Self-degradable polypropylene as well as preparation method and application thereof
By introducing specific structures into polypropylene and using specific catalyst systems, a self-degradable polypropylene that can be automatically oxidized and degraded under room temperature without light was prepared, which solved the problem of slow degradation of polypropylene in natural conditions and achieved efficient degradation effect.
Patent Information
- Application Number
- CN202510200540.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-21
- Publication Date
- 2025-05-27
AI Technical Summary
The existing polypropylene plastics degraded very slowly under natural conditions, resulting in serious environmental problems. The existing degradation methods are not suitable for room temperature without light.
By controlling the mass ratio of isotropic polypropylene and random polypropylene, and introducing structure A and tension bond structure B into the polymer, the polymerization reaction was carried out using Ziegler-Natta catalyst supported by magnesium chloride and modified aluminoxane as co-catalysts to prepare a self-degradable polypropylene that can be automatically oxidized and degraded under room temperature without light.
The automatic oxidation and degradation of polypropylene under room temperature without light was achieved. After ten years, the weight average molecular weight dropped to 7% and 5% of the initial value, which significantly improved the degradation efficiency of polypropylene.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of polypropylene materials, and in particular to a self-degrading polypropylene and its preparation method and application. Background Art
[0002] Polypropylene is one of the four general-purpose thermoplastic resins, and has the advantages of light weight, non-toxicity, chemical resistance, heat resistance, high wear resistance and easy processability, etc., and has been widely used in many fields. However, a large amount of polypropylene plastic waste is discarded every year after use. At present, the treatment of polypropylene plastic waste is mainly carried out by burying. Without light and catalyst in this environment, it is a huge challenge to break the carbon-carbon single bond of polypropylene under natural conditions (room temperature). The degradation of these polypropylene plastic wastes is very slow under natural conditions and composite conditions, causing serious environmental problems.
[0003] The existing degradation methods of polypropylene plastics mainly include thermal degradation, thermo-oxidative degradation, photo-degradation, catalytic degradation or the combination of factors such as light, heat, oxygen, catalyst, etc. to achieve degradation. For example, relevant research shows that polypropylene can be converted into complex hydrocarbon mixtures through pyrolysis above 500 °C or transition metal-catalyzed pyrolysis; and relevant research uses tungsten oxide catalyst to reduce the degradation temperature of polypropylene to 320 °C, and polypropylene can be cracked and generate a mixture mainly composed of small molecule olefins. However, although polypropylene plastics can be degraded by thermal degradation, the temperature required for thermal degradation is relatively high, which makes the degradation conditions of polypropylene plastics relatively harsh. Relevant research shows that by using nano-titanium dioxide as a photo-degradant to prepare degradable polypropylene materials, although photo-degradation can reduce the degradation temperature, due to the narrow light response range and easy agglomeration of nano-titanium dioxide itself, its further use as a photo-degradant is limited. It can be seen that the existing methods for degrading polypropylene are not suitable for the degradation environment of polypropylene plastic waste under natural conditions and composite conditions. Therefore, if a polypropylene that can be automatically oxidized and degraded at room temperature without light can be provided, the problems of harsh degradation conditions and low degradation efficiency of polypropylene can be solved. Summary of the Invention
[0004] The purpose of the present invention is to provide a self-degrading polypropylene that can be automatically oxidized and degraded at room temperature without light, and its preparation method and application.
[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:
[0006] The present invention provides a self-degrading polypropylene, which includes isotactic polypropylene and atactic polypropylene, and the mass ratio of the isotactic polypropylene to the atactic polypropylene is (85-97):(3-15);
[0007] The isotactic polypropylene and atactic polypropylene include Structure A, and the characteristic peaks of the nuclear magnetic resonance carbon spectrum of Structure A are 17.2 ppm, 17.6 ppm, 31.6 ppm and 42.4 ppm;
[0008] The molar content of Structure A in the isotactic polypropylene and atactic polypropylene is independently ≥ 0.03 mol%;
[0009] The atactic polypropylene includes a strained bond Structure B, and the molar content of Structure B in the atactic polypropylene > 0.08 mol%; the content of this strained bond Structure B is represented by the molar content of the characteristic peaks at 68.4 ppm, 42.1 ppm and 17.9 ppm in the nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene.
[0010] The present invention also provides a preparation method of the self-degrading polypropylene described in the above technical solution, including:
[0011] Mixing propylene, a main catalyst and a cocatalyst, and carrying out a polymerization reaction to obtain self-degrading polypropylene;
[0012] The main catalyst is a magnesium chloride-supported Ziegler-Natta catalyst, and the internal electron donor of the magnesium chloride-supported Ziegler-Natta catalyst is 9,9-bis(methoxymethyl)fluorene;
[0013] The cocatalyst includes one or more of modified aluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum and diethylaluminum monochloride.
[0014] Preferably, the mass ratio of the main catalyst to the amount of substance of the cocatalyst is (40 - 65) mg : (0.1 - 0.4) mmol.
[0015] Preferably, the temperature of the polymerization reaction is 93 - 105 °C; the time of the polymerization reaction is 1 - 1.5 h.
[0016] Preferably, the preparation method of the main catalyst includes:
[0017] (1) Mixing anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate to obtain a mixed solution,
[0018] (2) Sequentially mixing the mixed solution obtained in the step (1) with titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene, and carrying out a coordination reaction to obtain the main catalyst.
[0019] Preferably, the molar ratio of anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate in the step (1) is (0.02 - 0.06) : (70 - 80) : (0.1 - 0.2) : (0.01 - 0.03).
[0020] Preferably, the molar ratio of anhydrous magnesium chloride in step (1), titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene in step (2) is (0.01 - 0.05):(0.4 - 0.5):(0.01 - 0.02).
[0021] Preferably, the temperature of the coordination reaction in step (2) is 70 - 90 °C, and the time of the coordination reaction is 1 - 5 h.
[0022] Preferably, the preparation method of the modified aluminoxane includes: subjecting aluminoxane to vacuum heating to obtain the modified aluminoxane; the temperature of the vacuum heating is 50 - 90 °C, the time of the vacuum heating is 6 - 8 h, and the vacuum degree of the vacuum heating is 0.1 - 10 Pa.
[0023] The present invention also provides the application of the self-degrading polypropylene described in the above technical solution or the self-degrading polypropylene prepared by the preparation method described in the above technical solution in self-degrading polypropylene products;
[0024] The method for the application of the self-degrading polypropylene in self-degrading polypropylene products is: preparing the self-degrading polypropylene into plastic products, or mixing the structure A and structure B of the self-degrading polypropylene with polypropylene and then preparing into plastic products.
[0025] The present invention provides a self-degrading polypropylene, including isotactic polypropylene and atactic polypropylene, and the mass ratio of the isotactic polypropylene to the atactic polypropylene is (85 - 97):(3 - 15); the isotactic polypropylene and the atactic polypropylene include structure A, and the characteristic peaks of the nuclear magnetic resonance carbon spectrum of structure A are 17.2 ppm, 17.6 ppm, 31.6 ppm and 42.4 ppm; the molar content of structure A in the isotactic polypropylene and the atactic polypropylene is independently ≥ 0.03 mol%; the atactic polypropylene includes a strained bond structure B, and the molar content of structure B in the atactic polypropylene > 0.08 mol%; the content of the strained bond structure B is represented by the molar content of the characteristic peaks at 68.4 ppm, 42.1 ppm and 17.9 ppm in the nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene. In the polypropylene provided by the present invention, the isotactic polypropylene and the atactic polypropylene include structure A, and the atactic polypropylene includes a strained bond structure B. In the presence of these two structures, they can cooperate synergistically, so that the polypropylene material undergoes an auto-oxidation process in the natural state of no light and room temperature. The results of the examples show that the initial melting point of the polypropylene material provided by the present invention is 162.5 - 163.5 °C, the crystallinity is 45 - 50%, and the weight-average molecular weight is 1.10 - 3.60×10 5g / mol, with a molecular weight distribution index of 5.2 to 6.6. After being stored for ten years at room temperature without light, the weight-average molecular weight is 7% and 5% of the initial value, while for ordinary industrial-grade polypropylene under the same conditions, the molecular weight is over 90% of the initial value. Description of the Drawings
[0026] Figure 1 It is the high-temperature nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene prepared in Example 1 of the present invention, where the corresponding characteristic peaks are 17.2 ppm, 17.6 ppm, and 17.9 ppm;
[0027] Figure 2 It is the high-temperature nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene prepared in Example 1 of the present invention, where the corresponding characteristic peaks are 42.1 ppm and 42.4 ppm;
[0028] Figure 3 It is the high-temperature nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene prepared in Example 1 of the present invention, where the corresponding characteristic peaks are represented by the molar contents at 68.4 pp and 17.9 ppm. Detailed Embodiments
[0029] The present invention provides a self-degrading polypropylene, which includes isotactic polypropylene and atactic polypropylene, and the mass ratio of the isotactic polypropylene to the atactic polypropylene is (85 - 97):(3 - 15);
[0030] The isotactic polypropylene and the atactic polypropylene include Structure A, and the nuclear magnetic resonance carbon spectrum characteristic peaks of Structure A are 17.2 ppm, 17.6 ppm, 31.6 ppm, and 42.4 ppm;
[0031] The molar content of Structure A in the isotactic polypropylene and the atactic polypropylene is independently ≥ 0.03 mol%;
[0032] The atactic polypropylene includes a strained bond Structure B, and the molar content of Structure B in the atactic polypropylene > 0.08 mol%; the content of the strained bond Structure B is represented by the molar contents of the characteristic peaks at 68.4 ppm, 42.1 ppm, and 17.9 ppm in the nuclear magnetic resonance carbon spectrum.
[0033] The self-degrading polypropylene provided by the present invention includes isotactic polypropylene and atactic polypropylene. In the present invention, the mass ratio of the isotactic polypropylene to the atactic polypropylene is (85 - 97):(3 - 15), preferably (85 - 94):(6 - 15). In the embodiments of the present invention, the mass ratio of the isotactic polypropylene to the atactic polypropylene can be 94:6, 91:9, or 85:15. Controlling the mass ratio of the isotactic polypropylene to the atactic polypropylene in the self-degrading polypropylene provided by the present invention within the above range can endow the self-degrading polypropylene with excellent initial mechanical properties.
[0034] In the present invention, the isotactic polypropylene and atactic polypropylene include Structure A, and the characteristic peaks of the nuclear magnetic resonance carbon spectrum of Structure A are 17.2 ppm, 17.6 ppm, 31.6 ppm, and 42.4 ppm. In the present invention, when the above characteristic peaks simultaneously appear in the nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene, it indicates that it has Structure A. In the present invention, the molecular formula of Structure A is preferably as shown in Formula (1):
[0035]
[0036] In the present invention, P in Formula (1) is preferably polypropylene.
[0037] In the present invention, the molar content of Structure A in the isotactic polypropylene and atactic polypropylene is independently ≥0.03 mol%, preferably ≥0.05 mol%. In the present invention, the content of Structure A is characterized by the average value of the molar content of the above-mentioned characteristic peaks of the nuclear magnetic resonance carbon spectrum.
[0038] In the present invention, the atactic polypropylene includes a strained bond Structure B. In the present invention, during the nuclear magnetic resonance carbon spectrum test of the self-degrading polypropylene, the strained bond Structure B will undergo a chemical reaction as shown in Formula (2) to obtain Structure C. In the nuclear magnetic resonance carbon spectrum, the presence of Structure C is represented by characteristic peaks at 68.4 ppm, 42.1 ppm, and 17.9 ppm. In the present invention, the molecular chain of synthetic polypropylene is composed of chain segments with different configurations, including isotactic chain segments composed of syndiotactic configurations and atactic chain segments composed of atactic configurations. Among them, the isotactic chain segments are in a helical conformation, while the atactic chain segments are in a random conformation. The m and n chain segments in Formula (2) (representing m or n propylene units, where m and n are natural numbers greater than 10) represent isotactic chain segments, which are in a helical conformation; while the atactic chain segments, such as the s chain segment (s propylene units, where s is a natural number greater than 5), are in a random conformation. Therefore, the polypropylene molecular chain is a molecular chain composed of different conformations. At an appropriate m / s or n / s ratio, the transition between different conformations will generate tension, and this tension will cause some carbon-carbon single bonds (C-C) in the random S chain segments to become a C-C single bond called a strained bond (Structure B). Under high-temperature nuclear magnetic test conditions, at a test temperature of 110 - 125 °C for 24 h in the presence of trace oxygen, due to the existing tension in this strained bond, the carbon-carbon bond (C-C) is more likely to break and thus be oxidized by oxygen to form Structure C. We can calculate the content of this strained bond (Structure B) through the content of Structure C because they have a one-to-one corresponding relationship as shown in Formula (2).
[0039]
[0040] In the present invention, when the above characteristic peaks (at 68.4 ppm, 42.1 ppm, and 17.9 ppm) simultaneously appear in the nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene, they are the characteristic peaks of Structure C, and Structure C is obtained by oxidizing Structure B. Therefore, the presence of Structure C can indicate the presence of Structure B in the polypropylene. The content of Structure C is obtained from the molar content of the characteristic peaks of Structure C, and Structure B and Structure C are in one-to-one correspondence, thereby obtaining the content of Structure B.
[0041] In the present invention, the molar content of Structure B in the atactic polypropylene > 0.08 mol%, preferably ≥ 0.12 mol%. In the present invention, the contents of Structure A and Structure B are controlled within the above ranges, and the two can act synergistically to endow the polypropylene with the ability of self-degradation under room temperature and without light.
[0042] The present invention also provides a method for preparing the self-degrading polypropylene according to the above technical solution, including:
[0043] Mixing propylene, a main catalyst, and a cocatalyst, and carrying out a polymerization reaction to obtain the self-degrading polypropylene;
[0044] The main catalyst is a Ziegler-Natta catalyst supported on magnesium chloride, and the internal electron donor of the Ziegler-Natta catalyst supported on magnesium chloride is 9,9-bis(methoxymethyl)fluorene;
[0045] The cocatalyst includes one or more of modified aluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, and diethylaluminum monochloride.
[0046] In the present invention, propylene, a main catalyst, and a cocatalyst are mixed, and a polymerization reaction is carried out to obtain the self-degrading polypropylene.
[0047] In the present invention, the main catalyst is a Ziegler-Natta catalyst supported on magnesium chloride, and the internal electron donor of the Ziegler-Natta catalyst supported on magnesium chloride is 9,9-bis(methoxymethyl)fluorene. In the present invention, 9,9-bis(methoxymethyl)fluorene is used as the internal electron donor of the Ziegler-Natta catalyst supported on magnesium chloride. The internal electron donor can limit the insertion mode of propylene monomers during the polymerization process at high temperature (93 - 105 °C), enabling the structural units in the polymer molecular chain to be arranged in a specific regular manner, improving the isotacticity of polymers such as polypropylene, and at the same time endowing the polypropylene with Structures A and B.
[0048] In the present invention, the preparation method of the main catalyst preferably includes:
[0049] (1) Mixing anhydrous magnesium chloride, toluene, epichlorohydrin, and tributyl phosphate to obtain a mixed solution,
[0050] (2) Mix the mixed solution obtained in step (1) with titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene in sequence to carry out a coordination reaction to obtain a main catalyst.
[0051] The present invention preferably mixes anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate to obtain a mixed solution.
[0052] In the present invention, the molar ratio of the anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate is preferably (0.02 - 0.06):(70 - 80):(0.1 - 0.2):(0.01 - 0.03), and more preferably 0.05:75:0.1:0.03. Limiting the above components within the above ranges in the present invention can completely dissolve the anhydrous magnesium chloride and promote the subsequent reaction.
[0053] The present invention has no special limitation on the method of mixing the anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate, as long as the anhydrous magnesium chloride can be completely dissolved.
[0054] After obtaining the mixed solution, the present invention preferably mixes the mixed solution with titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene in sequence to carry out a coordination reaction to obtain a main catalyst.
[0055] In the present invention, the molar ratio of the anhydrous magnesium chloride, titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene is preferably (0.01 - 0.05):(0.4 - 0.5):(0.01 - 0.02), and more preferably 0.05:0.45:0.015. Controlling the amounts of the components within the above ranges in the present invention can load rich titanium compounds on the magnesium chloride and improve the activity of the catalyst.
[0056] In the present invention, the method of mixing the mixed solution with titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene in sequence is preferably: dropping titanium tetrachloride into the mixed solution, and then adding 9,9-bis(methoxymethyl)fluorene. The present invention has no special limitation on the dropping rate, and it can be adjusted as needed to prevent uneven reaction caused by too fast mixing of titanium tetrachloride and the mixed solution.
[0057] In the present invention, the temperature of the coordination reaction is preferably 70 - 90°C, and more preferably 80°C; the time of the coordination reaction is preferably 1 - 5 h, and more preferably 3 h. The present invention can promote the coordination reaction to be more sufficient at the above temperature.
[0058] The present invention preferably filters, washes once, soaks in a titanium tetrachloride solution, washes twice and dries the product obtained from the coordination reaction to obtain a main catalyst.
[0059] The present invention does not impose any special limitation on the filtration method, and a conventional filtration method can be adopted as long as the product solid can be separated out.
[0060] In the present invention, the reagent for the first washing is preferably toluene. The present invention removes the impurities on the surface of the solid through the first washing.
[0061] In the present invention, the titanium tetrachloride solution is preferably a toluene solution of titanium tetrachloride. By soaking and treating with the titanium tetrachloride solution in the present invention, the activity of the catalyst can be improved. In the examples of the present invention, the molar ratio of titanium tetrachloride to the solvent in the titanium tetrachloride solution can be 0.45:50.
[0062] In the present invention, the reagent for the second washing is preferably hexane. The present invention removes the impurities on the surface of the solid through the second washing.
[0063] The present invention does not impose any special limitation on the temperature and time of drying, as long as the hexane on the surface of the solid can be sufficiently removed.
[0064] In the present invention, the cocatalyst includes one or more of modified aluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, and dichloroethylaluminum, and is preferably modified aluminoxane, a composite cocatalyst of modified aluminoxane and dichloroethylaluminum, or a composite cocatalyst of modified aluminoxane and tri-n-hexylaluminum. In the present invention, the molar ratio of modified aluminoxane to dichloroethylaluminum in the composite cocatalyst of modified aluminoxane and dichloroethylaluminum is preferably 10:(1-5), more preferably 10:(1-3). In the present invention, the molar ratio of modified aluminoxane to tri-n-hexylaluminum in the composite cocatalyst of modified aluminoxane and tri-n-hexylaluminum is preferably 10:(1-5), more preferably 10:(1-3). By adopting the above cocatalyst in the present invention, the catalytic activity of the main catalyst can be improved.
[0065] In the present invention, the preparation method of the modified aluminoxane preferably includes: subjecting aluminoxane to vacuum heating to obtain the modified aluminoxane.
[0066] In the present invention, the temperature of the vacuum heating is preferably 50-90°C, more preferably 80-90°C; the time of the vacuum heating is preferably 1-8 h, more preferably 2-6 h; the vacuum degree of the vacuum heating is preferably 0.1-10 Pa, more preferably 1-8 Pa. By carrying out the reaction under the above conditions in the present invention, trimethylaluminum in the aluminoxane can be removed, and an aluminoxane containing 0% of "free state" trimethylaluminum, that is, the modified aluminoxane, can be obtained.
[0067] In the present invention, the mass ratio of the main catalyst to the amount of substance of the cocatalyst is (40 - 65) mg : (0.1 - 0.4) mmol. By controlling the mass ratio of the main catalyst to the cocatalyst within the above range, the degradability of propylene can be improved in the present invention.
[0068] In the present invention, the gauge pressure of propylene during the polymerization reaction is preferably 0.12 - 0.5 MPa, more preferably 0.2 MPa. By controlling the gauge pressure of propylene during the polymerization reaction within the above range, the yield of the product can be improved in the present invention.
[0069] In the present invention, the temperature of the polymerization reaction is preferably 95 - 105 °C, more preferably 100 °C; the time of the polymerization reaction is preferably 1 - 1.5 h, more preferably 1 h. Under the above conditions in the present invention, it is more conducive to promoting the full progress of the polymerization reaction. In the present invention, the polymerization reaction is preferably carried out after heating from room temperature to the temperature of the polymerization reaction. In the present invention, the time for heating from room temperature to the temperature of the polymerization reaction is preferably ≤ 6 min. By controlling the time for heating from room temperature to the temperature of the polymerization reaction within the above range, the temperature can be rapidly increased from room temperature to the temperature of the polymerization reaction, reducing the occurrence of side reactions.
[0070] In the present invention, the method of the polymerization reaction is preferably the atmospheric pressure slurry polymerization method. There is no special limitation on the specific operation method of the atmospheric pressure slurry polymerization method in the present invention, and it can be carried out by using the conventional atmospheric pressure slurry polymerization method. In the present invention, the reagent for the polymerization reaction is preferably decane. There is no special limitation on the dosage of the decane in the present invention, and it can be adjusted according to the dosages of the used propylene and the catalyst. In the examples of the present invention, when the gauge pressure of propylene is 0.2 MPa and the catalyst dosage is 35 - 70 mg, the volume of the decane can be 150 mL.
[0071] In the present invention, it is preferred to wash the product obtained from the polymerization reaction to obtain self - degradable polypropylene. There is no special limitation on the washing method in the present invention, and by using the conventional washing method, the impurities in the catalyst and the product can be fully removed. In the examples of the present invention, the washing reagent can be a hydrochloric acid solution of ethanol.
[0072] The method provided by the present invention is simple. The catalyst prepared by using the conventional catalyst preparation method can obtain a structure that enables polypropylene to degrade at room temperature without light when used for preparing polypropylene, so that it can degrade at room temperature without light.
[0073] The present invention also provides the application of the self - degradable polypropylene described in the above technical solution in self - degradable polypropylene products.
[0074] In the present invention, the method for applying the self-degrading polypropylene in self-degrading polypropylene products is preferably as follows: preparing the self-degrading polypropylene into plastic products, or adding the structural units A and B of the self-degrading polypropylene to conventional polypropylene.
[0075] Since the self-degrading polypropylene provided by the present invention has structural units that can be degraded without light at room temperature, directly preparing it into plastic products, or adding structural units A and B to conventional polypropylene products can both achieve the effect of self-degradation without light at room temperature.
[0076] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.
[0077] Example 1
[0078] A method for preparing self-degrading polypropylene: Using the atmospheric pressure slurry polymerization method, after thoroughly displacing a 400 mL four-neck reaction flask with purified high-purity nitrogen, it is then displaced twice with propylene. At room temperature, 150 mL of decane is added while introducing propylene, and then 60 mg of the main catalyst (Cat.A), 1.6 mmol of the co-catalyst modified aluminoxane (abbreviated as MMAO, free trimethylaluminum content is 0), and 0.16 mmol of tri-n-hexylaluminum (Hex 3 Al) are added. The temperature is rapidly raised from room temperature to the polymerization temperature of 100 °C (the time taken from room temperature to 100 °C does not exceed 6 min), the propylene gauge pressure is 0.2 MPa, no hydrogen is added, and the polymerization time is 1 h. 8 g of the polymer is obtained. The sample is washed with a hydrochloric acid solution of ethanol to remove the catalyst, and self-degrading polypropylene is obtained;
[0079] After testing, the isotacticity of the self-degrading polypropylene is 94% (that is, the mass ratio of isotactic polypropylene to atactic polypropylene is 94:6), and the polymerization results are shown in Table 1. The melting point of this polypropylene is 163.2 °C, and the crystallinity is 50%;
[0080] The preparation method of the main catalyst in this example is as follows:
[0081] (1) Mix and dissolve 0.05 mol of anhydrous magnesium chloride, 75 mol of toluene, 0.1 mol of epichlorohydrin, and 0.03 mol of tributyl phosphate to obtain a mixed solution,
[0082] (2) 0.45 mol of titanium tetrachloride was added dropwise to the mixed solution obtained in step (1) above over a period of 1 h. Then, 0.015 mol of 9,9-bis(methoxymethyl)fluorene was added to the resulting solution, and the temperature was raised to 80 °C for a coordination reaction for 3 h. After filtration, it was washed twice with 100 mL of toluene. The resulting solid precipitate was treated with a mixture of toluene (50 mol) and titanium tetrachloride (0.45 mol) at 90 °C for 2 h, followed by filtration and drying to obtain the main catalyst;
[0083] In this example, the preparation method of MMAO was as follows: The aluminoxane was subjected to vacuum heating at a vacuum degree of 1 - 10 Pa, a temperature of 80 °C, and a time of 8 h to obtain MMAO (the content of free trimethylaluminum was 0).
[0084] Example 2
[0085] A preparation method of self-degrading polypropylene: Using the atmospheric pressure slurry polymerization method, after a dry 400 mL four-necked reaction flask was fully replaced with purified high-purity nitrogen, it was then replaced twice with propylene. At room temperature, 150 mL of decane was added while introducing propylene, and then 45 mg of the main catalyst (Cat.A) prepared by the method of Example 1 and 1.2 mmol of MMAO (the content of trimethylaluminum was 0) and 0.12 mmol of diethylaluminum chloride (ClEt 2 Al) prepared by the method of Example 1 were added. The temperature was rapidly raised to the polymerization temperature of 100 °C, the propylene gauge pressure was 0.2 MPa, no hydrogen was added, and the polymerization time was 1 h to obtain 8.3 g of polymer. The sample was washed with a hydrochloric acid solution of ethanol to remove the catalyst, obtaining self-degrading polypropylene;
[0086] After testing, the isotacticity of the self-degrading polypropylene was 85% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene was 85:15), and the polymerization results are shown in Table 1. The melting point of this polypropylene was 162.2 °C, and the crystallinity was 46%.
[0087] Example 3
[0088] A preparation method of self-degrading polypropylene: Using the atmospheric pressure slurry polymerization method, after a dry 400 mL four-necked reaction flask was fully replaced with purified high-purity nitrogen, it was then replaced twice with propylene. At room temperature, 150 mL of decane was added while introducing propylene, and then 45 mg of the main catalyst (Cat.A) prepared by the method of Example 1 and 1.2 mmol of MMAO (the content of free trimethylaluminum was 10%) were added. The temperature was rapidly raised to the polymerization temperature of 100 °C, the propylene gauge pressure was 0.2 MPa, no hydrogen was added, and the polymerization time was 1 h to obtain 16 g of polymer. The sample was washed with a hydrochloric acid solution of ethanol to remove the catalyst, obtaining self-degrading polypropylene;
[0089] After testing, the isotacticity of the self-degrading polypropylene is 91% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene is 91:9), and the polymerization results are shown in Table 1. The melting point of this polypropylene is 160.8 °C and the crystallinity is 47%;
[0090] In this example, the preparation method of MMAO is as follows: Add trimethylaluminum to the aluminoxane of Example 1 to prepare MMAO containing 10 w% of free trimethylaluminum.
[0091] Comparative Example 1
[0092] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after thoroughly replacing a dry 400 mL four-neck reaction flask with purified high-purity nitrogen, replace it with propylene twice. At room temperature, add 150 mL of decane while introducing propylene, then add 45 mg of the catalyst (Cat.A) prepared by the method of Example 1 and 1.2 mmol of trimethylaluminum as the cocatalyst, quickly raise the temperature to the polymerization temperature of 100 °C, the propylene gauge pressure is 0.2 MPa, without adding hydrogen, and the polymerization time is 1 h to obtain 5.6 g of polymer. The sample is washed with a hydrochloric acid solution of ethanol to remove the catalyst to obtain polypropylene;
[0093] After testing, the isotacticity of the polypropylene is 80% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene is 80:20), and the polymerization results are shown in Table 1.
[0094] Comparative Example 2
[0095] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after thoroughly replacing a dry 400 mL four-neck reaction flask with purified high-purity nitrogen, replace it with propylene twice. At room temperature, add 150 mL of decane while introducing propylene, then add 60 mg of the main catalyst (Cat.A) prepared by the method of Example 1 and 1.6 mmol of triethylaluminum (Et 3 Al), quickly raise the temperature to the polymerization temperature of 120 °C, the propylene gauge pressure is 0.2 MPa, without adding hydrogen, and the polymerization time is 1 h to obtain 5.3 g of polymer. The sample is washed with a hydrochloric acid solution of ethanol to remove the catalyst to obtain polypropylene;
[0096] After testing, the isotacticity of the polypropylene is 58% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene is 58:42), and the polymerization results are shown in Table 1.
[0097] Comparative Example 3
[0098] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after thoroughly replacing a dry 400 mL four-neck reaction flask with purified high-purity nitrogen, replace it with propylene twice. At room temperature, add 150 mL of decane while introducing propylene, then add 60 mg of the main catalyst (Cat.A) prepared by the method of Example 1 and 1.6 mmol of Et3 Al, rapidly heated to the polymerization temperature of 70 °C, with the propylene gauge pressure of 0.2 MPa, without adding hydrogen, and the polymerization time of 1 h, 24 g of polymer was obtained. The sample was washed with hydrochloric acid solution of ethanol to remove the catalyst, and polypropylene was obtained.
[0099] After testing, the isotacticity of the polypropylene was 94% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene was 94:6), and the polymerization results are shown in Table 1.
[0100] Comparative Example 4
[0101] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after the dry 400 mL four-neck reaction flask was fully replaced with purified high-purity nitrogen, it was replaced with propylene twice. At room temperature, 150 mL of decane was added under the introduction of propylene, and then 60 mg of the main catalyst (Cat.B), 1.2 mmol of MMAO (trimethylaluminum content is 0) and 1.2 mmol of Et 3 Al, 0.06 mmol of cyclohexylmethyldimethoxysilane (CHMMS) were added, rapidly heated to the polymerization temperature of 100 °C, with the propylene gauge pressure of 0.2 MPa, without adding hydrogen, and the polymerization time of 1 h, 8.5 g of polymer was obtained. The sample was washed with hydrochloric acid solution of ethanol to remove the catalyst, and polypropylene was obtained.
[0102] After testing, the isotacticity of the polypropylene was 80% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene was 80:20), and the polymerization results are shown in Table 1;
[0103] The preparation method of the main catalyst (Cat.B) is different from that of the main catalyst (Cat.A) in Example 1 in that dibutyl phthalate is used instead of 9,9-bis(methoxymethyl)fluorene, and the remaining steps are the same as those in Example 1.
[0104] Comparative Example 5
[0105] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after the dry 400 mL four-neck reaction flask was fully replaced with purified high-purity nitrogen, it was replaced with propylene twice. At room temperature, 150 mL of decane was added under the introduction of propylene, and then 45 mg of the main catalyst (Cat.B), 0.95 mmol of i-Bu 3 Al and 0.95 mmol of MMAO (trimethylaluminum content is 0), 0.048 mmol of CHMMS were added, rapidly heated to the polymerization temperature of 100 °C, with the propylene gauge pressure of 0.2 MPa, without adding hydrogen, and the polymerization time of 1 h, 10.8 g of polymer was obtained. The sample was washed with hydrochloric acid solution of ethanol to remove the catalyst, and polypropylene was obtained.
[0106] After testing, the isotacticity of the polypropylene was 81% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene was 81:19), and the polymerization results are shown in Table 1.
[0107] Comparative Example 6
[0108] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after thoroughly replacing a dry 400 mL four-neck reaction flask with purified high-purity nitrogen, it was replaced with propylene twice. At room temperature, 150 mL of decane was added while introducing propylene, and then 36.2 mg of the main catalyst (Cat.B) and 0.76 mmol of MMAO (trimethylaluminum content was 0), 0.38 mmol of n-hexylaluminum (Hex 3 Al), 0.038 mmol of CHMMS were added, and the temperature was quickly raised to the polymerization temperature of 100 °C, the propylene gauge pressure was 0.2 MPa, no hydrogen was added, the polymerization time was 1 h, 8.6 g of polymer was obtained, and the sample was washed with a hydrochloric acid solution of ethanol to remove the catalyst to obtain polypropylene;
[0109] After testing, the isotacticity of the polypropylene was 75% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene was 75:25), and the polymerization results are shown in Table 1.
[0110] Comparative Example 7
[0111] A method for preparing polypropylene: Using the atmospheric pressure slurry polymerization method, after thoroughly replacing a dry 400 mL four-neck reaction flask with purified high-purity nitrogen, it was replaced with propylene twice. At room temperature, 150 mL of decane was added while introducing propylene, and then 56 mg of the main catalyst (Cat.B) and 1.2 mmol of Et 3 Al, 0.06 mmol of CHMMS were added, and the temperature was quickly raised to the polymerization temperature of 70 °C, the propylene gauge pressure was 0.2 MPa, no hydrogen was added, the polymerization time was 1 h, 15.5 g of polymer was obtained, and the sample was washed with a hydrochloric acid solution of ethanol to remove the catalyst to obtain polypropylene;
[0112] After testing, the isotacticity of the polypropylene was 94% (i.e., the mass ratio of isotactic polypropylene to atactic polypropylene was 94:6), and the polymerization results are shown in Table 1.
[0113] Example 4
[0114] The self-degrading polypropylene obtained in Example 2 was extracted with boiling heptane to obtain isotactic polypropylene iPP-2 and atactic aPP-2. The sample of Comparative Example 4 and aPP-2 were mixed evenly by weight ratio of 1:1, and filled into a polyethylene sealable bag as the sample of Example 4.
[0115] Example 5
[0116] The polypropylene obtained in Example 2 was extracted with boiling heptane to obtain isotactic polypropylene iPP-2 and atactic aPP-2. The sample of Comparative Example 4 and aPP-2 were mixed evenly at a weight ratio of 85:15 and put into a polyethylene sealable bag as the sample of Example 5.
[0117] Comparative Example 8
[0118] The polypropylene obtained in Example 1 was extracted with boiling heptane to obtain isotactic polypropylene iPP-1 and atactic aPP-1. The isotactic polypropylene iPP-1 was separately put into a polyethylene sealable bag as the sample of Comparative Example 8.
[0119] Test Example
[0120] (1) The nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene prepared in Example 1 is as Figure 1 shown. It can be seen from Figure 1 that the corresponding characteristic peaks are 17.2 ppm, 17.6 ppm and 17.9 ppm, and these characteristic peaks can prove the existence of Structure A.
[0121] The nuclear magnetic resonance carbon spectrum of the self-degrading polypropylene prepared in Example 1 is as Figure 2 and Figure 3 shown. It can be seen from Figures 2 - 3 that characteristic peaks appear at 42.1 ppm, 42.4 ppm, 68.4 ppm and 17.9 ppm, and these characteristic peaks can prove the existence of Structure A and B.
[0122] (2) The basic properties of the catalysts and polypropylenes prepared in Examples 1 to 3 and Comparative Examples 1 to 7 are shown in Table 1:
[0123] Table 1 Basic Properties of Catalysts for Polypropylene Material Synthesis
[0124] Catalyst activity (gPP / gCat) Isotacticity of polypropylene (%) Example 1 133 94 Example 2 184 85 Example 3 355 91 Comparative Example 1 124 80 Comparative Example 2 88 58 Comparative Example 3 400 94 Comparative Example 4 150 80 Comparative Example 5 240 81 Comparative Example 6 238 75 Comparative Example 7 270 94
[0125] In Table 1, after extraction with boiling heptane, the weight ratio of the insoluble matter is called the isotacticity.
[0126] It can be seen from Table 1 that the polypropylene catalysts prepared in Examples 1 to 3 of the present invention have a relatively high isotacticity of polypropylene.
[0127] (3) The self-degrading polypropylenes prepared in Examples 1 to 5 and the polypropylenes prepared in Comparative Examples 1 to 8 were put into polyethylene sealable bags and stored in a laboratory drawer without light, without adding any other chemicals, and without increasing the oxygen concentration. The sealable bags were opened once every two years to randomly inspect the samples, and after ten years, the relevant parameters of all materials were systematically detected, and the results are shown in Table 2.
[0128] The molecular weight and its distribution index were measured by gel permeation chromatography (GPC) using Alliance GPCV 2000 from Waters Corporation, USA, at a measurement temperature of 150 °C. The nuclear magnetic resonance carbon spectrum (13C NMR) was determined using Bruker DMX400 from Germany, at a measurement temperature of 125 °C, with 5000 - 6000 scans, a sampling time of 5 s, and a delay time of 10 s. The melting point and crystallinity were measured by differential scanning calorimetry (DSC) using Netzsch DSC 200F3 from Germany, with a sample heating and cooling rate of 10 °C / min.
[0129] Table 2 Changes in molecular weight and its distribution of the samples prepared in Examples 1 - 5 and Comparative Examples 1 - 8 before and after degradation
[0130]
[0131]
[0132] (3) The self - degradable polypropylene prepared in Examples 1 - 2 and the polypropylene prepared in Comparative Examples 1 - 8 were placed in polyethylene sealed bags and stored in a laboratory drawer without light, without adding any other chemicals, and without increasing the oxygen concentration. The sealed bags were opened once every two years to randomly inspect the samples, and after ten years, the relevant parameters of all materials were systematically detected, and the results are shown in Tables 3 and 4.
[0133] Table 3 Changes in the content of Structure A of the samples prepared in Examples 1 - 2 and Comparative Examples 1 - 8 before and after degradation
[0134]
[0135] "--" indicates not measured. "None" indicates that the sample does not contain atactic polypropylene.
[0136] Table 4 Changes in the content of Structure B of the samples prepared in Examples 1 - 2 and Comparative Examples 1 - 8 before and after degradation
[0137]
[0138]
[0139] "--" indicates not measured. "None" indicates that the sample does not contain atactic polypropylene.
[0140] (4) Changes in structural parameters after 20 years of natural aging
[0141] After 20 years, the melting point of Example 1 was 139.9 °C, the melting point of Example 2 was 141.1 °C, the melting point of Example 5 was 139.9 °C, the melting point of Comparative Example 1 was 158.2 °C, and the melting point of Comparative Example 4 was 160.5 °C.
[0142] As can be seen from Tables 2 to 4, Examples 1 and 2 show that for Cat.A, in MMAO (containing 0% Me3Al) and Hex 3 Al or ClEt 2 Al, the atactic polypropylene in the polypropylene material obtained at 100 °C contains 0.05 mol% of Structure A and 0.12 mol% of Structure B. This polypropylene will automatically oxidize and degrade at room temperature. After ten years, only 5.9% and 5% of the initial amount remain.
[0143] Example 4 shows that when the above atactic polypropylene containing 0.05 mol% of Structure A and 0.12 mol% of Structure B is added to other polypropylenes and uniformly mixed, this material will also automatically oxidize and degrade at room temperature, and the molecular weight will decrease significantly.
[0144] Comparative Example 1 shows that for Cat.A, when trimethylaluminum is used as the cocatalyst during polymerization, the polypropylene obtained at 100 °C has atactic polypropylene containing 0.01% of Structure A and 0.08% of Structure B, and isotactic polypropylene containing 0.01% of Structure A and 0.06% of Structure B. After ten years, its weight-average molecular weight is 72% of the initial value, showing a certain degree of degradation.
[0145] Comparative Example 2 shows that for Cat.A, the polypropylene obtained by polymerization at 120 °C has atactic polypropylene without Structure A but containing 0.12% of Structure B. Its isotactic polypropylene contains no Structure A and B. After ten years, the weight-average molecular weight of this material is 94% of the initial value, showing only slight degradation.
[0146] Comparative Example 3 shows that for Cat.A, the polypropylene obtained by polymerization at 70 °C has atactic polypropylene and isotactic polypropylene without Structure A and B. After ten years, the weight-average molecular weight of this material is 95% of the initial value, showing only slight degradation.
[0147] Comparative Example 4 shows that for the industrially commonly used catalyst Cat.B and its external electron donor, the polypropylene obtained at 100 °C has atactic polypropylene containing 0.02% of Structure A and 0.03% of Structure B. Its isotactic polypropylene contains no Structure A and B. After ten years, its weight-average molecular weight is 95% of the initial value, showing only slight degradation.
[0148] Comparative Examples 5 and 6 show that for catalyst Cat.B, by changing the type and proportion of the cocatalyst, polypropylene is obtained. After ten years, its weight-average molecular weight is 93% and 96% of the initial value, respectively, showing only slight degradation.
[0149] Comparative Example 7 shows that for catalyst Cat.B, the polypropylene obtained at 70 °C has isotactic polypropylene containing no Structure A and B. After ten years, its weight-average molecular weight is 94% of the initial value, showing only slight degradation.
[0150] Comparative Example 8 shows that without the presence of atactic polypropylene and its simultaneously contained Structure A and Structure B, the polypropylene material, after ten years, has a weight-average molecular weight of 85% of the initial value, indicating only partial degradation.
[0151] It can be seen that polypropylene is obtained by polymerizing with Cat.A and Cat.B at 70 °C (the polymerization temperature for most industrial synthesis of polypropylene currently), and then the catalyst is removed by washing with a hydrochloric acid solution of ethanol. After ten years under conditions of no light, room temperature, no increase in oxygen concentration, and no catalyst, the weight-average molecular weight of these polypropylene materials is more than 94% of their initial values, indicating that these industrial-grade polypropylenes are all very stable under burial conditions.
[0152] With Cat.A and Cat.B, various polypropylene samples are obtained by polymerization at 100 °C or 120 °C under the action of different cocatalysts. Among these samples, if the atactic polypropylene does not contain Structure A and Structure B, or the content of Structure A in the atactic polypropylene is less than 0.05 mol% and the content of Structure B is less than 0.1 mol%, or the atactic polypropylene is removed, then after ten years under conditions of no light, room temperature, no increase in oxygen concentration, and no catalyst, the weight-average molecular weight of these polypropylene materials is more than 85% of their initial values, indicating that these polypropylenes are all very stable under burial conditions.
[0153] Using Cat.A prepared by the present invention (BMMF as the internal electron donor), the cocatalyst is MMAO (containing 0% "free state" Me 3 Al) and Hex 3 Al or ClEt 2 Al (the ratio of MMAO to alkyl aluminum is 10:1), and polymerization is carried out at 100 °C. For the two obtained polypropylenes, their atactic polypropylenes both contain 0.05% Structure A and 0.12% Structure B. After being stored under conditions of no light, no catalyst, and no increase in oxygen concentration for ten years, the weight-average molecular weights are 7% and 5% of the initial values respectively.
[0154] The atactic polypropylene containing 0.05% Structure A and 0.12% Structure B obtained in Example 2 and ordinary polypropylene (such as Comparative Example 4) are uniformly mixed. After ten years, for Example 4 with a uniform mixing weight ratio of 1:1, the weight-average molecular weight is 8100 g / mol, the number-average molecular weight is 3000 g / mol, and the number-average molecular weight of industrial paraffin is 400 - 800 g / mol for comparison.
[0155] ClEt 2 Al is generally considered not to be adoptable in the current industrial synthesis technology of polypropylene. However, the present invention uses a composite system of MMAO and ClEt 2 Al to obtain a higher proportion of atactic polypropylene component, and atactic polypropylene is the key component for the room-temperature auto-oxidative degradation of this polypropylene material.
[0156] The results of the melting point test after twenty years show that in the first decade, the degradation of Example 5 was slower, and in the second decade, the degradation of Example 5 accelerated, and the melting points were basically the same as those of Examples 1 and 2. The melting points of Examples 1, 2, and 5 changed from 162-163 °C to about 140 °C, while for Comparative Example 1, the melting point decreased from 160.7 °C to 158.2 °C, and for Comparative Example 2, the melting point decreased from 162 °C to 160.5 °C, indicating that their degradation was limited over a period of twenty years.
[0157] In short, the medium isotactic polypropylene and atactic polypropylene provided by the present invention include Structure A, and the atactic polypropylene includes the tension bond structure B. In the presence of these two structures, they can cooperate synergistically to cause the automatic oxidation process of the polypropylene material in the natural state without light at room temperature.
[0158] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.
Claims
1. A self-degradable polypropylene, comprising isotactic polypropylene and atactic polypropylene, wherein the mass ratio of the isotactic polypropylene to the atactic polypropylene is (85-97): (3-15); The isotactic polypropylene and the atactic polypropylene include structure A, and the characteristic peaks of the nuclear magnetic resonance carbon spectrum of the structure A are 17.2ppm, 17.6ppm, 31.6ppm and 42.4ppm; The molar content of structure A in the isotactic polypropylene and the atactic polypropylene is independently ≥ 0.03 mol%; The random polypropylene includes a tension bond structure B, and the molar content of the structure B in the random polypropylene is greater than 0.08 mol%. The content of the tension bond structure B is represented by the molar content of characteristic peaks at 68.4 ppm, 42.1 ppm and 17.9 ppm in the nuclear magnetic resonance carbon spectrum of the self-degradable polypropylene.
2. The method for preparing the self-degradable polypropylene according to claim 1, comprising: Propylene, a main catalyst and a co-catalyst are mixed to carry out a polymerization reaction to obtain self-degradable polypropylene; The main catalyst is a Ziegler-Natta catalyst supported by magnesium chloride, and the internal electron donor of the Ziegler-Natta catalyst supported by magnesium chloride is 9,9-bis(methoxymethyl)fluorene; The co-catalyst includes one or more of modified aluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum and diethylaluminum monochloride.
3. The preparation method according to claim 2, characterized in that: The mass ratio of the main catalyst to the mass ratio of the co-catalyst is (40-65) mg: (0.1-0.4) mmol.
4. The preparation method according to claim 2, characterized in that: The polymerization reaction temperature is 95-105° C. and the polymerization reaction time is 1-1.5 hours.
5. The preparation method according to claim 2, characterized in that: The preparation method of the main catalyst comprises: (1) mixing anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate to obtain a mixed solution, (2) The mixed solution obtained in step (1) is sequentially mixed with titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene to carry out coordination reaction to obtain a main catalyst.
6. The preparation method according to claim 5, characterized in that: In the step (1), the molar ratio of anhydrous magnesium chloride, toluene, epichlorohydrin and tributyl phosphate is (0.02-0.06): (70-80): (0.1-0.2): (0.01-0.03).
7. The preparation method according to claim 5, characterized in that: The molar ratio of the anhydrous magnesium chloride in step (1), titanium tetrachloride and 9,9-bis(methoxymethyl)fluorene in step (2) is (0.01-0.05):(0.4-0.5):(0.01-0.02).
8. The preparation method according to claim 5, characterized in that: The temperature of the coordination reaction in step (2) is 70 to 90° C., and the time of the coordination reaction is 1 to 5 hours.
9. The preparation method according to claim 2, characterized in that: The preparation method of the modified aluminoxane comprises: vacuum heating aluminoxane to obtain the modified aluminoxane; the vacuum heating temperature is 50-90°C; the vacuum heating time is 6-8h; the vacuum degree of the vacuum heating is 0.1-10Pa.
10. Use of the self-degradable polypropylene according to claim 1 or the self-degradable polypropylene prepared by the preparation method according to any one of claims 2 to 9 in self-degradable polypropylene products; The method for using the self-degradable polypropylene in self-degradable polypropylene products is: preparing the self-degradable polypropylene into plastic products, or mixing the structure A and structure B of the self-degradable polypropylene with polypropylene to prepare plastic products.