Nitrogen-containing polycyclic silane external electron donors and their use in olefin polymerization

Abstract

The present application relates to the technical field of olefin catalytic polymerization, and discloses a nitrogen-containing polycyclic silane external electron donor and its olefin polymerization application, aiming to solve the technical problem that existing external electron donors are difficult to realize high hydrogen regulation sensitivity while maintaining high polymer stereoregularity, the external electron donor has a polycyclic rigid skeleton composed of three heteroatoms selected from nitrogen or oxygen, and a silane group is connected to the end, which, together with a Ziegler-Natta main catalyst containing a titanium compound, an internal electron donor and an organic aluminum cocatalyst, forms a catalyst system, and is applied to the polymerization of propylene and other olefins, can adjust the catalyst active center through unique electronic and spatial effects under the synergistic action of the internal electron donor, thereby improving the hydrogen regulation sensitivity while maintaining high catalyst activity and polymer stereoregularity, producing polyolefin products with ultrahigh melt flow rate, and showing good performance regulation flexibility.

Description

Technical Field

[0001] This invention relates to the field of olefin catalytic polymerization technology, and in particular to a nitrogen-containing polycyclic silane external electron donor and its application in olefin polymerization. Background Technology

[0002] Ziegler-Natta catalysts are the core catalytic system in the olefin polymerization industry, typically consisting of a solid titanium-based main catalyst, an organoaluminum co-catalyst, and an external electron donor. The external electron donor, as a key regulating component, works synergistically with the internal electron donor in the main catalyst to influence the catalyst's polymerization activity, stereodirectivity, and hydrogen sensitivity, thereby controlling the molecular weight distribution, melt flow properties, and isotacticity of the resulting polyolefins. This allows for flexible production of different performance grades of products using the same main catalyst.

[0003] Currently, several related external electron donor technologies have been disclosed in the prior art. For example, Chinese Patent CN115043868A discloses a five-membered cyclic aminosilane external electron donor, which improves the melt flowability and isotacticity of polypropylene through a single nitrogen-containing five-membered ring structure. In addition, Chinese Patent CN115043867A discloses a six-membered cyclic aminosilane external electron donor, which also optimizes the flowability and regularity of polymers based on a single nitrogen-containing ring system structure. These technologies are all aimed at improving the performance of external electron donors by introducing nitrogen heterocyclic structures.

[0004] However, existing external electron donors still have certain limitations, especially those based on a single nitrogen heterocyclic structure. When pursuing high hydrogen sensitivity to produce ultra-high flowability polyolefins, it is often difficult to maintain the high stereoregulation of the catalyst system at the same time. In other words, existing external electron donors cannot achieve a good synergy and balance between hydrogen sensitivity and stereoregulation, which limits their application in the production of high-end polyolefin grades that need to meet comprehensive performance requirements such as high flowability and high isotacticity. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to maintain high activity and high isotacticity of the system while improving hydrogen regulation sensitivity during the polymerization process. To this end, we propose a nitrogen-containing polycyclic silane external electron donor and its olefin polymerization application.

[0006] To achieve the above objectives, this application adopts the following technical solution: a nitrogen-containing polycyclic silane external electron donor having the structural formula shown in Formula I.

[0007] In this context, A, B, and C are each independently selected from nitrogen or oxygen atoms, and R1, R2, and R3 are each independently selected from alkyl groups having 1-2 carbon atoms.

[0008] Preferably, A, B, and C are all nitrogen atoms.

[0009] Preferably, A and C are oxygen atoms, and B is a nitrogen atom.

[0010] Preferably, R1, R2 and R3 are all methyl groups.

[0011] Preferably, at least one of R1, R2 and R3 is an ethyl group.

[0012] A catalyst system for olefin polymerization includes the nitrogen-containing polycyclic silane external electron donor, and the system further includes a solid titanium catalyst component and an organoaluminum co-catalyst. The solid titanium catalyst component includes a titanium compound supported on a magnesium halide support and an internal electron donor.

[0013] Preferably, the internal electron donor is a phthalate compound.

[0014] Preferably, the organoaluminum co-catalyst is triethylaluminum or triisobutylaluminum.

[0015] An olefin polymerization method, wherein propylene monomer is polymerized under polymerization reaction conditions in the presence of the catalyst system described above.

[0016] Preferably, the polymerization is a liquid-phase bulk polymerization, the reaction temperature is 60℃-80℃, and hydrogen is introduced as a molecular weight regulator during the polymerization process.

[0017] The technical effects and advantages of this invention are as follows: In this invention, through molecular structural innovation, a silane compound with both a rigid polycyclic skeleton and multiple heteroatom synergies is constructed as an external electron donor. The polycyclic system composed of three bridgehead nitrogen / oxygen atoms serves as the core unit for electron donation and spatial regulation. The rigid skeleton and the lone pair electrons of the heteroatoms provide strong and tunable coordination ability. A silane group is introduced at the end of the ring system, enabling it to compete for coordination and synergize with the titanium active center and internal electron donor in the Ziegler-Natta catalyst. This regulates the microchemical environment of the catalyst active center, achieving high activity and high isotacticity of the system while improving hydrogen regulation sensitivity during polymerization. Detailed Implementation

[0018] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following specific embodiments are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0019] This invention relates to a nitrogen-containing polycyclic silane external electron donor, which can be applied to olefin polymerization catalytic systems, and its structural formula is shown in Formula 1.

[0020] Formula 1:

[0021] A, B, and C are each independently selected from nitrogen (N) or oxygen (O) atoms. That is, the three bridgehead heteroatoms in the polycyclic structure can all be nitrogen, all be oxygen, or exist in any combination of nitrogen and oxygen, such as two being oxygen and one being nitrogen, or two being nitrogen and one being oxygen, and all other possible combinations.

[0022] Groups R1, R2 and R3 are each independently selected from alkyl groups having 1-2 carbon atoms, preferably methyl or ethyl.

[0023] The core feature of this external electron donor lies in its rigid polycyclic framework combined with one or more nitrogen and oxygen heteroatoms, as well as the terminal silane group, which endows the molecule with unique electronic effects and spatial geometry, enabling it to specifically interact with the active center in the Ziegler-Natta catalyst, thereby significantly regulating polymerization behavior.

[0024] In a preferred embodiment, the external electron donor is a fully nitrogen-containing polycyclic silane, i.e., A, B, and C are all nitrogen atoms; in another preferred embodiment, the external electron donor has a central nitrogen atom, i.e., A and C are oxygen atoms, and B is a nitrogen atom.

[0025] Groups R1, R2, and R3 can be the same or different; for example, all can be methyl, all can be ethyl, or a mixture of methyl and ethyl. Small variations in these groups can be used to finely tune the electron cloud density and steric hindrance of the compound, thereby optimizing its performance as an external electron donor.

[0026] The synthesis of the compounds of this invention refers to heterocyclic compounds and silanization reaction methods known in the art. Generally, the corresponding nitrogen / oxygen-containing polycyclic core can be synthesized first, and then it can be silanized with the corresponding chlorosilane under alkaline conditions to obtain the target product. The reaction is usually carried out in an anhydrous organic solvent under an inert atmosphere. The specific synthetic route and purification method can be adjusted according to the different starting materials. This is conventional technology for those skilled in the art and is not the focus of this invention, so it will not be described in detail.

[0027] The present invention also provides a catalyst system for olefin polymerization, specifically composed of a solid catalyst component, a co-catalyst, and an external electron donor.

[0028] The solid catalyst component is a Ziegler-Natta type catalyst, which typically comprises an inorganic support, at least one internal electron donor, and a transition metal compound supported thereon. The preferred inorganic carrier is magnesium halide, especially activated anhydrous magnesium chloride; The transition metal compound is preferably a titanium compound, such as titanium tetrachloride, titanium trichloride, titanate, etc., and more preferably titanium tetrachloride; Internal electron donors are key internal components used to regulate the structure of the active center during catalyst preparation. Specifically, they are phthalate esters. The presence of internal electron donors helps to improve the stereodirection and activity of the catalyst.

[0029] The cocatalyst is an organoaluminum compound, preferably including trialkylaluminum, such as triethylaluminum (TEAL) or triisobutylaluminum (TIBA). During polymerization, the organoaluminum compound is used to activate the titanium centers in the solid catalyst component.

[0030] The external electron donor of the present invention is added during the polymerization process. Through competitive coordination or synergistic effect with the internal electron donor, it further finely regulates the microenvironment of the active center. The combined effect of the external and internal electron donors can enhance the catalyst's sensitivity to hydrogen and produce polymers with extremely high melt flow rates while maintaining high activity and high stereotacticity.

[0031] The catalyst system is usually pre-complexed and activated before polymerization. Specifically, under an inert atmosphere, the metered solid catalyst components, the solution of organoaluminum compound, and the solution of the external electron donor of the present invention are mixed in an inert solvent such as hexane or heptane at room temperature, and allowed to stand for 5-30 minutes to form a uniform suspension or solution of catalyst species before being injected into the reactor.

[0032] The proportions of each component can be adjusted within a wide range. The preferred molar ratio of Al in the organoaluminum compound to Ti in the solid catalyst component is 50-200:1. The preferred molar ratio of Si to Ti in the external electron donor compound is 5-50:1. The optimization of these ratios depends on the specific catalyst system, the target polymer product, and the polymerization process conditions.

[0033] The present invention also provides a method for olefin polymerization, the method comprising, in the presence of the above-described catalyst system, contacting and reacting one or more olefin monomers under polymerization reaction conditions to generate polyolefins.

[0034] The olefin monomer is preferably propylene, used to produce isotactic polypropylene, or it may be ethylene, or a mixture of ethylene and α-olefins (such as 1-butene, 1-ethylene), used to produce linear low-density polyethylene (LLDPE) or impact copolymers. The polymerization reaction conditions are conventional conditions in the art, and processes such as liquid-phase bulk polymerization, slurry polymerization or gas-phase polymerization can be used. For propylene polymerization, liquid-phase bulk polymerization is the preferred method in industry. The preferred polymerization temperature is 60-80℃; the polymerization pressure is usually the pressure that maintains the liquefaction of the reaction medium or keeps the gas phase stable. Hydrogen can be added to the reaction system as a molecular weight regulator, depending on the molecular weight requirements of the target polymer.

[0035] The application of a nitrogen-containing polycyclic silane external electron donor in olefin polymerization specifically includes the following steps: S1: Use high-purity inert gas to thoroughly purge and replace the polymerization reactor to remove impurities such as moisture and oxygen that are toxic to the catalyst. S2: Add liquid propylene monomer to the reactor in a metered manner. According to the molecular weight requirement of the target polymer, add a specific amount of hydrogen gas to the system as a molecular weight regulator, and heat the reactor to 60-80℃.

[0036] S3: Inject the activated catalyst system into the reactor. After reacting for 0.9-1.2 hours, release the unreacted monomers by depressurization and collect the generated polymer powder. After vacuum drying at 30°C for 2 hours, the finished product is obtained.

[0037] To more clearly illustrate the technical effects of the present invention, rather than to limit the scope of the invention, the following description is provided in conjunction with specific embodiments and comparative examples.

[0038] Example 1 In this embodiment, a nitrogen-containing polycyclic silane external electron donor of the present invention is used to polymerize propylene. The product is labeled as ED1, and its structural formula is shown in Formula 2. Formula 2:

[0039] In the structural formula of ED1, A, B, and C are all nitrogen atoms, and groups R1, R2, and R3 are all methyl groups (-CH3).

[0040] The specific operating steps are as follows: S1: Select a 2L stainless steel high-pressure reactor and purge the reactor thoroughly with high-purity nitrogen. S2: At room temperature, add 0.55L of refined liquid propylene to the reactor, introduce 1.2g of hydrogen gas, stir and heat to raise the temperature inside the reactor to 70℃; S3: In another dry container, premix 0.75 mL of a 1.0 mol / L heptane solution of triethylaluminum (TEAL), 1.1 mL of a 0.05 mol / L hexane solution of ED1, and 6.0 mg of solid catalyst, and let stand for 5 min to complete the pre-complexation. The solid catalyst is a commercially available fourth-generation phthalate catalyst, whose main components are titanium compounds supported on magnesium chloride and diisobutyl phthalate as internal electron donors. The titanium content is about 2.7 wt%, and the internal electron donor content is about 13.2 wt%.

[0041] S4: When the temperature of the reactor stabilizes at 70℃, inject the pre-complexed catalyst mixture into the reactor in one go. After reacting for 1 hour, quickly release the pressure inside the reactor to terminate the reaction. Collect the obtained polypropylene powder and vacuum dry it at 30℃ for 2 hours.

[0042] Example 2 The operation steps of this embodiment are consistent with those of embodiment 1. The only difference is that the external electron donor ED1 is replaced with an equimolar amount of another external electron donor of the present invention, denoted as ED2, the structural formula of which is shown in formula 3. Formula 3:

[0043] In the structural formula of ED2, A and C are oxygen atoms, B is a nitrogen atom, and groups R1, R2, and R3 are all methyl groups (-CH3).

[0044] Example 3 The operation steps of this embodiment are consistent with those of embodiment 1. The only difference is that the external electron donor ED1 is replaced with an equimolar amount of another external electron donor of the present invention, denoted as ED3, the structural formula of which is shown in formula 4. Formula 4:

[0045] In the structural formula of ED3, A, B and C are all nitrogen atoms, R1 and R2 are methyl (-CH3) groups, and R3 is ethyl (-C2H5).

[0046] Example 4 The operation steps of this embodiment are consistent with those of embodiment 1. The only difference is that the external electron donor ED1 is replaced with an equimolar amount of another external electron donor of the present invention, denoted as ED4, the structural formula of which is shown in formula 5. Formula 5:

[0047] In the structural formula of ED4, A and C are oxygen atoms, B is a nitrogen atom, R1 and R3 are methyl (-CH3), and R2 is ethyl (-C2H5).

[0048] Comparative Example 1 The comparative example follows the same operating steps as Example 1, except that the external electron donor ED1 is replaced with an equimolar amount of the industrially commonly used external electron donor cyclohexylmethyldimethoxysilane (D-Donor).

[0049] Comparative Example 2 The comparative example follows the same procedure as Example 1, except that the external electron donor ED1 is replaced with an equimolar amount of the industrially commonly used external electron donor dicyclopentyldimethoxysilane (U-Donor).

[0050] Comparative Example 3 The comparative example follows the same procedure as Example 1, except that the external electron donor ED1 is replaced with an equimolar amount of the industrially commonly used external electron donor diisopropyldimethoxysilane (TO1-Donor).

[0051] To verify the actual effect of the nitrogen-containing polycyclic silane external electron donor provided by the present invention, the finished products obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests using standard methods in the art, so as to objectively evaluate the influence of different external electron donors on the performance of the polymerization products.

[0052] The polymerization activity of the catalyst is calculated based on the mass of polymer produced per gram of solid catalyst component per unit time. The heptane extraction method was used. 2g of dried polymer sample was weighed and placed in a Soxhlet extractor. After extraction by reflux with boiling heptane for 6 hours, the remaining insoluble matter was dried to constant weight. The isotacticity index xylene soluble matter (XS) was calculated based on the percentage of its mass to the initial sample mass. The lower the XS value, the higher the isotacticity. According to ASTM D1238 standard, at 230℃ and 2.16kg load, the melt flow rate (MFR) is determined based on the mass of polymer melt passing through a standard die every 10 minutes. This indicator directly reflects the flow properties of the polymer. The molecular weight distribution (MWD) was determined using a high-temperature gel permeation chromatography system equipped with an infrared detector. 1,2,4-trichlorobenzene was used as the solvent, and the test was conducted at 150 °C. The ratio of the weight-average molecular weight to the number-average molecular weight was recorded as the molecular weight distribution.

[0053] The polymerization results and product performance results of all examples and comparative examples are shown in Table 1.

[0054]

[0055] Table 1 According to the data in Table 1, under the same amount of hydrogen, the melt flow rate of Examples 1-4 ranged from 530.2 to 954.3 g / 10 min, which was significantly higher than that of Comparative Example 1 and Comparative Example 2. In particular, the melt flow rate of Example 4 reached as high as 954.3 g / 10 min, indicating that the external electron donor of the present invention can endow the catalyst system with extremely high hydrogen sensitivity, and can more efficiently utilize hydrogen to regulate molecular weight, thereby producing polypropylene products with ultra-high flowability to meet the production requirements of high-end grades.

[0056] The XS values ​​of Examples 1 and 2 were 4.5% and 5.3%, respectively, showing high isotacticity characteristics, which were comparable to or even better than those of Comparative Examples 1 and 2. The XS values ​​of Examples 3 and 4 were slightly higher, but still remained within an acceptable range. This indicates that the external electron donor of the present invention can maintain good stereotacticity of the catalyst system while achieving extremely high hydrogen sensitivity. The catalyst activity in each embodiment of the present invention is maintained at a good level of 30.7-37.1 kg / g Cat.h, and the molecular weight distribution of the obtained polymer is between 4.8 and 5.7, which is a moderate range. A moderate molecular weight distribution is beneficial to improving the processing performance of the polymer.

[0057] Comparing the data from Examples 1-4, it can be seen that by adjusting the type of heteroatom in the external electron donor molecule and the alkyl substituents on the silicon atom, the hydrogen sensitivity of the catalyst and the isotacticity of the product can be effectively controlled within a certain range.

[0058] Example 4 demonstrates that while achieving the highest melt flow rate, the activity and isotacticity remain well balanced. This proves that the external electron donor of the present invention has good controllability, providing an effective means to flexibly produce polypropylene grades with different performance requirements by selecting different external electron donors without changing the main catalyst.

[0059] In summary, the nitrogen-containing polycyclic silane external electron donor of the present invention, when applied to the Ziegler-Natta catalyst system with phthalate as the internal electron donor, can synergistically achieve high catalyst activity, high isotacticity retention and excellent hydrogen regulation sensitivity, and is particularly suitable for the production of high-flow polypropylene products, and exhibits good performance regulation potential.

[0060] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A nitrogen-containing polycyclic silane external electron donor, characterized in that, It has the following structural formula as shown in Equation I: In this context, A, B, and C are each independently selected from nitrogen or oxygen atoms, and R1, R2, and R3 are each independently selected from alkyl groups having 1-2 carbon atoms.

2. The nitrogen-containing polycyclic silane external electron donor according to claim 1, characterized in that: A, B, and C are all nitrogen atoms.

3. The nitrogen-containing polycyclic silane external electron donor according to claim 1, characterized in that: A and C are oxygen atoms, and B is a nitrogen atom.

4. The nitrogen-containing polycyclic silane external electron donor according to claim 2 or 3, characterized in that: R1, R2 and R3 are all methyl groups.

5. A nitrogen-containing polycyclic silane external electron donor according to claim 2 or 3, characterized in that: At least one of R1, R2 and R3 is an ethyl group.

6. A catalyst system for olefin polymerization, comprising a nitrogen-containing polycyclic silane external electron donor as described in any one of claims 1-5, characterized in that: The system also includes a solid titanium catalyst component and an organoaluminum co-catalyst, wherein the solid titanium catalyst component comprises a titanium compound supported on a magnesium halide support and an internal electron donor.

7. The catalyst system for olefin polymerization according to claim 6, characterized in that: The internal electron donor is a phthalate ester compound.

8. The catalyst system for olefin polymerization according to claim 6, characterized in that: The organoaluminum co-catalyst is triethylaluminum or triisobutylaluminum.

9. A method for olefin polymerization, characterized in that, Includes polymerizing propylene monomers under polymerization conditions in the presence of a catalyst system as described in any one of claims 6-8.

10. The olefin polymerization method according to claim 9, characterized in that: The polymerization is a liquid-phase bulk polymerization with a reaction temperature of 60℃-80℃, and hydrogen is introduced as a molecular weight regulator during the polymerization process.

Images