Catalyst system for preparing polypropylene with wide molecular weight distribution and high melt strength and application of catalyst system

Abstract

The invention provides a catalyst system for preparing polyolefin with wide molecular weight distribution and high melt strength and application of the catalyst system, and belongs to the technical field of olefin polymerization. The catalyst system comprises the following components and reaction products thereof: A, a catalyst component; b, an organic aluminum compound; c, an external electron donor compound; the external electron donor compound comprises a silane external electron donor compound, a cyanic acid ester external electron donor compound and a glycol ester external electron donor compound. According to the invention, a specific catalyst component containing cyanic acid ester and diol ester electron donor compounds is used, and a silane external electron body is added to be matched with cyanic acid ester and diol ester external electron donors for use, so that a catalyst system is formed; through a special preparation process, the prepared polymer has relatively wide molecular weight distribution and relatively high proportion of supermolecules. The method provided by the invention is simple, is easy for industrial production, can be used for preparing high-performance products, and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to a catalyst system for preparing polypropylene with wide molecular weight distribution and high melt strength and application thereof, belonging to the technical field of olefin polymerization. Background Art

[0002] Conventional semi-crystalline linear isotactic polypropylene (iPP) has a relatively narrow molecular weight distribution, low melt strength, and is difficult to process by thermoforming, which limits its application areas. High melt strength polypropylene has been widely used in thermoforming, foaming, extrusion coating, and other fields due to its high melt strength, yield strength, flexural modulus, heat deformation temperature, melting point, crystallization temperature, and short crystallization time. In these applications, high melt strength polypropylene used in thermoforming can demold parts at higher temperatures, shorten the molding cycle, and increase production; during the foaming process, it can resist the rupture of the micropore wall, increase the foaming ratio, reduce the density, and increase the closed cell rate; during the extrusion coating process, it exhibits a faster coating speed and very small necking. Therefore, high melt strength polypropylene is the research focus of polypropylene production technology innovation, and it is also the technical bottleneck for the expansion of polypropylene application areas and high performance.

[0003] At present, the conventional methods for improving the melt strength of polypropylene are: polymerization technology, reactive extrusion and irradiation modification methods. The polymerization technology method now includes one-step method, two-step method, copolymerization method and in-situ polymerization method. The foreign patent technology is based on Chisso's US 6225432B1 using CGC (constrained geometry catalysts) constrained geometry catalysts to branch the polymer long chain; Chinese invention patents CN200710179266.7 and CN 201010147765.X respectively graft copolymerize propylene with α, ω-non-conjugated diene, styrene and substituted styrene monomers (T-type monomers) to form long chain branches. The polymerization technology method can accurately control the length of the branch chain and the distribution of the branch structure in the polymer main chain. In the industry of preparing high melt strength polypropylene with Ziegler-Natta catalyst, the introduction of other monomers, or the addition of more reactors while changing the types of materials in different reactors, increases the reaction raw materials, increases the processing steps such as recovery and purification, and the process is cumbersome. The practicality of constructing long-chain branched structures based on metallocene catalytic systems still needs to be improved.

[0004] The reaction extrusion method prepares high melt strength polypropylene by adding peroxide and other multifunctional reaction monomers to polypropylene. That is, peroxide and a third monomer are added to polypropylene powder, and long-chain branched polypropylene is generated after reaction, thereby improving the melt strength of polypropylene. The reaction extrusion method must add a variety of chemical components to produce high melt strength polypropylene, which increases production costs on the one hand, and also causes fluctuations in product quality due to the control of the amount added. More importantly, the long-term presence of additives in the polymer will lead to a gradual deterioration of the yellowness index and physical properties of the product. Some of the added compounds are still toxic and cannot be used for contact with food and medicine. Many research institutions at home and abroad use this method to produce high melt strength polypropylene with a long-chain branched structure.

[0005] Irradiation modification is to select appropriate radiation source and dose to irradiate polypropylene, so that the polypropylene molecular chain is cross-linked to produce long branched structure, thereby improving the melt strength of polypropylene. In terms of the selection of radiation source, electron rays generated by electron accelerators or gamma rays generated by 60Co are currently mainly used.

[0006] In summary, it is very necessary to develop high-performance high-melt-strength polypropylene, and a production technology that is both economical and environmentally friendly. Among them, the catalyst in-situ generation method is the most applicable, environmentally friendly, simple and most stable industrial production method for product performance. This method is to prepare a wide molecular weight distribution polypropylene in a reactor using a specific catalyst to achieve high melt strength of the final polymer. It is usually to selectively add external electron donors with different hydrogen sensitivity at different polymerization stages, and to adjust the size of the molecular weight by adjusting the hydrogen concentration in different reactors, thereby realizing the preparation of polypropylene containing both high molecular weight fractions and low molecular weight fractions, wherein the high molecular weight fraction ensures the melt strength of the final polymer, and the broadened molecular weight distribution ensures its good processing performance. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a catalyst system and its application for preparing polypropylene with wide molecular weight distribution and high melt strength through systematic research. The present invention adopts a Ziegler-Natta catalyst component containing internal electron donors such as cyanoesters and diol esters and / or other types of compounds. When forming the catalyst, a unique catalyst system is formed by rationally compounding three different types of external electron donors, namely silanes, cyanoesters and diol esters. The method of direct polymerization in a reactor obtains polypropylene with wide molecular weight distribution and containing more ultra-high molecular weight fractions, and the polymer has ultra-high melt strength.

[0008] The internal electron donor used in the present invention comprises a Ziegler-Natta catalyst component of a cyanate ester and a diol ester, and based on the total weight of the catalyst component, contains 1.0 wt% to 5.0 wt% of titanium element, 0.5 wt% to 10.0 wt% of a diol ester internal electron donor compound, 3.0 wt% to 20.0 wt% of a cyanate ester internal electron donor compound, and the molar ratio of the diol ester internal electron donor compound to the cyanate ester internal electron donor compound is 0.025:1 to 0.8:1; preferably, based on the total weight of the catalyst component, contains 1.3 wt% to 4.0 wt% of titanium element, 0.8 wt% to 6 wt% of a diol ester internal electron donor compound, 5 wt% to 15 wt% of a cyanate ester internal electron donor compound, and the molar ratio of the diol ester internal electron donor compound to the cyanate internal electron donor compound is (0.05 to 0.6):1.

[0009] Optionally, the cyanoester internal electron donor compound has a structure shown in general formula (I):

[0010]

[0011] In the general formula (I), R 1 and R 2 Independently selected from linear C 1 ~C 4 Alkyl, branched C 1 ~C 4 Alkyl; R 3 and R 4 Independently selected from C 3 ~C 6 Isoalkyl, C 3 ~C 6 Secondary alkyl and C 3 ~C 6 Cycloalkyl.

[0012] Optionally, the cyano ester internal electron donor compound is selected from cyanosuccinate compounds, preferably 2,3-dinon-linear alkyl-2-cyanosuccinate diester compounds, more preferably 2,3-diisopropyl-2-dicyanosuccinic acid dimethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isopropyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isobutyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid-1-methyl-4-ethyl ester (R 1 = methyl, R 2 =ethyl), 2,3-diisopropyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R1 =Ethyl, R 2 = methyl), 2,3-diisopropyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-diisopropyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl), dimethyl 2,3-diisobutyl-2-dicyanosuccinate, diethyl 2,3-diisobutyl-2-dicyanosuccinate, di-n-propyl 2,3-diisobutyl-2-dicyanosuccinate, diisopropyl 2,3-diisobutyl-2-dicyanosuccinate, di-n-butyl 2,3-diisobutyl-2-dicyanosuccinate, diisobutyl 2,3-diisobutyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-diisobutyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-diisobutyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl), dimethyl 2,3-di-sec-butyl-2-dicyanosuccinate, diethyl 2,3-di-sec-butyl-2-dicyanosuccinate, di-n-propyl 2,3-di-sec-butyl-2-dicyanosuccinate, diisopropyl 2,3-di-sec-butyl-2-dicyanosuccinate, di-n-butyl 2,3-di-sec-butyl-2-dicyanosuccinate, diisobutyl 2,3-di-sec-butyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-di-sec-butyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-di-sec-butyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2=n-butyl), dimethyl 2,3-dicyclopentyl-2-dicyanosuccinate, diethyl 2,3-dicyclopentyl-2-dicyanosuccinate, di-n-propyl 2,3-dicyclopentyl-2-dicyanosuccinate, diisopropyl 2,3-dicyclopentyl-2-dicyanosuccinate, di-n-butyl 2,3-dicyclopentyl-2-dicyanosuccinate, diisobutyl 2,3-dicyclopentyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-dicyclopentyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-dicyclopentyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl), dimethyl 2,3-dicyclohexyl-2-dicyanosuccinate, diethyl 2,3-dicyclohexyl-2-dicyanosuccinate, di-n-propyl 2,3-dicyclohexyl-2-dicyanosuccinate, diisopropyl 2,3-dicyclohexyl-2-dicyanosuccinate, di-n-butyl 2,3-dicyclohexyl-2-dicyanosuccinate, diisobutyl 2,3-dicyclohexyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-dicyclohexyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-dicyclohexyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-dicyclohexyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-dicyclohexyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl). Among them, more preferred are diethyl 2,3-diisopropyl-2-dicyanosuccinate, di-n-propyl 2,3-diisopropyl-2-dicyanosuccinate, diisopropyl 2,3-diisopropyl-2-dicyanosuccinate, di-n-butyl 2,3-diisopropyl-2-dicyanosuccinate, and diisobutyl 2,3-diisopropyl-2-dicyanosuccinate. The above internal electron donor compounds can be used alone or in combination.

[0013] Optionally, in the present invention, the 2,3-dinon-linear alkyl-2-cyanosuccinic acid diester compound is prepared according to the method disclosed in International Patent Application No. PCT / CN2010 / 000202.

[0014] Optionally, the diol ester internal electron donor compound has a structure shown in general formula (II):

[0015]

[0016] In the general formula (II), R 1 ~R 6 , R 1 ~R 2n are independently selected from hydrogen, halogen, substituted or unsubstituted linear or branched C 1 ~C 20 Alkyl, substituted or unsubstituted C 3 ~C 20 Cycloalkyl, substituted or unsubstituted C 6 ~C 20 Aryl, C 7 ~C 20 Alkaryl, substituted or unsubstituted C 7 ~C 20 Arylalkyl, substituted or unsubstituted C 2 ~C 10 Alkenyl, substituted or unsubstituted C 10 ~C 20 Condensed ring aromatic or substituted or unsubstituted C 10 ~C 20 Ester group.

[0017] Optionally, in the general formula (II), R 1 and R 2 Not hydrogen, R 3 ~R 6 and R 1 ~R 2n Any one of the groups optionally contains one or more heteroatoms as substitutes for carbon atoms or hydrogen atoms or both, wherein the heteroatoms are selected from nitrogen, oxygen, sulfur, silicon, phosphorus or halogen atoms, and R 3 ~R 6 and R 1 ~R 2n One or more of the groups may optionally form a ring with each other, and n is an integer of 0 to 10.

[0018] Among the diol ester internal electron donor compounds represented by the general formula (II), preferably included are compounds represented by the general formula (III):

[0019]

[0020] In the general formula (III), R 1 ~R 6 , R 1 ~R 2 are independently selected from hydrogen, halogen atoms, linear or branched C 1 ~C 20 Alkyl, C 3 ~C 20 Cycloalkyl, C 6 ~C 20 Aryl, C 7 ~C 20 Alkyl or C 7 ~C 20 Aralkyl.

[0021] In the above-mentioned solid catalyst component of the present invention, the internal electron donor compound is disclosed in Chinese patents CN1436766A and CN1436796A, and all relevant contents disclosed in the patents are introduced into the present invention as reference.

[0022] Optionally, the diol ester internal electron donor compound represented by the general formula (III) includes 2-ethyl-1,3-propanediol dibenzoate, 2-propyl-1,3-propanediol dibenzoate, 2-isopropyl-2-isopentyl-1,3-propanediol dibenzoate, 1,3-butanediol dimethyl benzoate, 2-methyl-1,3-butanediol di-m-chlorobenzoate, 2,3-dimethyl-1,3-butanediol dibenzoate, 1 ,3-pentanediol neopentanoate, 2,4-pentanediol dibenzoate, 2-methyl-1,3-pentanediol benzoic acid cinnamate, 2,2-dimethyl-1,3-pentanediol dibenzoate, 2,4-heptanediol dibenzoate, 2-methyl-3,5-heptanediol dibenzoate, 4-ethyl-3,5-heptanediol dibenzoate, etc., preferably 2,4-pentanediol dibenzoate and 4-ethyl-3,5-heptanediol dibenzoate.

[0023] The present invention also relates to a catalyst system for olefin polymerization, comprising the following components and reaction products thereof:

[0024] A, the catalyst component of the present invention;

[0025] B. Organoaluminum compounds;

[0026] C. External electron donor compounds;

[0027] The external electron donor compounds include silane-based external electron donor compounds, cyanate-based external electron donor compounds and glycol-ester-based external electron donor compounds.

[0028] Optionally, the general formula of the organoaluminum compound is AlR n X 3-n, where R is hydrogen or a hydrocarbon group with 1 to 20 carbon atoms; X is a halogen, and n is an integer where 0 < n ≤ 3.

[0029] Optionally, the organoaluminum compound is selected from trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, monochlorodiethylaluminum, monochlorodiisobutylaluminum, dichloroethylaluminum and other alkylaluminum halides, among which triethylaluminum and triisobutylaluminum are preferred.

[0030] Optionally, the ratio between the organoaluminum compound and the catalyst component is 5 to 5000 in terms of the molar ratio of aluminum element to titanium element, preferably 20 to 500.

[0031] Optionally, the silane external donor compound is selected from at least one of the compounds with the general formula R1R2 m Si(OR3) 3-m , R4 n Si(OR5) 4-n and R6R7Si(OR8) 2 , or a mixture of any two or more of them in any proportion, where m and n are independently integers from 0 to 2, R1 and R2 are the same or different C 1 -C 10 linear or branched or cyclic aliphatic groups, R3, R4, R5, R6 and R8 are the same or different C 1 -C 3 linear aliphatic groups, and R7 is a C 3 -C 6 branched or cyclic aliphatic group.

[0032] Optionally, specific examples of the silane external donor compound include but are not limited to tetramethoxysilane, n-propyltriethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, vinyltrimethoxysilane, n-propyltrimethoxysilane, tetraethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisobutyldimethoxysilane, methylcyclohexyldimethoxysilane, methylisobutyldimethoxysilane, dicyclohexyldimethoxysilane, phenyltrimethoxysilane, dicyclopentyldimethoxysilane, etc.

[0033] Optionally, the ratio between the organoaluminum compound and the silane external donor compound is 0.5:1 to 200:1 in terms of the molar ratio of aluminum element to silicon element, preferably 1:1 to 100:1.

[0034] Optionally, the cyanate ester external donor compound has the structure shown in the general formula (Ⅰ):

[0035]

[0036] In the general formula (I), R 1 and R 2 Independently selected from linear C 1 ~C 4 Alkyl, branched C 1 ~C 4 Alkyl; R 3 and R 4 Independently selected from C 3 ~C 6 Isoalkyl, C 3 ~C 6 Secondary alkyl and C 3 ~C 6 Cycloalkyl.

[0037] Optionally, the cyano ester external electron donor compound is selected from cyanosuccinate compounds, preferably 2,3-dinon-linear alkyl-2-cyanosuccinate diester compounds, more preferably 2,3-diisopropyl-2-dicyanosuccinic acid dimethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isopropyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isobutyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid-1-methyl-4-ethyl ester (R 1 = methyl, R 2 =ethyl), 2,3-diisopropyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-diisopropyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-diisopropyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl), dimethyl 2,3-diisobutyl-2-dicyanosuccinate, diethyl 2,3-diisobutyl-2-dicyanosuccinate, di-n-propyl 2,3-diisobutyl-2-dicyanosuccinate, diisopropyl 2,3-diisobutyl-2-dicyanosuccinate, di-n-butyl 2,3-diisobutyl-2-dicyanosuccinate, diisobutyl 2,3-diisobutyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-diisobutyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2= methyl), 2,3-diisobutyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl), dimethyl 2,3-di-sec-butyl-2-dicyanosuccinate, diethyl 2,3-di-sec-butyl-2-dicyanosuccinate, di-n-propyl 2,3-di-sec-butyl-2-dicyanosuccinate, diisopropyl 2,3-di-sec-butyl-2-dicyanosuccinate, di-n-butyl 2,3-di-sec-butyl-2-dicyanosuccinate, diisobutyl 2,3-di-sec-butyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-di-sec-butyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-di-sec-butyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl), dimethyl 2,3-dicyclopentyl-2-dicyanosuccinate, diethyl 2,3-dicyclopentyl-2-dicyanosuccinate, di-n-propyl 2,3-dicyclopentyl-2-dicyanosuccinate, diisopropyl 2,3-dicyclopentyl-2-dicyanosuccinate, di-n-butyl 2,3-dicyclopentyl-2-dicyanosuccinate, diisobutyl 2,3-dicyclopentyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-dicyclopentyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-dicyclopentyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2=n-butyl), dimethyl 2,3-dicyclohexyl-2-dicyanosuccinate, diethyl 2,3-dicyclohexyl-2-dicyanosuccinate, di-n-propyl 2,3-dicyclohexyl-2-dicyanosuccinate, diisopropyl 2,3-dicyclohexyl-2-dicyanosuccinate, di-n-butyl 2,3-dicyclohexyl-2-dicyanosuccinate, diisobutyl 2,3-dicyclohexyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-dicyclohexyl-2-cyanosuccinate (R 1 = methyl, R 2 =ethyl), 2,3-dicyclohexyl-2-cyanosuccinic acid-1-ethyl ester-4-methyl ester (R 1 =Ethyl, R 2 = methyl), 2,3-dicyclohexyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester (R 1 = n-butyl, R 2 =ethyl), 2,3-dicyclohexyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester (R 1 =Ethyl, R 2 =n-butyl). Among them, preferably 2,3-diisopropyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid diisobutyl ester. The above-mentioned external electron donor compounds can be used alone or in combination.

[0038] Optionally, in the present invention, the 2,3-dinon-linear alkyl-2-cyanosuccinic acid diester compound is prepared according to the method disclosed in International Patent Application No. PCT / CN2010 / 000202.

[0039] Optionally, the molar ratio of the organoaluminum compound to the cyanate ester external electron donor compound is 0.5:1 to 100:1, preferably 1:1 to 50:1, based on the molar ratio of aluminum element to cyano group.

[0040] Optionally, the diol ester external electron donor compound has a structure represented by general formula (II):

[0041]

[0042] In general formula (II), R 1 ~R 6 , R 1 ~R 2n are independently selected from hydrogen, halogen, substituted or unsubstituted linear or branched C 1 ~C 20 Alkyl, substituted or unsubstituted C 3 ~C 20Cycloalkyl, substituted or unsubstituted C 6 ~C 20 Aryl, substituted or unsubstituted C 7 ~C 20 Alkaryl, substituted or unsubstituted C 7 ~C 20 Arylalkyl, substituted or unsubstituted C 2 ~C 10 Alkenyl, substituted or unsubstituted C 10 ~C 20 Condensed ring aromatic or substituted or unsubstituted C 10 ~C 20 Ester group.

[0043] Optionally, R 1 and R 2 Not hydrogen, R 3 ~R 6 and R 1 ~R 2n Any one of the groups optionally contains one or more heteroatoms as substitutes for carbon atoms or hydrogen atoms or both, wherein the heteroatoms are selected from nitrogen, oxygen, sulfur, silicon, phosphorus or halogen atoms, and R 3 ~R 6 and R 1 ~R 2n One or more of the groups may optionally form a ring with each other, and n is an integer of 0 to 10.

[0044] Among the diol ester-based external electron donor compounds represented by the general formula (II), it is preferred that a compound represented by the general formula (III) is included.

[0045]

[0046] In the general formula (III), R 1 ~R 6 , R 1 ~R 2 are independently selected from hydrogen, halogen atoms, linear or branched C 1 ~C 20 Alkyl, C 3 ~C 20 Cycloalkyl, C 6 ~C 20 Aryl, C 7 ~C 20 Alkyl or C 7 ~C 20 Aralkyl.

[0047] Optionally, the above-mentioned external electron donor compound is disclosed in Chinese patents CN1436766A and CN1436796A, and all relevant contents disclosed in the patents are incorporated into the present invention as reference.

[0048] Optionally, the diol ester external electron donor compound represented by the general formula (III) includes 2-ethyl-1,3-propanediol dibenzoate, 2-propyl-1,3-propanediol dibenzoate, 2-isopropyl-2-isopentyl-1,3-propanediol dibenzoate, 1,3-butanediol dimethyl benzoate, 2-methyl-1,3-butanediol di-m-chlorobenzoate, 2,3-dimethyl-1,3-butanediol dibenzoate, 1 ,3-pentanediol neopentanoate, 2,4-pentanediol dibenzoate, 2-methyl-1,3-pentanediol benzoic acid cinnamate, 2,2-dimethyl-1,3-pentanediol dibenzoate, 2,4-heptanediol dibenzoate, 2-methyl-3,5-heptanediol dibenzoate, 4-ethyl-3,5-heptanediol dibenzoate, etc., preferably 2,4-pentanediol dibenzoate and 4-ethyl-3,5-heptanediol dibenzoate.

[0049] Optionally, the amount of the glycol ester external electron donor compound added is 0.5:1 to 100:1, preferably 1:1 to 50:1, in terms of the molar ratio of the organoaluminum compound to the glycol ester external electron donor.

[0050] Optionally, the addition ratio of the three external electron donor compounds, namely, the silane external electron donor compound, the cyanate external electron donor compound and the diol ester external electron donor compound, is 1:0.01-100:0.01-100 in molar ratio, preferably 1:0.02-50:0.02-50.

[0051] The present invention also provides a method for polymerizing polyolefins, the method comprising: contacting one or more olefins with the catalyst system provided by the present invention under olefin polymerization conditions, wherein at least one of the olefins is a olefin having a general formula of CH 2 =CHR represented by olefins, wherein R is hydrogen or C 1 ~C 6 The polyolefin polymerization method provided by the present invention can be used for homopolymerization of olefins, and can also be used for copolymerization of multiple olefins.

[0052] Specific examples of the olefin include, but are not limited to, at least one of ethylene, propylene, 1-n-butene, 1-n-pentene, 1-n-hexene, 1-n-octene and 4-methyl-1-pentene; preferably, the olefin is at least one of ethylene, propylene, 1-n-butene, 4-methyl-1-pentene and 1-n-hexene; more preferably, the olefin is propylene.

[0053] According to the present invention, the solid catalyst component, the organic aluminum compound as a co-catalyst and the external electron donor compound can be contacted before contacting the olefin monomer, which is called "pre-contact" or "pre-complexation" in the industry; the three components can also be added to the olefin monomer separately before the polymerization reaction, that is, no "pre-contact" is implemented. According to the olefin polymerization method provided by the present invention, it is preferred that the components in the olefin polymerization catalyst system adopt the "pre-contact" method. The time of "pre-contact" is 0.1 to 60 minutes, preferably 1 to 40 minutes; the temperature of "pre-contact" is -20°C to 80°C, preferably 0°C to 60°C.

[0054] The catalyst system is first polymerized to a certain extent in the presence of a small amount of olefin monomer to obtain a prepolymerized catalyst, and then the prepolymerized catalyst is further contacted with the olefin monomer to react to obtain an olefin polymer. This technology is called the "prepolymerization" process in the industry, which helps to improve the polymerization activity of the catalyst and the bulk density of the polymer. According to the olefin polymerization method provided by the present invention, the "prepolymerization" process may be adopted, or the "prepolymerization" process may not be adopted, and the "prepolymerization" process is preferably adopted. The "prepolymerization" ratio is 1 to 1000 gPP / gCat when the olefin monomer is propylene, preferably 2 to 500 gPP / gCat; the "prepolymerization" temperature is -20°C to 80°C, preferably 0°C to 50°C.

[0055] According to the polymerization method for preparing polyolefin with high melt strength of the present invention, the polymerization conditions may be conventional conditions in the art, and the amount of catalyst used may be the amount of various catalysts used in the prior art.

[0056] The present invention also provides a polypropylene with a wide molecular weight distribution and high melt strength, wherein the molecular weight distribution Mw / Mn of the polypropylene is 7.0 to 20.0, and the melt strength of the polypropylene is 0.15 to 0.70N;

[0057] The method for preparing polypropylene comprises contacting and reacting propylene monomer with a catalyst system; the catalyst system is selected from at least one of the above-mentioned catalyst systems of the present invention. DETAILED DESCRIPTION

[0058] The present invention will be specifically described by way of examples, but the present invention is not limited to the following examples.

[0059] The test method involved in the present invention is as follows:

[0060] (1) Titanium content in catalyst: tested by 721 spectrophotometer.

[0061] (2) Melt index (MI) of polymer: measured according to the test standard GB / T3682-2000.

[0062] (3) Content of internal electron donor in catalyst component (cyanate content): measured by Waters 600E liquid chromatography.

[0063] (4) Activity: Catalyst activity = (mass of polyolefin produced) g / (mass of catalyst solid component) g.

[0064] (5) Polymer molecular weight distribution MWD (MWD = Mw / Mn): measured using PL-GPC220 with trichlorobenzene as solvent at 150°C (standard sample: polystyrene, flow rate: 1.0 ml / min, column: 3xPlgel 10um MlxED-B 300x7.5 nm).

[0065] (6) Melt strength: A Rheoten melt strength tester produced by Geottfert Werkstoff Pruefmaschinen of Germany was used. The instrument comprises a pair of rollers rotating in opposite directions. The polymer melt is extruded from a capillary and stretched vertically through the rollers. The stretching force can be measured by a measuring element.

[0066] Example 1

[0067] (1) Preparation of catalyst components

[0068] The catalyst components were prepared according to patent CN201510707980.3, with a titanium content of 3.0%, a 3,5-heptanediol dibenzoate (abbreviated as "S") content of 2.5%, and a 2,3-diisopropyl-2-dicyanosuccinic acid diethyl ester (abbreviated as "JS1") content of 13.4%.

[0069] (2) Olefin polymerization

[0070] Using propylene as the olefin, the polymerization was carried out according to the following steps:

[0071] In a 5-liter stainless steel autoclave with a stirrer, after replacing with nitrogen, 5 ml of a hexane solution of triethylaluminum (the concentration of triethylaluminum is 0.5 mmol / m1) was introduced in a nitrogen flow at room temperature, 2.0 ml of a hexane solution of the first external electron donor S (the concentration of 3,5-heptanediol dibenzoate is 0.02 mmol / ml), 10 ml of anhydrous hexane and 10 mg of a solid catalyst component were added, and pre-contacted at 6°C for 5 min; 3.0 ml of a hexane solution of the second external electron donor JS1 (the concentration of JS1 is 0.02 mmol / ml) was added, and pre-contacted at 6°C for 5 min; 1.0 ml of a hexane solution of the third external electron donor cyclohexylmethyldimethoxysilane (CHMMS) (the concentration of CHMMS is 0.10 mmol / ml) was added, and pre-contacted at 10°C for 8 min. The autoclave was closed, and 1.8 L of hydrogen (under standard conditions) and 2.0 L of liquid propylene were introduced; stirring was started, and after prepolymerization at 10°C for 20 minutes, the temperature was raised to 70°C within 10 minutes. After polymerization at 70°C for 2 hours, stirring was stopped, unpolymerized propylene monomer was removed, and the polymer was collected.

[0072] Example 2

[0073] (1) Preparation of catalyst components

[0074] Same as Example 1.

[0075] (2) Olefin polymerization

[0076] The same procedures as in Example 1 are followed except that cyclohexylmethyldimethoxysilane (CHMMS) is replaced by 2,2-diisobutyl-1,3-dimethoxysilane (DIBMP).

[0077] Example 3

[0078] (1) Preparation of catalyst components

[0079] Same as Example 1.

[0080] (2) Olefin polymerization

[0081] The same procedures as in Example 1 were followed except that the hexane solution of cyclohexylmethyldimethoxysilane (CHMMS) was changed from 1.0 ml to 2.0 ml.

[0082] Example 4

[0083] (1) Preparation of catalyst components

[0084] Same as Example 1.

[0085] (2) Olefin polymerization

[0086] The same procedures as in Example 1 are followed except that the hexane solution of the first external electron donor is changed from 2.0 ml to 3.0 ml and the hexane solution of the second external electron donor is changed from 3.0 ml to 5.0 ml.

[0087] Example 5

[0088] (1) Preparation of catalyst components

[0089] Same as Example 1.

[0090] (2) Olefin polymerization

[0091] The same procedures as in Example 1 are followed except that the hexane solution of the first external electron donor is changed from 2.0 ml to 1.0 ml and the hexane solution of the second external electron donor is changed from 3.0 ml to 1.0 ml.

[0092] Example 6

[0093] (1) Preparation of catalyst components

[0094] Same as Example 1.

[0095] (2) Olefin polymerization

[0096] The same method as in Example 1 is adopted except that the pre-contact time after adding the first external electron donor is changed from 5 min to 1 min, the pre-contact time after adding the second external electron donor is changed from 5 min to 2 min, and the pre-contact time after adding silane is changed from 8 min to 3 min.

[0097] Example 7

[0098] (1) Preparation of catalyst components

[0099] Same as Example 1.

[0100] (2) Olefin polymerization

[0101] The same procedures as in Example 1 are as follows except that the pre-contact time after adding the first electron donor is changed from 5 min to 8 min, the pre-contact time after adding the second electron donor is changed from 5 min to 10 min, and the pre-contact time after adding the third electron donor is changed from 8 min to 15 min.

[0102] Example 8

[0103] (1) Preparation of catalyst components

[0104] Same as Example 1.

[0105] (2) Olefin polymerization

[0106] Using propylene as the olefin, the polymerization was carried out according to the following steps:

[0107] Except that the prepolymerization time was changed from 20 min to 2 min, the rest was the same as in Example 1.

[0108] Example 9

[0109] (1) Preparation of catalyst components

[0110] Same as Example 1.

[0111] (2) Olefin polymerization

[0112] The process is the same as in Example 1 except that the first external electron donor is changed from 3,5-heptanediol dibenzoate (abbreviated as "S") to 2,4-pentanediol dibenzoate (abbreviated as "F").

[0113] Comparative Example 1

[0114] (1) Preparation of catalyst components

[0115] Take 10g of alkoxymagnesium of the same specification as in Example 1, 50ml of toluene, and 2.5ml of di-n-butyl phthalate (abbreviated as "DNBP") to prepare a suspension; add 10ml of toluene and 90ml of titanium tetrachloride to a 300ml reactor that has been repeatedly replaced with high-purity nitrogen, heat it to 80°C, then add the prepared suspension to the reactor, keep it at this temperature for 1 hour, continue to heat it to 112°C, keep it at this temperature for 2 hours, and then filter the liquid clean. Then add 120ml of toluene and 30ml of titanium tetrachloride to a mixed solution, heat it to 110°C, stir it for 1 hour, do this 3 times, filter out the liquid, wash the resulting solid with 150ml of hexane 4 times, filter out the liquid and dry it to obtain a solid catalyst component. Titanium content 2.5%, di-n-butyl phthalate content 13.89%.

[0116] (2) Olefin polymerization

[0117] Using propylene as the olefin, the polymerization was carried out according to the following steps:

[0118] In a 5-liter stainless steel autoclave with a stirrer, after replacing with nitrogen, 5 ml of triethylaluminum hexane solution (triethylaluminum concentration is 0.5 mmol / ml), 1.0 ml of cyclohexylmethyldimethoxysilane (CHMMS) hexane solution (CHMMS concentration is 0.10 mmol / ml), 10 ml of anhydrous hexane and 10 mg of solid catalyst component were introduced in a nitrogen flow at room temperature, and pre-contacted at 10°C for 8 minutes. The autoclave was closed, and 1.8 L of hydrogen (under standard conditions) and 2.0 L of liquid propylene were introduced; stirring was turned on, and after prepolymerization at 10°C for 20 minutes, the temperature was raised to 70°C within 10 minutes. After polymerization reaction at 70°C for 2 hours, stirring was stopped, unpolymerized propylene monomer was removed, and the polymer was collected.

[0119] Table 1 Electron donor composition of the catalyst system

[0120]

[0121]

[0122] Table 2 Propylene polymerization data

[0123]

[0124]

[0125] From the comparison of the data in the above table, it can be seen that the polymer obtained by using the catalyst system of the present invention has a wide molecular weight distribution, many macromolecules and high melt strength.

[0126] In the present invention, a Ziegler-Natta catalyst component containing an internal electron donor including cyanate esters and diol esters and / or other types of compounds is used. When forming the catalyst, a unique catalyst system is formed by rationally compounding three different types of external electron donors, namely silanes, cyanate esters and diol esters. The polypropylene prepared by the catalyst has a wider molecular weight distribution and a higher proportion of ultra-large molecules. The ultra-high molecular weight fraction ensures its higher melt strength, while the wider molecular weight distribution ensures good processing properties of the polymer. The method provided by the present invention is simple, easy to industrialize, and can prepare high-performance products, with broad application prospects.

[0127] Any numerical value mentioned in the present invention includes all values ​​that increase by one unit each time from the lowest value to the highest value if there is only an interval of two units between any minimum value and any maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed lowest and highest values ​​are considered to have been disclosed.

[0128] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A catalyst system for olefin polymerization, comprising the following components and reaction products thereof: A. Catalyst components; B. Organoaluminum compounds; C. External electron donor compounds; The external electron donor compounds include silane-based external electron donor compounds, cyanate-based external electron donor compounds and glycol-ester-based external electron donor compounds.

2. The catalyst system according to claim 1, characterized in that The molar ratio of the organoaluminum compound to the catalyst component is 5 to 5000, preferably 20 to 500, based on the molar ratio of the aluminum element to the titanium element; And / or, the molar ratio of the organoaluminum compound to the silane-based external electron donor compound is 0.5:1 to 200:1, preferably 1:1 to 100:1, based on the molar ratio of aluminum element to silicon element; And / or, the molar ratio of the organoaluminum compound to the cyanate ester external electron donor compound is 0.5:1 to 100:1, preferably 1:1 to 50:1, based on the molar ratio of aluminum element to cyano group; and / or, the molar ratio of the organoaluminum compound to the diol ester external electron donor compound is 0.5:1 to 100:1, preferably 1:1 to 50:1; And / or, the molar ratio of the silane-based external electron donor compound, the cyanate-based external electron donor compound and the diol ester-based external electron donor compound is 1:0.01-100:0.01-100, preferably 1:0.02-50:0.02-50.

3. The catalyst system according to claim 1 or 2, characterized in that The silane external electron donor compound is selected from the general formula R1R2 m Si(OR3) 3-m 、R4 n Si(OR5) 4-n and R6R7Si(OR8)2, wherein m and n are independently integers of 0 to 2, and R1 and R2 are the same or different C1 to C 10 A straight chain, branched or cyclic aliphatic group, R3, R4, R5, R6 and R8 are the same or different C1-C3 straight chain aliphatic groups, and R7 is a C3-C6 branched or cyclic aliphatic group; Preferably, the silane-based external electron donor compound is selected from at least one of tetramethoxysilane, n-propyltriethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, vinyltrimethoxysilane, n-propyltrimethoxysilane, tetraethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisobutyldimethoxysilane, methylcyclohexyldimethoxysilane, methylisobutyldimethoxysilane, dicyclohexyldimethoxysilane, phenyltrimethoxysilane, and dicyclopentyldimethoxysilane.

4. The catalyst system according to any one of claims 1 to 3, characterized in that The cyanoester external electron donor compound has a structure shown in the general formula (I): In the general formula (I), R 1 and R 2 R is independently selected from a linear C1-C4 alkyl group and a branched C1-C4 alkyl group; 3 and R 4 Independently selected from C3-C6 isoalkyl, C3-C6 secondary alkyl and C3-C6 cycloalkyl; Preferably, the cyano ester external electron donor compound is selected from cyanosuccinate compounds, more preferably 2,3-dinon-linear alkyl-2-cyanosuccinate diester compounds, and more preferably 2,3-diisopropyl-2-dicyanosuccinic acid dimethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isopropyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isobutyl ester, 2,3-diisopropyl-2-cyanosuccinic acid-1-methyl-4-ethyl ester, 2,3-diisopropyl-2-cyanosuccinic acid 2,3-diisopropyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester, 2,3-diisopropyl-2-cyanosuccinic acid-1-ethyl-4-n-butyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid dimethyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid diisobutyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid-1-methyl-4-ethyl ester, 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl 2,3-diisobutyl-2-cyanosuccinic acid-4-methyl ester, 2,3-diisobutyl-2-cyanosuccinic acid-1-n-butyl ester-4-ethyl ester, 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid dimethyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid diethyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid diisobutyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid-1-methyl ester-4-ethyl ester, 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl ester-4- Methyl ester, 2,3-di-sec-butyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester, 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl-4-n-butyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid dimethyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid diethyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid di-n-propyl ester , 2,3-dicyclopentyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid diisobutyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid-1-methyl-4-ethyl ester, 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl-4-methyl ester, 2,3-Dicyclopentyl-2-cyanosuccinic acid-1-butyl-4-ethyl ester, 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl-4-butyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid dimethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid dimethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-dicyclohexyl-2 - At least one of di-n-butyl dicyanobutanedioate, diisobutyl 2,3-dicyclohexyl-2-dicyanobutanedioate, 1-methyl-4-ethyl 2,3-dicyclohexyl-2-cyanobutanedioate, 1-ethyl-4-methyl 2,3-dicyclohexyl-2-cyanobutanedioate, 1-n-butyl-4-ethyl 2,3-dicyclohexyl-2-cyanobutanedioate, and 1-ethyl-4-n-butyl 2,3-dicyclohexyl-2-cyanobutanedioate.

5. The catalyst system according to any one of claims 1 to 4, characterized in that The diol ester external electron donor compound has a structure shown in general formula (II): In the general formula (II), R1 to R6, R 1 ~R 2n independently selected from hydrogen, halogen, substituted or unsubstituted straight or branched chain C1-C 20 Alkyl, substituted or unsubstituted C3~C 20 Cycloalkyl, substituted or unsubstituted C6~C 20 Aryl, substituted or unsubstituted C7~C 20 Alkyl, substituted or unsubstituted C7~C 20 Arylalkyl, substituted or unsubstituted C2~C 10 Alkenyl, substituted or unsubstituted C 10 ~C 20 Condensed ring aromatic or substituted or unsubstituted C 10 ~C 20 Ester group; Preferably, in the general formula (II), R1 and R2 are not hydrogen, R3 to R6 and R 1 ~R 2n Any one of the groups optionally contains one or more heteroatoms as a substitute for a carbon atom or a hydrogen atom or both, wherein the heteroatoms are selected from nitrogen, oxygen, sulfur, silicon, phosphorus or halogen atoms, R3 to R6 and R 1 ~R 2n One or more of the groups optionally form a ring with each other, and n is an integer from 0 to 10; Preferably, the diol ester external electron donor compound comprises a compound represented by general formula (III): In the general formula (III), R1 to R6, R 1 ~R 2 independently selected from hydrogen, halogen atoms, straight or branched C1-C 20 Alkyl, C3~C 20 Cycloalkyl, C6~C 20 Aryl, C7~C 20 Alkyl or C7~C 20 Aralkyl; Preferably, the compound represented by general formula (III) includes at least one of 2-ethyl-1,3-propanediol dibenzoate, 2-propyl-1,3-propanediol dibenzoate, 2-isopropyl-2-isopentyl-1,3-propanediol dibenzoate, 1,3-butanediol dimethyl benzoate, 2-methyl-1,3-butanediol di-m-chlorobenzoate, 2,3-dimethyl-1,3-butanediol dibenzoate, 1,3-pentanediol pivalate, 2,4-pentanediol dibenzoate, 2-methyl-1,3-pentanediol benzoic acid cinnamate, 2,2-dimethyl-1,3-pentanediol dibenzoate, 2,4-heptanediol dibenzoate, 2-methyl-3,5-heptanediol dibenzoate and 4-ethyl-3,5-heptanediol dibenzoate.

6. The catalyst system according to any one of claims 1 to 5, characterized in that The general formula of the organoaluminum compound is AlR n X 3-n , where R is hydrogen or a hydrocarbon group with 1 to 20 carbon atoms; X is a halogen, and n is an integer where 0 < n ≤ 3; Preferably, the organoaluminum compound is at least one selected from trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, diethylaluminum monochloride, diisobutylaluminum monochloride, diethylaluminum monochloride, diisobutylaluminum monochloride, and ethylaluminum dichloride; And / or, the catalyst component contains titanium element, a glycol ester internal electron donor compound and a cyano ester internal electron donor compound.

7. The catalyst system according to claim 6, characterized in that Based on the total weight of the catalyst component, it contains 1.0 wt% to 5.0 wt% of titanium element, 0.5 wt% to 10.0 wt% of a glycol ester internal electron donor compound, and 3.0 wt% to 20.0 wt% of a cyanate internal electron donor compound, and the molar ratio of the glycol ester internal electron donor compound to the cyanate internal electron donor compound is 0.025:1 to 0.8:1; Preferably, based on the total weight of the catalyst component, it contains 1.3 wt% to 4.0 wt% of titanium element, 0.8 wt% to 6 wt% of diol ester internal electron donor compound, 5 wt% to 15 wt% of cyanate internal electron donor compound, and the molar ratio of diol ester internal electron donor compound to cyanate internal electron donor compound is (0.05 to 0.6):1; And / or, the cyanoester internal electron donor compound has a structure represented by the general formula (I): In the general formula (I), R 1 and R 2 R is independently selected from a linear C1-C4 alkyl group and a branched C1-C4 alkyl group; 3 and R 4 Independently selected from C3-C6 isoalkyl, C3-C6 secondary alkyl and C3-C6 cycloalkyl; Preferably, the cyano ester internal electron donor compound is selected from cyanosuccinate compounds, more preferably 2,3-dinon-linear alkyl-2-cyanosuccinate diester compounds, and more preferably 2,3-diisopropyl-2-dicyanosuccinic acid dimethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isopropyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisopropyl-2-dicyanosuccinic acid di-isobutyl ester, 2,3-diisopropyl-2-cyanosuccinic acid-1-methyl-4-ethyl ester, 2,3-diisopropyl-2-cyanosuccinic acid 2,3-diisopropyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester, 2,3-diisopropyl-2-cyanosuccinic acid-1-ethyl-4-n-butyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid dimethyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid diethyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid diisobutyl ester, 2,3-diisobutyl-2-dicyanosuccinic acid-1-methyl-4-ethyl ester, 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl 2,3-diisobutyl-2-cyanosuccinic acid-4-methyl ester, 2,3-diisobutyl-2-cyanosuccinic acid-1-n-butyl ester-4-ethyl ester, 2,3-diisobutyl-2-cyanosuccinic acid-1-ethyl ester-4-n-butyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid dimethyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid diethyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid diisobutyl ester, 2,3-di-sec-butyl-2-dicyanosuccinic acid-1-methyl ester-4-ethyl ester, 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl ester-4- Methyl ester, 2,3-di-sec-butyl-2-cyanosuccinic acid-1-n-butyl-4-ethyl ester, 2,3-di-sec-butyl-2-cyanosuccinic acid-1-ethyl-4-n-butyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid dimethyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid diethyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid di-n-propyl ester , 2,3-dicyclopentyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid di-n-butyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid diisobutyl ester, 2,3-dicyclopentyl-2-dicyanosuccinic acid-1-methyl-4-ethyl ester, 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl-4-methyl ester, 2,3-Dicyclopentyl-2-cyanosuccinic acid-1-butyl-4-ethyl ester, 2,3-dicyclopentyl-2-cyanosuccinic acid-1-ethyl-4-butyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid dimethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid dimethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diethyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid di-n-propyl ester, 2,3-dicyclohexyl-2-dicyanosuccinic acid diisopropyl ester, 2,3-dicyclohexyl-2 - at least one of di-n-butyl dicyanosuccinate, diisobutyl 2,3-dicyclohexyl-2-dicyanosuccinate, 1-methyl-4-ethyl 2,3-dicyclohexyl-2-cyanosuccinate, 1-ethyl-4-methyl 2,3-dicyclohexyl-2-cyanosuccinate, 1-n-butyl-4-ethyl 2,3-dicyclohexyl-2-cyanosuccinate, and 1-ethyl-4-n-butyl 2,3-dicyclohexyl-2-cyanosuccinate; And / or, the diol ester internal electron donor compound has a structure represented by general formula (II): In the general formula (II), R1 to R6, R 1 ~R 2n independently selected from hydrogen, halogen, substituted or unsubstituted straight or branched chain C1-C 20 Alkyl, substituted or unsubstituted C3~C 20 Cycloalkyl, substituted or unsubstituted C6~C 20 Aryl, substituted or unsubstituted C7~C 20 Alkyl, substituted or unsubstituted C7~C 20 Arylalkyl, substituted or unsubstituted C2~C 10 Alkenyl, substituted or unsubstituted C 10 ~C 20 Condensed ring aromatic or substituted or unsubstituted C 10 ~C 20 Ester group; Preferably, in the general formula (II), R1 and R2 are not hydrogen, R3 to R6 and R 1 ~R 2n Any one of the groups optionally contains one or more heteroatoms as a substitute for a carbon atom or a hydrogen atom or both, wherein the heteroatoms are selected from nitrogen, oxygen, sulfur, silicon, phosphorus or halogen atoms, R3 to R6 and R 1 ~R 2n One or more of the groups optionally form a ring with each other, and n is an integer from 0 to 10; Preferably, the diol ester internal electron donor compound comprises a compound represented by general formula (III); In the general formula (III), R1 to R6, R 1 ~R 2 independently selected from hydrogen, halogen atoms, straight or branched C1-C 20 Alkyl, C3~C 20 Cycloalkyl, C6~C 20 Aryl, C7~C 20 Alkyl or C7~C 20 Aralkyl; Preferably, the compound represented by general formula (III) includes at least one of 2-ethyl-1,3-propanediol dibenzoate, 2-propyl-1,3-propanediol dibenzoate, 2-isopropyl-2-isopentyl-1,3-propanediol dibenzoate, 1,3-butanediol dimethyl benzoate, 2-methyl-1,3-butanediol di-m-chlorobenzoate, 2,3-dimethyl-1,3-butanediol dibenzoate, 1,3-pentanediol pivalate, 2,4-pentanediol dibenzoate, 2-methyl-1,3-pentanediol benzoic acid cinnamate, 2,2-dimethyl-1,3-pentanediol dibenzoate, 2,4-heptanediol dibenzoate, 2-methyl-3,5-heptanediol dibenzoate and 4-ethyl-3,5-heptanediol dibenzoate.

8. A method for polymerizing polyolefins, characterized in that: The polymerization method comprises: contacting one or more olefin monomers with a catalyst system under olefin polymerization conditions, at least one of the olefin monomers being an olefin represented by the general formula CH2=CHR, wherein R is hydrogen or a C1-C6 alkyl group; The catalyst system is selected from at least one of the catalyst systems described in any one of claims 1 to 7.

9. The polymerization method according to claim 8, characterized in that The olefin monomer is selected from at least one of ethylene, propylene, 1-n-butene, 1-n-pentene, 1-n-hexene, 1-n-octene and 4-methyl-1-pentene; And / or, the catalyst component, the organoaluminum compound and the external electron donor compound are pre-contacted before contacting the olefin monomer; the pre-contact time is 0.1 to 60 minutes, preferably 1 to 40 minutes; the pre-contact temperature is -20°C to 80°C, preferably 0°C to 60°C; And / or, the catalyst system is first prepolymerized in the presence of a small amount of olefin monomer to obtain a prepolymerized catalyst, and then the prepolymerized catalyst is further contacted with the olefin monomer to react to obtain polyolefin; the prepolymerization temperature is -20°C to 80°C, preferably 0°C to 50°C; the prepolymerization rate is 1 to 1000 gPP / gCat, preferably 2 to 500 gPP / gCat when the olefin monomer is propylene.

10. A polypropylene with a wide molecular weight distribution and high melt strength, characterized in that: The molecular weight distribution Mw / Mn of the polypropylene is 7.0 to 20.0, and the melt strength of the polypropylene is 0.15 to 0.70N; The method for preparing polypropylene comprises contacting propylene monomer with a catalyst system for reaction; the catalyst system is selected from at least one of the catalyst systems described in any one of claims 1 to 7.

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