Transition metal compound, catalyst composition and method for preparing polypropylene by using transition metal compound and catalyst composition

Abstract

Provided are a transition metal compound, a catalyst composition, and a method for preparing a polypropylene using the same, which can prepare a polypropylene having a low weight average molecular weight, a high melt index, and a narrow molecular weight distribution, and thus can be used in a non-woven fabric having ultra-low basis weight properties and high strength properties.

Description

Cross-references to related applications

[0001] This application claims priority based on Korean Patent Application No. 10-2024-0067859, filed on May 24, 2024, and Korean Patent Application No. 10-2025-0067013, filed on May 22, 2025, all of which are disclosed in the Korean patent applications and are incorporated herein by reference as part of this specification. Technical Field

[0002] This invention relates to a transition metal compound, a catalyst composition, and a method for preparing polypropylene using the same, which can produce polypropylene with low weight-average molecular weight, high melt index, and narrow molecular weight distribution, thereby exhibiting excellent fiber spinnability and strength properties, and thus can be used for nonwoven fabrics with ultra-low basis weight and high strength properties. Background Technology

[0003] Olefin polymerization catalyst systems can be divided into Ziegler-Natta and metallocene catalyst systems, and these two highly active catalyst systems have been developed based on their respective characteristics.

[0004] Since its invention in the 1950s, Ziegler-Natta catalysts have been widely used in existing commercial processes. However, as a multi-site catalyst with multiple active sites, it is characterized by a wide molecular weight distribution of the polymer and an uneven composition distribution of the comonomer, which limits the attainment of desired physical properties.

[0005] On the other hand, metallocene catalysts are composed of a main catalyst with transition metal compounds as the main component and a co-catalyst based on organometallic compounds with aluminum as the main component. These catalysts are homogeneous complex catalysts and belong to the category of single-point catalysts. Due to their single-point characteristics, polymers with narrow molecular weight distributions and uniform comonomer composition can be obtained. Furthermore, their advantage lies in the ability to modify the stereoregularity, copolymerization characteristics, molecular weight, and crystallinity of the polymer by altering the ligand structure of the catalyst and changing the polymerization conditions.

[0006] In recent years, due to changing environmental awareness, many product lines are striving to reduce the generation of volatile organic compounds (VOCs). However, Ziegler-Natta catalysts (Z / N) used in the production of polypropylene have the problem of generating high TVOCs. Especially in various commercially available polypropylene products, those using Ziegler-Natta catalysts are mainstream, but in recent years, the shift towards products using metallocene catalysts with lower odor and lower elution properties is accelerating.

[0007] With increasing global focus on sustainability, the need to reduce plastic use is also growing. One aspect of this is reducing the use of single-use hygiene products, which requires reducing the use of polymer fibers primarily used in the production of such products.

[0008] For polymer fibers, the basis weight can be controlled by adjusting the molecular weight distribution during nonwoven fabric production. A narrower molecular weight distribution results in superior spinnability and strength properties, thus allowing for a reduction in basis weight during nonwoven fabric production. Meltblown (M / B) nonwoven fabric is a polypropylene product with a very high melt index; to obtain good spinning properties, a narrow molecular weight distribution below 2.6 is typically required.

[0009] Therefore, it is necessary to study a method to adjust the molecular weight distribution of polypropylene in order to reduce the basis weight when manufacturing nonwoven fabrics. Summary of the Invention

[0010] [Technical Issues] One object of the present invention is to provide a novel transition metal compound that can be used to prepare polypropylene with low weight-average molecular weight, high melt index and narrow molecular weight distribution, thereby exhibiting excellent fiber spinnability and strength properties, and ultimately can be used to prepare nonwoven fabrics with ultra-low basis weight and high strength properties.

[0011] Another object of the present invention is to provide a catalyst composition comprising the transition metal compound, and a method for preparing polypropylene using the catalyst composition.

[0012] [Technical Solution] The present invention provides a transition metal compound represented by the following chemical formula 1.

[0013] [Chemical Formula 1]

[0014] In chemical formula 1, M is a group 4 transition metal. R1 and R1' are either the same as or different from each other, and each is independently unsubstituted or replaced by one or more of C. 1-20 Alkyl, C 1-20 Alkoxy, C 2-30 Alkoxyalkyl, C 6-30 Aryl, C 7-30 Arylalkyl and C 7-30 Substituents of alkylaryl groups substituted with C 6-30 Aryl, R2 to R4 and R2' to R4' may be the same as or different from each other, and each is independently hydrogen, deuterium, or C. 1-30 Alkyl, C 6-30 Aryl, C7-30 Arylalkyl or C 7-30 alkylaryl, R5 and R6 may be the same as or different from each other, and each is independently C. 1-20 alkyl, X1 and X2 may be the same as or different from each other, and each is independently a halogen group or C. 1-20 Alkyl groups, and n is an integer between 1 and 20.

[0015] Furthermore, the present invention also provides a catalyst composition comprising the aforementioned transition metal compound.

[0016] Furthermore, the present invention also provides a method for preparing polypropylene, the method comprising the step of polymerizing propylene monomer in the presence of the catalyst composition.

[0017] [Beneficial effects of the invention] The transition metal compounds according to the present invention can be used to prepare polypropylene that exhibits excellent spinnability and strength properties due to having low weight-average molecular weight, high melt index and narrow molecular weight distribution.

[0018] Furthermore, polypropylene prepared using the transition metal compound or a catalyst composition containing the compound has a low weight-average molecular weight, a high melt index, and a narrow molecular weight distribution, and therefore can be used to manufacture nonwovens with ultra-low basis weight and high strength properties, especially low-brittle, microfibrillated meltblown nonwovens. Detailed Implementation

[0019] The terminology used in this specification is for describing exemplary embodiments only and is not intended to limit the invention.

[0020] Unless the context clearly indicates otherwise, singular expressions also include plural expressions.

[0021] In this specification, terms such as “comprising,” “equipped with,” or “having” are intended to describe the implemented features, figures, steps, components, or combinations thereof, and do not exclude the possibility of one or more other features, figures, steps, components, combinations thereof, or additions.

[0022] Furthermore, the term "to" used in the description of numerical ranges in this specification indicates that both the upper and lower limits are included. For example, "1 to 3" means above 1 and below 3.

[0023] In addition, in this specification, "room temperature" means 20±5°C.

[0024] This invention can be modified and taken in various forms, and specific embodiments will be described in detail below. However, this does not mean that the invention is limited to the specific forms disclosed, but should be understood to include all modifications, equivalents, and substitutions within the spirit and scope of the invention.

[0025] The transition metal compound, catalyst composition, and method for preparing polypropylene using the catalyst composition according to the present invention will be described in detail below.

[0026] The transition metal compounds according to the present invention are represented by the following chemical formula 1: [Chemical Formula 1]

[0027] In chemical formula 1, M is a group 4 transition metal. R1 and R1' are either the same as or different from each other, and each is independently unsubstituted or replaced by one or more of C. 1-20 Alkyl, C 1-20 Alkoxy, C 2-30 Alkoxyalkyl, C 6-30 Aryl, C 7-30 Arylalkyl and C 7-30 Substituents of alkylaryl groups substituted with C 6-30 Aryl, R2 to R4 and R2' to R4' are either the same or different from each other, and each is independently hydrogen, deuterium, or C. 1-30 Alkyl, C 6-30 Aryl, C 7-30 Arylalkyl or C 7-30 alkylaryl, R5 and R6 may be the same as or different from each other, and each is independently C. 1-20 alkyl, X1 and X2 may be the same as or different from each other, and each is independently a halogen group or a C group. 1-20 Alkyl groups, and n is an integer between 1 and 20.

[0028] Unless otherwise stated herein, the following terms may be defined as follows.

[0029] Halogens can be fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0030] C 1-20 Alkyl groups (1 to 20 carbon atoms) can be straight-chain, branched, or cyclic. Specifically, C 1-20 Alkyl groups can be C 1-20 Straight-chain alkyl; C 1-12 Straight-chain alkyl; C 1-5 Straight-chain alkyl; C3-20 Branched or cyclic alkyl groups; C 3-15 Branched or cyclic alkyl groups; or C 3-12 Branched or cyclic alkyl groups. More specifically, C 1-20 Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, or cyclooctyl.

[0031] C 1-20 Alkoxy groups can be straight-chain, branched, or cyclic. Specifically, C 1-20 Alkoxy groups can be C 1-20 Straight-chain alkoxy; C 1-12 Straight-chain alkoxy; C 1-5 Straight-chain alkoxy; C 3-20 Branched or cyclic alkoxy groups; C 3-15 Branched or cyclic alkoxy groups; or C 3-12 Branched or cyclic alkoxy groups. More specifically, C 1-20 Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentoxy, neopentoxy, or cyclohexyloxy.

[0032] C 2-20 The alkoxyalkyl group can be a functional group in which one or more hydrogen atoms of the above-mentioned alkyl groups are substituted with alkoxy groups. More specifically, C 2-20 Examples of alkoxyalkyl groups include, but are not limited to, methoxymethyl, methoxyethyl, ethoxymethyl, isopropoxymethyl, isopropoxyethyl, isopropoxypropyl, isopropoxyhexyl, tert-butoxymethyl, tert-butoxyethyl, tert-butoxypropyl, and tert-butoxyhexyl alkoxyalkyl groups.

[0033] C 6-30 The aryl group can be monocyclic, bicyclic, or tricyclic aromatic hydrocarbons. Specifically, C 6-30 Aryl groups can be C 6-18 Aryl or C 6-12 Aryl. More specifically, C 6-30 Examples of aryl groups include, but are not limited to, phenyl, biphenyl, naphthyl, anthraceneyl, phenanthryl, or fluoreneyl.

[0034] C 7-30 Alkyl aryl refers to an aromatic ring in which one or more hydrogen atoms are replaced by the aforementioned alkyl group. Specifically, C 7-30 Alkyl aryl groups can be C 7-20 Alkyl aryl, or C 7-14 Alkyl aryl. More specifically, C 7-30 Examples of alkylaryl groups include, but are not limited to, methylphenyl, ethylphenyl, tert-butylphenyl, methylbiphenyl, or methylnaphthyl.

[0035] C 7-30 Arylalkyl refers to a substituent in which one or more hydrogen atoms on the aforementioned alkyl group are replaced by the aforementioned aryl group. Specifically, the C 7-30 Arylalkyl groups can be C 7-20 Arylalkyl, can also be C 7-14 Arylalkyl. More specifically, the C 7-30 Examples of arylalkyl groups include, but are not limited to, benzyl, phenethyl, biphenylmethyl, naphthylmethyl, etc.

[0036] Furthermore, the Group 4 transition metal can be titanium (Ti), zirconium (Zr), hafnium (Hf), or ruthenium (Rf), specifically titanium (Ti), zirconium (Zr), or hafnium (Hf), but is not limited to these.

[0037] Meanwhile, the transition metal compound of the present invention, as shown in Chemical Formula 1, comprises two indene structures, wherein the carbon at position 2 is replaced by an isopropyl group and the carbon at position 4 is replaced by a C-type group. 6-30 Aryl substitution, the C 6-30 The aryl group is not substituted or is selected from one or more C 1-20 Alkyl, C 1-20 Alkoxy, C 2-30 Alkoxyalkyl, C 6-30 Aryl, C 7-30 Arylalkyl and C 7-30 The alkylaryl groups are substituted, and the indene structure is linked by silicon bridging groups. Furthermore, the silicon bridging groups contain tether groups composed of alkoxyalkyl groups, which contain long alkylene chains. Due to this characteristic structure, the transition metal compound can be used to prepare polypropylene with low weight-average molecular weight, high melt index, and narrow molecular weight distribution, thus exhibiting excellent spinnability and strength properties. Therefore, it can be used to prepare nonwoven fabrics with ultra-low basis weight and high strength properties, especially low-brittle microfiberized meltblown nonwoven fabrics.

[0038] Specifically, the transition metal compound has a structure as shown in Formula 1, wherein the two indene structures are connected by a bridging group, thus exhibiting high structural stability. In particular, its structural stability can be further improved when the two indene structures are substituted with the same substituents at the same positions, thereby having the same structure.

[0039] Furthermore, in the polymerization reaction for preparing polypropylene, propylene and hydrogen undergo a competitive reaction. By replacing the carbon at position 2 of the indene structure in Formula 1 with a bulkier isopropyl group, the metal center achieves a certain spatial arrangement, thereby increasing the reactivity of hydrogen, which is smaller in volume than propylene, and ultimately enhancing the reactivity of hydrogen during polymerization. Moreover, due to the high reactivity of hydrogen, only a small amount of hydrogen is needed to produce a product with a high melt index (high MI polypropylene).

[0040] In addition, by introducing electron-donating substituents (R1 and R1') at the 4-position carbon of the indene structure, specifically unsubstituted or with one or more substituents selected from C... 1-20 Alkyl, C 1-20 Alkoxy, C 2-30 Alkoxyalkyl, C 6-30 Aryl, C 7-30 Arylalkyl and C 7-30 Substituents of alkylaryl groups substituted with C 6-30 The aryl group can donate sufficient electrons to the Group 4 transition metal atom in the bridging structure of Formula 1. As a result, the cationic properties of the Group 4 transition metal M are enhanced, thereby improving the catalyst activity and the reaction rate, enabling the preparation of polypropylene with a higher molecular weight under the same conditions during the polymerization reaction.

[0041] Furthermore, when C 6-30 aryl groups are selected from one or more C 1-20 Alkyl, C 1-20 Alkoxy, C 2-30 Alkoxyalkyl, C 6-30 Aryl, C 7-30 Arylalkyl and C 7-30 When alkylaryl groups are substituted, they can donate more electrons to the aryl group through inductive effects. Furthermore, increasing the available angle by increasing the overall size of the transition metal compound can promote monomer entry, thus exhibiting higher catalytic activity.

[0042] Furthermore, since the transition metal compound donates electrons to the Group 4 transition metal M in the form of two indene structures connected by a bridging base, it can exhibit high structural stability.

[0043] Furthermore, the bridging group comprises an alkoxyalkyl chain group, which can act as a Lewis base as an oxygen donor. Due to the presence of this chain group, it can be loaded by chemical bonding with the support, thereby preventing the catalyst precursor from detaching from the support during polymerization and ensuring process stability. Specifically, if leaching of the catalyst precursor occurs, scaling phenomena such as polymer entanglement on the reactor surface during polymerization can occur. Transition metal compounds exhibit excellent binding properties with the support during the preparation of supported catalysts, minimizing leaching phenomena of the precursor from the support during polymerization (e.g., propylene polymerization), thereby improving process stability and catalyst activity in propylene polymerization and significantly reducing process failures (reactor scaling, clogging) even in long-term production.

[0044] Specifically, in chemical formula 1, M can be titanium (Ti), zirconium (Zr), or hafnium (Hf).

[0045] Furthermore, specifically, in chemical formula 1, R1 and R1' can be the same as or different from each other, and can each be independently unsubstituted or selected from C. 1-12 Alkyl, C 1-12 Alkoxy, C 2-20 Alkoxyalkyl, C 6-20 Aryl, C 7-20 Arylalkyl and C 7-20 One or more substituents in the alkyl aryl group substituted C 6-18 Aryl. More specifically, R1 and R1' can be the same, and can be unsubstituted or selected from C. 1-6 straight-chain alkyl, C 3-6 Branched alkyl, C 1-6 Straight-chain alkoxy, C 3-6 Branched alkoxy groups and C 6-12 One or more substituents in the aryl group substituted C 6-12 Aryl. More specifically, R1 and R1' can be the same and can be tert-butylphenyl, 2,4-di-tert-butylphenyl, methylphenyl, isopropoxyphenyl, or biphenyl.

[0046] Furthermore, in chemical formula 1, specifically, R2 to R4 and R2' to R4' can each be hydrogen.

[0047] Furthermore, in chemical formula 1, specifically, R5 can be C 3-12 Branched alkyl groups, R6 can be C 1-6 Straight-chain alkyl or C 3-6 Branched alkyl groups. More specifically, R5 can be tert-butyl and R6 can be methyl.

[0048] Furthermore, in chemical formula 1, specifically, X1 and X2 may be the same as or different from each other, and may each be chlorine or methyl independently.

[0049] Furthermore, in chemical formula 1, specifically, n can be an integer between 1 and 20. More specifically, n can be an integer greater than 1, greater than 2, or greater than 4, and less than 20, less than 12, less than 10, less than 8, or less than 6.

[0050] More specifically, transition metal compounds can be any of the compounds represented by the following chemical formulas 1-1 to 1-6:

[0051]

[0052] Transition metal compounds represented by chemical formula 1 can be synthesized by applying known reactions.

[0053] For example, as shown in the following reaction formula 1, transition metal compounds can be prepared by a method comprising the following steps: Step 1: reacting an indene compound (i) with a halosilane compound (silane) as a bridging group to prepare a ligand compound (ii) in which two indene groups are linked by a silicon bridging group; Step 2: reacting the ligand compound (ii) with a halide salt (metal halide) of a Group 4 transition metal to prepare a transition metal compound (1) of formula 1. The following reaction formula 1 is merely an example to illustrate the present invention, and the present invention is not necessarily limited thereto.

[0054] [Reaction Formula 1]

[0055] In reaction formula 1, each substituent is defined as above, and X is a halogen element.

[0056] Specifically, the method for preparing the transition metal compound according to the embodiments of the present invention includes: Step 1: In the presence of alkyl lithium, such as n-butyllithium (n-BuLi), indene compound (i) (e.g., 2-isopropyl-4-tert-butylphenylindene) is reacted with a halosilane compound (e.g., (6-tert-butoxyhexyl)dichloromethylsilane or (6-tert-butoxybutyl)dichloromethylsilane) as a bridging group to prepare ligand compound (ii); Step 2: Ligand compound (ii) is reacted with a halide salt (metal halide) of a Group 4 transition metal, such as ZrCl4, to prepare transition metal compound (1) of formula 1.

[0057] Furthermore, according to the present invention, a catalyst composition comprising the transition metal compound is provided.

[0058] Specifically, the catalyst composition may contain a transition metal compound as a single component.

[0059] In addition to transition metal compounds, the catalyst composition may further include one or more supports and co-catalysts.

[0060] When a support is further included, the catalyst composition can be in the form of a supported metallocene catalyst. When using a supported metallocene catalyst, the prepared polypropylene exhibits excellent morphology and physical properties, making it suitable for conventional slurry polymerization, bulk polymerization, or gas-phase polymerization processes.

[0061] Specifically, the support can be silica, silica-alumina composite material, or silica-magnesium oxide composite material, and one or a mixture of two or more of these can be used. Furthermore, as a support, a support with highly reactive hydroxyl, silanol, or siloxane groups on its surface can be used; for this purpose, a calcined surface-modified support or a support whose surface moisture has been removed by drying can be used.

[0062] In the aforementioned carriers, regarding silica, since the silica carrier and the functional groups of the compound of Formula 1 are loaded through chemical bonding, almost no catalyst is released from the carrier surface during propylene polymerization. Thus, when preparing polypropylene by slurry or gas-phase polymerization, scaling caused by adhesion of reactor walls or polymer particles can be minimized.

[0063] Furthermore, when loaded onto a support, the loading range of the compound of Formula 1 can be, for example, 10 μmol or more, or 12 μmol or more, or 14 μmol or more, and less than 30 μmol, or less than 20 μmol, or less than 16 μmol per weight of support based on about 1 g of silica. When the loading reaches the above range, it is beneficial for the preparation of polypropylene.

[0064] In addition, when the catalyst composition also contains a co-catalyst, the co-catalyst may specifically include one or more compounds represented by the following chemical formulas 2 to 4.

[0065] [Chemical Formula 2] -[Al(R 22 )-O] m - In chemical formula 2, R 22 They may be the same as or different from each other, and each is independently a halogen group, C 1-20 Alkyl or C 1-20 Halogenated alkyl groups; m is an integer greater than or equal to 2; [Chemical Formula 3] J(R 23 )3 In chemical formula 3, R 23 They may be the same as or different from each other, and each is independently a halogen group, C 1-20 Alkyl or C 1-20 Halogenated alkyl groups; J represents aluminum or boron; [Chemical Formula 4] [EH] + [ZQ4] - In chemical formula 4, E is a neutral or cationic Lewis base; H represents a hydrogen atom; Z is a group 13 element; Q are the same as or different from each other, and each is independently C. 6-20 Aryl or C 1-20 Alkyl, wherein C 6-20 Aryl or C 1-20The alkyl group is not substituted or is replaced by one or more groups selected from halogen groups, C 1-20 Alkyl, C 1-20 Alkoxy and C 6-20 Substitution of aryloxy groups.

[0066] Examples of compounds represented by Formula 2 include aluminum oxane-based compounds, such as methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, or butylaluminoxane, any one or a mixture of two or more of them may be used.

[0067] Examples of compounds represented by Formula 3 include trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, dimethylaluminum chloride, triisopropylaluminum, trisec-butylaluminum, tricyclopentylaluminum, tripentylaluminum, triisopentylaluminum, trihexylaluminum, trioctylaluminum, ethyldimethylaluminum, methyldiethylaluminum, triphenylaluminum, tri-p-tolylaluminum, dimethylmethoxyaluminum, dimethylethoxyaluminum, trimethylboron, triethylboron, triisobutylboron, tripropylboron, tributylboron, etc., and more specifically, it can be selected from trimethylaluminum, triethylaluminum, and triisobutylaluminum.

[0068] Examples of compounds represented by Formula 4 include triethylammonium tetraphenylborane, tributylammonium tetraphenylborane, trimethylammonium tetraphenylborane, tripropylammonium tetraphenylborane, trimethylammonium tetra(p-tolyl)borane, trimethylammonium tetra(o,p-dimethylphenyl)borane, tributylammonium tetra(p-trifluoromethylphenyl)borane, trimethylammonium tetra(p-trifluoromethylphenyl)borane, tributylammonium tetrapentafluorophenylborane, N,N-diethylphenylammonium tetraphenylborane, N,N-diethylphenylammonium tetrapentafluorophenylborane, diethylammonium tetrapentafluorophenylborane, triphenylphosphonium tetraphenylborane, trimethylphosphonium tetraphenylborane, triethylammonium tetraphenylaluminum, tributylammonium tetraphenylaluminum, trimethylammonium tetraphenylaluminum, tripropylammonium tetraphenylaluminum, and trimethylammonium tetra(p-tolyl). Aluminum, tripropylammonium tetra(p-tolyl)aluminum, triethylammonium tetra(o,p-dimethylphenyl)aluminum, tributylammonium tetra(p-trifluoromethylphenyl)aluminum, trimethylammonium tetra(p-trifluoromethylphenyl)aluminum, tributylammonium tetrapentafluorophenylaluminum, N,N-diethylphenylammonium tetraphenylaluminum, N,N-diethylphenylammonium tetrapentafluorophenylaluminum, diethylammonium tetrapentafluorophenylaluminum, triphenylphosphonium tetraphenylaluminum, trimethylphosphonium tetraphenylaluminum, tripropylammonium tetra(p-tolyl)boron, triethylammonium tetra(o,p-dimethylphenyl)boron, tributylammonium tetra(p-trifluoromethylphenyl)boron, triphenylcarbium tetra(p-trifluoromethylphenyl)boron or triphenylcarbium tetrapentafluorophenylboron, and mixtures thereof may be used.

[0069] In the aforementioned cocatalysts, the use of the compound of Formula 2 in conjunction with the compound of Formula 1 can enhance catalyst activity. More specifically, alkylaluminoxanes, such as methylaluminoxanes, can also be used as cocatalysts. Alkylaluminoxane-based cocatalysts can act as scavengers of hydroxyl groups on the support surface, thereby enhancing catalyst activity and converting halogen groups in the catalyst precursor to methyl groups, promoting the growth of polypropylene chains.

[0070] The co-catalyst can be loaded at a concentration of 1 mmol or more, or 2 mmol or more, or less than 10 mmol or less, or less than 5 mmol per weight of the carrier (e.g., based on 1 g of silica). When the concentration is within the above range, the co-catalyst can enhance the catalyst activity.

[0071] In catalyst compositions, the loading degree varies with the degree of bonding between the support and the transition metal compound. When the transition metal compound, serving as a catalyst precursor, is not firmly supported, leaching occurs, meaning the catalyst precursor detaches from the support during polymerization. If this happens, the polymerization process stability is significantly reduced, leading to process problems (reactor scaling, clogging) in long-term production. To address this issue, transition metal compounds of Formula 1 possess optimized structures and substituent properties, enabling them to form high bond strength with the support, thereby significantly reducing the leaching of Group 4 transition metals such as titanium and zirconium. As a result, excellent process stability is maintained even in long-term production. Furthermore, polypropylene with controllable physical properties can be readily prepared.

[0072] Therefore, the present invention provides a method for preparing polypropylene, comprising the step of polymerizing propylene monomer in the presence of a catalyst composition.

[0073] Polymerization can be carried out by homopolymerization of propylene using a continuous slurry polymerization reactor, a circulating slurry reactor, a gas phase reactor, or a solution reactor.

[0074] Furthermore, the temperature during the polymerization reaction can be above 20°C, above 50°C, or above 70°C, and below 200°C, below 150°C, or below 120°C.

[0075] In addition, the pressure during the polymerization process can be above 10 bar, above 15 bar, above 20 bar and below 50 bar, below 40 bar, or below 35 bar.

[0076] Furthermore, the above-mentioned catalyst composition can be added directly to the polymerization reaction, or it can be dissolved or diluted in a solvent before addition. Examples of solvents include aliphatic hydrocarbon solvents with 5 to 12 carbon atoms, such as pentane, hexane, heptane, nonane, and decane; aromatic hydrocarbon solvents, such as toluene and benzene; or hydrocarbon solvents substituted with one or more chlorine atoms, such as dichloromethane and chlorobenzene; any one or a mixture of two or more of these solvents can be used. Additionally, trace amounts of water or air (which are catalyst poisons) can be removed from the solvent by treating it with a small amount of alkylaluminum before use.

[0077] As described above, the transition metal compounds according to the present invention exhibit excellent hydrogen reactivity when used as polymerization catalysts for the preparation of polypropylene. Therefore, polypropylene with a melt index (high MI) suitable for manufacturing fibers or nonwoven fabrics, for example, MI of 200.0 g / 10 min to 1000.0 g / 10 min, can be prepared with only a small amount of hydrogen input.

[0078] For example, during the polymerization reaction, hydrogen can be introduced in amounts ranging from 0.1 to 30% by volume based on the total volume of propylene monomers. More specifically, based on the total weight of propylene monomers, the amount of hydrogen introduced can be more than 0.1% by volume, more than 1% by volume, more than 5% by volume, or more than 10% by volume, and less than 30% by volume, less than 25% by volume, less than 20% by volume, or less than 15% by volume.

[0079] Furthermore, the polymerization reaction can be a homopolymerization reaction that polymerizes only propylene monomers. Therefore, the polypropylene of the present invention can be a homopolymer.

[0080] The polypropylene of the present invention, prepared by polymerization, has a low weight-average molecular weight, a high melt index, and a narrow molecular weight distribution.

[0081] Specifically, the polypropylene may satisfy all of the following conditions (i) to (iii): (i) Molecular weight distribution: below 2.60 (ii) Weight-average molecular weight: 50,000 to 100,000 g / mol (iii) Melt index, measured at 230°C and 2.16 kg according to ASTM D1238: 200.0 to 1,000.0 g / 10 min.

[0082] Specifically, the polypropylene has a narrow molecular weight distribution (Mw / Mn) of less than 2.60. This narrow molecular weight distribution gives it excellent spinning and strength properties, enabling ultra-low basis weight in the manufacture of fibers or nonwoven fabrics (especially meltblown nonwoven fabrics). More specifically, the molecular weight distribution of the polypropylene can be less than 2.60, less than 2.55, less than 2.52, less than 2.50, or less than 2.30. There is no particular limitation on the lower limit of the molecular weight distribution; for example, it can be greater than 1.00, greater than 1.50, greater than 2.00, greater than 2.10, greater than 2.15, or greater than 2.18.

[0083] Furthermore, polypropylene has a low weight-average molecular weight of 50,000 to 100,000 g / mol. Due to this low weight-average molecular weight, polypropylene has a high melt index, thus improving its fiber spinnability or processability, while also exhibiting excellent rigidity. Specifically, the weight-average molecular weight of polypropylene can be above 50,000 g / mol, or above 60,000 g / mol, or above 70,000 g / mol, or above 75,000 g / mol and below 100,000 g / mol, or below 90,000 g / mol, or below 87,000 g / mol.

[0084] In this invention, the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of polypropylene are measured using gel permeation chromatography (GPC, manufactured by Waters Corporation), and then calculated as the ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn). Here, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are the converted molecular weights of polystyrene analyzed by gel permeation chromatography (GPC). The specific measurement methods are described in the experimental examples below.

[0085] Furthermore, the polypropylene has a high melt index (MI) of 200.0 to 1,000.0 g / 10 min. 2.16 (ASTM D1238, 230°C, 2.16 kg). This high melt index enables it to exhibit excellent strength properties, resulting in ultra-low basis weight and excellent strength properties when manufacturing nonwoven fabrics, especially meltblown nonwoven fabrics. Specifically, the MI of polypropylene... 2.16 It can be above 200.0g / 10min, above 400.0g / 10min, above 500.0g / 10min, above 600.0g / 10min or above 650.0g / 10min, and below 1000.0g / 10min, below 800.0g / 10min, below 750.0g / 10min or below 710.0g / 10min.

[0086] The polypropylene of this invention, while meeting the physical property requirements, exhibits superior fiber spinnability and high rigidity compared to polypropylene prepared by traditional Ziegler-Natta catalysts, homopolymer polypropylene or propylene copolymers or polybutene prepared by traditional metallocene catalysts. Therefore, it can produce ultra-low basis weight, high-rigidity nonwoven fabrics, reducing the amount of plastic used in products such as diapers, especially low-brittleness, microfibrillated meltblown nonwoven fabrics.

[0087] The effects and functions of the present invention will be described in more detail below through specific embodiments. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0088] <Preparation of Transition Metal Compounds> Synthesis example 1

[0089] Step 1: Ligand Synthesis 15.0 g (51.6 mmol) of 2-isopropyl-4-tert-butylphenylindene was dissolved in a 1 / 1 toluene / THF solution (172 mL), and then a 2.5 M hexane solvent solution (22.7 mL) of n-butyllithium was slowly added dropwise at 0°C, and the mixture was stirred at room temperature for 4 hours. Then, 7.40 g of (6-tert-butoxyhexyl)dichloromethylsilane was slowly added dropwise to the mixture at -78°C, and the mixture was stirred for about 10 minutes, followed by stirring at room temperature for 1 day. The organic layer was then separated by adding water, and the solvent was removed by vacuum distillation to obtain (6-tert-butoxyhexyl)(methyl)-bis(2-isopropyl-4-tert-butylphenylindene)silane.

[0090] Step 2: Synthesis of transition metal compounds 43 mL of toluene and 21.5 mL of diethyl ether were injected into the dried ligand and stirred. The resulting reaction product was cooled to -78°C, and then n-butyllithium (2.5 M, 22.7 mL) was slowly added dropwise with stirring. After the addition of n-butyllithium was complete, the resulting mixture was stirred further at room temperature for about 4 hours, cooled to -20°C, and then a solution of ZrCl4 (6 g) dissolved in toluene was added. The resulting mixture was stirred at 25°C for 12 hours and then dried to remove the solvent. THF was added to the resulting dried product and stirred, and then dried under vacuum. The product was filtered with dichloromethane (DCM), dried, and recrystallized from toluene / hexane. As a result, the transition metal compound (1-1) with the above structure was obtained as a yellow powder (yield: 35%).

[0091] 1H NMR (500 MHz, CDCl3) δ 7.69 - 7.54 (m, 5H), 7.47 (dd, J = 11.5, 4.8 Hz, 5H), 7.35 (d, J = 6.9 Hz, 2H), 7.09 (ddd, J = 8.7, 7.0, 3.8 Hz, 2H),7.00 (s, 2H), 3.38 (t, J = 6.5 Hz, 2H), 3.26 - 3.09 (m, 2H), 2.07 - 1.79 (m,3H), 1.75 - 1.45 (m, 7H), 1.44 - 1.29 (m, 22H), 1.20 (s, 9H), 1.16 - 1.04 (m, 12H). Synthesis example 2 (1-2) Except for replacing (6-tert-butoxybutyl)dichloromethylsilane with (6-tert-butoxyhexyl)dichloromethylsilane in step 1 of Synthesis Example 1, the transition metal compounds (1-2) with the above structures were prepared by the same method as in Synthesis Example 1.

[0092] 1H NMR (500 MHz, CDCl3) δ 7.62 (m, J = 8.6 Hz, 5H), 7.54 (m, J = 8.7Hz, 1H), 7.47 (m, J = 7.9 Hz, 4H), 7.36 (d, J = 6.9 Hz, 2H), 7.10 (q, J = 7.9Hz, 2H), 7.01 (s, 2H), 3.51 (t, J = 6.1 Hz, 2H), 3.29 - 3.13 (m, 2H), 2.12 -1.79 (m, 5H), 1.73 - 1.61 (m, 1H), 1.37 (d, J = 17.2 Hz, 22H), 1.26 - 1.21(m, 9H), 1.12 (t, J = 7.2 Hz, 12H). Synthesis example 3 (1-3) Except that 2-isopropyl-4-methylphenylindene was used instead of 2-isopropyl-4-tert-butylphenylindene in step 1 of Synthesis Example 1, and (6-tert-butoxybutyl)dichloromethylsilane was used instead of (6-tert-butoxyhexyl)dichloromethylsilane, the transition metal compounds (1-3) with the above structures were prepared by the same method as in Synthesis Example 1.

[0093] 1H NMR (500 MHz, CDCl3) δ 7.50 (d, J = 8.9 Hz, 1H), 7.43 (m, 5H), 7.23 (m, 2H), 7.15 (S, 3H), 7.14 (s, 2H), 6.99 (m, 2H), 6.85 (d, J = 4.0 Hz,2H), 3.39 (t, J = 6.3 Hz, 2H), 3.08 (m, 2H), 2.27 (s, 6H), 1.96 – 1.91 (m,1H), 1.87 – 1.82 (m, 2H), 1.79 – 1.74 (m, 2H), 1.58 – 1.52 (m, 1H), 1.27 (s, 3H), 1.13 (S, 9H), 1.02 – 0.98 (m, 12H). Synthesis example 4 (1-4) Except that in step 1 of Synthesis Example 1, 2-isopropyl-4-isopropoxyphenylindene was used instead of 2-isopropyl-4-tert-butylphenylindene, and (6-tert-butoxybutyl)dichloromethylsilane was used instead of (6-tert-butoxyhexyl)dichloromethylsilane, the transition metal compounds (1-4) with the above structures were prepared by the same method as in Synthesis Example 1.

[0094] 1H NMR (500 MHz, CDCl3) δ 7.62 – 7.51 (m, 6H), 7.34 – 7.32 (m, 2H), 7.13 – 7.07 (m, 2H), 7.01 – 6.96 (m, 6H), 4.59 (m, 2H), 3.51 (t, J = 6.3 Hz,2H), 3.22 (m, 2H), 2.07 – 2.00 (m, 1H), 1.99 – 1.94 (m, 2H), 1.92 – 1.86 (m,2H), 1.39 – 1.36 (m, 16H), 1.25 (s, 9H), 1.15 – 1.10 (m, 12H) Synthesis example 5 (1-5) Except that in step 1 of Synthesis Example 1, 2-isopropyl-4-(2,4-dimethylphenyl)indene was used instead of 2-isopropyl-4-tert-butylphenylindene, and (6-tert-butoxybutyl)dichloromethylsilane was used instead of (6-tert-butoxyhexyl)dichloromethylsilane, the transition metal compounds (1-5) with the above structures were prepared by the same method as in Synthesis Example 1.

[0095] 1H NMR (500 MHz, CDCl3) δ 7.63 (d, J = 6.9 Hz, 1H), 7.57 (m, 4H), 7.54 (d, 2H), 7.42 – 7.40 (m, 4H), 7.13 – 7.08 (m, 2H), 7.03 (s, 2H), 3.51(t, J = 6.3 Hz, 2H), 3.25 – 3.16 (m, 2H), 2.09 – 1.85 (m, 6H), 1.39 (s, 6H), 1.32 (s, 36H), 1.24 (s, 9H), 1.12 – 1.08 (m, 12H) Synthesis example 6 (1-6) Except that 2-isopropyl-4-biphenylindene was used instead of 2-isopropyl-4-tert-butylphenylindene in step 1 of Synthesis Example 1, and (6-tert-butoxybutyl)dichloromethylsilane was used instead of (6-tert-butoxyhexyl)dichloromethylsilane, the transition metal compounds (1-6) with the above structures were prepared by the same method as in Synthesis Example 1.

[0096] 1H NMR (500 MHz, CDCl3) δ 7.63 – 7.61 (m, 4H), 7.58 – 7.54 (m, 6H), 7.51 – 7.50 (m, 4H), 7.44 (d, 1H), 7.32 – 7.28 (m, 6H), 7.24 – 7.19 (m, 2H),7.02 – 6.98 (m, 2H), 6.90 (d, 2H), 3.38 (t, J = 6.3 Hz, 2H), 3.09 (m, 2H),1.95 – 1.90 (m, 1H), 1.88 – 1.82 (m, 2H), 1.79 – 1.73 (m, 2H), 1.58 – 1.52(m, 1H), 1.27 (s, 3H), 1.12 (s, 9H), 1.02 – 0.99 (m, 12H) Example 1 Preparation of catalyst composition 32 mL of toluene was added to the Pico reactor, followed by 5 g of silica. 10 mmol of methylaluminoxane (MAO) was added to the reactor, and the reaction was carried out at 90°C for 24 hours. The resulting reaction product precipitated, the supernatant was removed, and the remaining precipitate was washed twice with toluene. 70 μmol of the transition metal compound (1-1) prepared in Synthesis Example 1 was dissolved in toluene and added to the washed product, and the reaction was carried out at 50°C for 3 hours. After the reaction was complete, when the reaction product precipitated, the supernatant was removed, and the remaining precipitate was washed with toluene. The precipitate was then washed again with hexane, and 3 wt% Atmer was added to the hexane solution, followed by stirring for 10 minutes. After stirring, when the reaction product precipitated, the supernatant was removed, and the remaining precipitate was vacuum dried to obtain a solid particulate catalyst composition.

[0097] Preparation of polypropylene The stainless steel reactor was purged with argon, and 1.5 mL of triethylaluminum, 20 mL of hydrogen, and 200 mL of propylene were added sequentially at room temperature. At this point, the amount of hydrogen added was equivalent to 10% of the total volume of the propylene monomer. After stirring for 10 minutes, the catalyst composition prepared above was introduced into the reactor under nitrogen pressure. Polymerization was carried out at a polymerization pressure of approximately 30 bar and a polymerization temperature of 70°C for 30 minutes, after which unreacted propylene was discharged.

[0098] In the preparation of polypropylene, the catalyst activity (activity, kgPP / gCat•hr) was calculated as the ratio of the weight of polymer (kg PP) generated per unit time (hr) to the weight (g) of the catalyst composition used. The results showed that the activity of the catalyst composition was 2.95 kgPP / gCat•hr.

[0099] Example 2 Except that in the preparation of the catalyst composition in Example 1, the transition metal compound (1-2) prepared in Synthesis Example 2 was used instead of transition metal compound (1-1), the catalyst composition and polypropylene were prepared according to the same method as in Example 1. Furthermore, the catalyst activity of the catalyst composition calculated using the same method as in Example 1 was 2.39 kgPP / gCat•hr.

[0100] Example 3 Except that in the preparation of the catalyst composition in Example 1, the transition metal compound (1-3) prepared in Synthesis Example 3 was used instead of the transition metal compound (1-1), the catalyst composition and polypropylene were prepared according to the same method as in Example 1. Furthermore, the catalyst activity of the catalyst composition calculated using the same method as in Example 1 was 2.09 kgPP / gCat•hr.

[0101] Example 4 Except that in the preparation of the catalyst composition in Example 1, the transition metal compound (1-4) prepared in Synthesis Example 4 was used instead of the transition metal compound (1-1), the catalyst composition and polypropylene were prepared according to the same method as in Example 1. Furthermore, the catalyst activity of the catalyst composition calculated using the same method as in Example 1 was 1.10 kgPP / gCat•hr.

[0102] Example 5 Except that in the preparation of the catalyst composition in Example 1, the transition metal compound (1-5) prepared in Synthesis Example 5 was used instead of the transition metal compound (1-1), the catalyst composition and polypropylene were prepared according to the same method as in Example 1. Furthermore, the catalytic activity of the catalyst composition calculated using the same method as in Example 1 was 2.31 kgPP / gCat•hr.

[0103] Example 6 Except that in the preparation of the catalyst composition in Example 1, the transition metal compound (1-6) prepared in Synthesis Example 6 was used instead of the transition metal compound (1-1), the catalyst composition and polypropylene were prepared according to the same method as in Example 1. Furthermore, the catalytic activity of the catalyst composition was calculated to be 2.13 kgPP / gCat•hr according to the same method as in Example 1.

[0104] Comparative Example 1 Except that in the preparation of the catalyst composition in Example 1, a transition metal compound (a) with the following structure was used instead of transition metal compound (1-1), the catalyst composition and polypropylene were prepared in the same manner as in Example 1.

[0105] (a) Comparative Example 2 Except that in the preparation of the catalyst composition in Example 1, a transition metal compound (b) having the following structure was used instead of transition metal compound (1-1), the catalyst composition and polypropylene were prepared in the same manner as in Example 1.

[0106] (b) Comparative Example 3 Except that in the preparation of the catalyst composition in Example 1, a transition metal compound (c) having the following structure was used instead of transition metal compound (1-1), the catalyst composition and polypropylene were prepared in the same manner as in Example 1.

[0107] (c) Comparative Example 4 Except that in the preparation of the catalyst composition in Example 1, a transition metal compound (d) having the following structure was used instead of transition metal compound (1-1), the catalyst composition and polypropylene were prepared in the same manner as in Example 1.

[0108] (d) Comparative Example 5 Except that in the preparation of the catalyst composition in Example 1, a transition metal compound (e) having the following structure was used instead of transition metal compound (1-1), the catalyst composition and polypropylene were prepared in the same manner as in Example 1.

[0109] (e) Experimental Example The physical properties of the polypropylene prepared in the above examples and comparative examples were measured, and the results are shown in Table 1.

[0110] (1) Weight-average molecular weight (Mw) and molecular weight distribution (MWD) The weight-average molecular weight (Mw, g / mol) and number-average molecular weight (Mn, g / mol) of polypropylene were determined by gel permeation chromatography (GPC), and the molecular weight distribution (MWD = Mw / Mn) was obtained by dividing the measured weight-average molecular weight by the number-average molecular weight.

[0111] Specifically, the gel permeation chromatography (GPC) apparatus used was a Waters PL-GPC220 instrument, and the chromatographic column was a Polymer Laboratories PLgel MIX-B type 300 mm column. The measurement temperature was 160°C, the solvent was 1,2,4-trichlorobenzene, and the flow rate was 1 mL / min. Using the GPC analyzer (PL-GPC220), the prepared polypropylene sample was dissolved in 1,2,4-trichlorobenzene containing 0.0125% BHT, heated at 160°C for 3 hours for pretreatment, and then prepared to a concentration of 10 mg / 10 mL, which was then supplied in 200 μL increments. Mw and Mn values ​​were obtained from a calibration curve formed using polystyrene standard samples. Nine polystyrene standard samples were used, with weight-average molecular weights of 2,000 g / mol, 10,000 g / mol, 30,000 g / mol, 70,000 g / mol, 200,000 g / mol, 700,000 g / mol, 2,000,000 g / mol, 4,000,000 g / mol, and 10,000,000 g / mol.

[0112] (2) Melt index (MI) 2.16 ) Melt index was determined according to ASTM D1238 (condition E, 230°C, 2.16 kg load) (g / 10 min).

[0113] Table 1

[0114] Experimental results show that the polypropylene prepared using the catalyst compositions of Examples 1 to 6 (each containing the transition metal compounds prepared in Synthetic Examples 1 to 6) exhibits a narrow molecular weight distribution, below 2.60, despite its low weight-average molecular weight and high melt index. Therefore, it can be predicted that the polypropylene will exhibit excellent spinning properties and improved strength properties during fiber spinning, making it advantageous for producing nonwoven fabrics with ultra-low basis weight and high strength in disposable hygiene products such as diapers.

[0115] Meanwhile, the polypropylene prepared using the catalyst compositions of Comparative Examples 1, 3, 4, and 5 (comprising transition metal compounds (a), (c), (d), and (e)) in which the carbon at the 2-position of two indenyl structures is substituted with a methyl group, respectively) exhibited a wide molecular weight distribution, high weight-average molecular weight, and low melt index. Therefore, it can be predicted that the polypropylene of Comparative Examples 1, 3, 4, and 5 has poor spinning properties and low strength properties, making it difficult to prepare ultra-low basis weight and high-strength nonwoven fabrics.

[0116] Furthermore, polypropylene prepared using the catalyst composition of Comparative Example 2 (which contains a transition metal compound (b) in which the carbon at the 2-position of one of the two indenyl structures is replaced by an isopropyl group and the other by a methyl group) exhibits a narrow molecular weight distribution, but due to its high weight-average molecular weight and low melt index, it is predicted that it will be difficult to prepare nonwoven fabrics with ultra-low basis weight and high strength.

[0117] The experimental results above show that the transition metal compounds of the present invention can be used to prepare polypropylene with low weight-average molecular weight, high melt index and narrow molecular weight distribution below 2.60, thereby exhibiting excellent fiber spinnability and strength properties, and thus can be used for nonwoven fabrics with ultra-low basis weight and high strength properties.

Claims

1. A transition metal compound represented by the following chemical formula 1: [Chemical Formula 1] In chemical formula 1, M is a group 4 transition metal. R1 and R1' are either the same as or different from each other, and each is independently either unsubstituted or selected from C. 1-20 Alkyl, C 1-20 Alkoxy, C 2-30 Alkoxyalkyl, C 6-30 Aryl, C 7-30 Arylalkyl and C 7-30 One or more substituents of alkylaryl group substituted C 6-30 Aryl, R2 to R4 and R2' to R4' are either the same or different from each other, and each is independently hydrogen, deuterium, or C. 1-30 Alkyl, C 6-30 Aryl, C 7-30 Arylalkyl or C 7-30 Alkyl aryl, R5 and R6 may be the same as or different from each other, and each is independently C. 1-20 alkyl, X1 and X2 may be the same as or different from each other, and each is independently a halogen group or a C group. 1-20 Alkyl groups, and n is an integer between 1 and 20.

2. The transition metal compound according to claim 1, wherein, M represents titanium, zirconium, or hafnium.

3. The transition metal compound according to claim 1, wherein, R1 and R1' are either the same as or different from each other, and each is independently unsubstituted or selected from C. 1-12 Alkyl, C 1-12 Alkoxy, C 2-20 Alkoxyalkyl, C 6-20 Aryl, C 7-20 Arylalkyl and C 7-20 One or more substituents in the alkyl aryl group substituted C 6-18 Aryl.

4. The transition metal compound according to claim 1, wherein, R1 and R1' are identical to each other and are either unsubstituted or selected from C. 1-6 straight-chain alkyl, C 3-6 Branched alkyl, C 1-6 Straight-chain alkoxy, C 3-6 Branched alkoxy groups and C 6-12 One or more substituents in the aryl group substituted C 6-12 Aryl.

5. The transition metal compound according to claim 1, wherein, R1 and R1' are identical to each other and are tert-butylphenyl, 2,4-di-tert-butylphenyl, methylphenyl, isopropoxyphenyl, or biphenyl.

6. The transition metal compound according to claim 1, wherein, R2 to R4 and R2' to R4' are each hydrogen.

7. The transition metal compound according to claim 1, wherein, R5 is C 3-12 Branched alkyl group, R6 is C 1-6 Straight-chain alkyl or branched-chain alkyl.

8. The transition metal compound according to claim 1, wherein, R5 is tert-butyl, and R6 is methyl.

9. The transition metal compound according to claim 1, wherein, X1 and X2 may be the same as or different from each other, and each is independently chlorine or methyl.

10. The transition metal compound according to claim 1, wherein, n is an integer between 1 and 6.

11. The transition metal compound according to claim 1, wherein, The transition metal compound is any one of the compounds represented by the following chemical formulas 1-1 to 1-6: 。 12. A catalyst composition comprising the transition metal compound of claim 1.

13. The catalyst composition according to claim 12, further comprising one or more co-catalysts and a support.

14. The catalyst composition according to claim 13, wherein the co-catalyst is selected from compounds represented by the following chemical formulas 2 to 4: [Chemical Formula 2] -[Al(R 22 )-O] m - In chemical formula 2, R 22 They may be the same as or different from each other, and each is independently a halogen, C 1-20 Alkyl or C 1-20 Halogenated alkyl groups; m is an integer greater than or equal to 2; [Chemical Formula 3] J(R 23 )3 In chemical formula 3, R 23 They may be the same as or different from each other, and each is independently a halogen group, C 1-20 Alkyl or C 1-20 Halogenated alkyl groups; J represents aluminum or boron; [Chemical Formula 4] [E-H] + [ZQ4] - In chemical formula 4, E is a neutral or cationic Lewis base; H represents a hydrogen atom; Z is a group 13 element; Q are the same as or different from each other, and each is independently C. 6-20 Aryl or C 1-20 Alkyl, wherein C 6-20 Aryl or C 1-20 The alkyl group is not substituted or is replaced by one or more groups selected from halogen groups, C 1-20 Alkyl, C 1-20 Alkoxy and C 6-20 Substitution of aryloxy groups.

15. The catalyst composition according to claim 13, wherein, The carrier includes silicon oxide, silicon oxide-alumina composite material, silicon oxide-magnesium oxide composite material, or a mixture thereof.

16. A method for preparing polypropylene, comprising the step of polymerizing propylene monomer in the presence of the catalyst composition according to claim 12.

17. The method for preparing polypropylene according to claim 16, wherein, The polymerization is carried out by introducing hydrogen gas at a rate of 0.1 to 30% by volume based on the total volume of propylene monomers.

18. The method for preparing polypropylene according to claim 16, wherein, The polypropylene satisfies the following conditions (i) to (iii): (i) Molecular weight distribution: below 2.60 (ii) Weight-average molecular weight: 50,000 to 100,000 g / mol (iii) Melt index, measured at 230°C and 2.16 kg according to ASTM D1238: 200.0 to 1,000.0 g / 10 min.

Images