ligand (L); "n" is 0 or 1, preferably 1.

In a preferred embodiment, a method for producing a homopolymer of polypropylene is provided, the method comprising the following steps: a) polymerizing propylene in the presence of a metallocene catalyst in a first reactor to produce a first homopolymer distillate of polypropylene, wherein the MFR ₂ of the first homopolymer distillate is 1 to 50 g/10min as measured according to ISO 1133; b) transferring the first homopolymer distillate to a second reactor; c) polymerizing propylene in the presence of the first homopolymer distillate in a second reactor to produce a second homopolymer distillate of polypropylene; and d) discharging a polypropylene homopolymer containing the first homopolymer distillate and the second homopolymer distillate from the second reactor, wherein the MFR ₂ of the polypropylene homopolymer is 20 to 200 g/10min as measured according to ISO 1133, wherein the metallocene catalyst comprises a metallocene complex and a carrier, wherein the carrier comprises silicon dioxide, wherein the distribution ratio between the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate is 20 wt%:80 wt% to 80 wt%:20 wt%,

Wherein, the metallocene complex is an organic metal compound (C), and the organic metal compound (C) is represented by the following chemical formula (Ia): (L) ₂ R _n MX ₂ (Ia) wherein, "M" is zirconium or einsteinium; each "X" is a σ-ligand; each "L" is an optionally substituted cyclopentadienyl, indenyl or tetrahydroindenyl; "R" is a SiMe ₂ bridging group connecting the organic ligand (L); "n" is 0 or 1, preferably 1.

Therefore, the above problems can be solved by moderately broadening the weight average molecular weight (Mw) of the polypropylene homopolymer product, i.e., bimodal production. Moderately broadening and bimodal production of polypropylene homopolymer means, for example, producing a polypropylene homopolymer with a higher Mw (i.e., lower MFR) in the first reactor and a polypropylene homopolymer with a lower Mw (i.e., higher MFR) in the second reactor.

The present invention can provide many advantages. Significantly better flowability can enable the use of polypropylene homopolymer in molding applications, especially injection molding applications. Excellent flowability can further be accompanied by high stiffness. High stiffness is important for many uses of polypropylene.

At the same time, the process according to the invention is advantageous in terms of the economy of equipment and reactor balance. Fine tuning of the desired distribution between reactors can be achieved by controlling the weight average molecular weight (Mw) or melt flow rate, which in turn can be controlled by hydrogen feed.

To illustrate the above, for example, when producing a high Mw polypropylene homopolymer in the first reactor, a small amount of hydrogen is usually used to control the Mw and thus obtain a lower reactivity. Therefore, a larger amount of catalyst is required. In the second polymerization reactor, a lower Mw polypropylene homopolymer is produced, so a larger amount of hydrogen is required, which in turn speeds up production and helps with distribution control. This is important because as a function of time, a decay of the polymerization reaction can be seen due to the lifetime of the catalyst.

In step a), propylene is polymerized in the presence of a metallocene catalyst in a first reactor to produce a first polypropylene homopolymer fraction, preferably a first isomeric polypropylene homopolymer fraction, having an MFR ₂ of 1 to 50 g/10min, measured according to ISO 1133.

Preferably, step a) is carried out at a reactor temperature of 60 to 100°C, more preferably 65 to 90°C, and most preferably 70 to 80°C.

Preferably, step a) is carried out at a reactor pressure of 1 to 150 bar, more preferably 35 to 60 bar, even more preferably 40 to 55 bar, and most preferably 43 to 52 bar.

The first polypropylene homopolymer fraction produced in step a) preferably has an MFR ₂ determined according to ISO 1133 of 5 to 40 g/10min, more preferably of 10 to 30 g/10min.

Preferably, the first polypropylene homopolymer distillate has a cold xylene soluble distillate content (XCS) of 0.1 to 5.0 wt%, more preferably 0.5 to 4.0 wt%, still more preferably 1.0 to 3.0 wt%, and most preferably 2.0 to 2.8 wt%, as determined according to ISO 16152.

Step a) is preferably a slurry polymerization step, i.e., the polymerization of the polypropylene monomers is carried out in slurry.

The slurry polymerization in step a) is preferably a bulk polymerization process. "Bulk polymerization" refers herein to a process in which the polymerization is carried out in a liquid monomer in the substantial absence of an inert diluent. However, as is known to those of ordinary skill in the art, monomers used in commercial production are never pure, but always contain aliphatic hydrocarbons as impurities. For example, propylene monomer may contain up to 5% of propane as an impurity. Since propylene is consumed in the reaction and is also recycled from the reaction effluent back to the polymerization, inert components tend to accumulate, and therefore, the reaction medium may contain up to 40 wt% of other compounds besides the monomer. However, it should be understood that such a polymerization method is still within the meaning of "bulk polymerization" as defined above.

Step a) of the method of the present invention can be carried out in any known reactor, such as a loop reactor, a stirred reactor or a gas phase reactor. When step a) uses slurry polymerization, preferably bulk polymerization, step a) is preferably carried out in a continuous stirred tank reactor, and more preferably in a loop reactor.

Preferably, the first reactor is a loop reactor. In such a reactor, the slurry is circulated at high speed along a closed pipe by using a circulation pump. Loop reactors are generally known in the art to which the present invention belongs, and examples are given in, for example, US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654. Therefore, it is preferred to carry out the first polymerization stage in a loop reactor in the form of slurry polymerization.

Preferably, hydrogen is used in the first polymerization step a) to control the MFR ₂ of the first polypropylene homopolymer fraction. As will be appreciated by those skilled in the art, the amount of hydrogen required to achieve the desired MFR ₂ depends on the catalyst used and the polymerization conditions.

Preferably, in step a), the ratio of hydrogen feed to propylene feed is 0.10 to 0.50 mol/kmol, more preferably 0.15 to 0.40 mol/kmol, most preferably 0.20 to 0.30 mol/kmol.

Preferably, step a) uses an average residence time of 15 to 120 min, preferably 20 to 80 min. As is well known in the art to which the present invention belongs, the average residence time τ can be calculated by the following equation (1): Equation (1) where _VR is the volume of the reaction space (the volume of the reactor in the case of a loop flow reactor, the volume of the fluidized bed in the case of a fluidized bed reactor, or the volume of the gas phase reactor in the case of a gas phase reactor), and _Qo is the volume flow rate of the product stream (including polymer product and fluid reaction mixture).

The production rate is appropriately controlled by the catalyst feed rate. The production rate can also be influenced by the choice of appropriate monomer concentration. The desired monomer concentration can then be achieved by appropriately adjusting the propylene feed rate.

In step b), the first polypropylene homopolymer obtained in step a) is transferred to a second reactor, preferably directly to the second reactor. Preferably, the first polypropylene homopolymer distillate is transferred to the second reactor in the form of slurry. The slurry preferably comprises the first polypropylene homopolymer distillate, unreacted monomers and a metallocene catalyst.

The slurry can be discharged from the first reactor continuously or intermittently. A preferred way of intermittent discharge is to use settling legs, in which the slurry is concentrated before a batch of concentrated slurry is discharged from the reactor. The use of settling legs is disclosed in US-A-3374211, US-A-3242150 and EP-A-1310295, among others. Continuous discharge has been disclosed in EP-A-891990, EP-A-1415999, EP-A-1591460 and WO-A-2007/025640, among others. As disclosed in EP-A-1310295 and EP-A-1591460, continuous discharge is advantageously combined with a suitable concentration method. Preferably, the slurry is continuously discharged from the first reactor.

Preferably, the slurry discharged from the first reactor is directly transferred to the second reactor to produce the second polypropylene homopolymer fraction. "Directly" means that the slurry is introduced from the first reactor into the second reactor without any separation step, such as a burst separation step.

In step c), propylene is polymerized in the presence of the first polypropylene homopolymer distillate in a second reactor to obtain a second polypropylene homopolymer distillate, preferably a second same row polypropylene homopolymer distillate.

Step c) is preferably a gas phase polymerization step, that is, step c) is carried out in a gas phase reactor. Any suitable gas phase reactor known in the art to which the present invention belongs can be used, preferably, for example, a fluidized bed gas phase reactor.

Preferably, step c) uses an average residence time of 0.5 to 8 hours, more preferably 1 to 5 hours. It can be referred to the above equation (1).

The gases used are usually: a non-reactive gas such as nitrogen, or a low boiling point hydrocarbon such as propane; and the monomer, i.e. propylene.

Preferably, the reactor temperature in step c) is in the range of 60 to 90°C, more preferably 75 to 85°C.

Furthermore, step c) is preferably carried out at a reactor pressure in the range of 15 to 35 bar, more preferably 20 to 30 bar.

Preferably, the reactor temperature in step c) is in the range of 75 to 85°C, and step c) is carried out at a reactor pressure in the range of 20 to 30 bar.

Preferably, the metallocene catalyst used in step a) is present in the second reactor during the polymerization in step c). This is accomplished by transferring the metallocene catalyst used in step a) to the second reactor, preferably via a slurry. If desired, fresh metallocene catalyst may be added to the second reactor in step c).

A chain transfer agent, preferably hydrogen, is preferably added in step c). Preferably, in step c), the ratio of hydrogen feed to propylene feed used is 5.0 to 40.0 mol/kmol, more preferably 15.0 to 35.0 mol/kmol, and most preferably 20.0 to 30.0 mol/kmol.

A second polypropylene homopolymer distillate is obtained in the second reactor. Preferably, the combined first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate have an MFR ₂ of 20 to 200 g/10min, more preferably 30 to 100 g/10min, and even more preferably 40 to 80 g/10min, determined according to ISO 1133.

Preferably, the second polypropylene homopolymer distillate has a higher MFR ₂ than the first polypropylene homopolymer distillate.

In step d), a polypropylene homopolymer containing the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate is discharged from the second reactor. The discharged polypropylene homopolymer containing the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate may be further processed, for example, mixed with an additive.

Preferably, the method of the present invention further comprises step e): transferring the polypropylene homopolymer obtained in step d) to a third reactor downstream of the second reactor. In the third reactor, propylene and optionally one or more comonomers can be polymerized, the comonomers being selected from α-olefins having 2 to 10 carbon atoms, more preferably 4 to 10 carbon atoms. Preferably, the third reactor is a gas phase reactor.

Preferably, the polypropylene homopolymer obtained according to the process of the present invention is a homopolymer of polypropylene.

The MFR ₂ of the polypropylene homopolymer is preferably from 30 to 100 g/10min, more preferably from 40 to 80 g/10min, measured according to ISO 1133.

Preferably, the polypropylene homopolymer has a cold xylene soluble distillate content (XCS) of 0.1 to 4.0 wt%, more preferably 0.5 to 3.0 wt%, still more preferably 1.0 to 2.5 wt%, and most preferably 1.5 to 2.1 wt%, as determined according to ISO 16152.

Preferably, the polypropylene homopolymer is a bimodal polypropylene homopolymer.

Preferably, the polypropylene homopolymer has a flexural modulus of 1500 to 1650 MPa, more preferably 1550 to 1630 MPa, measured according to ISO 178.

Preferably, the polypropylene homopolymer has a melting _Tm temperature of 145.0 to 165.0°C, more preferably 150.0 to 160.0°C, as determined by DSC according to ISO 11357.

The polypropylene homopolymer has a crystallization temperature Tc of 100 to 140°C, measured by DSC according to ISO 11357.

Preferably, the distribution ratio between the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate is 30:70 to 70:30, more preferably 35:65 to 65:35. The distribution ratio is expressed as wt%/wt%.

Preferably, the first reactor is a loop flow reactor and the second reactor is a gas phase reactor.

A suitable process is the slurry-gas phase process consistent with the above, which has been developed, for example, by Borealis and is known as Borstar® technology. In this regard, reference is made to European patent applications EP 0887379 A1 and EP 0517868 A1.

A prepolymerization step a') may be performed before steps a) to d) of the method according to the present invention. Therefore, the method according to the present invention preferably further comprises a prepolymerization step a') before step a), i.e., step a'): prepolymerizing propylene in the presence of a metallocene catalyst.

The purpose of prepolymerization is to polymerize a small amount of polymer onto the catalyst at low temperature and/or low monomer concentration, thereby controlling the initial catalyst breakup and the growth rate of the polymer particles. Thus, a smooth particle morphology can be ensured and localized particle overheating, which ultimately leads to particle agglomeration in the reactor, can be avoided. By controlling the above parameters, serious reactor operation problems and poor process performance can be avoided.

Another advantage of using a prepolymerization step is that it can improve the performance of the catalyst, for example especially in slurry polymerization, and/or modify the properties of the final polymer.

The prepolymerization step is preferably carried out as slurry polymerization. Preferably, the slurry polymerization is bulk polymerization. Bulk polymerization is as described above.

The reactor temperature in the prepolymerization step is usually 0 to 90°C, preferably 5 to 70°C, more preferably 10 to 50°C, and most preferably 15 to 30°C.

Reactor pressure is not critical and is typically 1 to 150 bar, preferably 40 to 80 bar.

The average retention time of step a') is preferably 15 to 45 minutes. It can be referred to the above equation (1).

Preferably, the monomer is polymerized in an amount of 0.1 to 1000 g of the monomer per 1 g of the solid metallocene catalyst in the prepolymerization step.

As is known to those skilled in the art, not all catalyst particles recovered from a prepolymerization reactor contain the same amount of prepolymer. Instead, each particle contains its own characteristic amount, which depends on the residence time of the particles in the prepolymerization reactor, and more specifically, on residence time distribution effects (e.g., particle size, molecular properties, etc.), which are well manifested in polymerization reactors, especially in continuous polymerization reactors. Since some catalyst particles stay in the reactor for a relatively long time and some stay for a relatively short time, the amount of prepolymer on different particles is also different, and some individual particles may contain an amount of prepolymer that exceeds the above limits. However, the average amount of prepolymer on the catalyst is usually within the above-specified limits.

In step a'), propylene is prepolymerized in the presence of a metallocene catalyst to produce a prepolymer. A prepolymer is a small amount of polymer produced in a prepolymerization reactor at low temperature and/or low monomer concentration. As known in the art to which the present invention pertains, the molecular weight of the prepolymer can be controlled using hydrogen. In addition, as disclosed in WO-A-96/19503 and WO-A-96/32420, an antistatic additive can be used to prevent the prepolymer particles from adhering to each other or to the walls of the reactor.

Preferably, the amount of prepolymer produced in the prepolymerization step is 1.0 to 5.0 wt % relative to the polypropylene homopolymer.

The polypropylene homopolymer is prepared in the presence of a metallocene catalyst, preferably at least one metallocene catalyst. The metallocene catalyst generally comprises a metallocene/activator reaction product impregnated in a porous support having a maximum internal pore volume. The metallocene complex comprises: a ligand, generally a bridged ligand, a transition metal from Group IVa to Group VIa, and an organoaluminum compound. The catalytic metal compound is generally a metal halide.

The metallocene catalyst of the present invention can be any supported metallocene catalyst suitable for producing isomeric polypropylene homopolymer.

Preferably, the metallocene catalyst consists of a metallocene complex and a carrier, wherein the carrier consists of silicon dioxide.

The metallocene catalyst preferably comprises: a metallocene complex; a co-catalyst system comprising a boron-containing co-catalyst and/or an aluminoxane co-catalyst; and a carrier, preferably a carrier comprising or consisting of silicon dioxide.

Examples of suitable metallocene compounds are given, among others, in EP 629631, EP 629632, WO 00/26266, WO 02/002576, WO 02/002575, WO 99/12943, WO 98/40331, EP 776913, EP 1074557, WO 99/42497, EP 2402353, EP 2729479 and EP 2746289.

The metallocene complex is ideally an organometallic compound (C) comprising a transition metal (M) or a ruthenium or ruthenium from Group 3 to Group 10 of the Periodic Table of the Elements (IUPAC 2007). The term "organometallic compound (C)" according to the present invention includes any metallocene compound of a transition metal which carries at least one organic (coordinating) ligand and exhibits catalytic activity alone or together with a co-catalyst. Transition metal compounds are well known in the art and the present invention covers compounds of metals from Groups 3 to 10, for example Groups 3 to 7, or Groups 3 to 6, such as Groups 4 to 6 of the Periodic Table of the Elements (IUPAC 2007), and ruthenium or ruthenium.

In one embodiment, the organometallic compound (C) is represented by the following chemical formula (I): (L) _m R _n MX _q (I) wherein, "M" is a transition metal of Group 3 to Group 10 of the Periodic Table of the Elements (IUPAC 2007); each "X" is independently a monocationic ligand, such as a σ-ligand; each "L" is independently an organic ligand coordinated to the transition metal "M";"R" is a bridging group connecting the organic ligand (L); "m" is 1, 2 or 3, preferably 2; "n" is 0, 1 or 2, preferably 1; "q" is 1, 2 or 3, preferably 2; and m+q is equal to the valency of the transition metal (M).

"M" is preferably selected from the group consisting of zirconium (Zr), halogen (Hf) or titanium (Ti), and more preferably selected from the group consisting of zirconium (Zr) and halogen (Hf).

In a more preferred definition, each organic ligand (L) is independently: (a) a substituted or unsubstituted cyclopentadienyl or a bicyclic or polycyclic derivative of a cyclopentadienyl, which optionally carries further substituents and/or one or more heterocyclic atoms from Groups 13 to 16 of the Periodic Table of the Elements (IUPAC); or (b) an acyclic η ¹ to η ⁴ or η ⁶ ligand consisting of atoms from Groups 13 to 16 of the Periodic Table of the Elements, wherein the open chain ligand may be fused to one or two, preferably two, aromatic or non-aromatic rings and/or carries further substituents; or (c) a cyclic η ¹ to η ⁴ or η ⁶ , monodentate, bidentate or multidentate ligands, consisting of unsubstituted or substituted monocyclic, bicyclic or polycyclic ring systems, the ring systems being selected from aromatic, non-aromatic or partially saturated ring systems, such ring systems optionally having one or more heteroatoms selected from Groups 15 and 16 of the Periodic Table of Elements.

The organometallic compound (C) preferably used in the present invention has at least one organic ligand (L) belonging to the above group (a). Such organometallic compounds are called metallocenes.

More preferably, at least one organic ligand (L), more preferably two organic ligands (L) are selected from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl which may be independently substituted or unsubstituted.

Furthermore, when the organic ligand (L) is substituted, preferably at least one organic ligand (L), preferably both organic ligands (L) comprise one or more substituents independently selected from _C1 to _C20 alkyl or silicon groups, wherein the substituents optionally contain one or more heteroatoms selected from Groups 14 to 16 and/or are optionally substituted with halogen atoms.

Whenever used in the present invention, the term _C1 - _C20 alkyl includes _C1 - _C20 alkyl, _C2 - _C20 alkenyl, _C2 - _C20 alkynyl, _C3 - _C20 cycloalkyl _{, C3-C20 cycloalkenyl, C6-C20 aryl, C7-C20 alkaryl, or C7-C20 aralkyl , or a mixture of these} groups, for example, cycloalkyl substituted by alkyl.

Furthermore, two substituents which may be the same or different and which are attached to adjacent C atoms of the ring of the ligand (L) may also together form another monocyclic or polycyclic ring fused to the ring.

Preferred alkyl groups are independently selected from: linear or branched C ₁ -C ₁₀ alkyl groups, which may be interrupted by one or more heteroatoms from Groups 14 to 16, such as O, N or S; and substituted or unsubstituted C ₆ -C ₂₀ aryl groups.

The straight or branched C1-C10 alkyl group which is optionally interrupted by one or more heteroatoms from Groups 14 to 16 is more preferably selected from methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, C ₅ -C ₆ cycloalkyl, OR, SR, wherein R is C ₁ -C _{‏ 10} alkyl;

The C ₆ -C ₂₀ aryl group is more preferably a phenyl group, which may be optionally substituted with 1 or 2 C ₁ -C ₁₀ alkyl groups as defined above.

In the present invention, "σ-ligand" refers to a group that bonds to the transition metal (M) via a σ bond.

In addition, the ligand "X" is preferably independently selected from the group consisting of hydrogen, halogen, _{C1 - C20} alkyl, _C1 - _C20 alkoxy, C2- _C20 alkenyl, _C2 - _C20 alkynyl, _C3 - _C12 cycloalkyl, _C6 - _C20 aryl, _C6 -C20 aryloxy, C7- _C20 arylalkyl, _C7 - _C20 arylalkenyl, -SR _" , -Pr" ₃ , -SiR" ₃ , -OSiR" ₃ , and -NR" ₂ , wherein each R" is independently _hydrogen , _C1 - _C20 alkyl, _C2 - _C20 alkenyl, _C2 - _C20 alkynyl, _C3 - _C12 cycloalkyl, or _C6 - _C20 aryl.

The ligand "X" is more preferably selected from halogen, C ₁ -C ₆ alkyl, C ₅ -C ₆ cycloalkyl, C ₁ -C ₆ alkoxy, phenyl, and benzyl.

The bridging group "R" can be a divalent bridge, preferably selected from _-R'2C- , -R'2C- _CR'2- , _-R'2Si- , _-R'2Si - _SiR'2- , and _-R'2Ge- , wherein each R' is independently a hydrogen atom, a _C1 - _C20 alkyl group, a _C2 - _C10 cycloalkyl group, a tri( _C1 - _C20 alkyl)silyl group, a _C6 - _C20 aryl group, a _C7 - _C20 aralkyl group, and _{a C7} - _C20 alkylaryl group.

More preferably, the bridging group "R" is a divalent bridging group selected from -R' ₂ C-, -R' ₂ Si-, wherein each R' is independently a hydrogen atom, a C ₁ -C ₂₀ alkyl group, a C ₂ -C ₁₀ cycloalkyl group, a C ₆ -C ₂₀ aryl group, a C ₇ -C ₂₀ aralkyl group, and a C ₇ -C ₂₀ alkylaryl group.

Another subgroup of organometallic compounds (C) of formula (I) are known as non-metallocenes, in which the transition metal (M), preferably a transition metal from Group 4 to Group 6, suitably Ti, Zr or Hf, has ligands other than cyclopentadienyl ligands.

The term "non-metallocene" as used herein refers to compounds which do not carry a cyclopentadienyl ligand or a fused derivative thereof, but carry one or more non-cyclopentadienyl η- or σ-, monodentate, bidentate or polydentate ligands. Such ligands can be selected from the groups (b) and (c) defined above and are described, for example, in WO 01/70395, WO 97/10248, WO 99/41290 and WO 99/10353 and are further described in the document by V. C. Gibson et al., Angew. Chem. Int. Ed., engl., vol 38, 1999, pp 428 447, the contents of which are incorporated herein by reference.

However, the organometallic compound (C) of the present invention is preferably a metallocene as defined above.

Metallocenes are described in many patents. Just a few examples are listed below; EP 260130, WO 97/28170, WO 98/46616, WO 98/49208, WO 98/040331, WO 99/12981, WO 99/19335, WO 98/56831, WO 00/34341, WO 00/148034, EP 42310 1. EP 537130, WO 2002/02576, WO 2005/105863, WO 2006097497, WO 2007/116034, WO 2007/107448, WO 2009/027075, WO 2009/054832, WO 2012/001052 and EP 2532687, the disclosures of which are incorporated herein by reference. In addition, metallocenes are widely described in academic and scientific articles.

In a preferred embodiment, the organometallic compound (C) is represented by the following chemical formula (Ia): (L) ₂ R _n MX ₂ (Ia) wherein, "M" is zirconium or einsteinium; each "X" is a σ-ligand; each "L" is an optionally substituted cyclopentadienyl, indenyl or tetrahydroindenyl; "R" is a SiMe ₂ bridging group connecting the organic ligand (L); and "n" is 0 or 1, preferably 1.

The metallocene catalyst complex of the present invention is preferably asymmetric. Asymmetric simply means that the two ligands forming the metallocene are different, that is, each ligand carries a set of chemically different substituents.

The metallocene catalyst complexes of the present invention are generally chiral, racemic bridged, bis-indenyl C ₁ -symmetric metallocenes in their anti-configuration. Although such complexes are formally C ₁ -symmetric, ideally, these complexes retain pseudo-C ₂ -symmetry because they maintain C ₂ -symmetry near the metal center rather than at the periphery of the ligands. Due to their chemical nature, anti- and cis-isomeric pairs are formed during the synthesis of the complexes (in the case of C ₁ -symmetric complexes). For the purposes of the present invention, racemic-anti refers to the two indenyl ligands being oriented in opposite directions relative to the cyclopentadienyl-metal-cyclopentadienyl plane, and racemic-syn refers to the two indenyl ligands being oriented in the same direction relative to the cyclopentadienyl-metal-cyclopentadienyl plane, as shown in the figure below.

Formula (I) and any subformulae are intended to encompass both cis and trans configurations. Preferred metallocene catalyst complexes are in the trans configuration.

The metallocene catalyst complex of the present invention is usually in the form of a racemic-trans isomer. Therefore, ideally, at least 95 mol%, such as at least 98 mol%, and especially at least 99 mol% of the metallocene catalyst complex is in the form of a racemic-trans isomer.

More preferably, the metallocene catalyst is represented by the chemical formula (II): Chemical formula (II)

Mt is einsteinium or zirconium;

Each X is a σ-ligand;

Each R ¹ is independently the same or different and is a CH ₂ -R ⁷ group, wherein R ⁷ is hydrogen, a linear or branched C ₁ -C ₆ alkyl group, a C ₃ -C ₈ cycloalkyl group, or a C ₆ -C ₁₀ aryl group,

Each R ² is independently a -CH=, -CY=, -CH ₂ -, -CHY- or -CY ₂ - group, wherein Y is a C ₁ -C ₁₀ alkyl group, and n is 2 to 6,

Each ^R3 and ^R4 may independently be the same or different and is hydrogen, a linear or branched _C1 - _C6 alkyl group, an OY group, a _C7 - _C20 aralkyl group, a _C7 - _C20 alkaryl group, or a _C6 - _C20 aryl group, wherein at least one ^R3 and at least one ^R4 on each phenyl group is not hydrogen, and optionally, two adjacent ^R3 or ^R4 groups may be part of a ring containing the phenyl carbon to which they are bonded,

^R5 is a linear or branched _C1 - _C6 alkyl group, a _C7 - _C20 aralkyl group, a _C7 - _C20 alkaryl group, or a _C6 - _C20 aryl group,

R ⁶ is a C(R ⁸ ) ₃ group, wherein R ⁸ is a linear or branched C ₁ -C ₆ alkyl group, and

Each R is independently a C ₁ -C ₂₀ alkyl group.

Mt is preferably zirconium.

Preferably, each X is independently a hydrogen atom, a halogen atom, a C ₁ -C ₆ alkoxy group, or an R' group, wherein R' is a C ₁ -C ₆ alkyl group, a phenyl group, or a benzyl group. Most preferably, X is chlorine, a benzyl group, or a methyl group. Preferably, the two X groups are the same. The best choice is two chlorine groups, two methyl groups, or two benzyl groups, especially two chlorine groups.

Each R is independently a C ₁ -C ₂₀ alkyl group, such as a C ₆ -C ₂₀ aryl group, a C ₇ -C ₂₀ aralkyl group, or a C ₇ -C ₂₀ alkaryl group. The term C ₁ -C ₂₀ alkyl group also includes a C ₁ -C ₂₀ alkyl group, a C ₂ -C ₂₀ alkenyl group, a C ₂ -C ₂₀ alkynyl group, a C ₃ -C ₂₀ cycloalkyl group, a C ₃ -C ₂₀ cycloalkenyl group, a C ₆ -C ₂₀ aryl group, a C ₇ -C ₂₀ alkaryl group, or a C ₇ -C ₂₀ aralkyl group, or a mixture of these groups, such as a cycloalkyl group substituted with an alkyl group. Unless otherwise specified, preferred C ₁ -C ₂₀ alkyl groups are C ₁ -C ₂₀ alkyl groups, C ₄ -C ₂₀ cycloalkyl groups, C ₅ -C ₂₀ cycloalkyl-alkyl groups, C ₇ -C ₂₀ alkaryl groups, C ₇ -C ₂₀ aralkyl groups, or C ₆ -C ₂₀ aryl groups.

Preferably, the two R groups are the same. Preferably, R is C ₁ -C ₁₀ alkyl or C ₆ -C ₁₀ aryl, such as methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, C ₅ -C ₆ cycloalkyl, cyclohexylmethyl, phenyl or benzyl; more preferably, both R are C ₁ -C ₆ alkyl, C ₃ -C ₈ cycloalkyl, or C ₆ aryl, such as C ₁ -C ₄ alkyl, C ₅ -C ₆ cycloalkyl, or C ₆ aryl; and most preferably, both R are methyl, or one is methyl and the other is cyclohexyl. Most preferably, the bridging group is a -Si(CH ₃ ) ₂ - group.

Each R ¹ is independently the same or different and is a CH ₂ -R ⁷ group, wherein R ⁷ is hydrogen; a straight or branched C ₁ -C ₆ alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl; a C ₃ -C ₈ cycloalkyl group (such as cyclohexyl); or a C ₆ -C ₁₀ aryl group (preferably phenyl).

Preferably, the two ^R1 groups are the same and are _CH2 - ^R7 groups, wherein ^R7 is hydrogen or a linear or branched _C1 - _C4 alkyl group; more preferably, the two ^R1 groups are the same and are _CH2 - ^R7 groups, wherein ^R7 is hydrogen or a linear or branched _C1 - _C3 alkyl group. Most preferably, both ^R1 groups are methyl groups.

Each R ² is independently a —CH=, —CY=, —CH ₂ —, —CHY— or —CY ₂ — group, wherein Y is a C ₁ -C ₁₀ alkyl group, preferably a C ₁ -C ₄ alkyl group, and wherein n is 2 to 6, preferably 3 to 4.

Each substituent ^R3 and ^R4 may be independently the same or different and is hydrogen, a straight or branched _C1 - _C6 alkyl group, an OY group, a _C7 - _C20 aralkyl group, a _C7 - _C20 alkaryl group, or a _C6 - _C20 aryl group, preferably hydrogen, a straight or branched _C1 - _C6 alkyl group, or a _C6 - _C20 aryl group, and optionally, two adjacent ^R3 or ^R4 groups may be part of a ring containing the phenyl carbon to which they are bonded. More preferably, ^R3 and ^R4 are hydrogen, a straight or branched _C1 - _C4 alkyl group, or an OY group, wherein Y is a _C1 - _C4 alkyl group. Even more preferably, each R ³ and R ⁴ is independently hydrogen, methyl, ethyl, isopropyl, tert-butyl or methoxy, especially hydrogen, methyl or tert-butyl, wherein at least one R ³ and at least one R ⁴ of each phenyl group is not hydrogen.

Therefore, preferably, one or two R ³ on each phenyl group is not hydrogen; more preferably, R ³ on the two phenyl groups are the same, for example, R ³ on the two phenyl groups are both 3',5'-dimethyl or 4'-tert-butyl.

For the indenyl moiety, preferably, one or both R ⁴ on the phenyl group is not hydrogen; more preferably, both R 4 are not hydrogen; most preferably, the two R ⁴ are the same, such as 3',5'-dimethyl or 3',5'-di-tert-butyl.

^R5 is a straight or branched _C1 - _C6 alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, C7 _{- C20} aralkyl, _C7 - _C20 alkaryl, or _C6 - _C20 aryl. ^R5 is preferably a straight or branched _C1 - _C6 alkyl group or _C6 - _C20 aryl group, more preferably a straight _C1 - _C4 alkyl group, even more preferably a _C1 - _C2 alkyl group, and most preferably a methyl group.

R ⁶ is a C(R ⁸ ) ₃ group, wherein R ⁸ is a linear or branched C ₁ -C ₆ alkyl group.

Each R is independently C ₁ -C ₂₀ alkyl, C ₆ -C ₂₀ aryl, C ₇ -C ₂₀ aralkyl, or C ₇ -C ₂₀ alkylaryl. Preferably, each R ⁸ is the same or different, wherein R ⁸ is a linear or branched C ₁ -C ₄ alkyl; more preferably, each R ⁸ is the same and is a C ₁ -C ₂ alkyl. Most preferably, all R ⁸ groups are methyl.

In another preferred embodiment, the organometallic compound (C) is represented by the following chemical formula (III): Chemical formula (III) wherein, Mt is einsteinium or zirconium, preferably zirconium; each R ³ and R ⁴ may be independently the same or different and is hydrogen or a linear or branched C ₁ -C ₆ alkyl group, wherein at least one R ³ and at least one R ⁴ of each phenyl group is not hydrogen.

Specific metallocene catalyst complexes include: rac-trans-dimethylsilanediyl[2-methyl-4,8-bis-(4'-tert-butylphenyl)-1,5,6,7-tetrahydro-s-dicyclopentadienylbenzo-1-yl][2-methyl-4-(3',5'-dimethyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride; rac-trans-dimethylsilanediyl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-dicyclopentadienylbenzo-1-yl][2-methyl-4-(3',5'-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride; rac-trans-dimethylsilanediyl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-dicyclopentadienyl-1-yl][2-methyl-4-(3',5'-di-tert-butylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride; or its corresponding dimethylzirconium analog. MC-1 MC-2 MC-3

The ligands required to form the metallocene catalysts of the present invention can be synthesized by any method, and an organic chemist with ordinary knowledge can design various synthetic schemes to make the necessary ligand materials. For example, WO 2007/116034 discloses the necessary chemistry. Synthetic schemes can also be generally found in WO 2002/02576, WO 2011/135004, WO 2012/084961, WO 2012/001052, WO 2011/076780 and WO 2015/158790.

In order to form an active catalyst species, it is usually necessary to use a promoter as is well known in the art.

According to the present invention, it is preferred to use a co-catalyst system comprising a boron-containing co-catalyst and/or an aluminoxane co-catalyst in combination with the metallocene catalyst defined above.

The aluminoxane co-catalyst may be one of formula (IV): (IV)

wherein n is generally 6 to 20, and R has the following meanings.

Aluminoxanes are formed when an organoaluminum compound is partially hydrolyzed, such as an organoaluminum compound of the formula AlR ₃ , AlR ₂ Y, and Al ₂ R ₃ Y ₃ , wherein R can be, for example, a C ₁ -C ₁₀ alkyl group, preferably a C ₁ -C ₅ alkyl group, a C ₃ -C ₁₀ cycloalkyl group, a C ₇ -C ₁₂ aralkyl group or an alkaryl group, and/or a phenyl or naphthyl group, and wherein Y can be: hydrogen; a halogen, preferably chlorine or bromine; or a C ₁ -C ₁₀ alkoxy group, preferably methoxy or ethoxy. The resulting oxygen-containing aluminoxane is usually not a pure compound, but a mixture of oligomers of the formula (III).

The preferred aluminoxane is methylaluminoxane (MAO). Since the aluminoxane used as a co-catalyst according to the present invention is not a pure compound due to its preparation method, the volume molar concentration of the aluminoxane solution hereinafter is based on its aluminum content.

In addition, according to the present invention, a boron-containing co-catalyst may be used instead of an aluminoxane co-catalyst, or an aluminoxane co-catalyst may be used in combination with a boron-containing co-catalyst.

It will be appreciated by those skilled in the art that when a boron-based co-catalyst is used, the complex is generally pre-alkylated by reacting it with an alkyl aluminum compound such as TIBA. This procedure is well known and any suitable aluminum alkyl may be used, such as Al(C ₁ -C ₆ alkyl) ₃ . Preferred aluminum alkyl compounds are triethylaluminum, tri-isobutylaluminum, tri-isohexylaluminum, tri-n-octylaluminum, and tri-isooctylaluminum.

Alternatively, when a borate co-catalyst is used, the metallocene complex is in its alkylated form, i.e., for example, a dimethylmetallocene complex or a benzhydrylmetallocene complex may be used.

Boron-based co-catalysts of interest include those represented by the chemical formula (V): BY ₃ (V) wherein Y is the same or different and is: a hydrogen atom; an alkyl group having 1 to about 20 carbon atoms; an aryl group having 6 to about 15 carbon atoms; an alkaryl group, an aralkyl group, a halogenalkyl group, or a halogenaryl group each having 1 to 10 carbon atoms in the alkyl group and 6 to 20 carbon atoms in the aryl group; or fluorine, chlorine, bromine, or iodine. Preferred examples of Y are: methyl, propyl, isopropyl, isobutyl, or trifluoromethyl; an unsaturated group, such as an aryl or halogenaryl group, such as phenyl, tolyl, benzyl, p-fluorophenyl, 3,5-difluorophenyl, pentachlorophenyl, pentafluorophenyl, 3,4,5-trifluorophenyl, and 3,5-bis(trifluoromethyl)phenyl. Preferred options are trifluoroborane, triphenylborane, tri(4-fluorophenyl)borane, tri(3,5-difluorophenyl)borane, tri(4-fluoromethylphenyl)borane, tri(2,4,6-trifluorophenyl)borane, tri(pentafluorophenyl)borane, tri(tolyl)borane, tri(3,5-dimethylphenyl)borane, tri(3,5-difluorophenyl)borane, and/or tri(3,4,5-trifluorophenyl)borane.

Particularly preferred is tris(pentafluorophenyl)borane.

However, preference is given to using borates, ie compounds containing borate ³⁺ ions.

Such ionic promoters preferably contain non-coordinating anions such as tetrakis(pentafluorophenyl)borate and tetraphenylborate. Suitable counterions are protonated amines or aniline derivatives such as methylamine, aniline, dimethylamine, diethylamine, N-methylaniline, diphenylamine, N,N-dimethylaniline, trimethylamine, triethylamine, tri-n-butylammonium, methyldiphenylamine, pyridinium, p-bromo-N,N-dimethylaniline, or p-nitro-N,N-dimethylaniline.

According to the present invention, the preferred ionic compounds that can be used include: triethylammonium tetra(phenyl)borate, tributylammonium tetra(phenyl)borate, trimethylammonium tetra(methylphenyl)borate, tributylammonium tetra(methylphenyl)borate, tributylammonium tetra(pentafluorophenyl)borate, tripropylammonium tetra(dimethylphenyl)borate, tributylammonium tetra(trifluoromethylphenyl)borate, tributylammonium tetra(4-fluorophenyl)borate, N,N-dimethylcyclohexylammonium tetra(pentafluorophenyl)borate, N,N-dimethylbenzylammonium tetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(phenyl)borate, N,N-diethylphenylammonium tetra(phenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, N,N-di(propyl)ammonium tetrakis(pentafluorophenyl)borate, di(cyclohexyl)ammonium tetrakis(pentafluorophenyl)borate, triphenylphosphonium tetrakis(phenyl)borate, triethylphosphonium tetrakis(phenyl)borate, diphenylphosphonium tetrakis(phenyl)borate, tri(methylphenyl)phosphonium tetrakis(phenyl)borate, tri(dimethylphenyl)phosphonium tetrakis(phenyl)borate, triphenylcarbeniumtetrakis(pentafluorophenyl)borate, or ferrocene tetrakis(pentafluorophenyl)borate.

Preferably: triphenylcarbonium tetrakis(pentafluorophenyl)borate, N,N-dimethylcyclohexylammonium tetrakis(pentafluorophenyl)borate, or N,N-dimethylbenzylammonium tetrakis(pentafluorophenyl)borate.

Surprisingly, it has been found that certain boron promoters are particularly preferred.

Therefore, the preferred borate salts used in the present invention contain trityl ions. Therefore, the use of N,N-dimethylammonium tetrakis(pentafluorophenyl)borate and Ph ₃ CB(PhF ₅ ) ₄ and its analogs is particularly favored.

According to the present invention, the preferred co-catalyst is aluminoxane, more preferably methylaluminoxane; a combination of aluminoxane and an alkylaluminum, boron or borate co-catalyst; and a combination of aluminoxane and a boron-based co-catalyst.

Suitable amounts of promoters are well known to those of ordinary skill in the art.

The molar ratio of boron to the metal ion in the metallocene may be in the range of 0.5:1 to 10:1 mol/mol, preferably 1:1 to 10:1 mol/mol, and particularly 1:1 to 5:1 mol/mol.

The molar ratio of Al in the aluminoxane to the metal ion in the metallocene may be in the range of 1:1 to 2000:1 mol/mol, preferably 10:1 to 1000:1 mol/mol, more preferably 50:1 to 900:1 mol/mol, and most preferably 600:1 to 800:1 mol/mol.

The metallocene catalyst used in the polymerization method of the present invention is used in the form of a carrier. The carrier used contains silicon dioxide, preferably consists of silicon dioxide. In other words, the carrier is preferably a silicon dioxide carrier. The general knowledgeable person understands the procedures required for supporting the metallocene catalyst.

Particularly preferably, the support is a porous material so that the metallocene complex can be loaded into the pores of the support, for example, using a process similar to that described in WO 94/14856 (Mobil), WO 95/12622 (Borealis), and WO 2006/097497.

The average particle size of the carrier may generally be 10 to 100 μm. However, it has proven to be particularly advantageous if the average particle size of the carrier is 15 to 80 μm, preferably 18 to 50 μm.

The particle size distribution of the carrier will be described in detail below. Preferably, the D ₅₀ of the silica carrier is between 10 and 80 μm, preferably between 18 and 50 μm. In addition, preferably, the D ₁₀ of the silica carrier is between 5 and 30 μm, and the D ₉₀ is between 30 and 90 μm. Preferably, the span value of the carrier is 0.1 to 1.1, preferably 0.3 to 1.0.

The average particle size of the metallocene catalyst is preferably 20 to 50 μm, more preferably 25 to 45 μm, and most preferably 30 to 40 μm.

The particle size distribution of the metallocene catalyst will be described in detail below. The _D50 of the metallocene catalyst is preferably 30 to 80 μm, more preferably 32 to 50 μm, and most preferably 34 to 40 μm. In addition, the _D10 of the metallocene catalyst is preferably at most 29 μm, more preferably 15 to 29 μm, more preferably 20 to 28 μm, and most preferably 25 to 27 μm. The _D90 of the metallocene catalyst is preferably at least 45 μm, more preferably 45 to 70 μm, and most preferably 40 to 60 μm.

The average pore size of the support may be in the range of 10 to 100 nm, preferably 20 to 50 nm, and the pore volume is 1 to 3 ml/g, preferably 1.5 to 2.5 ml/g. The BET surface area of the silica support material is determined according to ASTM D3663 and the porosity parameter based on BJH according to ASTM D4641. Examples of suitable support materials are, for example, ES757 produced and sold by PQ Corporation, Sylopol 948 produced and sold by Grace, or SUNSPERA DM-L-303 silica produced by AGC Si-Tech Co. The support may optionally be calcined before being used in catalyst preparation to achieve an optimal silanol group content.

It will be appreciated that the polypropylene homopolymer may contain standard polymer additives. These typically form less than 5.0 wt%, e.g. less than 2.0 wt%, of the polymer material. Thus, additives such as antioxidants, phosphites, cling additives, pigments, colorants, fillers, antistatic agents, processing aids, nucleating agents, clarifiers etc. may be added after the polymerization process in the granulation step. These additives are well known in the industry and their use is familiar to the skilled person. Any additive present may be added as a separate raw material or in the form of a mixture with a carrier polymer, i.e. in the form of a so-called masterbatch. Experimental part Measurement methods

Any parameters mentioned in the detailed description of the invention are measured according to the tests given below. a ) Melt flow rate

The melt flow rate (MFR) is determined according to ISO 1133 and is expressed in g/10min. The MFR is an indication of the melt viscosity of the polymer. The MFR of PE is measured at 190°C and the MFR of PP is measured at 230°C. The load under which the melt flow rate was determined is usually indicated by a subscript, e.g. MFR ₂ is measured under a load of 2.16 kg (state D).

The MFR ₂ of the second polypropylene homopolymer fraction (PPH2) produced in the second reactor is determined according to equation (2): Equation (2) wherein, MFR(PPH) is the MFR ₂ of the polypropylene homopolymer (PPH), w(PPH1) and w(PPH2) are the weight fractions of the first polypropylene homopolymer distillate (PPH1) and the second polypropylene homopolymer distillate (PPH2) in the polypropylene homopolymer (PPH), and MFR(PPH1) is the MFR ₂ of the first polypropylene homopolymer distillate (PPH1) produced in the first reactor. b ) Particle size and particle size distribution

Particle size distribution is determined using laser diffraction measurement with a Coulter LS 200. Particle size and particle size distribution are measures of particle size. The D values (D ₁₀ (or d ₁₀ ), D ₅₀ (or d ₅₀ ) and D ₉₀ (or d ₉₀ )) represent the intercepts for 10%, 50% and 90% of the cumulative mass of a sample. The D values can be thought of as the diameter of a sphere, which divides the mass of a sample into specific percentages when the particles are arranged based on increasing mass. For example, D ₁₀ is the diameter at which 10% of the sample's mass is made up of particles with diameters less than the D ₁₀ value. _D50 is the particle diameter at which 50% of the sample mass has a diameter less than the _D50 value and 50% of the sample mass has a diameter greater than the _D50 value. _D90 is the diameter at which 90% of the sample mass consists of particles with a diameter less than the _D90 value. The _D50 value is also called the median particle size. Laser diffraction measurements are performed according to ISO 13320 to obtain the D value based on the volume distribution.

The distribution width or span of the particle size distribution is calculated from the D values D ₁₀ , D ₅₀ and D ₉₀ according to equation (3): Span = (D ₉₀ -D ₁₀ )/D ₅₀ Equation (3) c ) Density

The density of the polymer is measured according to ISO 1183/1872-2B. For the purpose of the present invention, the density of the blend can be calculated based on the density of each component: Where _ρb is the density of the blend, w _i is the weight fraction of component “ i ” in the blend, and ρ _i is the density of component “ i ”. d ) Overall density

Bulk density is measured according to ASTM D1895. e ) Differential Scanning Calorimetry ( DSC )

Differential Scanning Calorimetry (DSC) analysis was performed on 5 to 7 mg samples using a TA Instrument Q200 Differential Scanning Calorimeter (DSC) to measure melting temperature ( _Tm ), melting enthalpy ( _Hm ), crystallization temperature ( _Tc ), and heat of crystallization ( _Hc , _Hcr ). The DSC was run according to ISO 11357/Part 3/Method C2 in a hot/cold/hot cycle with a scan rate of 10°C/min over a temperature range of -30 to +225°C.

The crystallization temperature (T _c ) and the heat of crystallization (H _c ) are determined by the cooling step, while the melting temperature (T _m ) and the melting enthalpy (H _m ) are determined by the second heating step.

Throughout the present invention, the term T _c (or T _cr ) is understood to mean the peak temperature of crystallization determined by DSC at a cooling rate of 10 K/min (i.e. 0.16 K/sec). f ) Xylene cold soluble fraction

The cold xylene soluble fraction content (XCS) is determined according to ISO 16152 at 25°C.

A weighed sample is dissolved in hot xylene at reflux at 135 °C. The solution is then cooled under controlled conditions and kept at 25 °C for 30 minutes to ensure controlled crystallization of the insoluble fraction. The insoluble fraction is then separated by filtration. The xylene is evaporated from the filtrate, leaving the soluble fraction as residue. The percentage of this fraction is determined gravimetrically. XCS = (100 x m1 x V0) / (m0 x V1), where m0 represents the initial polymer amount (g), m1 defines the weight of the residue (g), V0 defines the initial volume (ml) and V1 defines the volume of the analyzed sample (ml). g ) Flexural modulus

Flexural modulus was measured in 3-point bending according to ISO 178 on injection molded specimens measuring 80 x 10 x 4 mm, prepared according to EN ISO 19069-2 at 200°C or 230°C. Materials a ) Catalyst

The following catalysts were used in the methods according to the comparative examples and embodiments of the present invention described in Table 1. Metallocene complexes were used as described in WO 2019/179959 A1:

A steel reactor equipped with a mechanical stirrer and filter was flushed with nitrogen and the reactor temperature was set to 20°C. Next, silica grade DM-L-303 from AGC Si-Tech Co, pre-calcined at 600°C (10 kg) was added from a feed bucket and then carefully pressurized and depressurized with nitrogen using a manual valve. Toluene (43.5 kg) was then added. The mixture was stirred for 30 minutes. Next, a 30 wt% solution of MAO in toluene from Lanxess (17.5 kg) was added over 140 minutes via the feed line at the top of the reactor. The reaction mixture was then heated to 90°C and stirred at 90°C for another two hours. The slurry was allowed to settle and the mother liquor was filtered off. The catalyst was washed twice with toluene (43.5 kg) at 90°C, followed by sedimentation and filtration.

Finally, the MAO treated _SiO2 was dried at 60°C for 2 hours under a stream of nitrogen and then dried under vacuum (~0.5 barg) with stirring for 14 hours. The MAO treated support was collected as a free flowing white powder and found to contain 15.0 wt% aluminum. A 30 wt% solution of MAO in toluene (2 kg) was added via a burette at 20°C to a steel reactor evacuated with nitrogen. Toluene (12.8 kg) was added with stirring. 129 g of the metallocene was added from a metal cylinder followed by a rinse of 1 kg of toluene. The mixture was stirred at 20°C for 60 minutes. Trityltetrakis(pentafluorophenyl)borate (127.2 g) was then added from a metal cylinder followed by a rinse of 1 kg of toluene. The mixture was stirred at room temperature for 1 hour. The resulting solution was added to the stirred filter cake of MAO-silica support prepared as described above over 12 hours. The filter cake was stirred for 30 minutes and then left without stirring for 30 minutes, then dried under a stream of nitrogen at 60°C for 2 hours and further dried under stirring under vacuum (~0.5 barg) for 15 hours. b ) Additives

Additive 1: Irganox 1010 (FF) (CAS-No. 6683-19-8) is available from BASF, Additive 2: Irganox 168 (FF) (CAS-No. 31570-04-4) is available from BASF, Additive 3: Irganox 1098 (FF) (CAS-No. 23128-74-7) is available from BASF. Example

The following three examples (comparative example CE01, and examples IE01 and IE02 of the present invention) were carried out in a Borstar pilot plant comprising a reactor train consisting of a prepolymerization reactor, a loop reactor and a gas phase reactor. CE01 is a high flow unimodal polypropylene homopolymer, while IE01 and IE02 are both bimodal high flow polypropylene homopolymers.

The process conditions and properties are shown in Table 1.

The base polymer powder was granulated in a twin-shaft extruder with a screw diameter of 18 mm at a melt temperature of 240°C and a throughput of 7 kg/h. The amounts of additives added are shown in Table 1.

Table 1 Example CE01 IE01 IE02 Polymer Type Single peak Twin Peaks Twin Peaks Prepolymerization Reactor Temperature (°C) 20 20 20 Pressure (kPa) 5019 4989 5009 Catalyst feed (kg/h) 3.0 3.6 3.1 _H2 /C3 feed ratio (mol/kmol) 0.03 0.03 0.03 Circular Flow Reactor Temperature(°C) 75 75 75 Pressure (kPa) 4904 4873 4898 C3 feed (kg/h) 181.2 181.0 173.6 _H2 /C3 feed ratio (mol/kmol) 0.37 0.21 0.28 Production rate (kg/h) 33.2 38.6 35.4 Polymer distribution (wt%) 68 64 61 MFR ₂ (g/10min) 70.0 12.9 27.5 XCS (wt%) 2.3 2.3 2.4 Gas phase sensor Temp.(°C) 80 80 80 Pressure(kPa) 2500 2500 2500 _H2 /C3 feed ratio (mol/kmol) 2.5 27.2 23.4 Polymer distribution (wt%) 32 36 39 MFR ₂ (g/10min) 78.3 45.4 71.3 Total production rate (kg/h) 48.8 60.0 58.0 Total productivity (kg PP/g catalyst) 16.0 16.5 18.7 Final material, powder MFR ₂ (g/10min) 83.9 43.0 74.5 XCS (wt%) 0.87 1.7 1.9 Overall density (kg/m ³ ) 393 404 412 APS (mm)* 1.24 1.14 1.15 Final material, granules MFR ₂ (g/10min) 83.6 40.9 70.4 _Tm (°C) 153.6 154.6 152.7 T _c (°C) 117.6 117.6 117.7 Additive 1 0.06 wt% 0.06 wt% 0.06 wt% Additive 2 0.06 wt% 0.06 wt% 0.06 wt% Additive 3 0.04 wt% 0.04 wt% 0.04 wt% Polydispersity index Mw/Mn (calculated) 4.3 5.59 4.94 Bending modulus (MPa) 1480 1600 1580 Quantity (kg) 400 400 400 *APS (average particle size) is the _D50 value, which is measured by the photographic eye of a camsizer device.

As can be seen from Table 1 above, the moderate broadening and bimodality of the molecular weight distribution, expressed as the polydispersity index, results in an increase in stiffness, expressed as the flexural modulus, of about 100 to 120 MPa. This is a significant improvement, especially from a process perspective.

Claims (14)

A method for producing a polypropylene homopolymer, the method comprising the following steps: a) polymerizing propylene in the presence of a metallocene catalyst in a first reactor to produce a first polypropylene homopolymer distillate, wherein the MFR ₂ of the first polypropylene homopolymer distillate is 1 to 50 g/10min as measured according to ISO 1133; b) transferring the first polypropylene homopolymer distillate to a second reactor; c) polymerizing propylene in the presence of the first polypropylene homopolymer distillate in the second reactor to produce a second polypropylene homopolymer distillate; and d) discharging a polypropylene homopolymer containing the first polypropylene homopolymer distillate and the second polypropylene homopolymer distillate from the second reactor, wherein the MFR ₂ of the polypropylene homopolymer is 20 to 200 g/10min as measured according to ISO 1133, wherein the metallocene catalyst comprises a metallocene complex and a carrier, wherein the carrier comprises silica, and wherein the distribution ratio between the first polypropylene homopolymer and the second polypropylene homopolymer is 20:80 to 80:20, wherein the metallocene complex is an organic metal compound (C), and the organic metal compound (C) is represented by the following chemical formula (Ia): (L) ₂ R _n MX ₂ (Ia) wherein, M is zirconium or einsteinium; each X is a σ-ligand; each L is an optionally substituted cyclopentadienyl, indenyl or tetrahydroindenyl; R is a SiMe ₂ bridging group connected to the organic ligand (L); and n is 0 or 1, preferably 1. The manufacturing method as described in any of the preceding claims, wherein the average particle size of the carrier is 10 to 100 µm. A method as claimed in any of the preceding claims, wherein the first polypropylene homopolymer distillate has an MFR ₂ of 5 to 40 g/10min measured according to ISO 1133. A method as claimed in any one of the preceding claims, wherein the MFR ₂ of the polypropylene homopolymer is from 30 to 100 g/10min, measured according to ISO 1133. The manufacturing method as described in any of the aforementioned claims, wherein the distribution ratio between the first polypropylene homopolymer dilution fraction and the second polypropylene homopolymer dilution fraction is 30:70 to 70:30. A manufacturing method as described in any of the preceding claims, wherein the first reactor is a circulating flow reactor and/or the second reactor is a gas phase reactor. A method as claimed in any of the preceding claims, wherein step a) is carried out at a temperature of 60 to 100°C and/or a pressure of 1 to 150 bar. A method as claimed in any of the preceding claims, wherein step c) is carried out at a temperature of 60 to 90°C and/or a pressure of 10 to 140 bar. The method of any of the preceding claims, wherein the first polypropylene homopolymer distillate has a cold xylene soluble distillate content (XCS) of 0.1 to 5.0 wt % as measured according to ISO 16152. A method of manufacturing as claimed in any of the preceding claims, wherein the polypropylene homopolymer has a cold xylene soluble distillate content (XCS) of 0.1 to 4.0 wt % as measured according to ISO 16152. A method as claimed in any of the preceding claims, wherein the polypropylene homopolymer is a bimodal polypropylene homopolymer. A method of manufacturing as claimed in any of the preceding claims, wherein the flexural modulus of the polypropylene homopolymer is 1500 to 1650 MPa as measured according to ISO 178. A method of manufacturing as claimed in any of the preceding claims, wherein the melting temperature _Tm of the polypropylene homopolymer is 145.0 to 165.0°C as measured by DSC according to ISO 11357. A method of manufacturing as claimed in any of the preceding claims, wherein the polypropylene homopolymer has a crystallization temperature _Tc of 100.0 to 140.0°C as measured by DSC according to ISO 11357.