Metallocene catalyst for synthesizing transparent polypropylene and preparation method thereof

Abstract

The invention relates to the technical field of polymer catalysts, and particularly discloses a metallocene catalyst for synthesizing transparent polypropylene and a preparation method of the metallocene catalyst. According to the present invention, the prepared dihalogen double norbornene alkyl zirconocene is adopted as the main catalyst, the MAO and the carrier are added to obtain the supported metallocene catalyst, and the metallocene ring is connected with the rotatable bridged ring compound with the unique steric hindrance in the form of the carbon-carbon single bond, such that the polymerization reaction of the propylene can be easily performed while the polymerization reaction of the propylene is catalyzed so as to achieve the good polymerization effect; a 1-hexene monomer can be well inserted, polypropylene randon copolymer is obtained, the polypropylene randon copolymer is used for catalyzing copolymerization of 1-hexene and propylene, branched chains with four carbons can be irregularly introduced to a polypropylene long chain, and the branched chains reduce the crystallinity of polypropylene and improve the transparency and softness of polypropylene.

Description

Technical Field

[0001] The invention relates to the technical field of polymer catalysts, and particularly discloses a metallocene catalyst for synthesizing transparent polypropylene and a preparation method thereof. Background Art

[0002] Transparent polypropylene (PP) has excellent transparency and gloss and is widely used in packaging, tableware, medical devices, and other fields. Since ordinary polypropylene is a partially crystalline material, its crystal size is too large, which affects light transmittance. There are two common methods for transparency modification: physical modification (such as the addition of a transparent nucleating agent) and chemical modification. The former is often accompanied by the introduction of impurities such as metal ions and organic matter, which limits the application of the product. The latter uses a catalyst to directly prepare random copolymer polypropylene. Compared with Ziegler-Natta (ZN) catalysts, metallocene catalyst products have lower volatile and precipitate content and are more valuable for research.

[0003] Metallocene catalysts refer to a type of catalyst composed of transition metal atoms and cyclopentadienyl ligands. They have the advantages of high catalytic activity and good copolymerization performance. By introducing comonomers during the propylene polymerization process, they can destroy the regularity and order of the molecular chain, hinder crystal formation, reduce crystallinity, refine spherulites, and thus improve PP transparency.

[0004] Currently, transparent polypropylene is primarily produced by copolymerizing propylene with a small amount of ethylene to form a random copolymer. However, this copolymer exhibits a high content of n-hexane extracts, limiting its application in food and medical applications. Therefore, it is necessary to design a random copolymer of propylene and 1-hexene catalyzed by a metallocene catalyst. This copolymer exhibits advantages such as a narrow molecular weight distribution, high transparency, and low volatile matter content. Applications include food and beverage packaging, cosmetics packaging, maternity and infant packaging, and pharmaceutical packaging. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to develop a random copolymer polypropylene which is obtained by copolymerizing propylene and 1-hexene using a metallocene catalyst and has the advantages of narrow molecular weight distribution, high transparency and low volatile matter content.

[0006] The technical solution adopted in the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a supported metallocene catalyst for synthesizing random copolymer polypropylene, comprising the following steps:

[0008] S1. Preparation of ligand: 5 mol of diketone compound and 0.2 to 0.3 equivalents of potassium hydroxide were added to a saturated NaCl solution and refluxed to obtain cyclopentenone;

[0009] In an inert gas atmosphere, using tetrahydrofuran (THF) as a solvent, 1 to 2 moles of hydrobromic acid and 1 to 2 moles of magnesium are added to 0.1 to 0.3 equivalents of norbornene, and the reaction is carried out at 70 to 90° C. to obtain a norbornyl Grignard reagent;

[0010] In an inert gas atmosphere, 1 mole of cyclopentenone and 1.5 to 2.5 moles of acetic acid are added to 0.8 to 1.3 moles of a norbornyl Grignard reagent, and the mixture is reacted at -5 to 5°C to obtain a ligand norbornyl cyclopentadiene;

[0011] S2. Preparation of the main catalyst: 1 mol of the norbornyl cyclopentadiene prepared in step S1 was dissolved in anhydrous tetrahydrofuran solvent to a concentration of 0.2 to 0.8 mol / L; a 5 to 20% n-BuLi n-hexane solution of 1 / 8 to 1 / 4 of the volume of anhydrous tetrahydrofuran solvent was added dropwise at -60 to -90 ° C. After sufficient reaction, 0.3 to 0.6 mol of zirconium tetrahalide was added, mixed thoroughly, filtered and drained, n-hexane was added and shaken to dissolve and filtered, and the filtrate was drained to obtain the main catalyst compound dihalogen bis-norbornyl zirconocene, the structure of which is shown in Formula 1;

[0012] Formula 1:

[0013] Wherein, R1 is an aliphatic hydrocarbon, and R2 is a halogen;

[0014] S3. Preparation of a supported metallocene catalyst: 1 part by volume of n-hexane and 5 parts by mass of a carrier were added, stirring was started, and MAO was added, fully heated at 60 to 90 ° C, cooled to room temperature, and filtered to obtain a MAO- carrier; 0.5 to 2 parts by mass of the main catalyst obtained in step S2, 0.8 to 1.2 parts by volume of toluene and all the above MAO- carriers were added, stirred thoroughly, filtered, and washed to obtain a supported metallocene catalyst;

[0015] The concentration of the carrier in n-hexane is 0.2-0.5 g / mL;

[0016] The MAO is methylaluminoxane, and the input ratio of the MAO to the main catalyst is measured by the mass ratio of Al / Zr, which ranges from 50 to 250.

[0017] Preferably, the diketone compound has 5 to 10 carbon atoms.

[0018] Furthermore, the diketone compound includes 2,5-hexanedione, 2,5-heptanedione, 2,5-octanedione, 6-methyl-2,5-heptanedione, and 2,5-nonanedione.

[0019] Furthermore, the R1 is a C1-C4 aliphatic hydrocarbon.

[0020] Preferably, the zirconium tetrahalide includes zirconium tetrachloride and zirconium tetrabromide.

[0021] Preferably, the carrier is silica gel.

[0022] In a second aspect, the present invention provides a supported metallocene catalyst for synthesizing random copolymer polypropylene, which is prepared by the method described in the first aspect.

[0023] In a third aspect, the present invention provides an application of the supported metallocene catalyst described in the second aspect for the synthesis of random copolymerized polypropylene, which specifically comprises the following steps:

[0024] Add liquid propylene, 1-hexene, cocatalyst, supported metallocene catalyst and solvent into the polymerization reactor; increase the temperature of the polymerization reactor to 50-180° C. to complete the polymerization reaction;

[0025] The amount of 1-hexene comonomer added is 0.1wt%-5wt% of the mass of propylene; the ratio of the mass of the supported metallocene catalyst added to the mass of the propylene liquid is 0.02-0.2mg / g; the cocatalyst is triisobutylaluminum, and its amount added is 1wt%-10wt% of the mass of propylene.

[0026] The solvent is selected from one of n-hexane, cyclohexane, toluene, p-xylene, m-xylene and THF;

[0027] Preferably, the polymerization time is 0.5-6h.

[0028] Preferably, after the polymerization is completed, the gas is evacuated and then the reactor is opened to pour out the polymer and vacuum dry it.

[0029] The beneficial effects achieved by the present invention are:

[0030] The present invention provides a method for preparing a supported metallocene catalyst for catalyzing the copolymerization of 1-hexene and propylene. The catalyst can randomly introduce four-carbon branches into the long polypropylene chain. These branches reduce the crystallinity of the polypropylene and improve its transparency and softness. Metallocene catalysts play an important role in the high-end polyolefin industry. Their research and application can achieve large-scale, high-quality development of the domestic polyolefin industry. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear and distinct, the present invention is further described in detail with reference to the following examples. It should be noted that the present invention is not limited to the following examples.

[0032] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0033] Example 1

[0034] The preparation and polymerization steps of the metallocene catalyst are as follows:

[0035] Step 1: Add 5 mol of 2,5-hexanedione and 0.25 equivalents of potassium hydroxide to a saturated NaCl solution and reflux to obtain 3-methyl-2-cyclopentene-1-one; in an N2 atmosphere, using THF as a solvent, add 1.5 mol of hydrobromic acid and 1.5 mol of magnesium rod to 1 mol of norbornene, and react at 80°C for 6 hours to obtain a norbornane Grignard reagent. Then, add 1 mol of 3-methyl-2-cyclopentene-1-one and 2 mol of acetic acid, and react at 0°C for 2 hours to obtain the ligand 1-norbornane-3-methylcyclopentadiene; in a glove box, add 0.05 mol of 1-norbornane-3-methylcyclopentadiene to a schlenk flask and add 100 mL of anhydrous THF solvent. Take it out from the glove box, add 20mL of n-BuLi n-hexane solution dropwise at -78°C, react for 12h, transfer the above schlenk flask to the glove box, add 0.02mol of zirconium tetrachloride, react for 24h, filter and dry, add 40mL of n-hexane, shake to dissolve and filter, and drain the filtrate to obtain the main catalyst compound bis(1-norbornane-3-methylcyclopentadienyl)zirconium dichloride, at this time R1=CH3, R2=Cl.

[0036] In a glove box, add 1 part by volume of n-hexane and 5 parts by mass of a silica gel support to a Schlenk flask, start stirring, add MAO, heat at 80°C for 4 hours, cool to room temperature, and filter to obtain a MAO-SiO2 support; add 1 part by mass of the main catalyst obtained in step S2, 1 part by volume of toluene solvent, and all of the above MAO-SiO2 supports, stir for 1 hour, filter, and wash to obtain a supported metallocene catalyst; the concentration of the silica gel support in n-hexane is 0.3 g / mL;

[0037] The MAO is methylaluminoxane, and the input ratio of the main catalyst is measured by the mass ratio of Al / Zr, which is 150;

[0038] Catalytic effect test:

[0039] To the polymerization reactor were added 1000 g of propylene, 800 mL of n-hexane as solvent, 2 wt% of 1-hexene, 100 mg of catalyst, 5% of triisobutylaluminum (the amount was calculated as a percentage of propylene by mass), the polymerization temperature was 80° C., and the polymerization time was 2 h.

[0040] Experimental results: The catalyst activity was 300 kgmPP / gZr·h, the molecular weight distribution PDI of the prepared random copolymer polypropylene was 4.7, and the haze was 27%.

[0041] Among them, the ligand 1-norbornane-3-methylcyclopentadiene NMR1 H NMR(400MHz, CDCl3-d)δ6.02-6.00(m,1H),5.80-5.78(m,1H),2.61(t,3H),2.49-2.39(m,1H),2.39- 2.32(m,1H),1.66(d,4H),1.63-1.56(m,2H),1.55-1.49(m,1H),1.46-1.35(m,2H),1.29(ddd,2H).

[0042] Example 2

[0043] The difference from the experimental method in Example 1 is that 2,5-hexanedione is replaced by 2,5-heptanedione, the input amount of 1-hexene is 1 wt %, the catalyst is 50 mg, the input amount of triisobutylaluminum is 3%, the polymerization temperature is 100° C., and the polymerization time is 0.5 h.

[0044] Experimental results: catalyst activity is 120 kgmPP / gZr·h, molecular weight distribution PDI is 4.4, and haze is 30%.

[0045] Example 3

[0046] The difference from the experimental method in Example 1 is that 2,5-hexanedione is replaced with 2,5-octanedione, the polymerization reaction solvent is cyclohexane, the input amount of 1-hexene is 0.1 wt %, the catalyst is 20 mg, the input amount of triisobutylaluminum is 5%, the polymerization temperature is 50° C., and the polymerization time is 6 h.

[0047] Experimental results: catalyst activity is 130 kgmPP / gZr·h, molecular weight distribution PDI is 5.3, and haze is 49%.

[0048] Example 4

[0049] The difference from the experimental method in Example 1 is that the polymerization reaction solvent is n-heptane, the input amount of 1-hexene is 5 wt %, the catalyst is 200 mg, the input amount of triisobutylaluminum is 10%, the polymerization temperature is 80° C., and the polymerization time is 1 h.

[0050] Experimental results: catalyst activity is 330 kgmPP / gZr·h, molecular weight distribution PDI is 3.6, and haze is 23%.

[0051] Example 5

[0052] The difference from the experimental method in Example 1 is that 2,5-hexanedione is replaced with 6-methyl-2,5-heptanedione, the polymerization reaction solvent is toluene, the input amount of 1-hexene is 2 wt %, the catalyst is 100 mg, the input amount of triisobutylaluminum is 5%, the polymerization temperature is 150° C., and the polymerization time is 2 h.

[0053] Experimental results: catalyst activity was 290 kgmPP / gZr·h, molecular weight distribution PDI was 4.3, and haze was 28%.

[0054] Example 6

[0055] The difference from the experimental method in Example 1 is that 2,5-hexanedione is replaced with 2,5-nonanedione, the Al / Zr ratio is 50, the polymerization reaction solvent is p-xylene, the 1-hexene input amount is 2 wt %, the catalyst is 100 mg, the triisobutylaluminum input amount is 5%, the polymerization temperature is 80° C., and the polymerization time is 2 h.

[0056] Experimental results: catalyst activity is 180 kgmPP / gZr·h, molecular weight distribution PDI is 4.5, and haze is 36%.

[0057] Example 7

[0058] The difference from the experimental method in Example 1 is that zirconium tetrachloride is replaced with zirconium tetrabromide, the Al / Zr ratio is 50, the amount of 1-hexene added is 3 wt %, the catalyst is 150 mg, the amount of triisobutylaluminum added is 5%, the polymerization temperature is 180° C., and the polymerization time is 3 h.

[0059] Experimental results: catalyst activity is 150 kgmPP / gZr·h, molecular weight distribution PDI is 3.8, and haze is 34%.

[0060] Example 8

[0061] The difference from the experimental method in Example 1 is that zirconium tetrachloride is replaced with zirconium tetrabromide, the Al / Zr ratio is 200, the 1-hexene input amount is 2 wt %, the catalyst is 100 mg, the triisobutylaluminum input amount is 5%, the polymerization temperature is 80° C., and the polymerization time is 2 h.

[0062] Experimental results: catalyst activity was 230 kgmPP / gZr·h, molecular weight distribution PDI was 5.0, and haze was 46%.

[0063] Example 9

[0064] The difference from the experimental method in Example 1 is that 2,5-hexanedione is replaced by 2,5-heptanedione, zirconium tetrachloride is replaced by zirconium tetrabromide, the Al / Zr ratio is 200, the polymerization solvent is m-xylene, the input amount of 1-hexene is 2 wt %, the catalyst is 80 mg, the input amount of triisobutylaluminum is 1%, the polymerization temperature is 80° C., and the polymerization time is 1 h.

[0065] Experimental results: catalyst activity is 80 kgmPP / gZr·h, molecular weight distribution PDI is 6.1, and haze is 50%.

[0066] Example 10

[0067] The difference from the experimental method in Example 1 is that zirconium tetrachloride is replaced with zirconium tetrabromide, the Al / Zr ratio is 250, the amount of 1-hexene added is 5 wt %, the catalyst is 150 mg, the amount of triisobutylaluminum added is 3%, the polymerization temperature is 80° C., and the polymerization time is 4 h.

[0068] Experimental results: catalyst activity was 310 kgmPP / gZr·h, molecular weight distribution PDI was 3.2, and haze was 30%.

[0069] Example 11

[0070] The difference from the experimental method in Example 1 is that 2,5-hexanedione is replaced by 2,5-octanedione, zirconium tetrachloride is replaced by zirconium tetrabromide, the Al / Zr ratio is 250, the polymerization solvent is THF, the amount of 1-hexene added is 2 wt %, the catalyst is 100 mg, the amount of triisobutylaluminum added is 8%, the polymerization temperature is 80° C., and the polymerization time is 1 h.

[0071] Experimental results: catalyst activity was 260 kgmPP / gZr·h, molecular weight distribution PDI was 4.7, and haze was 39%.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a supported metallocene catalyst for synthesizing random copolymer polypropylene, characterized in that: The steps include: S1. Preparation of ligand: 5 mol of diketone compound and 0.2 to 0.3 equivalents of potassium hydroxide were added to a saturated NaCl solution and refluxed to obtain cyclopentenone; In an inert gas atmosphere, using tetrahydrofuran (THF) as a solvent, 1 to 2 moles of hydrobromic acid and 1 to 2 moles of magnesium are added to 0.1 to 0.3 equivalents of norbornene, and the reaction is carried out at 70 to 90° C. to obtain a norbornyl Grignard reagent; In an inert gas atmosphere, 1 mole of cyclopentenone and 1.5 to 2.5 moles of acetic acid are added to 0.8 to 1.3 moles of a norbornyl Grignard reagent, and the mixture is reacted at -5 to 5°C to obtain a ligand norbornyl cyclopentadiene; S2. Preparation of the main catalyst: 1 mol of the norbornyl cyclopentadiene prepared in step S1 was dissolved in anhydrous tetrahydrofuran solvent to give a norbornyl cyclopentadiene concentration of 0.2 to 0.8 mol / L; anhydrous tetrahydrofuran solvent volume 1 / 8 to 1 / 4 of a 5 to 20% concentration of n-BuLi in n-hexane solution was added dropwise at -60 to -90 ° C. After sufficient reaction, 0.3 to 0.6 mol parts of zirconium tetrahalide were added, mixed thoroughly, filtered and dried, n-hexane was added and shaken to dissolve and filtered, and the filtrate was drained to obtain the main catalyst compound dihalogen bis-norbornyl zirconocene; S3. Preparation of a supported metallocene catalyst: 1 part by volume of n-hexane and 5 parts by mass of a carrier were added, stirring was started, and MAO was added, fully heated at 60 to 90 ° C, cooled to room temperature, and filtered to obtain a MAO- carrier; 0.5 to 2 parts by mass of the main catalyst obtained in step S2, 0.8 to 1.2 parts by volume of toluene and all the above MAO- carriers were added, stirred thoroughly, filtered, and washed to obtain a supported metallocene catalyst; The concentration of the carrier in n-hexane is 0.2-0.5 g / mL; The MAO is methylaluminoxane, and the input ratio of the MAO to the main catalyst is measured by the mass ratio of Al / Zr, which ranges from 50 to 250.

2. The method for preparing a supported metallocene catalyst for synthesizing random copolymer polypropylene according to claim 1, wherein: The diketone compound has 5 to 10 carbon atoms.

3. The method for preparing a supported metallocene catalyst for synthesizing random copolymer polypropylene according to claim 2, wherein: The diketone compounds include 2,5-hexanedione, 2,5-heptanedione, 2,5-octanedione, 6-methyl-2,5-heptanedione, and 2,5-nonanedione.

4. The method for preparing a supported metallocene catalyst for synthesizing random copolymer polypropylene according to claim 1, wherein: The zirconium tetrahalide includes zirconium tetrachloride and zirconium tetrabromide.

5. The method for preparing a supported metallocene catalyst for synthesizing random copolymer polypropylene according to claim 1, wherein: The carrier is a silica gel carrier.

6. A supported metallocene catalyst for synthesizing random copolymer polypropylene, prepared by the method according to any one of claims 1 to 5.

7. Use of the supported metallocene catalyst according to claim 6 for the synthesis of random copolymerized polypropylene, characterized in that: The specific steps include: Add liquid propylene, 1-hexene, cocatalyst, supported metallocene catalyst and solvent; increase the polymerization temperature to 50-180°C to complete the polymerization reaction; The amount of 1-hexene comonomer added is 0.1wt%-5wt% of the mass of propylene; the ratio of the mass of the supported metallocene catalyst added to the mass of the propylene liquid is 0.02-0.2mg / g; the cocatalyst is triisobutylaluminum, and its amount added is 1wt%-10wt% of the mass of propylene. The solvent is selected from one of n-hexane, cyclohexane, toluene, p-xylene, m-xylene and THF.

8. The use of the supported metallocene catalyst according to claim 7 for random copolymerization of polypropylene, characterized in that: The polymerization time is 0.5-6h.

9. Use of the supported metallocene catalyst according to claim 8 for random copolymerization of polypropylene, characterized in that: After the polymerization is completed, the gas is evacuated, the reactor is opened, the polymer is poured out, and vacuum dried.

10. Use of the supported metallocene catalyst according to claim 7 for random copolymerization of polypropylene, characterized in that: The reaction is completed in a polymerization reactor.